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Dry tappet clearance vs. Push Rod length
- Thread starter jayyau
- Start date
May I ask .What length push rods did you start with -34,-35,-36 ? These are 0-360 values and do not apply to the 0-320
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Are you sure you have all oil removed from the tappet body? Even a drop will effect the result. Also after the tappet body is free of oil use a pin at the bottom of the tappet to collapse the tappet body. Before installing get the crankshaft in the proper point in revolution; the point at which the valve is fully closed. Now you can install the tappet body, the push rod and rocker arms and check the clearance.
Bill
Bill
Remove hydraulic lifter plunger like on this video.
Collapse the lifter plunger like on this video.
There can be some minor differences in push rod lenghts with the same part number. Just because clearance is out of spec with one push rod of the same dash part number does not mean that one you have with the same dash part number will have the same clearance.
Please don't take this the wrong way, but are you taking steps to insure that you are checking the clearance when the cam lobe is on it's base? There is a process to follow that does not require removing the cylinder or otherwise looking at the cam/lifter arrangement. You should never have to look at that unless you expect some type of damage.
I don't know the ratio for the Lycoming rockers, but I would expect it to be in that neighborhood. I would have guessed closer to 1.4. Your math and logic are correct. See the other posters advise about collapsing your plungers before checking. However, the fact that you were able to measure any clearance seems to indicate that you have somehow drained the plungers. Please elaborate on the procedure you are following. Sometimes plungers can drain down on their own and pushing on the rod can partially drain the plunger. For accurate results, you will need to pull the plunger and clean the oil out.
Larry
Be advised that this does not always work. This method leaves oil in the plunger. If you allow the plunger to go right side up, the ball sticks to the opening and seals the plunger again. It is much better to clean the plunger of all oil before checking dry tappet clearance. Otherwise you can get odd results like you are getting now. Don't forget to oil them up before final assembly.
When you disassemble the plunger, you'll see that there is a spring in there. I can only be collapsed under pressure and it springs back after released. The tension of oil can hold ball on the seat, which is the mechanism for sealing the plunger. If this happens while installing the plunger in the tappet, it won't collapse or fully collapse when you press on the rocker to check the clearance. This is why removing the oil is recommended.
Larry
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Superior vs Lycoming Pushrod Lengths
to add one more variable to this:
I was going through the same process, trying to get the dry tappet clearances right on my engine. I did the same process, and ended up needing a slightly longer pushrod. Lycoming wasn't stocking the one I needed (I have a red-headed stepchild of an engine that had been decked in the '80s to increase compression, so it requires abnormally short pushrods). So, I ordered the Superior part number that was listed as the the required length. When I got it I could not even measure the tappet clearance because the rocker arm was contacting the head and the tappet clearance was something like 1/8"-3/16". I swapped cylinders, changed parts around, and finally measured the pushrods and found that the Superior part was shorter than the "same" Lycoming part by a significant amount. I talked to Superior about it, and after a few rounds of parts and discussing we determined that, sure enough, the Superior part and the "same" Lycoming part differ by a rather significant amount. I forget the exact value, but it was something like 0.050" or more.
So, when swapping pushrods and ordering new ones, be sure to buy the pushrods form the same vendor.
to add one more variable to this:
I was going through the same process, trying to get the dry tappet clearances right on my engine. I did the same process, and ended up needing a slightly longer pushrod. Lycoming wasn't stocking the one I needed (I have a red-headed stepchild of an engine that had been decked in the '80s to increase compression, so it requires abnormally short pushrods). So, I ordered the Superior part number that was listed as the the required length. When I got it I could not even measure the tappet clearance because the rocker arm was contacting the head and the tappet clearance was something like 1/8"-3/16". I swapped cylinders, changed parts around, and finally measured the pushrods and found that the Superior part was shorter than the "same" Lycoming part by a significant amount. I talked to Superior about it, and after a few rounds of parts and discussing we determined that, sure enough, the Superior part and the "same" Lycoming part differ by a rather significant amount. I forget the exact value, but it was something like 0.050" or more.
So, when swapping pushrods and ordering new ones, be sure to buy the pushrods form the same vendor.
I avoided all these problems. after moving parts all around, I had three pushrods that were too short to meet spec. For each one I determined how much longer I needed it to be, using a formula similar to the OP's. (found the factor on a post here). I sent the 3 pushrods to Manton pushrods (I don't have calipars or mic's that large). They measured my existing rods and added/deleted the dimension I provided for each and they shipped me 3 new custom pushrods. I paid $10.50 per pushrod and the quality far exceeds the Lycoming. Pushrods are quite a bit beefier, but the weight penalty is insignificant in my opinion. They cater to the racing business where everyone needs thick-wallled pushrods, so they don't carry the thin-wall material.
