nevhunter wrote: ↑Mon Feb 06, 2023 1:07 am
Thinner ones are BETTER if they are of the right metal and fitted with enough interference. Thick inserts have no give and can split the head or just crack it. If Inserts come loose it will generally be the exhaust ones affected as if the heat does not get out of the insert it will SHRINK itself by getting red hot. Good finish ensures good contact and heat flow. A roughly formed recess could be the trouble. All the GAS and Unleaded use insert are good. Nev
Thanks Nev, good information. Mine were as thin as fencing wire though and the new valve springs were I suspect just too much for them. New ones sorted by a very experienced bike head man.
Michael.
Some sizes of things that actually work would be good.
It has crossed my mind that the guy who did mine might have only ever done alloy heads before my cast-iron one turned up, and the cast-iron will run hotter (the bike was being used for long 70mph motorway trips - which it had no trouble with until I got the head 'fixed up' ).
I assume he'd have looked at it pretty carefully when he got it back after the first failure and checked for any machining problems. But maybe not...
'55 Huntmaster, '56 VH, ' 51 VH, '62 Arrow, '80 R100RT, '00 Sprint ST (now with a new Arrow project, and just now those 4-stroke Ariel parts can't even make one running bike...)
Alloy heads are much more difficult. Better if the head metal is a good quality. You need the insert to go deeper into the port for more area in contact. Heavy valve springs can still force it deeper into the port. Even reverse tapered cast in ones can come loose when racing. There's no need for the dia to be more that 2 MM above the valve head size.. Don't put a thick one in and then bore out the ID. Bore close to finish size before putting it IN. Side valves run hotter valve seats than OHV's do and they usually BLUE more exhaust pipe length also. Nev
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