Compression test results - Opinions please

[Agno]

Hello everyone,

 

After doing a track day my car has developed a misfire due to oil build up on the plugs. I suspect that the motor has had it because it was breathing very heavily at the track and is of unknown condition. My results are as follows:

 

Dry: 85, 80, 70, 85, 110, 115

Wet: 110, 95, 75, 90, 135, 130

 

The engine was run till warm before the tests. All fluids were new about 1200km ago and were all below full.

 

So, should I be on the lookout for a new engine?

 

Thanks in advance,

Alex

[Scoota G]

That one is very low. I am suspecting broken, worn ring with ovalish bores. Time for another on unless you want to spend $1600 machining the one you have.

[Agno]

I just realised (rather embarrassingly) that I forgot to pin the throttle open when I ran the tests. It's my understanding that I'll get the same outcome but with higher numbers? I'll do it again anyway but I thought I should also confirm this too.

[Riceburner]

Hmmmmm  doesn't look promising.

 

The datto blocks are pretty tuff, if nothings broken the bores may still be ok and not glazed. You may get away with a rings, bearing rebuild and cheap doesn't mean unreliable. Rebuilds don't have to be expensive.

 

Hastings brand rings are great from all reports I've read, NDC bearings if you can get them. I use both of these due to expert recommendations.

 

How far you go will depends on the engines purpose and what your prepared to spend.....

[Riceburner]

Maybe the Experts can chime in. Pete, Ledge?

[lightmaster240z]

Talk to Pete about a rebuild that suit your budget and your needs. You wont be unhappy with the re suits. I for one was very happy with Pete's amazing work.

Bruce   

[peter mc]

sorry thats not very well  time to pull it down and check it out , make a desision on what to do when you know how it is in there .

[luvemfast]

You really need to do it again, WOT this time Alex 

But it's not looking good.  :'(

[Agno]

WOT test done. 155, 160, 155, 155, 155, 150 dry. Didn't bother doing a wet test because they are good numbers. Now I am thoroughly confused though, what else could be causing my plugs to oil up and make my car blow white smoke?

[peter mc]

the oil is passing the rings mate simple, comp tests do not tell the hole story

[nizm0zed]

correct, the comp test will only give one part of the story.

you'd need to do a leak down test on each cylinder as well to know more, but its pretty safe to say that a 'new' short block should be on order.

either another unknown condition block to keep it going, or maybe one to rebuild and get set up before swapping it in?

I would agree with Pete that the rings are gone and its leaking oil past them.

 

Maybe time for the patented Aussie outback "AJAX re-boring" yeh? 

 

[Ledge]

HI

Gareth i think you may have confused me with someone else, i am no engine expert, I can hold

my own against some engine builders but not the likes of Pete Mc.

As Pete said oil is getting in the chambers and comp test isn't definitive so i would be pulling it down.

Cheaper to find it now than have bits of engine go through your exhaust pipe

 

Cheers

Paul

[MaygZ]

Is there a chance it's stem seals that are causing the problem?

 

It wouldn't be right if a different opinion wasn't thrown it to cause confusion 

[Zedman240®]

Is the white smoke continous or just on take off or when you back off the pedal? +1 on the valve seals...

[Agno]

Given the WOT results I think the bottom end is pretty safe. I have organised for the local mechanic to do a leakdown test for an extra piece of info. Is there a definitive test I can do to test specifically for valve stem seals?

[MaygZ]

Given the WOT results I think the bottom end is pretty safe. I have organised for the local mechanic to do a leakdown test for an extra piece of info. Is there a definitive test I can do to test specifically for valve stem seals?

 

Yes.  drive the car and have some behind you - you can do it stationary but its not as effective IMO.  They are watching for smoke.  Stem seals will leak most when engine RPM is higher and throttle is closed.  Drive along at 60 or so and lift off the throttle.  If the seals are weak then you should get white smoke.

 

If the smoke is black it could indicate worn cylinders/rings due it running rich.  Depending on carb model, a puff of black smoke is OK due to accelerator pump opperation, but more than a second or two of black smoke means it's running rich.  This has the effect of washing the lubrication off the cylinder walls producing increased wear.

 

Another way of doing the stem seals test is to let it idle for a while and then accelerate - again white smoke.  The first test is more conclusive IMO.

 

Good luck - stem seals is a much easier job.  If you end up rebuilding the bottom end make sure you relacce the stem seals anyway.  They are cheap and easy to replace.