Low compression in cylinder 1 on 240D
 

Hello to the group. I've been having a rough idle problem/starting problem on my 240D that started in June. Starting was getting more and more difficult but ran fine after start. The car does use oil which is about a quart every 600 miles.

Then one day all of a sudden the engine started running as though on only 3 cylinders and had a very rough idle. I did a compression test and all cylinders were around 300-340 except cylinder number 1 which was 100 which explained why it ran so rough. So I did the simple test to see if it was either the valves or the rings so I poured about 1 tablespoon of oil into the glow plug hole and did a retest of the compression.....similar result....about 110. I decided it was the valves because the compression never came up appreciably.

Last month I pulled the head off and sent it off to the machine shop that specialises in head rebuilding. The head came back professionally rebuilt with brand new exhaust valves and a brand new gasket kit with new head gasket. Installed the head and attempted a start. I got the same result. It was very hard to start but eventually got it stated and ran rough at idle just like before but seemed to run a little better. I did another compression test and the results came out the same with number 1 cylinder at 100. I poured some oil into number 1 cylinder and retested the compression I still have the same low compression. I always though that if it was the rings, the compression would shoot way up with the oil poured into the cylinder......this never happened during the compression test. What am I doing wrong? I am so discouraged by this after spending all the time and money taking the head off and getting it rebuilt just to have the same results. I know it isn't the head so it's got to be the rings but can the rings be so bad that the oil can't make a temporary seal for the test? I've read Marvel Mystery Oil but does that really help? What do you guys think?

Thanks

Herb

100 is awfully low, maybe a ring actually broke or stuck and it's just too much of a space for some oil to compensate for it..... I'd say you're past the point of Marvel Mystery Oil being helpful.

I'm sure it's really discouraging to have done all of that head work only for the bottom end to be the issue, but just think of how awesome your car will be once you either redo or replace the bottom end!

I resurrected a 190D OM601 engine with low compression in cyl 1, also < 100psi, by doing the following.

1) removed head.
2) removed oil pan and pushed all pistons out from below.
3) honed cylinder 1, cleaned ring grooves, load of carbon, replaced rings.
4) It bought the compression back to > 300psi ( cold ).
5) The compression on the other 3 cyl are OK but I cleaned the ring grooves anyway.
6) Now the engine runs like a champ.

I am not sure how easy to do it with a OM616 but you may be in luck as it is cyl 1. It may be possible to push the cyl 1 piston out by removing the lower oil pan only.

Good luck.

What did the Cylinder look like when you had the Head off. Broken Piston Rings will sometime score the Cylinder.

Despite the comment on the Marvel Mystery Oil I think it is worth a try.

Remove a Glow Plug and dump about 1/4 cup into the GP hole and let it sit for 1 weak. Rotate the Engine and repeat the does for another Week.
In fact if you have the time repeat the one week treatment as many times as you like till the Bottle is empty.

You will need to change the Oil before you drive it due to the Marvel Mystery Oil in it.
Or I suppose you could drain out the Oil before you start the Marvel Mystery Oil treatment and reinstall the same Oil before you run the Engine. If I did this I would have to put a Note on the Steering Wheel not to start the Car and not remove the note until the Oil back in the Crankcase.

There is other chemicals People have dumped into the cylinder that are stronger then the MM Oil and they are in some of the sticking ring threads.

I am curious why you did not measure the Cylinder Bores while the Head was off to get some idea what was going on?

This is the very reason I use a cylinder pressure tester. I bought it from Assenmacher(?) some time ago. I tried to buy a larger one ( 4 inch bores.. up to 6 inch.) last year but they told me they stopped making them.

It uses bolts through two swing arms to hold down a rubber sealed plate to the top of the cylinder bore gasket deck. It has a shop air line attachment so you can use your 'leak down' tool to see if each cylinder is good, or needing attention before you fit the cylinder head.

Saved me many a time and do this to new motors I build too.


.

Was any alternative fuels ever used with the engine? Did you do a valve adjustment after the head was back to insure the gaps were correct?

Diesel911,
I didn't get a chance to see the cylinder itself when I had the head off fearing that turning the crank would mess up the timing of injection pump during the time I had tension of the chain; it would be my luck that as I turned the crank, the chain would somehow get loose and mess up timing at the injection pump.

At the time the piston was at TDC for cylinder 1 so there wasn't any way for me to look for scoring. I didn't measure the cylinder bores unfortunately but I was able to determine that you can feel with your fingernail a ridge within the cylinder walls of cylinders 2 and 3.....but with 300 + in the compression test I didn't go further.

Yes. I used biodiesel from a dealer which is refined and had the glycerine removed. And I did adjust the valves before the start.

When putting in MMO do you configure that cylinder at TDC or at BDC or does it matter?

MMO ain't going to work, not with 100psi cylinder.

I turned the engine CW/CCW whichever may I wanted when I overhauled my engine. It is not going to alter the timing as long as you strap the chain to the sprocket wheel. It is NOT going to jump a tooth with the OM60x engine. It is physically impossible. I ain't sure about the OM616 but I would expect it to be the same.

ah kay,

Did you have any broken piston rings on your car when you took the pistons out?