Larry
After you clean the oil out of the plunger it needs to be collapsed before reinstalling into the tappet body. You collapse the plunger by using a small pin or needdle at the very tip of the plunger opening at the bottom. Hope this makes sense.
Bill
LifeofReiley
Well Known Member
Back many years ago there was a well known builder wrapping up a 540 re-build for his EAB project... had custom adjustable push rods fabricated like in the Hot Rod cars. As I recall, it worked out very well for him.
Do you understand cam crank relationship. It's not just TDC, it is TDC on the compression stroke. If you are not insuring it is TDC on the compression/power stroke, you could be at TDC on the intake/exhaust stroke. If the latter is the case, both lobes could be on their ramp. Again, don't mean to insult your intelligence, just want to be sure. Doesn't seem likely, given the excessive lash
Larry
The plunger contains a decent amount of oil. If you will not be fully disassembling the plunger and just soaking it, you should first drain the oil. You do this by using a toothpick to hold the ball off the seat and then compress the plunger fully. If you don't do this, you are not removing the oil. Also, be sure to get the gas out of it in the same way. You can also separate the plunger form the base assembly. The spring holds it in. This is my recommendation.
I'll restate that the plunger can only be collapsed under pressure. The spring prevents it from staying in a collapsed state. Therefore if oil remains in the plunger, subsequent attempts to collapse it will likely not work without the toothpick. Once the thick oil is out, you'll have no problem fully collapsing it
The fact that you are seeing too large of reduction in lash, seems to indicate that the plunger is not fully collapsing after installing the new rod. Fully removing oil from the plunger should give more consistent and reliable results.
Larry
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The cylinder was on the top dead center and compression stoke, the plunger was disassembled and soaked/washed in the solvent. Then I put the plunger back together, twisted the cylinder clockwise until I head a click which engaged the spring. Before I put the plunger back in, I shook and heard the ball rattle freely inside of the plunger.
By swapping between the old/new push rod, I got big reduction with Dry Tappet Clearance, the ratio was close to 1:3 instead of 1:1.28.
At one point, I even thought about the curvature of the push rod end, that's why I went a little further and ordered a genuine Lycoming push rod, but the result remains no change.
any way, I'll try it again this weekend, and be sure to follow all your recommendation. Thanks a lot.
By swapping between the old/new push rod, I got big reduction with Dry Tappet Clearance, the ratio was close to 1:3 instead of 1:1.28.
At one point, I even thought about the curvature of the push rod end, that's why I went a little further and ordered a genuine Lycoming push rod, but the result remains no change.
any way, I'll try it again this weekend, and be sure to follow all your recommendation. Thanks a lot.
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DanBaier
Well Known Member
The Lycoming reference for lengths is at http://www.lycoming.com/Portals/0/t...060K (06-21-2010)/Push Rod Identification.pdf - the lengths are approximates. What I found, once in the same situation, is that it seemed nearly impossible to depend on the incremental values to get to the correct pushrod. Faced with the same situation, the advice to me was to just try a -34 pushrod (O-360) and by trial and error go up / down from there. There was variation in the -34 pushrods, but ultimately they worked. I can't quite see where you started so I wouldn't know what to suggest for a O-320 but would expect it to be the -13, -14, or -15 (assuming a flat tappets).
The issues of oil in the lifter and measuring at TDC have been covered by other posters.
I don't think I'd probably take it for granted the correct pushrods are installed and at this point you should probably get everything pinned down correcty.
Did you mean '0.190' or '0.019'?
It also seems there could be some issues with how you're measuring - that has to be sorted out and I'd probably get that resolved before doing anything else or you'll be chasing variations that aren't really there. Keep in mind that if you clean the lifters, even with a minor amount of rotating the prop (to take measurements, etc.) the lifters will reload and could throw off bad results.
Dan
The issues of oil in the lifter and measuring at TDC have been covered by other posters.
I don't think I'd probably take it for granted the correct pushrods are installed and at this point you should probably get everything pinned down correcty.
Did you mean '0.190' or '0.019'?
