Compression

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mrhollywood

mrhollywood

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What should the stock compression be on my slant 225? I'll be doing the compression on my car for the first time tomorrow .I've never done it before and I'm assuming it can be done with one person?
 
Well this doesn't sound good....... here's what I got 1-45 2-45 3-45 4-60 5-0 6-0. Any ideas?
 
Burned/bent valves or skipped timing chain with those readings.
 
A blown head gasket between 5 and 6 is a possibility.

All your numbers are low though. Was the engine warm and did you hold the throttle and choke open? Also, how many crank revolution per test. It can take at least three revolutions to build to full pressure.

You should test once and then a second time after adding a few squirts of oil into the cylinder. If compression increases more than about 10psi when adding oil it indicates warn out rings. If compression stays close to the same, then valves.

A leak down test would be the next step. But if you don't have a leak down tester you can do a poor man's test. If you can rig up a fitting to apply compressed air to the cylinder then you can listen for where the air is escaping. Oil cap = rings, tail pipe = exhaust valve, carb = intake valve.
 
I've also read that if an engine has been sitting a long time the rings can get stuck. If so, then running it for a while might free them up.
 
It was warmed up.also I cranked the engine over three times per cylinder. My gut feeling is timing chain and head gasket.
 
Dat ***** has jumped time. Does it even run?
 
I was thinking the cranking PSI should be about 100... Maybe that's not new though.
 
Check the valve timing first before you pull the cover to make sure that's the problem. It could be the problem is only in the head. Also, If the chain skipped far enough, it may have bent valves so you may have to take off the head anyway. If the valve timing is ok, adjust the valve clearance and retest the compression. If it's still bad, you'll need to pull the head and do a valve job. The actual compression readings can vary depending on engine wear, cranking speed, compression ratio, etc. The readings should all be over 100 psi and within 20lbs of each other regardless. As for having the throttle open during the test......I've never seen that make any significant difference.
 
One thing I also noticed is cylinder 6 has oil deposits on the spark plug. Valve seat?
 
If it was "warmed up", it ran: but with 45 psi I dont see how it even lit off. Put some ATF in the cylinders, like a few squirts from an oil can in each spark plug and let it sit overnight or as long as you can, that seems to loosen stuck rings pretty good. Do a compression test with the plugs out and coil wire pulled. Screw it in, bump 3 revolutions or until the pressure stops going up. note and repeat on next cylinder.
 
I did the valve lash after doing the compression test. Cylinder 5 exhaust was the only "tight" one. I haven't done another test after that though.
 
Ok I did the timing chain and here's what I got for compression. 1-60,2-60,3-60,4-70,5-0,6-0.
What do you guys think rings or head gasket? It started smoking the other day and there is oil deposits on the plugs for cylinder 5&6 . If it is the rings can I remove them with the engine still in the car? The haynes manual said you can remove the oil pan and unbolt each rod and push it thru the top but it seem like a pain with the k member in the way.
 
If the valve have clearence, you'll need to pull the head and take a look inside. If the problem is only in the head, you can just do a valve job and get it back and running. If it needs rings and/or pistons, pull the engine out and do it right.
 
I'll check the valves first. If I do have to change the rings should I hone the cylinder walls?
 
I recall never measuring more than 140 psi in my 225, even w/ a new rebuilt short block. Before ripping it open, try a few sanity checks. Turn it over by hand with a socket wrench. If you can feel each cylinder like a firm spring, your engine is sound, so try another compression gage. It may not be sealing fully. On a slant, you probably should remove the spark plug tubes first to insure a good seal on the spark ports. You likely need new rubber seals on those anyway. Did somebody put a regular Shraeder valve in the end of your gage fitting? Those will give grossly wrong readings. Maybe the gage's rubber hose has cracks.

I suggest that because I think that with the readings you post the car would either not run or would pour out blue smoke. Of course it could be the valves. If it runs and you have a fairly steady reading on a vacuum gage, then bad valves in that many cylinders is hard to imagine. However, you do say you get some smoke.

I think you can re-ring in the car. I did that in my V-8 C-body with a similar K-frame. I think it is much easier than pulling the engine, but others disagree. You can hone the cylinders with an electric drill and a ~$10 stone tool. Just clean very well with soap and water. You also need a ring compressor (<$10 Harbor Freight). A ring expander pliers is nice, but not essential. Soak the pistons in gasoline or similar to clean well before the new rings. Also replace the rod bearings and maybe the main bearings (can do w/ crank in by pushing the shell around, plus the rear seal. And clean, clean, clean.
 
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