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Cylinder removal question

slngsht

Well Known Member
I've read several places not to rotate the crank when cylinders are taken off the engine. However, cylinder removal instructions say:

Rotate the crankshaft to place the piston of the No. 1 cylinder at top center of the compression stroke.
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Removal of the remaining cylinders and pistons may be done in any sequence, but less turning of the crankshaft is involved if the cylinders are removed in firing order 1-3-2-4.

This is the procedure I followed - should I be worried about turning the crank during this process?
 
the main issue is the rods banging around inside/against the case. String some rubber bands through the wrist pin hole and studs (form an "X"), and the rods will stay off the case. Rotate at will after that
 
I didn't do that at the time, but took care to protect the rods from hitting the case by placing padding between rod and case when I turned the engine according to order in the directions. I thought besides the rod contact issue, the problem was reduced clamping force increasing change of a main bearing moving - at least that is what I thought I read.
 
I didn't do that at the time, but took care to protect the rods from hitting the case by placing padding between rod and case when I turned the engine according to order in the directions. I thought besides the rod contact issue, the problem was reduced clamping force increasing change of a main bearing moving - at least that is what I thought I read.

You are correct. You can use spacers and plates to tighten the through-bolts back down after removing cylinders and prior to rotating.
 
You are correct. You can use spacers and plates to tighten the through-bolts back down after removing cylinders and prior to rotating.

I have removed all 4 cylinders per lycoming instructions without any kind of plates. Is this cause enough for worry? I haven?t turned the engine any more than necessary. Any way to check without tearing down the whole thing?

Bottom end is only at 700 and very clean.
 
I have removed all 4 cylinders per lycoming instructions without any kind of plates. Is this cause enough for worry? I haven?t turned the engine any more than necessary. Any way to check without tearing down the whole thing?

Bottom end is only at 700 and very clean.

Lycoming will tell you that this is a bad thing - and it probably can be. However, you won?t be the first that has done it and not had a problem. If the airplane is going to sit without jugs for awhile, I?d put plates ad nuts on, just on case the prop gets turned more. If you torque it all up (with torque plates installed), you can spin the prop (with the rods properly supported so they don?t bang around) andsatisfy yourself that it is smooth, and that the bearings haven?t spun.

For future reference, ideally, when you pull a jug, you immediately replace it with a torque plate and tighten the nuts on the through bolts back up before going on to the next one.
 
Lycoming will tell you that this is a bad thing - and it probably can be. However, you won?t be the first that has done it and not had a problem. If the airplane is going to sit without jugs for awhile, I?d put plates ad nuts on, just on case the prop gets turned more. If you torque it all up (with torque plates installed), you can spin the prop (with the rods properly supported so they don?t bang around) andsatisfy yourself that it is smooth, and that the bearings haven?t spun.

For future reference, ideally, when you pull a jug, you immediately replace it with a torque plate and tighten the nuts on the through bolts back up before going on to the next one.

And if you don'e have torque plates, I have been told by a number of engine overhaul experts that you can use a stack of large area washers on the through studs.
 
Scott I have already taken all 4 off and in the process have turned engine 3/4 turn to get each cylinder to tdc without any plates. What to do from here???
 
And if you don'e have torque plates, I have been told by a number of engine overhaul experts that you can use a stack of large area washers on the through studs.

I used to do it that way until I learned why Lycoming doesn?t recommend that.

The problem with the stack of washers is that generally people use steel, and as they tighten the bolt, the washer can spin and scratch the much softer metal of the case, creating a leak path at the cylinder base. Better (if you don?t have the plates) is to take a flat chunk of steel that spans two through bolts and drill holes to accommodate the two holes - then it can?t spin. Accordign to Jim Doebler (former instructor at Lycoming), this is plenty acceptable, and doesn?t require you to pay what Lycoming wants or the torque plates!
 
I never use torque plates or stacks of washers. I put the case halves together, torque the perimeter bolts, put the cylinders on, and torque the thru bolts with the cylinders together. There's just no point in torque plates or stacks of washers, if you put everything together in a short time frame. I always recheck torque a few hours after running the engine, and I'm just about to the point of not bothering anymore since I've never found any problems. Its been years since I've found anything questionable on dimension checks on parts such as cylinders.
 