It also seems there could be some issues with how you're measuring - that has to be sorted out and I'd probably get that resolved before doing anything else or you'll be chasing variations that aren't really there. Keep in mind that if you clean the lifters, even with a minor amount of rotating the prop (to take measurements, etc.) the lifters will reload and could throw off bad results.
Dan
Sounds like you did everything right. How are you measuring the clearance? Feeler gauge between valve and rocker is best. I don't really understand how you are getting the results you are getting. How are you getting the precise rod lengths? I struggled to come up with a way to do this with the tools that I had.
Larry
Do you trust the builder? If you do, you should consider the possibility of wear on the cam lobes or tappet faces for the 5 in question. If the clearance was correct at rebuild, you have experienced unusual wear; Possibly excessive break-in wear from improperly ground tappets. something to think about. The clearance is excessive enough that even a shoddy rebuilder would consider swapping pushrods. I suppose it's possible they didn't even check them. I'm sure it wouldn't be the first time. However, these guys can lose their certificate for such things and I would expect it to be the exception.
I remember the range of pushrods offered by lycoming, from smallest to largest, was only about .110" (for appx.150 of lash adjustment). At .190" off, you're getting near the extreme edge and that would get my mind thinking of alternate theories.
The caps on the exhaust valves are there, correct? I remember them being pretty thick, so unlikely that's an issue.
Larry
That's a major league no no! Lifters can be replaced without cam replacement, but never the opposite. You should have mentioned that first. In a perfect world, the tappet wore into conformity with the cam. If you wore .100" off the cam lobe, you'll pay for that in performance through to TBO.
I understand the desire to avoid a tear down, however, I would not wallpaper over this by putting in longer pushrods just yet. If it were me, I would confirm how much lift you have left on each cam lobe. If an acceptable lift exists, then go ahead and consider the work around with pushrods.
I would find a stable way to put a dial indicator on each pushrod or plunger and rotate the crank through a full lobe rotation and measure the travel. Compare each intake to each other and each exhaust to each other. The intakes should all be the same as will the exhausts (I would assume different lifts for Intake and Exhaust, but don't know). I don't have spec's for the lift on these cams, but clearly 3 of your lobes are in pretty good shape so you should have a close reference value. Maybe one of the engines experts can give you the lift spec for your cam.
After that test, you'll know if you have wear on your cam. If you do, I would recommend replacing it with all new tappets this time.
EDIT: My recollection from past research is that when you put non-new, mismatched lifters they will not develop a rotation of lifter. This leads to long-term wearing of the lobe and lifter that never settles. A new lifter has a concave/convex (I forget which term is appropriate - It is a dish shape) surface that works with the slight angle cut of the lobe to initiate a rotation of the lifter. As the tappet wears into conformity with the lobe, this dish shape developes a mating that maintains rotation of the lifter. If the lifter does not rotate, excessive long-term wear is inevitable.
Larry
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Hi Larry,
"I would find a stable way to put a dial indicator on each pushrod or plunger and rotate the crank through a full lobe rotation and measure the travel."
Great advise, very scientific. I'll find a way to attach a dial indicator and measure the cam lobe travel. Thank you so much Larry.
Jay
"I would find a stable way to put a dial indicator on each pushrod or plunger and rotate the crank through a full lobe rotation and measure the travel."
Great advise, very scientific. I'll find a way to attach a dial indicator and measure the cam lobe travel. Thank you so much Larry.
Jay
You have some type of measuring error. The ratio is NOT 6:1. I might buy 1.6:1. That is the ratio for a small block ford with stronger valve springs than a lycoming. I am still guessing between 1.4:1 and 1.5:1. Either way it's not even in the same neighborhood as 6:1. You need to get a handle on your approach for measuring the the lash.
While the lobe measurements are encouraging the only real comparison is against like lobes. We need to see all four to be sure. But, given the above, I think you are having an issue with measurement. Are you sure you got the springs in the plungers fully seated? It takes a good push while turning. If you rotated the engine, the valve spring pressure would do it and explain your theory of "breaking in."
Larry
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If you got the tappet clearance right, you are good. I would still question the measurement of the pushrods themselves, but in the end all that matters is that the clearance is correct.
I would still confirm that you have a consistent lift across lobes to uncover the reason for the improper clearance before you started.
Good luck,
Larry
I would still confirm that you have a consistent lift across lobes to uncover the reason for the improper clearance before you started.
Good luck,
Larry
scarter770
Member
Manton and Smith Brothers are the premier pushrods builders in the country. I found Lycoming pushrod length random at best. I use Smith Brothers for all my requirements. Stock ratio is 1.28 to one.
