340 compression test. PSI??

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340Duster247

340Duster247

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Hey guys so I just did a compression test on my recently bought 71 340 duster. I got between 105-110psi across the board. Is this normal? I know nothing about the bottom end of this motor, just " rebuilt" it does have head work done tho.

I did the test because I get excessive blow by out of the breather. And shoots blue out the back when revved up good.
The PCV valve has good vacume.
 
It's good that there close to each other but it seems very low,and with the
excessive blowby and smoke it time for a rebuild.
 
Squirt a little oil in the cylinder and recheck compression. If it goes up with the oil you have ring issues. My 70 340 with a MP .484 cam was 150 PSI
 
340Duster247 said:
I know nothing about the bottom end of this motor, just " rebuilt" it does have head work done tho.
Click to expand...

I agree with William. I would expect a minimum of 150lbs on a stock cam 71'. Which leads me to the questions about the quote above. Was the whole engine rebuilt or just the heads? How long ago? Does it idle like it has a good size cam in it?...........And one more uncomfortable question.......Are you sure it's a 340 and not a 318 or 360 which would have numbers closer to the ones you got.
 
Was the engine warm or cold? All plugs out? Battery charger on battery? Three to four cranks per cylinder?
 
Hey thanks guys! It is a 340. The car has been in storage a lot over the years. I believe it was " rebuilt" around 2002 but I'm not a 100%. I don't know wether it was bored out or not. Cam seems to be lumpier then stock , (I've built a 318 duster in the past) but I don't know for sure. I know that there was head work done tho.
When I did the test the throttle was closed and not completely warmed up. ( I know I read more threads and I'm gonna test again with all plugs out, warmed up, and throttle blocked open)
I did squirt oil in on the first 2 cylinders after doing a dry test. And it barley increased at all Maybee from 100 to 102. So I decided to do all dry first to make sure they were even across all cylinders.
I've only owned the car for 2 weeks
 
First off, Congrats on the new Duster :thumrigh:. Second, i wasn't trying to be insulting about the engine size. There are some out there that really don't know...............I agree about doing the test again the proper way and trying to oil the cylinders. Might give more promising results. Also i'm wondering if it has sat long enough that the rings could just be sticking. If you don't get better numbers, you may also look into flushing the crankcase with something like Seafoam. I have never done it myself, but i know some members have and said it's pretty good stuff.
 
Hey thanks OMRick no offenece at all.lol. I believe it has sat for a while. Ill look I to seafoam or engine flush. I'll update everyone after I do the test again properly

Here's a pic of my old duster!!
5BD671E2-C5AF-483D-9DC5-22CADD27825D-459-0000006D172EAB64_zps1a9cb7c1.jpg
 
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