engine and drivetrain compression check with the engine out of car

[bey2002]

Hello need some technical advice. I am trying to compression check this engine before I install it in the car. Do I need to do any thing else before I apply voltage to the starter?

Thanks

[ray_]

Hold the throttle open while cranking.

 

Oh wait, it appears you have that covered!

 

There's oil in it, right?

 

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

 

Cheers,

['76mintgrün'02]

keep in mind that cold numbers will be lower than if the engine was at operating temperature.

 

[bey2002]

Yes there is oil in it. Do you know what the  good number are when the engine is cold. so far #1 plug is showing 110 psi.

['76mintgrün'02]

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.

[TobyB]

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...

 

hth

t

 

 

[bey2002]

Thanks for the advice.

These are the results From front of engine to back. plug#1  110psi  #2 70psi   #3 7 psi   #4 40psi.

This looks bad. The engine ran back in 2008. I switch cars due to rust and save this engine a a spare.

[TobyB]

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...

 

t