LOW COMPRESSION

[bushboy63]

My 230 has 50-70 psi compression in all cylinders; It set in a field for several years before we adopted it.

Would like to run it until next winter before a rebuild. Any cheap ideas on how to make it run better til then?

[Teoma]

My 230 has 50-70 psi compression in all cylinders; It set in a field for several years before we adopted it.

Would like to run it until next winter before a rebuild. Any cheap ideas on how to make it run better til then?

It could be a couple of things causing the low compression. You could try removing the plugs and squirting a liberal amount of penetrating oil in the cylinder. This will hopefully free up any stuck rings.
Also, if your oil pressure is ok, you can use a product called engine restore. It's an oil aditive that fills scratches in the cylinder walls. I get it at Canadian tire here and it's usually good for about a 20 lb bump in compression in old engines. The draw back is that if you have low oil pressure, it will crush out what's left of the bearings.

[Lifer]

With compression that low, I'm pretty sure a rebuild is in order! Using penetrating oil to free up the rings might loosen them up a little, but it won't appreciably increase the compression.

Using "Engine Restore" is a bad idea. It doesn't actually "restore" anything and can block oil passages, which will make the rebuild that much harder and more expensive.

Sorry I had to say that!

[bushboy63]

I only removed one plug at a time , should I have removed them all before checking compression?

[Teoma]

With compression that low, I'm pretty sure a rebuild is in order! Using penetrating oil to free up the rings might loosen them up a little, but it won't appreciably increase the compression.

Using "Engine Restore" is a bad idea. It doesn't actually "restore" anything and can block oil passages, which will make the rebuild that much harder and more expensive.

Sorry I had to say that!

hmmm I have used it regularly on my vehicles, especially when they get to over 100K miles and never had any problems so long as the bearings were good. I think that maybe the difference is that my engines get regular oil changes and I don't allow them to get gunked up with sludge. I have heard others say the same thing that you have mentioned but that is usually with old engines that they don't know the history of.

[Lifer]

For Bushboy: There's no need to remove all the plugs at once. The way you did it is just fine. We all do it that way.

For Teoma: You seem to be using "engine restore" in well-maintained engines, which is probably unnecessary. Still, any compound designed to "fill in" scoring in the cylinder walls will also "fill in" oil passages, which is not a good thing.

The ads for these products are designed to make the buyer question the condition of his/her engine without a valid inspection and to instill a sense of confidence that all will be okay if you purchase their products. Other "miracle cures" include "fix-a-flat" for tires and "stop-leak" for radiators, just to name a couple. The one thing they all have in common is that your neighborhood mechanic will roundly curse the day he was born when a customer brings his/her car to him after using them.

[Carter]

" For Bushboy: There's no need to remove all the plugs at once. The way you did it is just fine. We all do it that way. "

The way I was taught is to remove all the plugs and have the throttle wide open when doing the test.

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[Lifer]

Interesting read, Carter! I guess that's the way Dodge wanted it done. My Chilton's manual never mentioned doing it that way. I can understand doing the compression check when the engine is warm, but if it won't start ya still have to take a cold reading.

Also, why do they recommend an open throttle? Both valves are closed during the compression stroke and opening the throttle does not increase the amount of air drawn into the cylinder...only the fuel.

[pfrederi]

Interesting read, Carter! I guess that's the way Dodge wanted it done. My Chilton's manual never mentioned doing it that way. I can understand doing the compression check when the engine is warm, but if it won't start ya still have to take a cold reading.

Also, why do they recommend an open throttle? Both valves are closed during the compression stroke and opening the throttle does not increase the amount of air drawn into the cylinder...only the fuel.

Lifer The TM for my M274 also specifies wide open throttle. Having the throttle plate fully open allows the intake stroke to pull in as much air as possible. If you start compression stroke at a slight vacuum (if the throttle plate restricted the air flow during intake) then the final compression reading would be lower.

I can see that restriction being significant in smaller engines as the air volume in the intake manifold is fairly small...I am not as sure that it in a larger multi cylinder engine with a large air volume in the intake manifold it would be a significant factor.

Also as to removing all the spark plugs...It will reduce /eliminate the intake manifold vacuum. Think that a good engine has 17inches vacuum at idle, starting a compression stroke with that much vacuum is bound to affect the final compression reading.

[CREEPING DEATH]

It has been mentioned here (or maybe BE or even the old M37 Netzine) that lapping the valves is oftentimes worth a good boost in compression.

CD

[Lifer]

Thanks for the education, Paul. Dang! I'm 66 years old and still learning new stuff...either that or I'm relearning stuff I knew 50 years ago. You figure out which!

[Carter]

Haven't been back in a while Lifer, been putting disks, calipers and brake flex hoses on Sandy's car but Paul got exactly correct, thanks Paul, also, removing all the plugs speeds up the cranking of engine as it's not working against compression in the other cyls. which gives more uniform readings. Another way of saying what has already been said?