Compression test results 150 then 200 with oil? 6 bolt turbo block.

[milkandoj]

Ive bought a parts car, upon compression testing the motor it gave even results 150psi all within a few psi, seemed great, then i added oil and they all went up to 200 psi, far to high for a 6 bolt motor.

I know the engine has had the head rebuild, so I'm guessing its been shaved a lot, or 'maybe' had a rebuild in the past and NA pistons were used, raising the compression and its worn out giving the 150 results.
The motor was running when i got it. I don't believe the gauge is stuffed as it gave me 140+ on my motor with cams, which is right.

Any ideas?

 

[knochgoon24]

When you added oil, you added enough to effectively reduce your combustion chamber volume, resulting in the abnormally high reading.

This is why adding oil to see if rings are shot is a poor test. Preform a leakdown test instead and listen for noise out the dipstick tube.

 

[dsm-onster]

Yes, the oil in the chamber test is only SOMEWHAT telling with flattop or domed pistons. Even n/t 4g63 pistons are dished.

 

[FLASH1970]

150 compression on a stock 6 bolt motor I thought was good... (shrugs)

 

[donniekak]

The 150 is fine, especially being consistent across the board. Everyone is right about the oil just filling up the piston dish. If you want to do a wet test on dished pistons, just give a really quick spray of wd40 through the spark plug hole.

 

[milkandoj]

I hear what your saying with the shape of the pitons, and didn't put much oil in, 20ml or so and let it pump around and spray out the spark plug hole for a few cranks before it tested it, so shouldn't fill the chamber up.

So the raising to 200psi with the oil sounds normal i though it should only rise with oil fi the rings are worn, which made me think maybe the compression was raised and the rings worn?

 

[knochgoon24]

20 mL = 20 cc.
Just how big do you think the combustion chamber is? The head has 45cc for combustion. And there's just a few more added for the piston dish.

 

[Calan]

Funny how these types of threads seem to run in parallel.

http://www.dsmtuners.com/forums/maintenance-repairs/398503-need-help-compression.html#post152537205

 

[milkandoj]

20 mL = 20 cc.
Just how big do you think the combustion chamber is? The head has 45cc for combustion. And there's just a few more added for the piston dish.

That's why i put the oil in then cranked it over and let it come out the spark plug hole for a bit.

I just didn't get these results testing my motor in my car, only went up a few psi with a wet test, now this other motor is different.

Thanks for the input and links

 

[sonicnofadz]

When adding oil during a compression test, its best to test the cylinder multiple times to get a accurate compression reading. The oil added (you shouldn't be adding 20ml btw!) will be forced into the exhaust after a few cranks and should no longer be in the cylinder. If the compression goes up and stays up after several tests after the oil was added, the rings are probably worn.

 

[dsm-onster]

Look. You checked compression warmed up right? With no oil. If it checks out 150psi across the board and you're sure its a turbo block, then your gold. Obviously too much oil stayed in the combustion chamber. You have a perfectly fine stock 1g turbo block that suddenly reads 200psi after putting oil in the chamber. Let's not overcomplicate things here

Peak in the chamber with a flashlight and look for the upside down T . . . If so, you have a turbo block with great compression. You can relax

 

[milkandoj]

Look. You checked compression warmed up right? With no oil. If it checks out 150psi across the board and you're sure its a turbo block, then your gold. Obviously too much oil stayed in the combustion chamber. You have a perfectly fine stock 1g turbo block that suddenly reads 200psi after putting oil in the chamber. Let's not overcomplicate things here

Peak in the chamber with a flashlight and look for the upside down T . . . If so, you have a turbo block with great compression. You can relax

Had a look and it says 63DT on the pistons upside down.
So shes all sweet thanks for the help!