1978 450SL compression

[Richvale5]

I purchased a 78 450SL with over 105,000 miles at an auction since it appeared to be in very good condition and won it for an extremely low price.

It was last registered 10 years previously and was unable to get a response from the previous 2 owners about its history.

I pulled the valve covers and the cams and both top ends were exceptionally clean with almost no apparent wear and the timing chain was very tight and appeared almost new. In addition, the oil tubes are very tight and no movement on them.

I changed out the antifreeze which looked and smelled like it was recently replaced and completed an oil change which was black but I did not find metal shavings or water; just had not been changed for awhile, then drained all the gasoline from the tank.

I pulled the plugs then shot some oil fogger in each of the cylinders. All the spark plugs indicated that the engine was running a bit rich but did not have any oil deposits on them.

So far so good.

So I checked the compression and here is the problem. As you stand in front of the engine on the right (drivers) bank the closest on to me is cylinder# 1. Now that we have proper orientation on this, I found that number 1 read 60lbs, #2 60lbs, #3 66lbs. Number 4 read 132lbs and then on the left bank number 5-7 read between 126-134lbs then #8 read 91lbs.

I shot a couple of squirts oil into #2 and the pressure shot up from 60lbs to 155 lbs.

I assess that I have a bad head gasket between # 1-3 and also worn rings.

Does anyone have another thought about my assessment?

Also, my question to anyone that has experience with the vehicles is that I do not want to pull the heads off to find their condition and wanted to see if anyone had an idea how to check the heads that is not hard to preform without pulling them off the block.

Also, does anyone have an idea where I may be able to buy a short block if the heads are good.

Any response will be appreciated. Thank you.

[Richvale5]

test

[rumb]

Rich, sounds like there is no avoiding rebuilding your engine. The money you "saved" on the purchase price can now go to repairing your engine. You wont really know what is needed until the engine is taken apart.

What was the reading on 1 and 3 when you put oil in? why do you think you have a head gasket issue?

[t walgamuth]

I disagree.

I'd soak it good with marvel mystery oil in each cylinder and add same to oil in sump and to fuel, then I'd get it running and drive it. The low cylinders may well be just stuck rings from sitting.

The cylinders are probably not even worn at that mileage (if correct). Take it out and drive a couple hours on the highway for starters.

[Mike D]

I'm with T Walgamuth. IF the mileage you stated is accurate and the condition of the engine internals are as you state, then the engine is barely broken in.

Remove plugs, rotate the engine to TDC, advance approximately 1/8th turn, fill the cylinders with ATF, allow to sit for a minimum of 48 hours (preferably a week), spin engine by the starter to expel excess oil, re-install plugs and start. Drive it around a bit and re-check the compression.

I say ATF simply because it is my preference for long term soaking. MMO is fine, just not my choice.

My main concern with the car would be the condition of the CIS fuel system. 10 years is a long time for it to sit unused.

[t walgamuth]

Ditto on the CIS.

[Frank Reiner]

Originally Posted by Richvale5

So I checked the compression and here is the problem. As you stand in front of the engine on the right (drivers) bank the closest on to me is cylinder# 1. Now that we have proper orientation on this, I found that number 1 read 60lbs, #2 60lbs, #3 66lbs. Number 4 read 132lbs and then on the left bank number 5-7 read between 126-134lbs then #8 read 91lbs.

I shot a couple of squirts oil into #2 and the pressure shot up from 60lbs to 155 lbs.

As a consequence of the engine sitting for a long time, the hydraulic compensators have leaked down, and the valves are barely opening when trying to do a compression test. Hence, the low readings.
If the injection system will cooperate, fire it up, and when the clattering of the valve train ceases, recheck the compression.

Orientation of components in a car is with respect to the forward driving direction. To paraphrase Gertrude Stein: The Right Side, is The Right Side, is The Right Side, is The Right Side. The right hand cylinder bank is on the right hand side of the car, and the cylinders are #1-4; #5-8 are on the left.

[Richvale5]

Thank you for all the replies. At this time with the responses I have received are: !. Worn engine 2. Sticking rings 3. Hydraulic compensators.

I am making the assumption that this has not run in 10 years but given some of the indicators, it may be less than that.

My concern is that cylinders 1-3 read 60, 60 and 66 lbs and # 4 is 132lbs. To me, that is sounds like a head gasket and the other is issue when I put additional oil in the #2 cylinder and then shoots up to 155lbs; again, an example of worn rings.

So thus far: is there an agreement that by filling the offending cylinders with oil and letting them sit for a week may fix the issue due to stuck rings?

In addition, the oil pressure was good when I cranked the engine over during the compression test.

The next issue is the CIS component. Any thoughts as well on that?

Again, thank you all for your insight. As you well may know, these things can develop into serious money pits and so far, I am $700 in (including the car) and since I am not a trust-fund kid, I want to insure that I am doing the right thing by proceeding with this project.

[Sugar Bear]

Turn the engine by hand and see if the valves open/close. Put air in the cylinders to see where the compression loss/leak occurs. Soak the cylinders for stuck rings.

My guess is stuck rings. The bottom ends on those engines are very, very robust, short of an overheat the rings should be good.

[Tony H]

Was it stored outdoors? Stuck rings are possible as mentioned. If you have a blown head gasket(rare in these engines unless it was overheated) you may see bubbles in the radiator or hear hissing with the leakdown test. Can you use starting fluid and get it to run(at least to determine if there is internal damage and oil pressure) before you expend a lot of effort. With no history it could have been parked for many reasons. Also regarding the heads-most any engine will need the heads rebuilt. These are notorious for worn valve guides.

[Richvale5]

Thanks Sugar Bear and Tony. Have to say Sugar Bears quote was a groaner but funny. I will go ahead and put additional oil in the cylinders, give a couple of days at least and try it again. I think the car was stored outside since the passenger seat smells musty but the coolent looked new and the oil had no indications of water and I did not see any metal in the oil. I really appreciate this information!

[t walgamuth]

Originally Posted by Frank Reiner

As a consequence of the engine sitting for a long time, the hydraulic compensators have leaked down, and the valves are barely opening when trying to do a compression test. Hence, the low readings.
If the injection system will cooperate, fire it up, and when the clattering of the valve train ceases, recheck the compression.

Orientation of components in a car is with respect to the forward driving direction. To paraphrase Gertrude Stein: The Right Side, is The Right Side, is The Right Side, is The Right Side. The right hand cylinder bank is on the right hand side of the car, and the cylinders are #1-4; #5-8 are on the left.

Your explanation of the hydraulic compensators is very good, and it could cause low readings but if the non filling of the cylinders were the problem would it improve when oil is added to the cylinders?

[Tony H]

At cranking speed there cannot be much air passing through the valves for the lifters to be a problem? I think you need to get it to run to really determine your issues. Try the starting fluid.

[Benz Dr.]

Stay away from starting fluid unless you are familiar with how to use it.
1: it can be dangerous if used improperly
2: you can really damage your engine if you use too much.

This stuff can cause dry starts which isn't what you want for an engine that hasn't run in a long time. Spin your engine over until you see oil coming out of the oiler tubes. This should also fill up your hydraulic elements.

[rumb]

I agree with the further comments about oil in cylinders. I had not thought about things just being stuck from sitting so long. Let the oil sit for a while and then give the car an Italian Tuneup. (go drive the heck out of it)