Hi All,
I am boring a m117 4.5 to 96.5mm and using 560 pistons/rods and crankshaft in it. My question concerns the proper piston clearance to use. The manual shows .008-.018mm for the m117.965 aluminum block engine that the pistons came from and .02-.03mm for the m117.895 iron block engine the pistons are going into. The .008-.018mm works out to .0003"-.0007" and the .02-.03mm works out to .0008"-.0012". I'm thinking I should use the iron block clearance. Not sure if anyone has specific experience with this. My machine shop says "go by what the book says" but this is not a standard configuration.
Thanks

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

Tony:

Agreed on the iron block clearance; the expansion rate of the iron is lower than even that of the high silicon alloy used in the aluminum blocks.

I really do not know the answer but I would be concerned with the piston composition as well. It would occur to me that the pistons may be made to the specific block material. I would either get custom made pistons for the application or try and contact the original manufacturer or at least several piston manufacturers and get their opinion.

The 560 pistons have a NCC (nickel composite coating) which is a low friction coating compatible with iron bores but was intended to allow the pistons to work in an aluminum bore. (A lot of research) That was my initial concern. I have never heard of a piston compatiblity problem with an iron block(but I have not heard everything)-it is always an aluminum block-someone trying to run uncoated forged pistons or aluminum pistons. WORST case senario-if the pistons don't work and scuff the bores I can bore out and have custom pistons made. There is plenty enough cylinder wall left to safely go 98mm. I initially had the block bored to where the pistons would just fit so I could insure the 560 crank/rods/pistons would spin in the 450 block before I went to the expense of the rest of the machine work. Now the block is at the machine shop for final honing to size and parallel decking.
I need to give the machine shop a finished bore size so I think I will go with 3.8005" which is at the upper end of the iron block clearance. (converted to the 96.5 bore)

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

I am really considering going with custom pistons now. I feel confident the 560 pistons would work but with no concrete evidence I don't want to risk it. Custom pistons will allow me to use a small dish volume so I can raise my CR. I will start a new thread to get ideas.

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

Well what was the final verdict Tony?

I am going to use the 560 pistons. I obtained 8 good "1" size pistons so all my bores would be the same size. I had my block machined for .0015" clearance-a little more than spec-for peace of mind. The piston ring gap is still well within spec for new. For a iron block this should be fine. Some older domestic engines are spec'ed .004-.005" clearance new. I can't see the coating as an liability and it is actually a benefit due to it's self lubricating properties. The coating has no ferrous content since a Neodymium magnet will not stick to it. In fact I am strongly considering a skirt and crown coating like Swaintech so the coating issue would be mute.

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT