Airhead Heads

[Bob Distelcamp]

I have a general question, I was looking at a pair of R100 heads, The casting # is( 1 263 948 ) The owner
states that the heads are from a R100cs with 40mm Ext. ports. I have no way to measure the ports, can you
tell me from the cast number???

THANKS BOB D

[mattcfish]

A 100CS would have 40mm exhaust valves and 44mm intake if the heads are original.
Not sure if you can tell anything from the casting #'s.
The part numbers are...
11121337073
CYLINDER HEAD LEFT (from 11/78)

11121337074
CYLINDER HEAD RIGHT (from 11/78)

...but.... I don't think those are actually stamped on the heads.

[vanzen]

I am guessing, but I will say that the casting #s may not provide positive identification.
However, for @ $10.00, the price of a (cheap /Harbor Freight) set of vernier calipers –
the original issue, "I have no way to measure the ports"
would easily be resolved.

[chasbmw]

Mind you it's always possible to bore out 38mm exhausts so they will take 40mm pipes!

Charles

[vanzen]

40 mm = 1.5748 "
38 mm = 1.4960 "

Even a 12" ruler would provide an answer.

[Major Softie]

40 mm = 1.5748 "
38 mm = 1.4960 "

Even a 12" ruler would provide an answer.

1 - 9/16" = 1.5625"

1 - 1/2" = 1.5000"

Yep, a ruler that only goes down to sixteenths is all you need. 38mm is just a hair under 1 - 1/2", and 40mm is an almost imperceptible amount more than 1 - 9/16".