M130.980 recovered compression

[bracurrie]

I am not sure an answer is possible here without an engine rebuild, but some others may have insights from my experience.
I have thought that after replacing gas tank, and electrical fuel pump that my gas mileage was too high (19 mpg) so I asked a local mechanic to confirm that the fuel system was working per specifications.  I had accidentally pulled a spark plug wire out of spark plug socket trying to diagnose a miss-firing condition that developed after a 400 mile trip. I thought I had repaired the spark plug wire but the miss persisted and even worried me that the car was suffering some other dire problem.  The car would start and idle but there was a dead miss as it seemed to be running on five.  It was three months before I could get professional help.  I had the car flattop towed to the shop where the following occurred.
First they confirmed my spark plug fix was sound. Then they pulled the spark plugs and they were found to be gaped way too wide and two of them looked kinda wet.  A compression test revealed that the middle two cylinders had 10-20 compression while the others were 120 or so.  The tech who has extensive experience with older and/or well worn gasoline engines opted to put a little ATF into each cylinder, wait overnight, install plugs and start engine. After letting the engine warm up and burn off the ATF a subsequent compression test revealed compression numbers of 120 or so across all six and the car ran smooth and very well.
It was noted that the radiator was missing almost a gallon of coolant.  I have driven the car 150 miles around town with some high speed driving and the car  seems to run great.  But after the last run and after letting it cool completely I noticed some remaining pressure when I opened the radiator cap to check the coolant level which appears to be down a little from where it had been filled.
The car is a 1970 280 SE with only 87,000 miles confirmed by documentation.  When I bought the car three years ago The head was removed and the gasket replaced. It was properly torqued again after some miles.
Brad Currie

[MikeSimon]

Interesting. If the ATF really had an effect on the compression and restored it, I want to say that it will be a temporary fix. Whatever the ATF did to the rings and cylinder walls will wear off again.

[Bonnyboy]

I talked to an old school mechanic a few weeks back about a tired old engine that is smoking on start up (might be smoking more but haven't had it on the road yet) and he suggested ATF in the cylinders and let it sit for 4-5 days as a first step.  He said that if there is crud in the ring grooves and the rings are not travelling freely, the ATF may dissolve the crud and let the rings travel freely again.   Gonna do a compression test next to get a baseline.    If the ATF doesn't work the next thing i'm going to try is hotter plugs and then valve stem seals and if that doesn't work, its rebuild time 

 

 

[Cees Klumper]

Do monitor your coolant level and check whether your oil filler cap gets any 'mayonnaise/sludge' build up on the underside indicating coolant is leaking into the oil which would be bad.
Otherwise the atf may have succeeded in freeing piston rings.

[bracurrie]

Bad news. Did an exhaust gas leak test and it appears I have a leaking head gasket. My theory is that water got into the cylinders and stuck the rings.  The ATF freed them up. 
In any case I am now on the hunt for a head gasket and I hope the engine block deck and head are still straight.
Brad

[lurtch]

This is what I found after investigating the same problem you are having. At the top of the photo you can see two the four water passages adjacent to the cylinder that plug up with corrosion. Also notice the cylinder wall rust from the failed gasket.

Larry in CA

[bracurrie]

Also notice the cylinder wall rust from the failed gasket.

Did you end up having to machine your head or block deck? Or was it just the gasket?
Also, because it may have to be some time before I can get the engine apart how should I store the engine?  Should I drain the coolant from the engine?
Thank
Brad

[MikeSimon]

I did not know that ATF would free rings. I have used Marvel Mystery Oil in the past on engines for that purpose. Not on the Pagoda, though.

[rwmastel]

At the top of the photo you can see two the four water passages adjacent to the cylinder that plug up with corrosion.

What's the normal fix for this?  Is the blockage normally small or the entire passage?

Also notice the cylinder wall rust from the failed gasket.

When this happens, I assume the cylinder walls need to be bored.  Does that always require over sized pistons, or is the corrosion sometimes minor and only different rings required?

I have and engine rebuild in my future, so just asking general questions.

[Benz Dr.]

Cylinders usually wear more at the top where pressures are the highest. They can also go out of round with the thrust side wearing faster. Also, there can ridge wear at the top of the cylinder where the piston stops its upward motion which leaves the top of the cylinder at original specs and everything blow worn in different dimensions. The only way to fix this is to bore the cylinder out to the next larger size. If you are already at maximum over bore and you want to keep your original block, sleeve the bores then start over with standard pistons if you can get them.

If you happen to have a 3rd version engine in a 230SL, I would try to find the early gun drilled version connecting rods with early flat top pistons ( 24mm pin with 4 rings ) as those pistons will give another 15 - 20 PSI compression relative to those stepped top pistons. You could also look for the 25mm pin four ring intermediate pistons but there were far fewer of those engines made. At any rate, you would be looking for used connecting rods so plan ahead carefully.

[bracurrie]

I have arranged to have an a very experienced MB mechanic that is very familiar with the M130.980 engine to fix my engine.  He maintains that he can find a new head if needed. I hope not.
I was reading a British Mercedes enthusiast magazine from a couple of years ago and they prepared a W111 coupe with a M130 engine for the P2P vintage rally. They bored the engine one size but they didn't mention new pistons.  Do you simply use one size up rings or would I have to find the pistons?
Brad

[Cees Klumper]

I don't believe there is such a thing as 'one size up piston rings' to accomodate bored out cylinders; you will need new pistons + rings.

[bracurrie]

I had the occasion to talk to the tech who "recovered" my lost compression.  He mentioned that he remembered the compression was very even across all six cylinders. More hope that its just a bad head gasket.  It really hasn't been hot since the gasket was installed. The gasket that was installed might have been sketchy NOS.  It had been rather difficult to find at the time.
Brad