I used to do it that way until I learned why Lycoming doesn’t recommend that.

The problem with the stack of washers is that generally people use steel, and as they tighten the bolt, the washer can spin and scratch the much softer metal of the case, creating a leak path at the cylinder base. Better (if you don’t have the plates) is to take a flat chunk of steel that spans two through bolts and drill holes to accommodate the two holes - then it can’t spin. Accordign to Jim Doebler (former instructor at Lycoming), this is plenty acceptable, and doesn’t require you to pay what Lycoming wants or the torque plates!

Hmmmm, I can see the reasoning for danger of using the washer method.

I recently used in on recommendation from our engine over-hauler while doing a connecting rod bushing inspection and didn't have any problem, but I think I will make tools out of steel bar stock if I have to do that again (hopefully not)

I am somewhat in the same mindset as Bob.... I have remove a cyl a couple of times without doing anything while the cyl was off for a week and never had any problem.

I did do it in this latest case because we were under a time crunch while waiting for the inspection tool to show up, so I pulled all 4 cyl at one time (which I would have preferred to not have done).
 
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The bearings are doweled or locked in place by tangs like an automotive bearing. They cannot turn unless you separate the case haves some (small) distance. I?ve never understood this caution.
I would re-tension the through studs only (the long ones) using spacers and keep it surgically clean inside.
The place to get in trouble is reassembly and re-torquing. It?s not hard but find the latest Lyc SB/SI and follow it exactly with a known good torque wrench and hopefully a friend who?s done it before.
Also if the case is badly fretted (you won?t know) with a million hours on it, there is a smalll chance when you retorque the studs you?ll lose the main bearing clearance. It?s only .0015? or so to begin with. All you can do is make sure the crank turns free when done and push and shove the prop back and forth and make sure you can feel the end play. Check it again after first ground run.
Tim Andres
 
The cylinder base o-rings don't seal against the flat part of the case spigot. I can think of several reasons why I would not want the case flats to be damaged, but leaks are not on the list.

The center and rear crank bearings are tanged. The big front bearing is doweled. None of them can rotate just because the cylinders are off a previously assembled case.

The latest manuals specify using ST-222 "Torque Hold Down Plates" on initial case assembly, with a specific tightening sequence for the thru studs and case perimeter fasteners. The tightening is to be done immediately upon assembly, as the goals are (1) squeezing the fresh sealant line to near zero, and (2) setting bearing crush before moving anything.

Subsequent cylinder removal specifies using the ST-222 plates to keep the rods from flopping around (they have a rubber grommet to pad the center hole) OR supporting the rods with the used cylinder base o-rings. There is no reference to torquing the ST-222 plates, if used. There is no physical reason to do so.

POSTSCRIPT; looks like we had a 9AM burst of coffee-induced "Hey, wait a minute!" ;)
 
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I used to do it that way until I learned why Lycoming doesn’t recommend that.

The problem with the stack of washers is that generally people use steel, and as they tighten the bolt, the washer can spin and scratch the much softer metal of the case, creating a leak path at the cylinder base. Better (if you don’t have the plates) is to take a flat chunk of steel that spans two through bolts and drill holes to accommodate the two holes - then it can’t spin. Accordign to Jim Doebler (former instructor at Lycoming), this is plenty acceptable, and doesn’t require you to pay what Lycoming wants or the torque plates!

Hmmmm, I can see the reasoning for danger of using the washer method.

I recently used in on recommendation from our engine over-hauler while doing a connecting rod bushing inspection and didn't have any problem, but I think I will make tools out of steel bar stock if I have to do that again (hopefully not)

I am somewhat in the same mindset as Bob.... I have remove a cyl a couple of times without doing anything while the cyl was off for a week and never had any problem.

I did do it in this latest case because we were under a time crunch while waiting for the inspection tool to show up, so I pulled all 4 cyl at one time (which I would have preferred to not have done).