Out of curiosity, why did you hone cylinder #1 instead of replacing the cylinder sleeve?

Not on the OM601 engine I overhauled but on a OM603. There was a lot of coking around the rings and the the same got stuck in the grooves. I do not believe MMO will help with heavy coking. If it is only 100psi then you need to take a look at the cylinder wall. It is loo low to be caused by coking alone. The cylinder wall may have been scored by a broken ring or oval'ed.

Changing the sleeve is a big endeavor with engine out of the car. I left the short block in the car. You only need to hone it slightly to take out minor scoring and imperfection and compression can be restored. This has been my experience on 3 engines, 1 OM601 and 2 OM603.

Good luck.

Did you hear any lower end knocking? A really bad rod bearing could lower the compression result. How much I am not sure and it would have to be a pretty bad bearing to do so.

Might hold together with the cylinder not firing. Cylinder firing the rod is gone in a situation as bad as that. Usually the number one rod lets go on the four cylinder 616 before compression is lost.

Why such a crazy thought? Adding oil to the cylinder gave no upside at all. You had a hundred pound compression with or without it.

No. There wasn't any lower end knocking.

One thing you could have done with the head off, was pour light oil or kerosine in the #1 cylinder and see how fast it flows past the rings, compared to the other cylinders. It seems that #1 cylinder fails first in most 5 cyl M-B diesels. Mine did, with chunks of something bouncing around that left deep marks in the piston and pre-chamber. Mine did have the notorious "trap oxidizer" (1985 CA). When I tore it down, ~3 pistons had chunks missing around the ring grooves, so maybe they were close to going also.

One diagnostic I have done on my gas engines is to apply air with the piston at TDC compression, and listen & feel for where it is flowing out - exhaust pipe, intake, or crankcase. I could probably do that on my M-B diesels since my HF compression test kit uses a similar quick-connect fitting.

If you do remove your engine and tear down the block, look-up my post on changing my cylinder sleeves. It was easier than most people indicate. Getting good pistons can be expensive. I left my block with new sleeves, but haven't had the top milled or the sleeves honed. Someday, when I need it.

When I did it on My Volvo Diesel I did not orient the Pistons in any special place. However, the Pistons that were at the top did not get as much MM Oil as the others did as I used the Glow Plug holes to get the MM Oil inside.
So I rotated the Engine a week later and did it again.

If you did the Piston down near Bottom Dead Center there might be a small advantage in that bore is tighter down there and the Oil would not leak by as fast. You could also put more Oil in; all though I don't think that as a good idea as it is going to leak by.
I think it is better to put in 1/4 Cup-1/12 Cup per cylinder (I used 1/4 cup per cylinder but just remembered that My Volvo is a 6 Cylinder and the Cylinder diameter is smaller and also the Pistons are flatter on top so there is less places for the Oil to pool in on top of the Piston.) and let that set and repeat that later as the Oil is going to leak down. Only the Oil that stays in the ring and groove area is going to have a chance to eat on any Carbon.

I suggest looking up some diys on the soaking.

One of our Member suggested that if the Fuel Supply Pressure was on the low end that the first Element on the Fuel Injection Pump would receive more Fuel than the other cylinders.
If that is what is happening the number one cylinder would carry more of the load than the other cylinders and be worn more.

I was not going to get into that until he repairs the current issue. Basically with chronic low fuel pressure on the 616 engines I believe the first cylinder is forced to carry more of the load.

So more first cylinder wear issues are reported. Especially rod bearing failures. The five cylinder 617 also can display this issue but is not as common.

The low fuel pressure issue has to be present for a very long time I suspect. This is quite possible as well.

One possible culprit is the lift pump produces less fuel pressure by design than does the five cylinder turbo models. Since it only requires a spring change to upgrade the 616 lift pump I recommend doing it. No way to absolutely prove what I believe but it does make some sense.

Just to be sure I am clear. To my knowledge we have never had a case on this site with a 616. Any additional rod bearing clearance drops compression though.

It would take those rod bearings being in an overlap situation. This would jam up an engine . To drop off compression to a hundred pounds. Or horribly worn down well into the bearing material backing.

Actually we do have regular cases of diminished compression with the 3.5 litre diesel blocks. The rods bend a little and the compression becomes so low that cylinder will not fire. Generally speaking rods on the 616 are not plagued with this issue. A much more rugged engine from a time quality was dealt with properly.

I suspect you will probably find a piston/ wall issue really. Or perhaps broken rings. I also hear the pain of sending out the head.

For future reference. I set the head upside down and introduce a little thin fluid to see how the valves are seating. Before taking a head to a machine shop and after it comes back.

Since I have limited ability I also introduce air pressure to any suspect cylinder to find out where it is going. Unfortunatly I have little time to work on mechanical systems now. I can only hope some time gets freed up as I enjoy it when I do.

The 616 is no rocket ship but I truly like the two I have. If only a couple or even just one five speed manual transmission could be obtained for them would make my day.