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dumbjim
Hi all, I did a cylinder leakdown and am a bit confusion. All cylinders read under 15%. Just for giggles, I rotated the flywheel 360⁰s and got the same reading. Wouldn't it be tdc for compression stroke and 360⁰s later be exhaust stroke? If so why the same reading? To add to the confusion, I did a compression test with the throttle plate wide open, and got poor readings in the 80 psi range. What's going on? Thanks
dumbjim
Hi all, I did a cylinder leakdown and am a bit confusion. All cylinders read under 15%. Just for giggles, I rotated the flywheel 360⁰s and got the same reading. Wouldn't it be tdc for compression stroke and 360⁰s later be exhaust stroke? If so why the same reading? To add to the confusion, I did a compression test with the throttle plate wide open, and got poor readings in the 80 psi range. What's going on? Thanks
dumbjim
Hi all, I did a cylinder leakdown and am a bit confusion. All cylinders read under 15%. Just for giggles, I rotated the flywheel 360⁰s and got the same reading. Wouldn't it be tdc for compression stroke and 360⁰s later be exhaust stroke? If so why the same reading? To add to the confusion, I did a compression test with the throttle plate wide open, and got poor readings in the 80 psi range. What's going on? Thanks
bkrantz
Is this a running engine? Or an engine that has sat for years?
mepstein
From what I understand, 10-15% is rebuild time.
lesorubcheek
Just to make sure, did you happen to take leakdown readings with each cylinder TDC at firing position? If so, you'd have taken reading for 1, rotated 180, taken 4, rotated 180, taken 3, rotated 180, taken 2. Also, it's important what type leakdown gauge setup you're using. I've read that many of the differential gauge setups you can buy these days don't use a standard size opening in the orfice tube (0.040" FAA standard is the norm). So, unless you have some history of measurements with a particular setup, really all you can do is look at variance between cylinders.

As for the low comp readings, is there a schrader valve on the end where it screws into the plug hole? Setups that only have a schrader up top at the gauge base are notorious for low readings (especially on chainsaws!) Again, it's good to know what you're using to really offer any advice.

Dan
infraredcalvin
The question is also why did you take the leak down and compression tests? Is this a new to you, unknown motor? Has it been sitting? Was compression test done on warm motor? Does motor smoke or feel like it’s lost some power?

If it runs great and feels great I’d keep the oil clean adjust the valves on specified intervals and keep running her.
VaccaRabite
The numbers are not great, but as others have said we need more information.
Give us more details and we can help a good bit more.

Zach
Superhawk996
If you rotated the engine 360 degrees and still got 15% leakdown something isn't right with the way your doing the leakdown test and/or your gauge is not set up properly. Especially so with 80 psi compression.

There is nothing wrong with 15% leakdown (for a daily driver) thought it isn't "great" - especially on a used T4 engine.

Not too long ago 4% used to be a good number for a new race engine.

I had a Mazda Miata with 228k miles on it and it was running about 20% leakdown. Was it down on power - Sure! But it still ran great as a street driver and didn't burn a lick of oil.
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