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Rebuild: Problem in Valve Train

L

lr172

Well Known Member
Yesterday I finished the primary assembly of my O-320. Today I started checking the pushrod lengths. With everything installed, I am at least .140 long on the push rod.

I assembled everything, put the rocker in place and compressed the plunger. The rocker then sits high. an approximate measurement of the offset is about .125 (1/8") before I would slip the pin in both the boss and the rocker. My push rods are about the middle of the range, so I can only drop about .070 with shorter push rods.

Something must be wrong and the only thing that makes sense is that valves (re-ground) or the valve seats (new) were ground to far, leaving the valve stem sitting high. The cylinders were re-built by Harrison many years ago.

I am hoping that I missed something simple here. Any recommendations or ideas?

I appreciate anything you can offer.

Larry
 
Pushrods

Did you check more than one cylinder?? Are you absolutely certain you have the cam positioned properly for the check?? Hold the pushrod with some force toward the cam and get someone to turn the engine a bit and see if the pushrod moves. The next thing I would probably do is get a new short pushrod and measure the length against your pushrods.
If you exhaust all other options you can shorten some pushrods by removing one end, machine the tube end in a lathe, and reinstall the end.
 
So far, I have checked 2 cyl (4 valves). Will do the others later tonight. I pulled the idler gear and made sure the cam was 180* from peak for each test. I pushed pretty hard to be sure everything was seated.
 
jrs14855 said:
If you exhaust all other options you can shorten some pushrods by removing one end, machine the tube end in a lathe, and reinstall the end.
Click to expand...

I like this idea. I notice that the push rod have an installed tip, but it has two spot welds holding it on. Is there a non-destructive way of removing these tips? I should be able to mill them to size and re-weld them with a MIG welder.
 
Pushrod

IIRC not all of them are spot welded. You want the ones that are pressed in.
I would suggest that you order just one pushrod in the shortest length and compare it to what you have.
The other possibility-is there a difference between narrow and wide deck pushrods. I don't have a narrow deck catalog so I don't know. I have some pushrods, both new and used for wide deck if you want to try one for comparison.
 
Pushrod

Perhaps better yet take one of the pushrods over to Poplar Grove and ask them to identify it, or buy a new pushrod from them.
 
jrs14855 said:
.....
The other possibility-is there a difference between narrow and wide deck pushrods. I don't have a narrow deck catalog so I don't know. I have some pushrods, both new and used for wide deck if you want to try one for comparison.
Click to expand...

My parts catalogs shows the same pushrod numbers for both standard flange and wide flange in O-360 models.

Are the O-320s really that different between standard and wide flanges?

Could you have got hold of IO pushrods that are different?
 
My bet is on post #9.:)

Unless you either depress the ball with a plastic pick while compressing the lifter or disassemble the lifters and cleaned all oil out they will not compress fully. Know this from first hand experience.
 
RVDan said:
My bet is on post #9.:)

Unless you either depress the ball with a plastic pick while compressing the lifter or disassemble the lifters and cleaned all oil out they will not compress fully. Know this from first hand experience.
Click to expand...

+1 with Post 9 and RVDan. :)
 
+1 on the dry plunger. You probably have to remove the assembly, separate the pieces and clean them. Don't mix the parts - they should stay together and go back into the precise tappet they came from. Don't drop them (they're a throw away if you do.)

The pushrods should have the part number stamped on them (there are old / new style numbers). I wouldn't be recommending altering the length of the pushrod - just my preference. (Keep in mind oil travels through the pushrod to lubricate the top end of the cylinder - rocker arms.)

If you're close to Poplar Grove - that's a great resource. I've had very good luck with them myself.

Dan
 
By the way, even if you are sure to get the lifter compressing on your hand, don't pump the lifter once installed- it will pick up oil laying in the tappet body and then you start over cleaning oil from the lifter.
 
Pushrod

Lifters should not be pressurized if the engine has not run.

IIRC one of Mahlons tips was to just put pressure on the pushrod for a couple minutes and the lifter will bleed down.

I am more inclined to think this is some oddball pushrod issue. If I understand the op correctly it does not seem possible that excessive grinding on the valves could result in .14 mismatch. Most of my pushrods were too short with factory Lycoming cylinders. The rockers were used and reworked.
 
Pushrod length can vary slightly even with the same part number, new or old. I made a jig for pushrod total length measurement to help over come this frustration. Also found that the machined pushrod seat and/or valve tappet on the rocker arm can be different from one rocker to another, affecting initial valve lash set-up.
 
It's been a while so I can't recall who it was but they had a 540 and manufactured adjustable pushrods and ran them with roller rockers. Awesome set-up for sure. :) I love my roller rockers!!
 
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plungers are dry. I took each one apart personally and cleaned them. I used a very light bit of machine oil on the mating surfaces to avoid rusting. Nothing near the check ball and I am able to compress them in my hand until I hear a metal click. Lifter bodies have a bit of oil in them, but it is on the edges only with no pooling at the bottoms, therefore not in contact with the point of oil entrance on the plungers.

My push rods are double spot welded on both sides. They are original Lycoming from the 60's and have no part number marked on them. This engine ran to TBO over 15-20 years then sat in a garage for another 20.

I am going to research the push rod size. If the sizes match anything in the auto world, I can have some custom made, as that is common in the hot rod world.
 
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LifeofReiley said:
It's been a while so I can't recall who it was but they had a 540 and manufactured adjustable pushrods and ran them with roller rockers. Awesome set-up for sure. :) I love my roller rockers!!
Click to expand...

Me...I had adjustable roller rockers made with a taller ratio. Haven't run them yet.

I have an adjustable pushrod I made to use to get the length right, then measure OAL with a digital caliper. Then I call either Manton or Smith Bros. and have custom pushrods made. 1/4th the price, stronger, better.
 
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Uncovered something just now. The plungers that are original Lycoming and were assembled in this engine have no part number, but have a letter E on them as well as a series of dots. They are old Lyc, so I assumed were the correct plungers. I was given another set of newer plungers that I cleaned but haven't tested yet. They are part #78290. The interesting part is that the oil pickup stem is 3/8" on the old vs. 1/4" on the newer. This extra 1/8 must be contacting the sump area of the lifter body and keeping it from hitting it's natural seat on the lifter body. The newer plungers give me an arrangement that I would expect and will allow me to use.

Very interesting here. The original lifter bodies had a relief cut in them and had an SB recommendation from Lycoming not to re-use.

I guess if any of the newer plungers don't pass, I can probably cut an 1/8" off the stem of the old plungers.

Larry

EDIT;68312 I looked closer and the older plungers have a part number hand etched with the number 68312. The first couple of newer plungers seem to test ok after a good cleaning. I am optimistic.
 
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