Renault compression

[califkid_66]

I just did a quick compression
Test on my 821-30 Renault engine
I did a cold test to see if there were
major problems
I’m gonna retry with engine warm
and a wet test after
100 102 105 99
what do you guys think?

[jbcollier]

Nice and even and may be ok for a low compression engine.  Check it again when it’s warm.  Then add a squirt of oil in one cylinder, spin the engine over for two seconds to spread the oil and test again.  As long as the new reading is no more than 10% higher, it’s good.

[califkid_66]

Thanks jbcollier i will try that I was a bit worried at first and I didn’t know to much how to test my engine first thing was plugs which were black and sooty I looked at a spark plug chart  said to rich or running on choke or to much idling then for compression test I tried looking for how much Pressure it should read per cylinders  but I’m still not sureof the ratio  I saw one place says 10.25/1 and another  says 8.9/1  I don’t know i this is right but according to a formula I found  completion ratio times 14.7should give you how much-pressure you have per cylinder so at 10.25/1 you should have 150 per cylinder at 8.9/1 you should have 130 so my first reaction to de compression test was engine as no major problem except the compression is low so so normal wear but how low can you goand still run ok I’m gonna redo the test first warm up engine take compression then put oil to see how much difference it make see I didn’t know about the ten percent  like you mentioned So this is the next step it should tell me the condition of my rings then I can do a leak test
My worry is that the compression seems a bit on the low side a and being that all cylinders seem to have pretty much the same Pressure it might be low because the rings are starting to get wormedI’m still trying to figure out what the compression on This engine should be between like lowest and highest I guess
I will post the numbers with engine at running temp and then the
wet test to see
Thanks for your help!

[buzzer]

I presume you did the test with carb throttle bodies fully open

[califkid_66]

Buzzer I didn’t know what you meant when you said throttle open I have a spare carb and just looked through it and no my throttle was not open
would that change the readings
I’m gonna try with warm engine and open throttle to see if it makes a difference then I’ll do the wet test I guess every little detail makes a difference

[BDA]

I have made this mistake too. By not opening the throttle, you are restricted the flow of air to the combustion chamber. It makes a big difference. Compression tests should always be done with the throttle wide open. So if you're doing it by yourself, connect the gauge in the spark plug hole, floor the accelerator, and crank the engine for ten to fifteen seconds. If you have a BA (Beautiful Assistant) or even a not so beautiful one, one can hold the throttle wide open while the other cranks the engine.

[buzzer]

My guess is you will be ok after doing the test with the throttle fully open as yep it makes a big difference. I think we've all done it without opening the throttle and wondered why the reading was low. so should be happy days   

[jbcollier]

Compression testers have spring loaded check valves and different attachment methods that can affect the recorded reading.  So long connection hoses and stronger check valve springs may give lower readings depending on the size of the cylinder being tested.  These factors have less effect on large V8s (almost a litre capacity per cylinder) and more on 4 cylinder 250 cc.  So why do compression tests?  Good question.  It can be a useful way to monitor an engine during its operating life just make sure you use the same compression tester each time.

Myself?  I don’t test for compression on my engines unless there is an issue.  On engines with issues, I do.

Should you use wide open throttle?  I don’t because I’m not interested in achieving a theoretical figure.  i’m  just checking that there are no problems.

If you are interested in your engine’s actual condition, perform a leak down test.  Much more accurate than a compression test.

[califkid_66]

I redid the compression test and big difference the first numbers cold engine throttle closed second set of numbers engine warm throttle open

 100 105 102  99
 110 116 118 105

My compression tester is a cheap one
And because of the location of the plugs I didn’t tighten to hard I ran the engine a little while to warm it up until the fan went on I noticed a puddle of oil under passenger side of engine so im gonna check that first


 

[jbcollier]

Don’t forget to do “wet” test as well.

[califkid_66]

Yes I will but I want to see where that oil leak came from
It looks like it comes from the oil pressure sensor I just hope it’s not compression going to the base pushing out the oil
so next is find & fix leak and check valve adjustment

[califkid_66]

Adjusted my valves only two of them were off by 3 thousand
Then found the oil leak oil coming out of the dipstick did some research a hose connected to my valve cover was blocked so the crankase Pressure was high enough to push oil out  I unblocked it no more leaking  and a little air coming out of valve cover but no oil
So I was pretty happy so I did the wet test

Warm engine

Dry.    110 116 118 105
Wet.   138 160 155 140
  %.     25   37   31   33

I might have put a little to much oil in 2 and 3 but still it’s a bit more than ten percent
So I guess I need to do a ring job!!  I still have to do the leak test

[jbcollier]

Maybe.  This is the problem with a compression test.  If you put in too much oil, any engine will record an out-of-spec compression rise.  Getting just the right amount of oil can be tricky.  That's why I use compression tests as quick test for problem cylinders.  If results are suspicious, then perform a leak down test for a proper evaluation.  Why not just do a leak down test?  Because they are tricky to perform.  You have to balance the piston on exactly TDC in order to test the rings at the point where the most cylinder wear occurs.  If you are off even just a bit, the air pressure just turns the engine over.

[califkid_66]

The reason I didn’t do the leak test yet is I don’t have the tool yet I bought the compression tester to see if there was something major now I’m gonna get the leak tester 
funny thing is my spark plugs are black and sooty dry so if my rings would be bad wouldn’t they be full of oil?

[jbcollier]

Yes if your oil ring is bad.  Not necessarily if your compression rings are worn/broken.