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Piston dimension?

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bigdave
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Piston dimension?

Post by bigdave »

Working on a 1958 R60 vin 619236. When purchased, one piston was damaged by a valve head that went ballistic. The head was also destroyed and will be replaced. Cylinder does not show any damage. Good piston shows 72.45mm (1st oversize?)
I have seen, but can not find again, a description of the 2 types of pistons used in these old machines. The damaged piston measures 35mm from piston top to the center of the piston pin. This piston, and the other one, have 4 rings. I can see no ##s on the connecting rods.
I got a used set of cylinders with pistons that were advertised as for an "early" R60 that seem in good shape, but the dimension from piston top to pin center is 40mm. These pistons will not be used and will be for sale soon.
Guess my question is; because I need a new set of pistons, do I need ones with 3 or 4 rings? I can find sets with 3 rings, but not ones with 4 rings.
Yes, when I get that far the slingers will be replaced.
Any ideas or information is appreciated.
1987 R80RT
1965 R50/2 (now sold)
1958 R60 (project) Now running well
1973 R75/5 (recently sold)
1956 R26 (basket case project)

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vechorik1373
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Re: Piston dimension?

Post by vechorik1373 »

You wrote:

Working on a 1958 R60 vin 619236.
Good piston shows 72.45mm (1st oversize?) Yes, that is first over. But let me inform and caution you.
First of all, pistons are measured nominally. What that means is, a 72.45, or a 72.47 or a 72.49 are all nominally considered to be 72.5, first oversize.
R60 pistons up to 1961, are different from the later R60/2 pistons due to a change in rod length and a corresponding difference in crown height. The replacement piston you have is from an R60/2. As you know, it won't work. I don't know if you were trying to replace just one piston or not, but I would advise you to get a pair of new pistons, unless you are going to the trouble to carefully measure the weight of a used one, (if you find one) versus the other existing piston. You want them to weigh the same. You should not blindly take a used piston and use it, without making both of equal weight.


I have seen, but can not find again, a description of the 2 types of pistons used in these old machines. The damaged piston measures 35mm from piston top to the center of the piston pin. This piston, and the other one, have 4 rings. I can see no ##s on the connecting rods.
Four ring, (and the earlier 5 ring) pistons are no longer available. I suggest you buy a pair of new 3 ring pistons. The part number for the 72.5 pistons are 11 25 0 021 270 and if you need to go to the next oversize, 73 mm, they are 11 25 0 012 273.

I got a used set of cylinders with pistons that were advertised as for an "early" R60 that seem in good shape, but the dimension from piston top to pin center is 40mm.
There is no difference in the cylinders. They are all the same, as far as R60 versus R60/2. It is the rod length and crown height that is different between the two models.

These pistons will not be used and will be for sale soon.
Guess my question is; because I need a new set of pistons, do I need ones with 3 or 4 rings?
Three ring. And be sure you buy KS brand pistons. Don't waste your money on aftermarket brands, they are prone to swell up and seize, and the KS are the best quality, and they are one of the 3 original suppliers of pistons to BMW.

I can find sets with 3 rings, but not ones with 4 rings.
Yes, when I get that far the slingers will be replaced.
Any ideas or information is appreciated.
Vech
Technical Adviser, Former owner, Bench Mark Works
662 312 2838 cell 9 am to 4pm CST PLEASE!

bigdave
Posts: 38
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Location: Chambersburg, PA
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Re: Piston dimension?

Post by bigdave »

Once again --- Vech to the rescue. Thank you for all the VALUABLE information you provide. I will be ordering a set of new pistons soon.
Dave
1987 R80RT
1965 R50/2 (now sold)
1958 R60 (project) Now running well
1973 R75/5 (recently sold)
1956 R26 (basket case project)

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