8BA Compression Test - Is it worth and an engine strip down?

[waynet]

Folks,
8BA engine compression test indicate No.3 = 98 psi, No.8 = 79 psi. When adding a drop or two of oil to these cylinders they rise to around 112 psi. All other cylinders hover around 112 - 115 psi when dry.

Engine starts with a couple of squirts from the throttle and a push of the button. Engine oil pressure at cold idle 30 psi - hot idle 15 psi.

Is it worth the effort to replace the piston rings? Have never done a flathead before.

Thanks for any advice.

[Lawson Cox]

If it ain't broke, don't fix it. Sounds good to me. What concerns you?.

[tubman]

I agree with Lawson. I drove my '51 for 25 years with an engine that had 85-90 psi in all of the cylinders. It got me around fine. Most ordinary guys would kill for compression numbers like that.

Has the engine been sitting a while? If so a little "treatment" (MMO, Sea-Foam, etc.) might make everything right.

[Shu47]

If it is running good then I agree with the others and don't do anyting at all. Just drive it and enjoy. What I would do is occasionally redo the compression test and monitor it.

[waynet]

Originally Posted by Lawson Cox

If it ain't broke, don't fix it. Sounds good to me. What concerns you?.

Well the only small concern is what is the cause of lower compression on 3 & 8 particularly when they improve with a drop or two of oil? Stuck or broken rings?

[Kurt in NJ]

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drive it a 100 miles and check again.
then if it is still low do a leakdown test if you are still worried.
How evenly does it pull from low rpm (10 mph) in top gear?

[Jay in Mass]

Just drive it and enjoy it.

[waynet]

Originally Posted by Kurt in NJ

drive it a 100 miles and check again.
then if it is still low do a leakdown test if you are still worried.
How evenly does it pull from low rpm (10 mph) in top gear?

Pretty good. An occasional spit back in the carby when quickly flooring the throttle.

[GB SISSON]

Like others, I would drive as is and enjoy it. Summer is just around the corner. Seafoam and MMO are your friends if it has spent a lot of time sitting and has some stuck rings and sticking valves.

[aussie merc]

those numbers are magic seen worse numbers run perfectly fine soak the cylinders in a little light oil [mmo or such] for a week clear the cylinders and take for a good run and vary the load and eng speed if it runs fine keep on going down the road. A little 2 stroke oil in the fuel helps as well about the amount you would use in a gallon to a tank and dont be frightened to use regularly as no eng likes sitting idle

[Ggmac]

Drive it . Enjoy . If you get into it ,itll end up being a complete rebuild . I say this cause youll see something else is out of spec and youll be looking at $2000-3000 plus a long downtime.

[mfirth]

waynet, you mentioned "spit back" in the carburator. That could blow your power valve. You may have a valve sticking at times letting it spit back. Some MMO may help that.

[Ronnieroadster]

A leak down tester is the only way to truly know what the engines internal condition is.
Using the leak down tester you can easily determine the condition of the piston rings and easily determine how well the intake valve is seating and how well the exhaust valve is seating. The compression gauge was a handy way of checking a cylinder many years ago and of course for those who have one its the way to test now however being the 21st century there is a better way.
Ronnieroadster

[miniceptor86]

This is exactly why I haven’t done a compression test. ‘Cause if I knew it would gnaw on me and I’d have to fix it! As is it runs fine. The transmission however is gnawing on me. It’s noisy and when slowing down pops out of 2nd gear.

[GB SISSON]

Originally Posted by miniceptor86

This is exactly why I haven’t done a compression test. ‘Cause if I knew it would gnaw on me and I’d have to fix it! As is it runs fine. The transmission however is gnawing on me. It’s noisy and when slowing down pops out of 2nd gear.

If it didn't pop outa second gear it would a chevy. Ick.

[19Fordy]

waynet: Based on info. you have provided, I would say "don't take it apart".

Drive it and enjoy it.

[oldford2]

I second and third MMO in the gas tank and dribble some in the carb till it smokes. I have an injector in my 46 that feeds MMO into the carb. Great stuff.
John

[Crankster]

Originally Posted by Ronnieroadster

A leak down tester is the only way to truly know what the engines internal condition is. Using the leak down tester you can easily determine the condition of the piston rings and easily determine how well the intake valve is seating and how well the exhaust valve is seating.

I don't know that I'd agree with this necessarily, a compression test is kind of a "first cut" kind of thing. A leak down test is certainly indicated if or when it fails a compression test, to help narrow the exact cause down.

[waynet]

Originally Posted by mfirth

waynet, you mentioned "spit back" in the carburator. That could blow your power valve. You may have a valve sticking at times letting it spit back. Some MMO may help that.

I didn't think of that mfirth. I assumed the cause would be poor carburetor settings/jets or bad ignition timing. It only happens when I floor the throttle at low revs in any gear. Thanks for your input.

[38 coupe]

Lugging an engine (too much load at low engine speed) will cause rough running like waynet described, that is normal. I am guessing that mfirth is warning you that intentionally making your engine pop back through the intake is hazardous to the power valve in the carburetor.