350 Lightweight cylinder head recognition

Roderick · Post by **Roderick** » Mon Feb 21, 2011 4:44 pm

What distinguishes the 350 Lightweight head from the 250 Lightweight head? Are the valves or is anything else different?
Roderick

greasemonkey62 · Post by **greasemonkey62** » Tue Feb 22, 2011 12:23 pm

Information for the lightweights is very thin on the ground but it appears that all they did was to lengthen the stroke from 64.85 for the 250cc to 85.5 for the 350cc. I had a 350cc in the late 60`s and a pal had a 250cc and the engines looked identical apart from my tappet adjustment cover was tighter up under the petrol tank. I guess they were the same but don`t quote me, lol.

Trefor · Post by **Trefor** » Tue Feb 22, 2011 12:47 pm

Check the part numbers in the original spares lists?

ajscomboman · Post by **ajscomboman** » Tue Feb 22, 2011 6:49 pm

Depending if it's a CSR head or an early 250 head the inlet valves are a different size. Later CSR's were pretty much the same as the 350's with a big inlet valve.

cbranni · Post by **cbranni** » Tue Feb 22, 2011 9:09 pm

I think............only the 350's had a valve lifter,

greasemonkey62 · Post by **greasemonkey62** » Wed Feb 23, 2011 12:07 pm

my 350 lightweight did not have a valve lifter, I think that was the older 350 models and not the lightweights

BigAl350 · Post by **BigAl350** » Wed Feb 23, 2011 5:04 pm

Only the 350 Lightweights have a valve lifter, that's definitely true.

The 250CSR heads can be used on the 350s, so maybe that's why there was no valve lifter. Not that us stalwart, large-leg-muscled chaps need one!

Al

uncle rod · Post by **uncle rod** » Thu Feb 24, 2011 9:19 am

The valve lifter is on the rocker box not on the head. I have a 350 and a 250 head here on the bench and they appear to be the same. the 350 barrel has 12 fins and a flat piston the 250 has 9 fins and a spherical piston crown with valve pockets.
Regards Rod.

cbranni · Post by **cbranni** » Thu Feb 24, 2011 6:44 pm

There we are..............sorted, useful info for us lightweight lovers, thanks Rod

Roderick · Post by **Roderick** » Sat Mar 12, 2011 11:30 am

Thanks to everyone who hepled with this enquiry. Really appreciated. Roderick