Hot Rods engine question, low compression

customer calls, he can't get his car started. was running fine, he parked it for two weeks and it would not start. i had him check for spark, he did and shot it with starter fluid. still wouldn't start. had him change the plugs thinking they were flooded, still would not start.
towed it in to my shop. fooled with it most of the day, good spark, timing is on, no play in the timing chain, took the fuel tank out of the equation and tried to start it on known good fuel. carb is not flooding over, compression is very low in most cylinders, 25-60 in all but two, 95 and 110, "oiled" the cylinders and the pressures all increased 30-40 psi.
could he have flooded this thing so bad that it washed the cylinders down and destroyed the rings?

 

cam lobes? 350?

 

Sounds like the cam is wasted, how does the oil look? Shiny metal powder in it?

 

Not enough info really. sometimes the owner gives wrong info, or incomplete story.
I have one here now, guy said low power, then couldn't start. 4 cyl . I could tell by the way it cranked over, that it had one or two dead holes. Comp test; two at zero, one at 45 one at 60. It had 3 exhaust valve adjusters, so tight, that two of the valves were open. I have no idea how it ran when he put it in storage a few years ago. I adjusted, and It is running on all 4, but they will never come back to 125

Gas won't ruin rings. Most rings are chrome, and even if it's a vintage motor with cast iron rings, it still can't ruin it in several events

two cylinders are decent, so that is odd, if running fine 2 weeks ago.

I've seen these weird readings on:

vintage engine in junked car and badly stuck rings on most cyls

also a 318 street sweeper....even with special airfilters, they self destruct

lastly, a super overheated engine, so hot it would not shut off, due to pre-igniting

Smell the antifreeze; if it was cooked good, it will fail a smell test. It will smell awful

 

thanks, motor is a 400 pontiac, oil was full of gas, i changed it. the motor has a lot of blow by while cranking. at the owners request i changed the spark plugs again and the wires. i did get it to run for a bit but it was noisy and rough, then died. i have spark, fuel but low compression. i pulled one valave cover and the valves are moving and don't come loose.

 

Does it look like the valves are opening fully? Maybe the oil was so dilluted that the lifters won't pump up.

 

i will check tomorrow, would that give me low compression?

 

Sounds like broken or cracked rings. Was the engine rebuilt recently with new rings but the ridge ream wasn't cut out?
Or maybe if they are aftermarket cast aluminum pistons like in a rebuild kit, the ring lands broke off? And they are in the pan?
Another idea is that the valves are open due to misadjustment. back the rocker nuts off in the adjustment series if the valve train is adjustable till they click & see if it runs right after its readjust ( but if you added oil & the compression went up, its probably not open valves.

 

diluted oil will cause the lifters to collapse and not open the valves fully. 400 Pontiacs do not have a lot of compression to begin with, less than 8 to 1.......unless the heads have been changed....
BTW Pontiac rocker arms use a torqued nut, not "adjustable"

 

This may or may not help but I've found that you can tell an awful lot about whats going on with an engine by using a vacuum gauge...Here's a good link
http://www.gregsengine.com/using-a-vacuum-gauge.html

 

i put a vacuum gauge on it, it read 0 while cranking although i could feel a slight suction with my hand over the carb.

 

Vacuum gauge won't help much without the engine running.

 

From what information you have given, looks like the rings are stuck in the ring grooves due to a lack of lubrication since the oil was full of gas. This will cause overheating of the pistons/rings and the result is 'microwelding'.
You can try filling each cylinder with Diesel Fuel and let it soak for a few days. Keep adding to each cylinder to keep level up. After a few days, clear out the cylinders, add a squirt of oil to each cylinder. Drain the dilute oil, fill with new clean oil. Now check compression. If improved, attempt to start and run.

 

Pontiacs are notorious for their oem timing chains.

If it fails a compression test, the next step is to oil the cylinders and repeat it. If the compression comes up from oil it needs a rebuild because the rings, bores or cylinders are done. If compression does not come up with oil then a leak down test will help you figure out what's wrong.

My money is on the timing chain being the main culprit. Since they came up 30, it wouldn't be running at 50-60 compression.

 

A leak down test will help determine where the loss of compression is going.

