Tappet clearance

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Kaweeka

Filing Flight Plan
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David
Is there any way to measure tappet clearance on an IO360 angle valve without pulling the cylinder and push rod tubes? I obviously need to depressurize the lifters but don't think it's possible while it's still in the engine. Anyone have a trick to getting them out?
Thanks
 
Kaweeka said:
Is there any way to measure tappet clearance on an IO360 angle valve without pulling the cylinder and push rod tubes? I obviously need to depressurize the lifters but don't think it's possible while it's still in the engine. Anyone have a trick to getting them out?
Thanks
Click to expand...
Lots of fun, that. That engine doesn't need the cylinders pulled, just the pushrods and tubes, and the plungers in the lifters have to come out and get emptied and dried and everything reinstalled. And so help the guy that comes along and turns the propeller and pumps oil into them again...

What you're looking for is the dry tappet clearance. Page 6-23, paragraph 6-136, of the overhaul manual: http://www.grummanpilotsassociation...ming-60294-7-Direct-Drive-Overhaul-Manual.pdf
 
What are you trying to do ? There is a way to do a quick check but it’s not accurate as there may still be oil in the Lifter.
 
Magman said:
What are you trying to do ? There is a way to do a quick check but it’s not accurate as there may still be oil in the Lifter.
Click to expand...

Just guessing for fun:
-If it exceeds spec with oil, it’s an easy “no go”?
-Check with rocker installed and dial indicator on the end, at rest on cam base circle, then compress by hand? Need to remove valve spring?
 
455 Bravo Uniform said:
Just guessing for fun:
-If it exceeds spec with oil, it’s an easy “no go”?
-Check with rocker installed and dial indicator on the end, at rest on cam base circle, then compress by hand? Need to remove valve spring?
Click to expand...
That would be way out of spec. With the lifter dry, and on the heel of the cam, the rocker/valve stem clearance is to be within .028 to .080". That leaves adequate room at either end of the lifter's range for changing clearances due to heating of the cylinder, pushrod, valve stem, valve wear, and so on. The cylinder can get hotter than the pushrod, so the clearance can increase. If the lifter is maxed out when cold, it will be rattling at operating temps and pounding the valve stem and rocker.
 
This is a “ better than nothing” check that can only give you an idea of “way tight” or “ way loose”. If you are doing more than one jug it can also take more time than the proper way.
That said:

Lifters will bleed down at different rates depending on factors such as design, oil viscosity and temperature..

Turn prop so Intake Valve is open.

Allow to sit for 10? Minutes

Put your thumb on pushrod end of Rocket Arm and push as if trying to compress pushrod. Do not allow pressure to relax.

Turn crank until on base circle of Cam . Check clearance with Feeler Gage.

Repeat procedure for Exhaust if needed.

As I said ; this is a troubleshooting tool and not a replacement for the Lycoming Procedure.
 
Wondering about OP’s concern.

But again; I’ve never had a burning desire to go check Dry Lifter Clearance!
 
You realize this is a procedure during cylinder replacement or engine overhaul? It's not a periodic check and it is not normal to be replacing pushrods during the life of a cylinder or engine.
 
Silvaire said:
You realize this is a procedure during cylinder replacement or engine overhaul? It's not a periodic check and it is not normal to be replacing pushrods during the life of a cylinder or engine.
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No. No usual. But there are times, such as finding bronze chips in the oil filter. Pulled the rocker covers, found failing rocker bushings. It appeared that the recent field overhaul had neglected to replace them. Replacing them required a dry lifter check, since the new bushings altered the rocker position.
 
I’ve thought it would be a good idea to keep a record of accurate checks of DLC.
It could come in handy with low power and suspecting a Cam issue. However, I didn’t and haven’t seen one either.

I dimly recall a Bendix Distributor Block AD of 40ish years ago that required a DLC check if defective. It did not state WHY but my guess was cross-firing would overheat and stretch the Exhaust Valve causing low DLC.

I’m always amazed how thorough some Techs are with cylinder changes on small bore Contis. They even touch up the paint on the Llfter Cover to match the original . Wow!

Lycoming folks:You can’t remove Lifters to check DLC on Contis with Cover on.
 
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I was just saying that the OP seemed to just want to 'check' this for an unstated reason and I wanted to point out that you don't need to do that. You could pull your mags apart and check the distributor blocks and points and stuff. That would probably be a more fruitful use of time.
 
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