Focusing on just the exhaust valves, I've got a head that has a 5 angle valve job and .5mm oversized ss valves. I was wondering if it is ok to just swap in standard sized ss valves and it'll seat with the valve seats just as good? Or do the valve seats need to be recut to the new valves? If its "un-do-able" ...why? I'm just completely blank on machining processes.

Thanks!

 

yes the seats need to be recut for the new smaller valves,you cant put smaller or bigger valves than the seat is cut for because the seats on valves and head wont match-up and will not seal.PS if you try to put smaller valves in the head than you have now the machine shop will have to sink the hell out of the seats in the head to get the smaller valve to work.

 

if the valves that are in there are .5mm larger, they were probably used to make up for lost material in the 5-angle grinding. you can't really un-do a multi-angle valve job without losing more material, unless the surface is welded up first, but you also don't need to un-do it.

if you want to put oe valves back in for some reason, check with whoever did the machining work on that head if you can. i don't think the oe valves would need to be ground to fit, but they might be too small. one of the five surfaces in the valve seat will fit up to the one surface on the valve. this is how it works, provided that the valve seat/valve are the appropriate sizes.

 

I'm sorry I dont understand what u are trying to say.1st, honda heads are alum w/seat inserts so u cant weld the inserts ,but can replace them.2nd i'll agree that one of the 5 angles would match the valves seating surface but since it is smaller than the valve job presently on the head it would have to be a 60,65,or 70 deg. seat and would put the valves head well bellow the 45 deg seat already on the seat thus sinking the valve ,not a very good situation imo.PS why would you want a 60,65,or 70deg seat?If i'm misunderstanding you please elaborate.

 

Thanks for all the info guys. I just wanted to know because 3 exhaust valves are slightly bent and I am pressed for time so I thought maybe I can replace all 8 with some standard sized ferrera ss valves I already have here at home.

 

sorry...i spaced out on the whole aluminum head thing...my bad. i kept thinking back to the head i originally learned how to do machining on...('72 triumph gt6 mk3)

 

you would weld a seat on a triumph? or any other head?