The bearings are doweled or locked in place by tangs like an automotive bearing. They cannot turn unless you separate the case haves some (small) distance. I’ve never understood this caution.
I would re-tension the through studs only (the long ones) using spacers and keep it surgically clean inside.
The place to get in trouble is reassembly and re-torquing. It’s not hard but find the latest Lyc SB/SI and follow it exactly with a known good torque wrench and hopefully a friend who’s done it before.
Also if the case is badly fretted (you won’t know) with a million hours on it, there is a smalll chance when you retorque the studs you’ll lose the main bearing clearance. It’s only .0015” or so to begin with. All you can do is make sure the crank turns free when done and push and shove the prop back and forth and make sure you can feel the end play. Check it again after first ground run.
Tim Andres

I have seen one engine that had all cylinders pulled and no plates / washers used on the thru-studs. When the entire engine was torn down years later, it had a bearing turn against the dowel pin causing excess bearing wear and dowel pin canting to one side. Was the bearing damage and dowel pin caused when it was assembled more than 2,400 hours earlier or by the cylinder swap 600-hours earlier? I find it hard to believe that it was caused when it was assembled and ran that long.

Hold down torque plates or homemade version are cheap insurance when pulling a cylinder or cylinders.

I know I do not have photos of the bearing damage but may have one of the dowel pin. Will post another message with the photo if I can find it.
 
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I personally agree with the skepticism about the bearings moving once assembled properly - I was just supplying information that Lycoming’s school has presented. I think the more likely issue is scratching up the case using the washer method that peaople talk about - and wanted to make sure that folks realized that there was a better alternative to washers that doesn’t cost as much as those plates from Lycoming. Whether or not any of that is an issue I leave up to your own speculation (I think the scratches would have to be tremendously deep to be any kind of an issue) - I just think that in the interest of full disclosure, folks should be exposed to the full spectrum of information - from shade tree mechanic to the factory methods.

What I can tell you from my own experince is the remarkable difference in how the case turns on the crank (when mounted on a vertical engine stand) before and after tightening the through-bolts. It makes you a believer on how flexible the case is, and how much it can change shape as the bolts get tightened.
 
I appreciate the info guys. In my case, the cylinders have already been removed without pressure plate of any kind installed. Crank was turned by hand 3/4 of a turn as I moved through the firing order and removed one cylinder at a time. Engine has not been touched since.

Is the consensus here is to tear it down due to possibility of middle bearings moving?
 
not all mains are doweled

H2AD...no dowel pins.

eUvdvj
 
Dowel Pin movement

Here is an image of good dowel pin on main center bearing of a 4-cylinder Lycoming.

2018-04-06_11.28.38.jpg



Here is an image of what the dowel pin looks like where the bearing had turned.

2018-04-06_11.27.28.jpg


Are Lycoming Torque Plates or Hold Down Plates ST-222 needed when pulling a cylinder or cylinders and rotating the crankshaft? The above images are WHY I used them any time a cylinder is removed from a flying engine.

You mileage may vary and you may or may not want to do a little extra work when pulling a cylinder but the potential damage by not using them is why I use them.
 
Here is an image of good dowel pin on main center bearing of a 4-cylinder Lycoming.

Here is an image of what the dowel pin looks like where the bearing had turned.

Tell us more about what we're looking at here. Those are dowel pins in their sockets, in the case half, yes? Can you explain a mechanism or series of events which would somehow beat the snot out of that second dowel pin, merely by turning the crank in an unclamped case?

H2AD...no dowel pins.

Well, there was bound to be at least one. H2AD, all tanged, no dowels, check.
 
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Bore dimensions dictate whether or not a bearing crushes to stay locked. Not whether or not a tool is used. If this were the case many non-aircraft boxer engines would have the same issue. Take the air-cooled VW for example. There is no such thing as a torque plate in VW tool vernacular. The same obtuse thinking behind dowel pins gave you torque plates.
 
I must back up on a previous statement.

Re cylinder removal, earlier this AM I wrote that the latest manuals specify using the ST-222 plates to keep the rods from flopping around (they have a rubber grommet to pad the center hole) OR supporting the rods with the used cylinder base o-rings. There is no reference to torquing the ST-222 plates, if used.

