jmos4

Hi,

I picked up a 72 350 with 70-80 thousand on it, looks to be untouched from the factory. I did a compression test on it but every chart I find list 134 as max value and I am getting in the 125-100 range.

I did 3 test with a battery charger on the stand.

Dry test 1 high of 125 to 100 low
Dry test 2 high of 122 to 112 low
Wet test 10 squirts of oil, high 155-115 low
1 cylinder had a dry to wet change of 35psi

Is this motor ok to run or will I be throwing good money out the window resealing it and putting it in my car?

I have a limited budget currently so rather not have to do this again in 6 months.

Regards,

1970greensupreme

i'ts hard to judge an engine on a stand. To do a true compression test, the engine should be at least ran to operating temp. How long has the engine sat without running? Any sludge or does it look clean with say a valve cover removed. If it's sat for an extended time valves could not be seating well due to grime/rust on seats and valves. If the plugs look clean, ie no oil fouling. No sludge it may be worth installing it and get it running to judge it better.

AZ520

I did a cold compression test on a craigslist used engine that wasn't run for awhile, it had smog heads and low compression pistons and it had 150 in every hole. This was at 2000 ft elevation with a strong battery on the engine stand. All the manuals say do while warm, I have done both and haven't seen much of 5-10 psi difference. Hand cranking is no good, I have tried that and could only reach 60-90 psi on same engine. Sounds like your engine is in poor shape, rings, valves or both. Cylinder leakage test would be the next order of business.

1970greensupreme

Like I said, it all depends on how long it's been since it's run and how it was stored when it wasn't running.

olds 307 and 403

I picked up a "good running" 76 Olds 350. After swapping in the compression robbing Performer cam advanced 2 degrees, I had 140 to 142 psi all 8 cylinders. I also regasketed it with a neoprene rear main. The bearing looked perfect. With 20psi at 700 rpm in gear, 25 in park and 45 to 50 at hot cruise with 5w30, I would say it is another quality made Olds V8. It supposedly had 90,000 km on it. I used Kleenflo combustion chamber cleaner, tried seafoam, ATF etc to increase the compression lost on my other 350. It raised it from 115 to 150 in a cylinder, I was impressed. You may find it increases once it is ran. I suggest replacing the pan, valve cover, intake and rear main gasket as well as the timing cover and front seal. While it is apart, replace the timing chain. I could have ran both my 76 350's but most are not so lucky and the nylon cam gear end up in the oil pan.

AZ520

For sure, I was just offering up my person testing results. I think it would be a good idea to replace the head gaskets as well. Mine ran hot because some of the passages were clogged up. I found that out later when I added 62cc heads, runs cool as a cumber now.

joe_padavano

The differential among the cylinders is more important than the absolute reading. Personally I'd be more worried about the cylinder(s) that didn't come up with the wet test. That likely points to valve sealing problems. The other thing is that at 80K miles, the plastic cam gear teeth will be pretty much worn. At a minimum you want to change the timing set and since the motor is out, pull the pan and clean it out. Of course at that point, you MIGHTASWELL put in a new oil pump and neoprene rear main seal. I'd also strongly suggest replacing valve seals, as I suspect that if you pull the valve covers, you'll see pieces of them. Look for sludge in the oil drainback holes in the heads also. Of course, at that point you might want to pull the heads for a valve job, and at that point you are only rings and bearings away from a complete rebuild.

jmos4

Hi,

I thought the cylinders that came up in the wet test indicated bad rings or pistons and a leak down indicates valve seat and guide issues?

I am thinking of doing a quick reseal, reuse my 330 timing chain set, as it only has 3000 miles on it, also one of the few parts I can reuse.

Regards,