Piston Running-Clearance, OM-615..??

[Alastair]

Im currently re-building a spare OM-615 and have aquired some brand-new cylinder-liners for it, dirt cheap.

I plan to use the original pistons, as I cannot warrant spending out on new ones for this 'spare' engine, but the originals show 'acceptable' wear.

Ive seen conflicting info on the piston-running clearance to the bore. Could one of you kind folks look up in your extensive collection what the clearance is supposed to be. The liners are 'Unfinished' and need to be bored to size after pressing in the block.....

The Engine is a 1976 OM-615.937 and is the 2.2 Litre with a 87mm bore The pistons are made by MAHLE if that makes much difference..

Thanks!

[Alastair]

Anyone...?

My only source at the moment is the Paynes manual, which says 1 to 2 thousanths inch...

This sounds just a little 'snug'.....

[larry perkins]

i shoot for .001 unless the manual ask for #1 to have more, then follow manual.
build them tight and get oil pressure to the engine prior to starting it is my proceedure.
larry perkins lou ky

Remember, assembly lube is your friend.

[Alastair]

Thanks guys, Ill go for 'snug' unless my engine re-borer friend of many years standing comes up with a reason not to!

After careful examination of the Manual (Paynes ) it reckons, .0007 for nos. 1 pot and .001 for all others....The Turbo motor however has its own set of numbers, which dont apply in my case

Pre-Oiling and 'assembly Lube' is something Ive always been a bit fanatical about, as well as my proceedure for first-run and break-in....

[larry perkins]

hey guys, when you start a rebuilt,that wait till the oil pressure comes up could kill the engine,ask me how i know.
yep rebuilt a non turbo for a 1980 300d,got all clearances as close to specs as possible,had trouble getting the oil pressure up,seems like it took about 5 minutes of total run time,even removed the oil pan in between runs,couldnt see anything wrong,oil pan back on,fired it again and got pressure say within a minute. drove the car around local to fix all the other things(bought with bad engine,so this was my first drive)headed for the express way to go home, car stalled from too much blow by. started it and drove back to shop(slow) took engine apart and found 2 new cyl liners scored,installed new liners ,fitted origional pistons with new rings,and built a oil pump that would pressurize oil(45psi) system before i cranked one turn.
conclusuion,all my rebuilts have zero wait time for oil pressure. car has about 3k miles and am satisified that the delay for oil pressure(and i do use assembly lube) was the reason i got less than 25 miles on the first rebuild.
hope this helps
larry perkins

[Alastair]

I pre-fill oil-filter and allow to drain through oil-pump/bearings--Takes some time with new bearings in there on a cold engine, then re-fill and fit oil-filter, allowing it to sink slowly in the fresh oil-Top up and fit lid. This ensures there's oil priming up the pump, and in all the galleries before starting. While bleeding injection-system, if there's no pressure, -It dont get started, --but that has never happened yet !


The advantage of the 615/616 is you can remove the oil-pump drive skew-gear and spin the oil-pump by hand to generate pressure before starting too....

[Chas H]

Some pistons have the clearance marked on the top. I would research piston clearance and the measuring place on the piston thoroughly before machining.
I would not "shoot" for a clearance, I would expect the machinist to bore and finish the cylinders to exactly the proper size.