Smoke at start up? To do, or not to do..

[Allen F]

OK, under closer examination there is an obvious ridge at the top of the cylinder walls.  I think I will have to do the rings now.  Any suggestions on a source?

Allen

[ja17]

Hello Allen,

Just re-ringing a worn block can create bigger problems than before. Cylinders do not wear "round", they wear egg-shaped. Putting nice new round rings in worn egg shaped cylinders cause problems.

The rings in your engine may be working fine. A little cylinder wear does not mean the rings are not doing their job. A  wear ridge  usually indicates that an engine block may be worn too out of shape to install new rings however.
 
The problem is you do not know the condition of your rings. The safest and  unfortunately most expensive method is to bore the block oversize to clean up wear which will make the cylinders round again. New larger pistons with rings must be installed.
 
Now since you do not know if your original rings are sealing you may still choose to try re-assembly with a reconditioned head only. You have a good chance of success.
 
Another option; remove the oil subpan, unhook a connecting rod/piston assembly and push it out the top. Examine the condition of the pistons and rings! Use a ridge reamer to remove the wear ridge at the top of the cylinder before pushing the piston out or you may break a piston ring.

Joe Alexander
Blacklick, Ohio

[Cees Klumper]

Dan / Joe / (others) - is there any sort of maximum permissable wear (out-of-round and otherwise) of the cylinders up to where re-ringing (Deves, I know Dan) is a good idea ? It would be nice to get a feel for this since particularly the cost of pistons is so significant.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[ja17]

Hello Cees and Allen,

Remember new rings will not cure problems caused by worn cylinder walls. Mercedes rings are tough and last a long time. Badly worn cylinder walls or worn ring grooves are often the real cause of ring problems.
 
The maximum wear limit longitudinal and transverse direction is only 0.10mm or about 0.004". The permissable out-of-roundness and conicity wear limit of the cylinder bores is 0.05mm or 0.002" Not very forgiving!

Even if your engine is worn beyound these limits, your original rings may still be working fine. However if  you try replacing just the  rings pay attention to these wear limits.

Other brands of rings as mentioned may be a little softer or more forgiving and may adjust to a little more cylinder wear. Original ring sets are outrageously expensive. Manufacturers such as Deeves or Hastings supply rings at a fraction of the price. Softer alloys in their construction are easier on cylinder walls but may be more prone to damage from engine overheating. They also tend to wear at a faster rate than the hard original rings.

 Lots of things to consider.

Joe Alexander
Blacklick, Ohio

[Allen F]

Thanks Joe,

I am pretty sure I am going to take the pill and go all the way on this.  I have no plans on selling this vehicle, and I figure the pistions and rings won't get cheaper down the road.  

I will keep you posted on the costs and such as I go forward.

Allen

[Cees Klumper]

Allen - definitely shop around for the parts. There may be some 'pipeline' on the shelves. If you have the work done make sure the shop knows what they are doing. Sometimes expensive mistakes are made.

Cees Klumper in Amsterdam
'69 white 280 SL automatic