Compression question - '72 250

[rgnprof]

I had a free day, so I thought I would kill it working on my car. I have had an ongoing problem with white smoke on start-up and it seems to be getting worse (see my previous posts - I have tried everything to fix - replaced AT vacuum modulator, valve stem seals). I did the valve stem seals several months ago and I have always thought I didn't seat them properly, so I checked everything today. I bought the other seal installer for the exhaust valves and used it today, but everything looked fine.

I used compressed air and followed the shop manual and advice from here. I did notice something weird - when I went to remove the keepers on the intake valves, pushing down on the valve, air was expelled from the carbs. I also noticed a little gas leaking from the intake manifold right around the number 1 & 2 cylinders. I don't remember that happening before - when I removed the air and just let the piston keep the valve in place, no problem. Intake seals looked fine as well.

So, when I did a compression check after all of this I got the following readings:

1 - 130 psi
2 - 90 psi
3 - 140 psi
4 - 150 psi
5 - 150 psi
6 - 120 psi

Obviously, I'm concerned about #2 - any thoughts? I don't know yet if any of this helped the white smoke.

BTW, I did adjust the valves and check the timing when I was done and the spark plugs looked pretty good and absolutely no wiggle room with the valves and the guides. What does it usually mean when one cylinder is low like this? Can I keep driving the car? I don't know if it really matters, but I did check the compression engine cold.

Sorry this is long,
Ryan

[cth350]

did you do the old wet test; a little oil in each cylinder? That 90psi was either a fluke or you need a head gasket.

Another way to tell is how well balanced the carbs are. One cylinder severly out of wack will make them difficult to balance.

-CTH

[250 Coupe]

I would hazard a guess that you have a leaking head gasket.

If the "white smoke" dissapates within ten feet or so, it's actually water vapor caused by water being drawn into the combustion chamber. If you can still see the smoke drifting down the street then I'd be looking at transmission fluid as you mentioned.

The reason I'm thinking head gasket is the low compression in #2 coupled with the "gas leaking around the intake". That sounds more like you are pushing water out through a crack because there shouldn't be liquid fuel anywhere except in the fuel bowls.

The smoke goes away as it warms up due to the head expanding as it warms up. At some point it won't seal anymore and it will blow out the side of the gasket or into another cylinder.

The air from the carbs came from the valve you pushed down to remove the keepers on. You unseated it just enough to let air flow backout of the cylinder. This is the same principal as a leakdown tester uses to find leaking valves. Put pressure in the cylinder and listen at the carb, exhaust and oil filler to help locate bad valves or rings.


Michael

[rgnprof]

Thanks for the replies. I am going to try and check it again tomorrow - with the car warm (which is what the manual says). And I will add some oil and see what happens... If that changes the compression reading, what then?

Smoke goes away very quickly, easily within 10 seconds. I don't notice it at all while I'm driving the car.

Ryan

[250 Coupe]

A shot of oil in the spark plug hole with raise the compression if the rings are worn.

Michael

[rgnprof]

I just checked the compression in cylinder 2 after driving the car around and it was back up to 120 psi. Car runs fine but the jury is still out on whether I helped the smoke on start-up - I don't think so. I have no idea why the compression is better today. I'm not even sure what it's suppose to be for this car - I get different information from different manuals. And in response to CTH, the carbs are well-balanced and stay balanced so I don't have any problems there.

Ryan

[250 Coupe]

I'm still voting for a head gasket leak. As the aluminum head warms up, it will expand more than the steel head bolts and the cast iron block. Any small gap will tend to close up.

Early imports with aluminum heads had some problems with gaskets due to expansion. The engineers were used to cast iron and didn't compensate with bolt and gasket redesign.

It could be a loose bolt, you could retorque the bolts and probably seal it up. Some head gaskets do require a retorque after so many hours to take up initial crush.

I'm thinking that at some point you will blow the gasket by pulling out from a stop when the engine is still cold.

Also, are you losing coolant? If yes, then I really think its the gasket. And I really hope its not a crack.