Not entirely true. I did a quick survey of all the downloadable maintenance manuals currently posted by Lycoming. There are seven, dating from 2012 through 2017. The three manuals dated 2012 can be described as "light maintenance"; they don't cover cylinder removal and replacement. The later ones are much more comprehensive. Here are the pages dealing with cylinder removal:

https://www.lycoming.com/content/maintenance-manual-IO-390-C-Series

page 196

https://www.lycoming.com/content/maintenance-manual-IO-360-N1A

page 139

https://www.lycoming.com/content/mm-lio-360-b1g6

page 192

https://www.lycoming.com/CONTENT/MM-IO-360-P1A

page 186

The 390-C and the 360-N1A manuals do not require installation of torque plates after cylinder removal.

The 360-B1G6 and 360-P1A manuals state:

"IF A CYLINDER IS NOT TO BE IMMEDIATELY INSTALLED ON THE
CRANKCASE, INSTALL TORQUE HOLD-DOWN PLATES (ST-222) TO
MAINTAIN THE PRE-LOAD ON THE MAIN BEARINGS.

The manuals don't say so, but it's obvious that they intend the plates to be torqued to spec. The meaning of "immediately" is not so obvious. The conservative view would be "before moving anything" rather than any reference to clock time.

Now the fun part. The N1A and the P1A have the same crankshaft, thru stud, and bearing part numbers. I find it hard to imagine different main bearing saddle dimensions.

I'll make a phone call, but not tonight.
 
Bore dimensions dictate whether or not a bearing crushes to stay locked. Not whether or not a tool is used. If this were the case many non-aircraft boxer engines would have the same issue. Take the air-cooled VW for example. There is no such thing as a torque plate in VW tool vernacular. The same obtuse thinking behind dowel pins gave you torque plates.

The VW has separate studs for the bearing saddles - separate from the head studs. So, if the heads are off the full clamping on the crank bearing remains. All the air cooled VW's had a dowel for each bearing. At least '55 to '75. Types I, II, III and IV.

Are there any crankshaft bearings that don't have either a tang or dowels in a Lycoming?
 
What cracks me up about this Dan is you have looked in several Lycoming manuals and still don't have an answer. Lycoming documentation is awful. And, you have to check service letters in addition to looking at the OH manual. That said, have a look at the Continental IO-550 manual. Every answer one could ask for when assembling the engine is there, and everything is up-to-date.

A 550 is put together finger tight, and the manual specifies every fastener step-by-step. The last step in case mating and cylinder installation is to torque everything. No torque plate nonsense.
 
I appreciate the info guys. In my case, the cylinders have already been removed without pressure plate of any kind installed. Crank was turned by hand 3/4 of a turn as I moved through the firing order and removed one cylinder at a time. Engine has not been touched since.

Is the consensus here is to tear it down due to possibility of middle bearings moving?

Not sure you'll get consensus here, but as you have read and seen, the bearings cannot spin (at least in the case of spinning by hand), due to the tangs or pins. I can assure you that you will not have been the first to spin the crank by hand without a torque plate. I removed my cylinders at 100 hours to re-ring and did not use torque plates. Hasn't fallen out the sky or left bearing material in my filter for the last 400 hours. I did use nuts and washers to keep a light torque on the through studs while the cylinders were off. I wasn't worried about the bearings spinning. I was worried that the case half's would relax at the supports. I was concerned that too much relaxing would cause light separation and the re-application of torque to close it back up could very slightly move the bearings and cause a new wear pattern. I believe this is why Lyc recommends the use of torque plates when the cylinders are off for more than a few hours (I suppose warpage is another potential concern). However it is low risk. I just separated a 540 case this week and the bearing shells are still very tight in the case halves after 2000 hours.

Larry
 
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Here is an image of good dowel pin on main center bearing of a 4-cylinder Lycoming.

2018-04-06_11.28.38.jpg



Here is an image of what the dowel pin looks like where the bearing had turned.

2018-04-06_11.27.28.jpg


Are Lycoming Torque Plates or Hold Down Plates ST-222 needed when pulling a cylinder or cylinders and rotating the crankshaft? The above images are WHY I used them any time a cylinder is removed from a flying engine.

