Compression Leak

Baja_Tommy · Posted: Thu Jul 24, 2014 10:39 am Post subject: Compression Leak

I have a 68 baja bug with a high compression engine. I ran some compression testing on my engine over the past 2 days with the following results.

engine warmed up:
cylinder 1 - 110 psi
2 - 130
3 - 105
4 - 130

engine cold:
1 - 140
2 - 150
3 - 130
4 - 150

engine cold after injecting oil
1 - 155
2 - 160
3 - 150
4 - 155

From these results it looks like the rings are worn out.
The rings are only 7000 miles old though and they showed no visible signs of blowby on the pistons 800 miles ago. The engine did sit for 30 YEARS and was run a while without rebuilding it. The gap in the rings is less than .050" and the engine doesn't burn oil as far as I can tell.

I would like to know if the rings are really the problem and if I should be worried about the rings wearing out so fast.

theDrew · Posted: Thu Jul 24, 2014 5:46 pm Post subject:

I'm kind of having a similar issue -- few questions --
what rings are you using?
what carbs and what jetting? I think a rich AF can cause the wash the walls which will lower your compression.
how do your plugs look?
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Baja_Tommy · Posted: Thu Jul 24, 2014 6:18 pm Post subject:

My father built the engine, so the only thing I know about the rings is that they are not total seal and they are 88mm so they are not stock.

The engine has always run a single weber 44 idf. It used to run 50 idle, 170 main and a 165 air. I swapped them out to 50 idle, 150 main and 195 air a few months ago and now the plugs are a nice carmel brown. They were black previously and I got 13 mpg with black smoke puffing out the tail pipe!

It did run really rich for a long time. Appearently my father never changed the jets in the carb since the carb was new.

SOLUTION:
I talked to a buddy and he can do a compression leakdown test to find exactly where the leaks are without even taking the engine apart. I just hope the valves are good.

modok · Posted: Thu Jul 24, 2014 6:23 pm Post subject:

The results don't mean much to me but if you are so worried about it then maybe you have noticed some signs of blowby and power loss.

If they are thin wall 88 then maybe they are acting.......well........as expected.

Dale M. · Posted: Thu Jul 24, 2014 6:50 pm Post subject:

Numbers are not that bad...... Leakdown test will tell you more....In the mean time, drive it like you stole it....

Dale
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kielbasa · Posted: Thu Jul 24, 2014 7:16 pm Post subject:

Im curious, what is "high compression" to you?
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Baja_Tommy · Posted: Thu Jul 24, 2014 7:35 pm Post subject:

Well... the local vw expert said that my engine in stock form would pull the head studs over 142 psi so I guess higher than that is high.

I would guess that the cylinders are thick wall. The old ones were almost half as thick, which was probably why #3 was cracked.

I am also confused why the warmed up pressures are lower than the cold pressures. I thought it was the other way around. I did a compression test months ago part way warmed up and the results were around 170 psi. I first assumed the tester was broken when I saw 130!

I will do the leakdown test tomorrow hopefully.

modok · Posted: Thu Jul 24, 2014 7:43 pm Post subject:

I think you didn't prop the throttle open for that hot test

kielbasa · Posted: Thu Jul 24, 2014 8:12 pm Post subject:

Valves adjusted correctly
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bugguy076 · Posted: Fri Jul 25, 2014 3:02 am Post subject:

If you decide to replace the rings, C B Performance sells good quality replacement rings. I never used a better ring. They seat in quickly and they last.

Baja_Tommy · Posted: Fri Jul 25, 2014 7:59 am Post subject:

Valves are at .006.

I ran the hot test again with the throttle propped wide open and got different results.

1 - 160
2 - 156
3 - 156
4 - 168

They look better, but it's like #1 and 2 switched places, so I made sure to double check it.

Baja_Tommy · Posted: Fri Jul 25, 2014 8:00 am Post subject:

Valves are at .006.

I ran the hot test again with the throttle propped wide open and got different results.

1 - 160
2 - 156
3 - 156
4 - 168

They look pretty decent, but it's like #1 and 2 switched places, so I made sure to double check it.

yamaducci · Posted: Fri Jul 25, 2014 12:07 pm Post subject:

Looks Great. Run it!
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