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AustrianVespaGuy

rebuilt motor with wide range on compression, concern?

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At 400 miles with the rebuilt engine and did a valve adjustment and compression test today, cylinders 1-4 compression readings in order were 110, 110, 85, and 75. That's pretty different! Is it just not really broken in yet or should I be concerned that something is really wrong?

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I would change my underpants first, then go get a leakdown test.

And maybe a new compression tester.

That would be 'really really not good' in my book if the numbers are real.

t

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any decent garage can do it. or for the same amount of money you can buy the tool and do it yourself if you have a decent air compressor.

agree with toby...those are really bad numbers..both in value and consistency. were you holding the throttle open while doing the test? as it a stock spec rebuild?

who did the rebuild? i would take it back to them for the testing...

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Oh boy.

This would be a real long shot (but easy fix). Is there any way you did a really bad job adjusting the valves?

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Shit, you know what? I did forget to open the throttle when doing the test, although I'm not sure I can hang my hopes on that. Doubled checked the valve clearances and they are fine, but I don't have my own air compressor so I guess it's of to a so tomorrow afternoon. Does the engine need to be dead cold to run a good leak test? Local machine shop did the work on the short block. It seemed to me that they did a pretty good job, but maybe this is why it cost $4000 less than taking it to Korman :/

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I think taking it to the shop that did the work's a GOOD idea, initially.

That way they have a chance to 'splain things, Lucy!

If you don't like their story, then you can look for better ones.

Also, have them do a compression test to start, then a leakdown.

I think you're wise to not get too hopeful- closed throttle plates don't usually

make much difference in the unevenness, in my experience

sorry

t

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gee- I wonder is they thought that all the piston

ring end gaps were sopposed to all line up !?!?!?

one explaination where all the compression is goiing for all cylinders ?!?

please do CHECK ALL VALVE CLEARANCES F I R S T!

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To follow up, I guess it IS all in the technique. Re-tested the compression today, this time after driving the car with the engine warm and the throttle open, and got 110 psi on cyl. 4 and still read 110 psi on cyl. 1. Didn't test 2 & 3 because I was done burning my fingers at that point, and I can't really understand the huge difference, but I feel much more comfortable that nothing is horribly wrong now that I see 105 instead of 75, hooray! (With 9.5 pistons in an ideal world after break-in I should be ~125 psi, correct?) I'm still planning on going ahead and getting a full leak down test done on Saturday though, so will let you know if anything else new turns up there. Thanks guys!

-Carl

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110-125 is way too low. that is "time for a rebuild" range. my 9.5:1 with 292 cam and many miles showed 195psi +/- 5 across all four cyls. here is vid of the test

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110 isn't even MIN. reading! - that's a "BAD" reading calling for a rebuild

better find another tester before going any further

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