You mileage may vary and you may or may not want to do a little extra work when pulling a cylinder but the potential damage by not using them is why I use them.

Dan was more polite, however I'm sorry but there is simply no way to bend a dowel pin like that by turning a crank by hand. The implication drives unnecessary fear in those less experienced.

Larry
 
I?ll guess the back side of the bearings out of that engine would appear to be polished as the result of relative movement between the bearings and the main bearing boss in the case, they lost their ?crush?. Possibly caused by dimensional problems, or loss of studs torque, and that due to fretting. Eventually without crush the dowel took the rotational load.
Just speculating.
Tim Andres
 
Bent dowel

The bent dowel pen has taken quite a bit of abuse my guess is that that the baring was louse in journal, perhaps the case half's were reworked and repaired for use of an oversized bearing shell but a standard got installed and run or an undersized ( for repaired re ground crankshaft) got inadvertently installed and run ether can cause the condition showed in post #23. I can't believe that turning the crankshaft to the case by hand could cause that damage NO WAY NO HOW. Whether or not the case halfs torqued to specs or simply hand tight.
 
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Dan was more polite, however I'm sorry but there is simply no way to bend a dowel pin like that by turning a crank by hand. The implication drives unnecessary fear in those less experienced.

Larry

Larry:

Then explain what happened.

I have only been an A&P for 20 year so have not seen everything. I have only attended the Lycoming engine school once.

There was damage on the bearing from being too tight. There was damage on the back of the bearing where the dowel pin was pressed into the bearing.
 
The bent dowel pen has taken quite a bit of abuse my guess is that that the baring was louse in journal, perhaps the case half's were reworked and repaired for use of an oversized bearing shell but a standard got installed and run or an undersized ( for repaired re ground crankshaft) got inadvertently installed and run ether can cause the condition showed in post #23. I can't believe that turning the crankshaft to the case by hand could cause that damage NO WAY NO HOW. Whether or not the case halfs torqued to specs or simply hand tight.

People (A&Ps) with a lot more experience than I do say other wise.

Read this article.

Quote from the article: In short, Fuchs contends that there?s a significant risk that an engine might come apart after cylinder work (especially a top overhaul) even when the work is performed exactly as directed by the manufacturer.
How can that be? According to Fuchs, the root cause of spun bearings,
thrown rods, and separated cylinders is simply ?failure to achieve sufficient preload in the assembled fasteners.?

Not my words but words from people more experienced than I.
 
Larry:

Then explain what happened.

I have only been an A&P for 20 year so have not seen everything. I have only attended the Lycoming engine school once.

There was damage on the bearing from being too tight. There was damage on the back of the bearing where the dowel pin was pressed into the bearing.

If you have been around metal parts that long, you should know how much force it takes to bend a dowel pin, especially one that short. If unsure, go try to bend one that short with a 16 oz hammer and see how much force it takes. Clearly that engine had a spun bearing and many hours of high RPMs and their associated inertia/force trying to spin that loose bearing shell bent the pin. It is also possible / likely that there was some large metal chunks in the journal / bearing interface helping to transfer force from the crank to the bearing shell.

Either way, it was not from turning the crankshaft 3/4 of a rotation by hand.

Larry

. Go w
 
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Preload

I read that story and reread it a few more times made some valid points but the failure rate has to be very small or it would be more well known.I think a bigger problem comes from cranks being turned by crank shops with old equipment and dimensions not being true causing bearing problems . How many engine builders check dimensions before rebuilding engine if they get a crank back yellow tagged most just stick it in.
Bob
 
People (A&Ps) with a lot more experience than I do say other wise.

Read this article.

Quote from the article: In short, Fuchs contends that there’s a significant risk that an engine might come apart after cylinder work (especially a top overhaul) even when the work is performed exactly as directed by the manufacturer.

And that same class of expert says that running LOP is a ticking time bomb and you MUST reduce throttle before prop and an oil fiter not saftied will fall off and walking under a ladder will bring bad luck, etc. We all have an opinion, but I can't find a reason why removing a cylinder would cause a spun bearing. However, I do believe that maintenance events can introduce problems due to human error. Any time that you do anything to an engine, you run the risk of making a mistake and causing a problem.

