Dimensions of conrods

[R85/8]

Anyone know the official spec of the conrods?

My measurement makes them the same size as the 2002 BMW car conrods, but I want to be sure. There's lots of interesting conrods available if so...

BTW are the R45/65 conrods the same size as the larger bikes?

[barryh]

R45/65 rods are shorter.

Some interesting pictures of general R65 differences on page 4 of this 1979 road test

http://www.beemergarage.com/documents/r65rt1.pdf

[vanzen]

1981 R100 connecting rod Specifications:




I could not find R65 connecting rod specs, but the BMW part #s ARE different vs those to fit the R100.

[mattcfish]

Just a side note. Late /6 and R100 rods are a little lighter than the earlier /5, and 1975 /6 Con rods.
I've got a 2002. It would be nice if the rods did interchange (lots of hot rod con rods available for 2002's), but I believe there's some major differences...probably in the journal area etc. It may be possible to machine 2002 rods to work in airheads, then again, maybe not.... worth some research.

[R85/8]

Thanks for the info - verifies my measurements. It looks to me like the 2002 car rods are the same dimension. Now to get my hands on a 2002 rod for comparison.

There's a wide range of competition rods for the 2002 - inc titanium - so this could get more interesting.

...It may be possible to machine 2002 rods to work in airheads, then again, maybe not.... worth some research.

It certainly looks like there's not much in it.

I weighed 2 conrods - 618 and 619 gms.

[mattcfish]

I weighed 2 conrods - 618 and 619 gms.

The R100 rods I weighed came in at 499 and 500g (with small end bearing, without big end bearings or bolts).
I balanced them and used them on my build.
My very accurate scale only read up to 500g but my 1975 /6 rods and some /5 rods were all above the limit.
I wish I had some 2002 con rods to look at for you, lots of other parts in the pile.
Let us know what you find out.

Another note: Post 75 pushrods are 15g lighter each than earlier pushrods.

[melville]

I understood the car and bike rods shared a forging from 1970, but that the end products were quite different, particularly as regards the bolt/nut placement. Boxermotors tend to have the fastener heads on the piston side of the rod for case clearance and wrench access, but the inline car motors get the traditional placement on the cap side of the rod. Like so:



So they may get machined to the same specs, but be completely incompatible in use.

[mattcfish]

I understood the car and bike rods shared a forging from 1970, but that the end products were quite different, particularly as regards the bolt/nut placement. Boxermotors tend to have the fastener heads on the piston side of the rod for case clearance and wrench access, but the inline car motors get the traditional placement on the cap side of the rod. Like so:



So they may get machined to the same specs, but be completely incompatible in use.

I wonder what kind of clearance issue it would be?
The gold mine would be if VW rods could be made to work. Talk about aftermarket heaven, and cheap too.

[R85/8]

...The gold mine would be if VW rods could be made to work. Talk about aftermarket heaven, and cheap too.

They're the right way round too



Quick search http://www.tunacan.net/t4/tech/conrods.htm:
VW conrod 311B dimensions:
Center to center length 136mm (5.354")
Big end diameter 55mm
Big end width 22.7 mm
Small end diameter 22mm
Rod length to Stroke ratio (Rod ratio) 1.97:1 (69mm stroke)

This is a useful source of dimensions http://www-cdr.stanford.edu/~petrie/bmw ... gines.html

[mattcfish]

Look at the price for a set of 4!
http://www.lowbugget.com/lowbugget_h_rods.html

BMW 52mm vs VW 55mm big end and BMW 135mm vs VW 136mm center to center. Not going to work with that bottom end bore.