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Author Topic: 1.8L engine health?
fastbrewer
Member

Region: Utah
Car #: 93
Year : 1996
Posts: 83
Status: Offline
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Hello all,
I'm hoping one of you might be able to help me out further with diagnosing my engine.

1st. Compression #'s are even in all cylinders at 125 psi (4,300' Altitude) Pressures are the same with a bit of oil in the cylinder.

Leakage also even across all cylinders at about 10-12% and all coming out the oil fill hole.

I checked the mechanical timing and everything lines up fine. Crank at TDC + both cams with the notch at 12'0clock. and 19 teeth on the belt between the cam marks.

Retested after timing verification and same results as before. The engine does idle a bit rough, no horrible but slightly rough, and there is a lot of valvetrain noise. Engine was warm for all tests (160)

Can any of you give me an idea of what to look for next? Lifters, Rings, Valve Springs, worn Cam? I would think that if my low compression numbers were all related to the rings my leakage would be a lot higher.

I had the engine completely refreshed at the beginning of the season with new pistons, rings, valve springs, lifters. I did just come off of a 3 hour enduro though and did not change the oil before testing.

Thanks,
-Jon

davew Verified Driver Made Donation to Website
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Region: chicago
Car #: 72 and ?
Year : 90 and 90
Posts: 1051
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****Leakage also even across all cylinders at about 10-12% and all coming out the oil fill hole.****

That says it all. Motor needs to come apart and find out why you have excesive leakage past the rings/pistons

Compression numbers are also way low. Should be 190+

Do a search to find my explanation of how a leakage and compression tester work. It was a month or so ago.

Dave

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fastbrewer
Member

Region: Utah
Car #: 93
Year : 1996
Posts: 83
Status: Offline
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Thanks for the reply Dave, I found the post.

It looks like I was using an off tester. It was an older HF. I bought a new one today of a reputable brand. I haven't had a chance to retest the Miata but I did have to look at my truck and it is a much more reliable unit. I will retest the Miata tomorrow afternoon.

Bob Thornton - Race Engineering Verified Driver Made Donation to Website Series Champ
When the eagles are silent, the parrots begin to jabber. - Sir Winston Churchill

Region: Central Carolina
Car #: 48
Year : 1999
Posts: 1327
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Sounds like Rings to me.
Give me a call and we can salve the problem.
Thanks
704 202 5551
Bob Thornton
Race Engineering

--------------------
Bob Thornton
http://www.raceengineering.org
Race Engineering Championship Winning Engines

fastbrewer
Member

Region: Utah
Car #: 93
Year : 1996
Posts: 83
Status: Offline
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Will Do Bob!
Thanks

fastbrewer
Member

Region: Utah
Car #: 93
Year : 1996
Posts: 83
Status: Offline
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Bob, I'd still like to give you a call.
However I retested the car today using the new compression tester of a reputable brand and got much better results.

#. Dry/Wet
1. 160/170
2. 155/160
3. 157.5/170
4. 160/170

Again I am at altitude and If I am not mistaken the 1.8L specsare 185 p.s.i. at sea level. with the altitude correction (4,300') it would put that 185 spec at about 162-165.
Still showing leakage around the rings but not as bad as I originally thought.

I have given up on buying cheap tools just to save a bit of money. I always end up buying the more expensive ones later once I realize the cheap ones are just that, Cheap pieces of crap!
I was having a hard time believing that at 120 p.s.i. I only had leakage of 10-12%. I thought for sure that it should be in the 30-40% range.

-Jon

   

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