compression test results seem high?

Today mach71351c can over and we pulled my engine and did a compression test. I was told the engine had 8k miles one it. The results from the compression test where 185 to 190. This seems very high from what I've read? Engine was cold.

Any inputs is appreciated.

Jim

That seems very high to me also. I would expect something more around 140 or so. Was each cylinder with 10% of all the others?

Edit: So you pulled the engine and then did the compression check? How did you do the compression check?

We did the test before we pulled it. And yes between like five percent.

We did the test before we pulled it. And yes between like five percent.

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Thanks. I couldn't picture how to do a compression check with the engine on a stand.

Just checked my Haynes engine rebuild manual and it shows 134 - 162 to be acceptable. I'll wait for others with more knowledge to chime in.

That would put your compression ratio in the 12.5 to 13:1 range (at sea level). I would check the gauge.

I hooked my gauge too my air compressor and the psi reads the same. I drove the car for several weeks on 91 pump gas before I tore it down and it ran fine. Is there anything that could explain it?

That would put your compression ratio in the 12.5 to 13:1 range (at sea level). I would check the gauge.

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We were about 80ft above sea level.

It looks to me that Jim has 1970 2v heads on his car.

I guess the next question would be why the engine was pulled. Heavily carboned combustion chambers and pistons will raise compression, but I don't know if it would be that much, or that uniformly.

Another possibility is work performed by previous owners. 2V heads wouldn't require 91 octane gas.

I guess the next question would be why the engine was pulled. Heavily carboned combustion chambers and pistons will raise compression, but I don't know if it would be that much, or that uniformly.

Another possibility is work performed by previous owners. 2V heads wouldn't require 91 octane gas.

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Don

I'm not sure I understand your last statement. Could those reading actually be right and I have that high of compression on 91 octane? There heads where redone with the motor 8k ago and the motor seems really clean.

As for the heads the only number I can find is this one which I believe is the date stamp.

It is certainly a higher compression number, but I wouldn't worry about it.

Gauges vary and though it matches the reading on your air compressor, those gauges are not all that accurate either. If it ran well-don't worry. It may be a 12.5-1 compression engine-but if it didn't detonate/ping or otherwise misbehave I wouldn't waste the energy worrying about it

A stock 2V engine should run fine on 87 octane gas. Shaving the heads and/or domed pistons will raise the compression, possibly requiring higher octane fuel.

A clean running engine (not burning oil) may get some combustion chamber deposits from a rich carburetor or "dirty fuel", but not to the extent that it would raise the CR that much.

I agree with Jeff, if you don't have any driveability issues or pinging I wouldn't waste a lot of time on it.

Keep in mind that the Compression test doesn't give you a true test of what the compression ratio is. Because the engine is turned over repeatedly, while not running, the camshaft's pattern and duration make a difference in how test results will look.

Engines have both static and dynamic compression ratios- Static is pure math that ignores the camshaft, while dynamic is much more inclusive and looks at camshaft timing events as well.

Dynamic can be considerably lower than static.

Which is a roundabout way of saying- a 5% variation is great, high numbers suggest good ring seal and good valve seal. If you are really worried about it, tear it down, but I'd bet you will be wasting time and money.

Thanks for all the input. I figures that as it has had 8k miles on the engine and the top end look brand new, I wll close her back up, paint her, and stick her in a corner. God know I have a millon other things to work on

Jim

Thanks for all the input. I figures that as it has had 8k miles on the engine and the top end look brand new, I wll close her back up, paint her, and stick her in a corner. God know I have a millon other things to work on

Jim

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You bet! Except for the sticker her in a corner. Get that motor in a car and run it!

hang it on a stand and remove the carb. I also would tape over the intake opening.

If you don't remove and clean the carb, evaporated fuel may clog multiple metering orifices causing lots of trouble on restarting.

Drain the carb completely and pull the float bowls and spray out with carb cleaner then air dry, reassemble and store in a sealed plastic bag.

Make sure and turn the engine over by hand every month or so to prevent the rings from sticking to the cylinder walls. a very small amount of Marvels mystery oil is good for this as well, but limit it to 4-5 drops per cylinder, which is plenty to seep around the pistons and rings and keep it all fresh without fouling plugs on a restart.

Good luck!

Today mach71351c can over and we pulled my engine and did a compression test. I was told the engine had 8k miles one it. The results from the compression test where 185 to 190. This seems very high from what I've read? Engine was cold.

Any inputs is appreciated.

Jim

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Did a diesel mechanic rebuild it?

JK. I think it's fine especially since you've got 8,000 miles on it already.

Jim I would definitely get some Marvel mystery oil in the cylinders since you live so close to the beach.

Jim I would definitely get some Marvel mystery oil in the cylinders since you live so close to the beach.

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Mike I took Jeff's advice and ordered it from amazon this afternoon.

Thanks for the second on the opinion!

Jim

Compression test might be done with a warm engine, and all spark plugs out.

But correct me if I'm wrong.