[rgnprof]

OK, I've determined a few things. I am not losing coolant and the smoke that I have on start-up is definitely OIL. As posted earlier, I have checked and re-checked the valve stem seals and the guides - no problems there.

What else could it be and how can I check for sure?

Thanks.

Ryan

[nachi11744]

Hello,
You have one of two things going on here. Either the guides in that cylinder are worn or moving around OR the steel inserts in the coolant passages are very heavily corroded and are now big holes that are leaking coolant into the cylinder which is being burnt.
Check this:
1.Open the radiator cap on a cold engine, start it and see if coolant now burps out of the radiator filler neck, if not, then fit cap and tighten down and see if pressure builds up immediately in the system, try to squeeze the upper hose.
2.Check the valve lash on #2 a few times to see if it changes as the engine is run.
Hope that is some help.
I would still suspect the coolant leak angle. The heads on these engines have steel inserts in the waterways that causes galvanic corrosion and the holes become huge craters that evetually blow into the combustion chamber.

[rgnprof]

Nachi,

Coolant level is fine - I am burning oil.

Ryan

[ctaylor738]

Try pulling the vacuum fitting out of the intake manifold, and see if there is even a trace of ATF, just to rule that out. Plug the hole, run the engine for a while, let it sit overnight, start it, and see if the smoke is still there.

Otherwise, could be head gasket, valve guides, or rings. You will not know for sure until you pull the head and check it out. You definitely have some wear on the engine.

It would be interesting to see what a wet test shows. The best info I found said that a 30 psi increase from the oil means it's time for rings.

[rgnprof]

A brief update: no ATF fluid (I changed the vacuum modulator not too long ago). Pulled the plugs today and checked the compression again - all cylinders were 140 - 150 psi, except for #4, which was 120 psi. The plug for that cylinder also definitely looked different (a little blistered, looked hot) from the other 5. Added a little oil to that cylinder and did a 'wet test' and compression increased to 145-150 psi.

Contrary to what I said earlier, I don't know if I am buring oil or coolant now. I checked the oil and I am using less than ever - probably 1/2 quart over the past 1100 miles, which I don't think is too bad. But, I checked the coolant level and it is down an inch or 2 from the top. I am thinking a leaking head gasket and that I am getting water in to cylinder #4.

Any thoughts?

Can someone give me the general procedure for pulling the head - do I have to remove intake/exhaust manifold first, etc.? If I have to do that, I'm just hoping I don't have to plane it. I don't think I have enough of the head left to do that - I know it's been done at least once before.


Thanks,Ryan

[ctaylor738]

The best way to pull the head IMHO is to unhook the exhaust, coolant/heater hoses and fuel lines linkage, and use an engine hoist to to pull the entire assembly. You will need to remove the chain tensioner so you can get the sprocket off the cam. It's considered good form to remove the rockers. Highly recommend bringing the engine to TDC on #1 before you unhook the sprocket.

But you have a 30 psi wet increase on that bad cylinder. What's your plan for that?

[Arthur Dalton]

Before pulling anything , I would recommend a leak down test...

[autozen]

Been following this thread, and I can give you a little history on the M130 engine. The 68 and 69 year model engines were fairly bullet proof. The head was redesigned in 70 to reduce the flame front quench area and reduce emissions. There was some casting problem with the 70 and 71 heads, because the water jackets broke through in the 4th, 5th, or 6th cyl. When the problem first reared it's ugly head everyone sent the heads out to be welded and remachined, because new heads were pricy. It seemed like a good idea at the time until the heads broke through in another location and poured steam out the exhaust again. A new head was the only answer. In 72 the head was redesigned again, because MB went to low compression in the sixes and V/8s. All those engines were designed to run on regular. I don't know how many times I had to tell owners that their big honkin 4.5 liter engines did not require supreme. The 72 M130 engine faired better in the head failure department than the two previous years, but some did fail. I suggest carefully monitoring water consumption. You could buy one of those block check testers and check for hudrocarbons in the coolant, but I don't think you'll find any. There may be one other possibility. I think I have a couple of old M130 heads kicking around ( I never throw anything away ). I'll check to see if the ball bolts screw into the exhaust or intake port. One could be leaking oil.



Peter