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compression check with the engine out of car


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Hold the throttle open while cranking.


Oh wait, it appears you have that covered! :D


There's oil in it, right?


... there may be something else to keep in mind, but I dunno what it is!




Stop reading this! Don't you have anything better to do?? :P
'73 320i /M2 2.5; '85 ///M635CSi ; '73 320i ugly car; '99 AMG C43


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I do not know, but that sounds promising.

my numbers are on the low side @ 125ish, but it runs very well and does not smoke.

it is important that they be even.  cold test should provide that info, I would think. 

I do not have a lot of experience with this though.

Sometimes I hear of people adding oil through the spark plug hole prior to testing, to see if the numbers go up.

I think that is to see how well the rings are sealing.

Smarter people than me will likely chime in soon.



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What Tom said- look for even numbers,

after you check the valve lash (also, just needs to be even)


Also, give each cylinder an even number of 'pumps'- or, if you go for the 'max pressure'

method, make sure they all take about the same number of compression strokes to get there.


For comparo- tired old street engine, #150

Fresh race engine #125

Same race engine, different cam #185.


So your numbers WILL vary- 100+ is hopeful, but 4x 110 would be just fine.


Also, if one's low, don't freak- an engine that's been sitting can get a fine layer of rust

on one valve or seat.  It murders compression- but pounds off in the first good blast up the canyon.


So if your compression varies, try leakdown next...






"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Doesn't look good, I agree, but do a leakdown next.  A tiny bit of rust or loose carbon makes a mess of a compression

test.  The leakdown can tell you more...




"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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