compression test

[superbee]

Could someone tell what kind of compression I should be reading on my 51 218cid. Seems to be all over the place from 50-110 psi

 

Thanks    

[Plymouthy Adams]

50 - 110 PSI but you need to know a bit more about the engine, how long it has sat etc..was this a wet or dry compression test you did....average stong block 105 PSI even across the cylinders..(cranking speed)...the uneven reading tell me you have some issues going on within..dry rings right on down to stuck/burnt valves..

 

do a wet test and see if there are any changes...

Edited September 11, 2014 by Plymouthy Adams

[Don Coatney]

If your 70 superbee, or 68 dart had a 60 pound variation in compression what do you think would be wrong? The Mopar flathead is no different. Something is wrong internally in the engine.

 

[superbee]

I just picked up the car last month and have been driving it stock motor with 44k. Just to know I decided to do a test this is how I did it tell me if im wrong.
 

Pulled all the plugs put the gauge in #1 and cranked the motor over till the gauge stopped moving did this for all 6. The #1 was only 50psi so I added some oil retested and it went up to 100psi. I didn't bother wet testing the rest because at this point I figured I needed rings?? I did pull the head and was able to watch all the valves open and close but is there a chance they could still be bad?   

[Plymouthy Adams]

if you had continued the oil wet test you would have a better idea of what..and while the head is off (assuming here as you did not day it was reinstalled) you would at this time do a valve adjust and wile at this point..at minimum a valve lapping as an indicator to valve and seat condition..what was the valve lash on your valves I's and E's...did you read the head gasket on teardown and were the cylinder head chambers carbon'd up in any manner...these are things an inquiring mind needs to know..

Edited September 11, 2014 by Plymouthy Adams

[jeffsunzeri]

Yes, there is a chance the valves are bad. Obviously, look for cracks and chips at the edge of all the valves. Also look for uneven burn and color patterns on all the valves, especially the exhaust valves. Most damage will be apparent to the naked eye with good lighting, but it's not a bad idea to use a magnifying glass. On this engine, look especially at the valves at the rear of the block where coolant circulation may be an issue.

On the flathead, once you've got the head off, a large part of a valve job is done, so you might just want to go ahead and complete the valve job anyhow at this time.

[superbee]

if you had continued the oil wet test you would have a better idea of what..and while the head is off (assuming here as you did not day it was reinstalled) you would at this time do a valve adjust and wile at this point..at minimum a valve lapping as an indicator to valve and seat condition..what was the valve lash on your valves I's and E's...did you read the head gasket on teardown and were the cylinder head chambers carbon'd up in any manner...these are things an inquiring mind needs to know..

I didn't check valve lash or head gasket to be honest I never have or know how to check valve lash. Im pretty much a self taught and feel comfortable working on anything and with help from great fourm like this makes it even easier. At this point since I won't be driving the car till spring might be a good idea for freshen up the motor. I'll take a photo of the motor with the head off and post in the morning some of the valves are black and pitted.

[Plymouthy Adams]

black and pitted valves are only a concern if this is the condition of the valve face as it fits the valve seat...external condition of the head only reflects the carbon build up within the combustion chamber..(the sealing surface established with lapping is critical to compression and a no valve leak as is also the thickness of the valve after resurfacing on a machine to prevent edge from burning..some folks get this critical aspect a bit thin and cause accelerated damage))

 

do a search online on refreshing valves by hand lapping the seats...followed by a proper valve adjustment...also if you have not purchased a book..(factory reprint)..for your car...it is a good thing to have about..chocked full of facts, how-to's and safety cautions that will not only guide you but help to keep you and car safe..

 

also tons of good reading using the search engine above..be sure you are at the top of the forum and not just at the top of a thread within the forum...good luck...also visit our tech section under resources found on the brown banner above..

Edited September 11, 2014 by Plymouthy Adams