New Continental Cylinders - Check the Pushrod Clearances

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jepsen
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Joined: Fri May 27, 2005 3:59 pm

New Continental Cylinders - Check the Pushrod Clearances

Post by jepsen »

We have have N4033V since 1982, so needless to say we have changed a few cylinders over the years (most were rebuild since we kept a few spares on hand) and never had an issue with the Pushrod clearance. We finally joined the 20th century and installed a set of factory new continental "Air Boss" cylinders and we had to install 4 oversized pushrods. I suspect the manufacturing process has changed more than a little since the original cylinders were produced so this may be more common event going forward, I just wanted to advise my fellow 170 owners, to give this a serious look when you install factory new cylinders

Scott
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Bruce Fenstermacher
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Re: New Continental Cylinders - Check the Pushrod Clearances

Post by Bruce Fenstermacher »

Scott, you didn't say but was this at rebuild?

Lots of reasons you would need an oversized pushrod and I'm pretty comfortable saying none of them would be new cylinders of any make. Oh I suppose if the valve seats in those cylinders happened to be just a bit thicker than the rest combined with those valves not lapped quite as deep. But I doubt this really. If you only installed new cylinders and no bottom work then the wear is either cam, follower or rocker arm wear. And I'm guessing in this case it's the rockers, or least I hope it is and not a worn cam or followers.

Did you move rockers around to try to put those with more wear on those rods whose followers might have been a little thicker?

If you rebuilt the engine and the case halves wear shaved and the crank and cam bearing line bored, that would actually tighten the tolerance of the push rod. Follower thickness variation or resurfacing for wear would loosen the pushrod. And then finally there is the rocker arms. At about $600 a piece not many rockers are replaced I'd guess.

BTW it's not that uncommon to need the longer pushrod at overhaul these days. I have all but one oversized pushrod in my 2 hour old overhaul.
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Bruce Fenstermacher, Past President, TIC170A
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jepsen
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Re: New Continental Cylinders - Check the Pushrod Clearances

Post by jepsen »

Bruce,

This was not an overhaul, just 4 factory new continental cylinder to match to 2 in the back we installed a couple years ago. We have a disassembled "parts motor" so we did try different rockers arms but it didn't help much.

We reviewed this with our AI and a veteran of many overhauls, in his past experience, the vast majority of Continentals never required any special push-rods, but the vast majority of Lycomings did.

Considering the original cylinders were designed before WWII and Continental has made a number of significant changes since Superior came out with their "re-designed replacement cylinders" and gave Continental a little competition, it doesn't surprise me that everything doesn't just bolt on. But it is something anyone who installs a new cylinder should be checking.

We have done our first and second 1 hour break in flights, the engine sounds good and runs strong, now if we can just get the oil leaks to stop we will be OK

Scott
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Bruce Fenstermacher
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Re: New Continental Cylinders - Check the Pushrod Clearances

Post by Bruce Fenstermacher »

Well bottom line, proper procedure replacing any cylinder is not to assume the push rod that was used is still appropriate.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
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