 

Bought a 1973 Pontiac Grand Safari wagon back in the day. Brought it home and tore down the front of the engine. Timing chain was super stretched - could pull it out probably 1-1/2 inches or so on both sides. Installed new chain and car ran great another 60 or 70K miles. My mechanic friends said timing chains were the weak link (ha ha!) with the 400 Poncho engines. Might be a contributing factor if engine jumped time. Just saying. BTW, probably one of the best vehicles I've ever owned. I still miss it.

 

did a leak down test, followed by another compression check.
loosened the rockers so valves were closed and put air in cylinder, no air through exhaust, no air through carb. air could be felt out of vent tube on other side of engine and around pushrod/oil return holes in head. compression test after leak down 25psi. double checked movement in timing chain, zero play in chain as indicated by immediate movement of rotor.

 

A leak down test with rockers loose tests the sealing capability of cylinder regardless of cam timing or piston position. Sound like it passed that except for a little blow by. Soooo rings are prolly ok to get by & valves are good. Awesome.

Since the above is good the only other thing it could be is valve timing in relation to piston position.

Again pontiacs are notorious for their stock timing chains.

 

the air coming out the vent pipe is good? i would think it is rushing past the rings.

 

It is possible to flood an engine so bad you wash the oil off the rings and they don't seal. Solution is to give it a squirt of motor oil down each spark plug hole and spin the engine to spread the oil, and blow out old oil and gas.

Spark plugs from a badly flooded engine can get a conductive coating that prevents them from sparking and can't be removed by anything short of sandblasting. So see if the plugs are gooked up and check if they are firing. Best course of action is to clean and sandblast the plugs, or put in new plugs, start the engine and warm it up at a fast idle. Once the engine warms up and the oil circulates it will be good as new.

I know this doesn't sound right but have run into it numerous times. It is not uncommon in cold climates on a carburetor car that gets flooded badly.

Later... re read your description and it sounds like the engine was no hell to begin with, compression after oiling 60 - 140 PSI. Still if it ran before it should run now and the compression may come up once it warms up.

 

i have put oil in the cylinder a few times, first time just a little, spun the motor, took out the plugs and cleaned them , no go. oiled the cylinder a lot, spun the engine, put new plugs in, that is when it started, ran on a few cylinders then died, wouldn't restart. cleaned plugs tried again nothing. repeated oiling procedure, plug cleaning etc......no start, low compression. while cranking it chugs smoke out of breather.

 

with oil in the cylinders two of them were 125 and 150

 

so would I.

 

Did you do a leak down test with guages and timed and measured percentage of leak down? This tells you EXACTLY how much leaks.

Or did you introduce air into the cylinders and just listen? This tells you where to look for a leak.

How much air was coming out?
For some reason In my reading of your post I implied to myself that it was minimal however you never put a value to the leak. My bad there. If everything you put in the cylinder is coming out of the crankcase then of course its not good.

If all cylinders are leaking down thru the crankcase then you'll be looking at a rebuild.

 

the thing that makes me keep fooling with this is, it was a decent running car before it was parked. i have pulled frozen junk out of the woods and was able to get them started. could a timing gear jump and there would be no play?

 

while cranking it chugs smoke out of breather.

You left that part out.
That's a pretty serious case of blowby

Yes they can jump on the nylon gears

 

@31vickywithahemi sorry, i could feel the air coming out the vent tube, on my face as i walked around the other side of the motor. it could be felt easily through the head. i did not use a gage on it but a hose with a valve that i could introduce air slowly and shut the air off. by ear it held no pressure.

 

Could the diluted oil allowed the lifters to collapse? If this was the case fresh oil and a few minutes idling could cure it. If you can get it to run, even on 3 or 4 cylinders, long enough to circulate the fresh oil.

Or maybe take out the plugs and twirl the engine with the starter to circulate the oil?

Never had one that badly flooded. All mine ran with oiled cylinders and fresh plugs. They may have run very badly for the first minute or 2 but soon smoothed out and started hitting on all cylinders.

 

Without being there it is hard to diagnose but you seem to be on the right track. Sometimes it takes several tries before they start, but once they start chugging they blow the excess gas and oil out the tail pipe and one by one the cylinders start firing and after a few minute they run like any other car.