How can that be? According to Fuchs, the root cause of spun bearings,
thrown rods, and separated cylinders is simply “failure to achieve sufficient preload in the assembled fasteners.”

Not my words but words from people more experienced than I.

This makes complete sense. failing to properly install equipment to reach the proper bearing pre-load will certainly cause problems. However that doesn't mean we shouldn't do the work becuase we introduce the possibility of incorrectly reassembling it. It just means we should work harder to insure the people doing the work endeavor to not make these mistakes. Further, the issue with bearings is to get the correct level of crush to seat them firmly in the saddle. This only happens once at initial torquing. They are not a very springy material (mostly copper) and don't un-crush without the pre-load. If done correctly initially, when you take the torque off the saddle, the shells stay firmly in the saddle and stay there until re-torqued. They usually have to be twisted out. One could deduce that spinning the crank would loosen the shell from the saddle when the bolt torque is gone. However, I argue that if the shell is loose enough to spin in that case, it was doomed from the beginning. I cannot imagine the saddle would separate more than a couple thou, if that, when the studs are un-torqued. There are a lot of things working to hold it together beyond the bolt torque and very little force trying to separate it.

I think it is fair to say that best practice is to install bearings and torque, disassemble, then re-torque. This is the way most, non-production line, engines are assembled as it is the only way to measure the final bearing clearance. The only difference is that the crank is not in it and spinning. This kind of dispels the notion that un-torquing a bearing will cause it to spin.

All of that said, there sure does seem to be a lot of A&Ps that have observed spun bearings after a top overhaul. I simply don't know why this is.
 
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Read this article.

According to Fuchs, the root cause of spun bearings,thrown rods, and separated cylinders is simply “failure to achieve sufficient preload in the assembled fasteners.”

Good article. However, the subject matter (bolt tension preload should be more than applied stress in service) is entirely without engineering debate, and has nothing to do with the question at hand. The article deals with failure to apply the desired preload at assembly. Subsequent loss of preload is a different problem.
 
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Here is an image of good dowel pin on main center bearing of a 4-cylinder Lycoming.

Here is an image of what the dowel pin looks like where the bearing had turned.

Gary, jump in the Wayback Machine and consult SB's 326A and 327C.

From the SB:

Bearing and dowel failures on these engines can be attributed to movement of the mating surfaces of the crankcase halves at the bearing supports. This condition is due to gradual loosening of the crankcase thru-studs and shifting of the bearing inserts. In extreme cases the tendency of the bearing inserts to turn causes failure of the crankcase dowels and subsequent engine damage.

In other words, the dowels got beaten to death in service. It's the old fretting of the mating surfaces at the center main problem, which relaxed thru-bolt tension.

Note that if the clamp force is removed (at cylinder removal) from a center bearing that already had a beaten dowel and fretted parting surfaces, and then the crank was turned, it becomes possible for the bearing to shift. See the photos in 327C for one that shifted in service, with clamp force.

As you know, if a fretted case is re-torqued upon cylinder replacement, it pulls the bearing clearance tighter. It's not hard to see how (given a damaged dowel like the one in the photo) the bearing might then spin in the near future.

There is an oddity here. The photo seems to show a collared dowel, not a straight or stepped dowel. If so, what engine used a collared dowel in the center or rear main?
 
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Gary, jump in the Wayback Machine and consult SB's 326A and 327C.

Bearing and dowel failures on these engines can be attributed to movement of the mating surfaces of the crankcase halves at the bearing supports. This condition is due to gradual loosening of the crankcase thru-studs and shifting of the bearing inserts. In extreme cases the tendency of the bearing inserts to turn causes failure of the crankcase dowels and subsequent engine damage.

In other words, the dowels got beaten to death in service. It's the old fretting of the mating surfaces at the center main problem, which relaxed thru-bolt tension.

Note that if the clamp force is removed (at cylinder removal) from a center bearing that already had a beaten dowel and fretted parting surfaces, and then the crank was turned, it becomes possible for the bearing to shift. See the photos in 327C for one that shifted in service, with clamp force.

