Compression Test

Fastdemise · May 29, 2009

I just finished testing my engines compression. 01 XJ Sport with just over 100k on the clock. Wanted to see how good/bad the health of the engine was. I just want to know is there a certain amount of times you should turn the engine over or should you just turn it over until the pressure equalizes?

Compression Test. Did each cylinder twice.

1 - 165, 167
2 - 167, 165
3 - 165, 170
4 - 180, 175
5 - 175, 175
6 - 175, 175

Talyn · May 29, 2009

3 revolutions minimum. 120-150 psi is good with mo more than 30 psi between cylinders. Your numbers look excellent.

Fastdemise · May 29, 2009

I like the sound of that. Another thing I think just so I can hijack my own thread here is the best bang for my buck upgrade I did was just move the kick down line from the tranny about 4 clicks from being fully extended. You can play around with it but it's a wonderful mod that's completely free. ^_^

Talyn · May 29, 2009

errr... the first time you floor the skinny pedal the kick down will go where it should be, as the cable will pull the kick down line/cable toward the throttle body. Floor the pedal with the engine off and you will hear a few clicks, that is the cable adjusting itself.

wim hoppenbrouwers · May 29, 2009

http://www.650motorcycles.com/LeakDownTester.html

Is there someone that did this tests before?
I think it's better than a compression test. :looney:

winterbeater · May 29, 2009

Cylinder leakdown is also a common test, but takes a little more equipment. I think they both give you a little different information.

Wim, I know you like to make everything yourself, but over here, we let the Chinese make it all for us. Leakdown tester for $34. http://search.harborfreight.com/cpisearch/web/search.do?keyword=leakdown&Submit=Go

wim hoppenbrouwers · May 29, 2009

winterbeater said:
Cylinder leakdown is also a common test, but takes a little more equipment. I think they both give you a little different information.

Wim, I know you like to make everything yourself, but over here, we let the Chinese make it all for us. Leakdown tester for $34. http://search.harborfreight.com/cpisearch/web/search.do?keyword=leakdown&Submit=Go

Sold!
Only a connector hose to a fireplug from Snap-On costs double. LOL

Ecomike · May 30, 2009

Those are numbers to die for!

8Mud · May 30, 2009

wim hoppenbrouwers said:
Sold!
Only a connector hose to a fireplug from Snap-On costs double. LOL

I made my own out of an old compression gage (it was old and getting unreliable anyway). Removed the ball check valve and added a air inlet valve, some compression gages come with an air valve. The base of the compression valve usually seperates so you can remove the check valve.
I'd like to figure out how the guy pumped a 100 PSI into the cylinder (in the writeup) without the piston moving? I've been thinking of fabricating some sort of lock to catch the starter teeth. I've loosened off the harmonic balancer bolt trying to keep the motor from turning using only 60 PSI. I rarely use more than 30 or so PSI now.
I usually keep the pressure a lot lower, I've even used a bicycle pump (foot pump type) in place of compressed air.

cher96 · May 30, 2009

Get a life. Stop worrying! I would love those numbers.

Fastdemise · May 30, 2009

aww, sure glad I could share *cough brag cough* these numbers. It makes me happy, though I still feel they're too good to be true.

cher96 · May 30, 2009

Fastdemise said:
aww, sure glad I could share *cough brag cough* these numbers. It makes me happy, though I still feel they're too good to be true.

If you think that... then take it to a Professional and have it checked. However, I do not think you have to because it is not very hard to check out your compression and I am sure you know how to hold a Gauge to a spark plug hole. J/K LOL

wim hoppenbrouwers · May 30, 2009

8Mud said:
I made my own out of an old compression gage (it was old and getting unreliable anyway). Removed the ball check valve and added a air inlet valve, some compression gages come with an air valve. The base of the compression valve usually seperates so you can remove the check valve.
I'd like to figure out how the guy pumped a 100 PSI into the cylinder (in the writeup) without the piston moving? I've been thinking of fabricating some sort of lock to catch the starter teeth. I've loosened off the harmonic balancer bolt trying to keep the motor from turning using only 60 PSI. I rarely use more than 30 or so PSI now.
I usually keep the pressure a lot lower, I've even used a bicycle pump (foot pump type) in place of compressed air.

Yes. It is very difficult to pump in 7 bar (100 PSI) into the cylinder. At least I can do 3 bar.
The big advantage is ,that you can listen to the inletvalve or the outletvalve for leaking.
Difficult is also to find the TDC of the piston with closed valves. :confused1

Saudade · May 30, 2009

If you mark the plugs wire location on the dist housing (for those with 99s or earlier), you can remove the cap and crank by hand until the rotor lines up with one of these cyl marks. Since this represents ignition, the cyl will be on compression near TDC. Then check the timing mark on the balance. The degree indicator (crude as it is), then gets me right at TDC. If you go past just a few degrees, the pressure will attempt to turn the engine in rotation. A big breaker bar on the balance nut should hold her steady.

winterbeater · May 30, 2009

Just for clarification for the less experieced wrenchers, this TDC and holding the engine rotation is for CYLINDER LEAK DOWN testing. It is not necessary for COMPRESSION testing.

wim hoppenbrouwers · May 30, 2009

Saudade said:
If you mark the plugs wire location on the dist housing (for those with 99s or earlier), you can remove the cap and crank by hand until the rotor lines up with one of these cyl marks. Since this represents ignition, the cyl will be on compression near TDC. Then check the timing mark on the balance. The degree indicator (crude as it is), then gets me right at TDC. If you go past just a few degrees, the pressure will attempt to turn the engine in rotation. A big breaker bar on the balance nut should hold her steady.

OK. If I understand. You use the rotor of the distributor as a mark arrow.
The plug wire locations (6 times) can marked with a marker pen on the housing. :cheers:

Saudade · May 30, 2009

wim hoppenbrouwers said:
OK. If I understand. You use the rotor of the distributor as a mark arrow.
The plug wire locations (6 times) can marked with a marker pen on the housing. :cheers:

Yes. Just like when you're timing the dist when you reinstall it. You make a reference for #1 cyl on the dist, bring #1 to TDC compression, then drop the dist in so the rotor points at the mark. Soooo..... if you make marks for all the cyls, then when the rotor points at the mark, each of the cyl, in turn, will be near TDC on compression.

Of course, if you have a leakdown tester, you can screw it into the plug hole and hear/feel the air escape as you come up on compression to confirm

Fastdemise · Jun 9, 2009

How can this test be achieved if I have a 00-01 where it is a distributor less system?

Shorty · Jun 9, 2009

you would have a much tougher time w/out the distributor, but you could find cyl 1 TDC by rotating by hand and then follow the firing order cylinder by cylinder to get each one at TDC. Plug out, air escaping, use a dowel rod through the plug hole to determin piston upward travel-- when it stops moving, you're at TDC.

Your compression numbers look awefully high-- did you remove all the plugs and have the throttle wide open during the cranking??

Fastdemise · Jun 9, 2009

No plugs, throttle as far open as the screwdriver I was using would let me, which was about 90% WOT.

Compression Test

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