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Post by splischke on Oct 9, 2011 22:15:00 GMT -5
Top ring on #3 piston broke at 253 hours STOH. Air gushing into the crankcase on the leak-down test prompted a top-end tear down.  -Scott |
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pttim
New Member
Posts: 30
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Post by pttim on Oct 10, 2011 11:16:03 GMT -5
Scott,
Was the leakdown part of your yearly condition inspection or was it warranted by a problem you were experiencing?
Tim
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Post by soneraifred on Oct 10, 2011 12:16:40 GMT -5
Hi Scott:
I had a top ring fail twice on my 1850. One time it was because the wrong ring was supplied. It was 0.5 mm thinner than it was supposed to be, and I wasn't smart enough at the time to measure the ring side clearance. I don't remember why it happened the other time.
Now, I have a wheezing exhaust valve on #1 cylinder, so it's time to pull the head and lap the valves. Fortunately, it's also annual inspection time...
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Post by splischke on Oct 10, 2011 12:34:01 GMT -5
I perform a leak-down test with every oil change (25 hours). This may sound like overkill but after 500 hours of flying behind a VW, I feel the test is necessary to gauge the health of the top-end. The broken ring reinforced my opinion on this.
It takes me no more than 20 minutes to do the leak-down test and nothing needs to be removed from the engine other than the easy-to-reach bottom spark plugs. I purchased a 10mm adapter for the tester to allow using the bottom plugs.
I know some people feel the leak-down test is sometimes unreliable and has lead to unnecessary top-end overhauls or valve jobs. I can't argue with this but my experience shows that I have gained more good and useful information from the test than misleading information.
BTW, the ring broke 180 degrees from the gap. This may be a result of stressing the ring when reinstalling it after cleaning the cylinder set when it was new. And yes, I used a ring expander and did not over-expand or twist the ring.
This ring came with my Mahle cylinder and piston set. GPASC said it's difficult to get Mahle cylinders nowadays and if you can find them, the price is very high. AJ at LowBugget.com said the same. If you buy a new cylinder and piston set from GPASC today, you get a Chinese brand called AA. I already had my first issue with spanking new AAs when a bur wouldn't allow a wrist pin to insert. Nonetheless, experts say AAs are perfectly fine to use. Do you get a warm fuzzy feeling flying behind "Harbor Freight" cylinders and pistons?
-Scott
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hans
Full Member
Posts: 166
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Post by hans on Oct 10, 2011 13:36:26 GMT -5
Mahles are still available over here in Germany, but they do come at a premium...
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Post by heisan on Oct 10, 2011 16:41:47 GMT -5
CB Performance still carry Mahles, but they don't do splits.
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Post by splischke on Oct 10, 2011 17:59:12 GMT -5
CB Performance still carry Mahles, but they don't do splits. $370 for a set of 92mm. A year ago they were $250. Still far cheaper than one Lycoming jug. |
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peterzabriskie
Junior Member
"Did I make that part the best I possibly could have?" Unknown
Posts: 99
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Post by peterzabriskie on Oct 10, 2011 22:13:42 GMT -5
Congrats to my Mahle buyer 2 years ago. Guess I will miss them. Being homeless bites.
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