As you know, if a fretted case is re-torqued upon cylinder replacement, it pulls the bearing clearance tighter. It's not hard to see how (given a damaged dowel like the one in the photo) the bearing might then spin in the near future.

There is an oddity here. The photo seems to show a collared dowel, not a straight or stepped dowel. If so, what engine used a collared dowel in the center or rear main?

SB326A and SB327C both deal with 360 and 540 engines.

Subject engine is a 1961 vintage narrow deck 320 with 6,700 hours since new. Subject case was lapped and line bored ~2,600 hours earlier (15-years). Could not find e-Copies of SB326A or SB327C online but I have paper copies in my files. IF anyone wants an eCopy, let me know by email and I will mail you a scanned copy. The case is still sitting in my hangar if you desire to fly over and take a look. I no longer have the bearings I as tossed them when I moved last year.

The old narrow deck engine that I had problems with, have dowels on the front main, center, and rear bearings. The center main is where I discovered the problem but only on one half.

I am NOT a magazine article writer and do not have lots of words to explain everything. I found ONE engine that had a bent dowel pin. One problem does not mean that there are others or that there will not be others. People smarter than I warn to use caution when removing a cylinder. I am only trying to show what I believe may have been caused by removing all the cylinders and rotating the crankshaft when there is no torque on the through studs. I do not believe that this will happen to all engines that have cylinders removed but warn that something like this MAY happen if one is not careful.
 
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SB326A and SB327C both deal with 360 and 540 engines.

Subject engine is a 1961 vintage narrow deck 320 with 6,700 hours since new. Subject case was lapped and line bored ~2,600 hours earlier (15-years). Could not find e-Copies of SB326A or SB327C online but I have paper copies in my files. IF anyone wants an eCopy, let me know by email and I will mail you a scanned copy. The case is still sitting in my hangar if you desire to fly over and take a look. I no longer have the bearings I as tossed them when I moved last year.

The old narrow deck engine that I had problems with, have dowels on the front main, center, and rear bearings. The center main is where I discovered the problem but only on one half.

I am NOT a magazine article writer and do not have lots of words to explain everything. I found ONE engine that had a bent dowel pin. One problem does not mean that there are others or that there will not be others. People smarter than I warn to use caution when removing a cylinder. I am only trying to show what I believe may have been caused by removing all the cylinders and rotating the crankshaft when there is no torque on the through studs. I do not believe that this will happen to all engines that have cylinders removed but warn that something like this MAY happen if one is not careful.

I agree with Dan that fretting was a far more likely root cause for the bearing getting loose than the cylinder removal. Was that case modified with dowels on the through studs?

Larry
 
Interesting, just because they say it was line honed or bored, does not mean that they checked and confirmed the finished bore DIA.....precisely, after all, I bet a human did this work. I have returned blocks that were fresh machined to close tolerances only to bring them home and find a spec that was off. this subject example is probably already damaged but you can bolt and TQ the empty case back together and see what the crank bore measures. without that crush on the bearing insert steel outer shell it will make for a bad day.
 
The old narrow deck engine that I had problems with, have dowels on the front main, center, and rear bearings. The center main is where I discovered the problem but only on one half.

That too is interesting. How can one half rotate significantly, and not move the other half?

Earlier you mentioned 600 hours between cylinder replacement and the teardown resulting in these dowel pin photos. When did it begin to show a problem?

I am NOT a magazine article writer and do not have lots of words to explain everything.

I hear you buddy. Forgive me please. I just like to understand, and firmly believe that if I can't flesh it out in clear physical principles, it is either (1) not true, or (2) I have something yet to be learned.

My mom sent my brother and I to a parochial elementary school. Sometimes I think the information provided by Lycoming is closer to Catholic catechism than to technical guidance. We're expected to memorize and believe. Ask hard questions, and you get dogma in response.

Yes, the nuns may also have viewed me as a bad seed ;)

I found ONE engine that had a bent dowel pin.

I happily accept your caution to use torque plates. It may or may not be necessary, but it sure can't hurt.
 
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