Low compression numbers on stand.

[Lerak]

Hi Everyone,

 

So I finally found the time to get myself a compression tester and check the state of my motor which has been on an engine stand since last spring. The engine itself hasn’t run in over two years and has been stripped of all accessories, intake manifold and the plugs are pulled. 
 

The good news is that I got consistent numbers across all 4 cylinders...the bad news is that they all came in right around 100 psi. Based on the research I’ve done this suggests a really worn out motor but before I commit myself to looking for other options (rebuild or replace) I wanted to make sure that the variables around the engine’s current state and lack of use wouldn’t be skewing the numbers. For what it is worth, the oil pump didn’t even get oil up to the head until I got to the last cylinder. I know this because it started squirting out of a line next to the distributor all over me. 
 

Any advice is greatly appreciated. 
 

Cheers,

 

Karl

Edited March 25, 2020 by Lerak
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[Preyupy]

Compression numbers on a engine that has been sitting for 2 years are questionable at best.  The fact that they are even across the cylinders makes me think it's not all that bad.  You did not say how many miles are on it or what year and specification it is.  A stock Flat top piston E12 engine only makes a little over 8:1 compression.  With a sea level atmospheric pressure of 14.7 psi compress that 8X and you get 117.6psi.  The number will be better if it has higher compression pistons but then will go back down some with a higher lift camshaft.  

 

In other words 100 psi at cranking speeds on a engine that has sat that long does not sound all that bad to me.  

[Lerak]

Thanks so much for the reply, I’m cautiously encouraged. The engine is out of a ‘73, mileage unfortunately unknown but my guess is in the 120k range. I believe the car also sat in a field for a long time before I got it. It did run and drive before I took it all apart though with no obvious major issues. 

[Preyupy]

While you have it on the stand with everything off of it. Why don't you take the head off and look at the bores (look for rust pitting and scratches)  and have a general look at the overall condition.  I will give you a good reason to pull the oil pan and clean the sludge out of the bottom.  pull the front covers and replace the gaskets and seals, same with the rear crank seal.  The cost is virtually nothing but your time and it is very easy to do with common hand tools.  You may decide to take it all apart and do a full refresh depending on what your plans are but with it sitting on the stand why wouldn't you at least have a look?. If it was still in the car and you could start it I would say run it and after a few miles do the compression test again,  if you still get low numbers try and leak down test and you can figure out why the compression is low, (valves or rings)   

[Lerak]

Yeah that does sound logical. To be honest it is a job that intimidates me a little as I’ve never really dug into an engine before but give that it is out and accessible it makes sense to go one step further. Stay tuned for pics of the bores once I get the head off. Thanks again. 

[AustrianVespaGuy]

Pour a little oil down each of the plug holes and re-test.  If numbers go up significantly, it's because the oil is helping the rings seal better, indicating either that they were sealing poorly due to sitting, or your rings are pretty worn and you're getting some leak-by.  If the numbers DON'T change that much, then the long block is basically OK, and you either have 'decent' compression, or you're loosing some past the valve stem seals.

[Mike A]

Maybe it’s me , but with all the work you’ve done thus far and the work you can still DIY including the head I can’t understand why you would want to put it back in the car without going all the way. I wouldn’t hesitate to have a shop do a full bottom rebuild. Have the head done as well before it gets reassembled. ( The guides on mine failed at 140,000 mi) Money well spent , and if you can  do much of the gofer work for the shop, it won’t be that expensive. If it was mine I would always be worried about the health of that motor back in the car without the full service. Mike