Valve seatings in heads.

itma · Post by **itma** » Thu Jan 14, 2010 7:23 pm

quote: why, if the valve seats are cast iron? cast into an alloy head do we need to change them to another steel/iron seat to use unleaded petrol?

you don't
as has been proven by most classic bike riders.

GOLDSTAR · Post by **GOLDSTAR** » Thu Jan 14, 2010 9:01 pm

Thanks Itma, nice to have my views confirmed, kind regards

Stan Palmer · Post by **Stan Palmer** » Sun Jan 24, 2010 8:41 pm

John is coming to look at the G9 heads I have. The crankcase they came with is 1954 (there is no guarantee the heads were that year as I know nothing of their origin). I note that Johns bike is 1957. Just to help him avoid a disappointing result, as it's a fair step from Whitstable to Godstone, does anybody know if 1954 and 1957 heads are the same. Or, what should I check on the heads to ensure compatability with 1957 ?
Stan

Stan Palmer · Post by **Stan Palmer** » Sun Jan 24, 2010 8:55 pm

A bit more info, I did a search and found that one difference is in holding stud diameter. I have just been over and checked, they are indeed the earlier 5/16. Not much meat on the inner bosses, but 1/32 on radius is not much to enlarge anyway. I guess if that is the only difference they will be OK. I will recommend John brings his old dodgy head for comparison.
Stan

Chazzyb · Post by **Chazzyb** » Sun Jan 24, 2010 9:45 pm

quote: I will recommend John brings his old dodgy head for comparison.

Yeah, and the one off his bike <chortles>

wilko · Post by **wilko** » Mon Jan 25, 2010 4:25 am

The cases changed in '56 so they won't fit early too late or visa versa! Stud pattern is different,

Stan Palmer · Post by **Stan Palmer** » Mon Jan 25, 2010 7:59 am

Thanks for that Wilko, I will warn John to avoid a wasted journey.
I noted on the link to 'changes by year' on the twins that the compression ratio had changed, which might have been tolerable, but changed stud pattern is terminal.
Stan