Thanks
Steve
Canadian_JOY
Well Known Member
Am faced with changing two cylinders on an O-320 with exchange overhauled units this coming weekend. Wondering if anybody has the appropriate "how to" section of Lycoming manual in soft copy as I suspect we'll need to select the proper pushrods for these O/H'd cylinders?
If you have the appropriate section of the Lycoming manual in soft copy and could share it I'd be grateful.
If you have the appropriate section of the Lycoming manual in soft copy and could share it I'd be grateful.
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az_gila
Well Known Member
Section 5 of the Owners Manual - one version here - big file...
http://www.8kcab.com/Checklists_files/Lycoming 0-320 IO-320 LIO-320 Operation Manual.pdf
http://www.8kcab.com/Checklists_files/Lycoming 0-320 IO-320 LIO-320 Operation Manual.pdf
Canadian_JOY
Well Known Member
Thanks, Gil - that's just what I was looking for!
Finally I checked all the Cam travel in my O-320 B3B engine....
Exhaust cam travel, Cyliner 1/2/3/4 = 0.352"/0.333"/0.348"/0.359"
Intake cam travel, Cylinder 1/2/3/4 = 0.349"/0.346"/0.348"/0.351"
Only cylinder #2 exhaust cam travel is a little bit weak = 0.333", all others are right around 0.350". Good to know that the cam/tappet doesn't have abnormal wear. Thanks for the advise. It's a great learning experience.
My next task is to bring Dry tappet clearance back to spec (0.028" -- 0.080").
Exhaust cam travel, Cyliner 1/2/3/4 = 0.352"/0.333"/0.348"/0.359"
Intake cam travel, Cylinder 1/2/3/4 = 0.349"/0.346"/0.348"/0.351"
Only cylinder #2 exhaust cam travel is a little bit weak = 0.333", all others are right around 0.350". Good to know that the cam/tappet doesn't have abnormal wear. Thanks for the advise. It's a great learning experience.
My next task is to bring Dry tappet clearance back to spec (0.028" -- 0.080").
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Canadian_JOY
Well Known Member
Recently replaced two cylinders with overhauled units on an O-320-E2G. Overhaul shop indicated that -12 pushrods were really uncommon for installation with overhauled cylinders. I knew I had removed one -12 and the other three units were -13's. Just to be safe I ordered a set of 4 -14's and 4 -15's. When we installed the overhauled cylinders we found that one valve definitely needed a -12 (thank goodness we had one on hand). Two valves required -13's. The last valve was just barely in spec (0.030 clearance) with a -13 pushrod and could well have done with a -12 rod.
All of this just to say... make sure you've tried all the options as far as different pushrod lengths.
All of this just to say... make sure you've tried all the options as far as different pushrod lengths.
Interesting that #2 & #3 exhaust have such different lifts when they both operate off of the same cam lobe. What and I missing?
Hi Mel,
That was an over all travel, included the tappet.
Since I'm going to replace all the tappet sockets, I'll re-measure it again to confirm the number.
My dial indicator setup was a little bit awkward at the time of test, I finally bought a nice tool to finish the job.
This is the tool I bought from Harbor Freight, it worked very well checking the cam travel. I didn't use their dial indicator, I have a better indicator to do the job.
Here is the link for the tool....
http://www.harborfreight.com/clamping-dial-indicator-93051.html
That was an over all travel, included the tappet.
Since I'm going to replace all the tappet sockets, I'll re-measure it again to confirm the number.
My dial indicator setup was a little bit awkward at the time of test, I finally bought a nice tool to finish the job.
This is the tool I bought from Harbor Freight, it worked very well checking the cam travel. I didn't use their dial indicator, I have a better indicator to do the job.
Here is the link for the tool....
http://www.harborfreight.com/clamping-dial-indicator-93051.html
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scarter770
Member
Hi Jay
I have the IO540
I have the IO540
Wear.
Cam lobes can and do wear during break in, especially if the lifter base was not properly ground or an inadequate lube used. The break in process for cam/lifter interface is very challenging in the first 30 minutes. The wrong oil is enough to wreak havoc. We have been having this problem in the auto world with non-roller lifters since they mandated the ZDDP out of the oil 10 years ago.
Larry
EDIT: sorry, I mis-read your question. That is an odd finding. no explanation here. Could be a measurement error. If it is the same lobe, I don't believe it is possible to get different readings, if the reading is taken from the lifter base or push rod if spring is removed from plunger.
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