The International Cessna^® 170 Association

I had to replace a cylinder at annual due to a leaking exhuast valve.
Replaced with a rebuilt millennium cylinder. They were out of new. Put it together and were unable to achieve the propper dry tappit clearance.
A & P placed screw drivers between lifter and pushrods to bleed down the tappits but i suspect this is did not do the trick. Along the way whent to screw in the top spark pug and behold it had a bad thread in it that we coudnt clean up. So off the cylinder came and back to JJ airparts. So now the cylinder is back off and a new cylinder is in the box by the plane. My question is how do you properly bleed down the lifters with a cylinder off?
I have a problem believing you can not have enough of dry tappit clearance with a new cylinder. a new cam, new lifters, new rockers!
Anything you would do to regrinding to would lead to too much dry tappit clearance. IE undersize cam, Rocker faces reground = to too much dry tappit clearance.
JJ Airparts says there is no such thing as undersize push rods. only oversize.
So i have to believe we are not getting lifters bled down propperly
THX Brent

Take a wooden toothpick (the round heavier duty ones) or similar softer-than-steal device and push the little spring loaded check ball in the center of the lifter (pushrod side of lifter) down and they will bleed down. I believe the dry tappet clearance is 30-110 thousands. The last time I purchased different size pushrods I got them from Fresno Airparts.

Joe

Brent,
It's only been 40 years since I've monkeyed with these lifters in A&P school so take that into consideration when weighing my advice -- it's almost worth what you're paying for it.

I'd start with the easy stuff first. Are you sure you don't already have oversize pushrods? New standard pushrods should measure between 10.797" and 10.827", oversize ones 10.827" and 10.857".

Anything you would do to regrinding to would lead to too much dry tappit clearance. ...

Grinding the valve seat will decrease lash. Here's what Continental says about fixing that problem --something I'd only do as a last resort:

Joe Moilanen wrote:Take a wooden toothpick (the round heavier duty ones) or similar softer-than-steal device and push the little spring loaded check ball in the center of the lifter (pushrod side of lifter) down and they will bleed down.

I believe Joe is referring to check ball "D" that needs to be displaced to deflate the lifter.The TCM overhaul manual devotes a full chapter to the hydraulic tappets. Might be worth it for your mechanic to review Section 16 if he's as rusty as I am on them.

Why was it necessary to replace a cylinder due to an exhaust valve not seating properly? Maybe the exhaust seat or guide had to be replaced? Not being critical, just trying to understand if this is always the recommended solution to an exhaust valve not functioning properly.
I've had this occur twice over the past 5-10 yrs on two different cylinders. (Actually 3 times) First time the cylinder was removed, sent to a local cylinder shop and a new guide installed. Next two times, the latest being about two yrs ago. Both times I was able to clean up the exhaust valve (it wasn't burned) with grinding compound and some effort. This restored the compressions to high 70's. Just wonder why your A&P didn't do something similiar.

Brent,
Curious what the solution to this problem was?