M117 4.5 stuck rings or not? - PeachParts Mercedes-Benz Forum

rwd4evr · #1 05-15-2018, 01:50 AM

The 218,000 mile 4.5 in my 450 SLC is still running perfectly fine after massive amounts of abuse drifting, but it has what I believe is a head gasket oil galley leak externally over near the oil filter housing. I also may have cracked the oil pan bashing it into the ground on one of my favorite twisty roads. So since I blew the clutch up and the transmission has to come out I think my best bet is to pull the whole drivetrain and put another long block I have in it. I have an identical k-jet 4.5 from a 78 450sl fonzi and I stripped, with only 111,000 miles on it. I believe it was parked many years ago because of a fuel pressure regulator issue. I pulled the plugs and they looked very good, no major soot or oil and a nice golden brown. I did a compression test and found a few cylinders low in the 135 ish range. Highest was about 175 And one was down as low as 90 I think. Seeing how good the plugs were I found it hard to believe that the rings were shot or a valve seals were bad. I'm thinking the rings were just stuck from years of being pussy footed around and then parked for who knows how long. This car was seriously rusty. I found an ancient can of "diesel pep " ,that I think came in the trunk of a parts car I bought. It's diesel fuel additive and injector cleaner, it melted carbon off a piston in a bad block really well. I mixed it with just a bit of ATF put about 3oz in each cylinder then put a tube on a small blow gun and just gently gurgled it to get the stuff all around the high side of the Pistons. I turned it over slowly and jiggled it forward then reverse slightly to try to work the rings a bit and again after it sat a couple hours and repeated again awhile later. Then I cranked it with the starter and blew it all out(all over my fintail😞👎🏻DOH!) pretty thoroughly. I did another compression test and got almost dead even 175-180 on all cylinders. I know this would be normal when doing a "Wet compression test" with oil added to have significant compression increase. So I retested four or five times in all cylinders and then again after it sat overnight. Thr compression hasn't gone down at all. How long do "wet compression test" numbers stay high? Could this still be from the diesel pep ATF mixture Improving ring seal or did it really have stuck rings (or maybe crap around some valves)I freed up? Would putting plugs in it and cranking it help push any residual mixture out of the rings to get an accurate reading I can trust or do I have to fire it up? It's on the floor of my shop and all my good k-jet injection and ignition from my 450slc has to go on it before it will run.

So I want to be sure it's better than what I'm pulling out before I do the chain guides and swap 5.6 cams on whichever one I decide I'm going to put back in it.

Sugar Bear · #2 05-15-2018, 09:49 AM

Guessing the oil is staying in there for a very long time. You could wash it out with a solvent, I wouldn't. The other way is to start the engine.

This doesn't help the situation, if you have a borescope and see crosshatch without any corrosion it will probably be good. These motors have a VERY robust lower half.

Putting compressed air in the cylinders for a few minutes each cylinder might blow the oil out of the rings.

Good luck!!!

Diseasel300 · #3 05-15-2018, 11:57 AM

I'd expect the oil to say present for quite a while if the engine isn't being run. If you do have stuck rings, you should be able to hear air in the crankcase if you do a leakdown test.

If it's been sitting for a long time, you could have gummy crap on the valve seats, carbon holding things open, or indeed stuck rings. Good quality oil and some thrashing should bust them loose if it's just the sitting that's stuck them.

rwd4evr · #4 05-15-2018, 01:02 PM

Oh I know they are robust. The motor in the car was seeing 67-6800 rpm all day at two drift events. It's all forged below the Pistons. I think the compressed air in the cylinders sounds like the best plan. I don't even want to waste the almost new Bosch plugs crapping them up with the atf cleaner mix. I have a good feeling that they are freed up now though. At the very least I'm confident it's not a broken ring or something terminal. I don't think a little blow by will kill too much power at 6000+rpm anyway.

Frank Reiner · #5 05-15-2018, 01:22 PM

rwd:

From sitting a long time, some of the hydraulic cam follower pedestals had likely collapsed. The valve timing events had changed as a result, leading to a large variation in cranking pressures. Once the pedestals are refilled with oil, cranking pressures will exhibit less variation.

rwd4evr · #6 05-15-2018, 04:33 PM

That is possible too. Didn't think of that. I had the oil pressure gauge tube dumping back in the oil cap so oil pressure was probably a bit lower than normal. Probably some crud on the open valve seats too. Thanks frank!