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  #11  
Old 04-05-2018, 05:16 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by rvbuilder2002 View Post
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 doesnít 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 donít 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 canít spin. Accordign to Jim Doebler (former instructor at Lycoming), this is plenty acceptable, and doesnít require you to pay what Lycoming wants or the torque plates!
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  #12  
Old 04-05-2018, 05:25 PM
eaglen92ce eaglen92ce is offline
 
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Here is a good looking torque plate for Lycomings that does not cost to much!

http://ryanaircrafttools.com/product...torque-plates/
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  #13  
Old 04-05-2018, 06:32 PM
slngsht slngsht is offline
 
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Quote:
Originally Posted by eaglen92ce View Post
Here is a good looking torque plate for Lycomings that does not cost to much!

http://ryanaircrafttools.com/product...torque-plates/
I have a CNC plasma. I could've popped those out in an hour but instructions I was following didn't say to torque the case back down. Oh well. I'll look into doing the bottom end too and see what that costs.
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  #14  
Old 04-05-2018, 07:09 PM
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rocketbob rocketbob is offline
 
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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.
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  #15  
Old 04-05-2018, 09:58 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Ironflight View Post
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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Last edited by rvbuilder2002 : 04-05-2018 at 10:01 PM.
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  #16  
Old 04-06-2018, 08:10 AM
tim2542 tim2542 is offline
 
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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. Iíve 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. Itís not hard but find the latest Lyc SB/SI and follow it exactly with a known good torque wrench and hopefully a friend whoís done it before.
Also if the case is badly fretted (you wonít know) with a million hours on it, there is a smalll chance when you retorque the studs youíll lose the main bearing clearance. Itís only .0015Ē 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
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  #17  
Old 04-06-2018, 08:18 AM
tim2542 tim2542 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Hmmmm, I can see the reasoning for danger of using the washer method.
Actually if you look at one disassembled youíll seal the actual O ring seal surface is the beveled area below the flange surface.
Tim Andres
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  #18  
Old 04-06-2018, 08:23 AM
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DanH DanH is offline
 
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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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Last edited by DanH : 04-06-2018 at 08:26 AM.
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  #19  
Old 04-06-2018, 08:58 AM
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RV6_flyer RV6_flyer is offline
 
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Quote:
Originally Posted by Ironflight View Post
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!
Quote:
Originally Posted by rvbuilder2002 View Post
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).
Quote:
Originally Posted by tim2542 View Post
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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Last edited by RV6_flyer : 04-06-2018 at 09:40 AM. Reason: spelling
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  #20  
Old 04-06-2018, 09:06 AM
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Ironflight Ironflight is offline
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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.
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