hey

i removed my exhaust yesterday and what i took off from where the downpipes bolt to the engine appeared to be allen head bolts, according to the yamaha dealer it actually has the stud and nut set up but the nuts just look like the head of a normal allen bolt so since mine have welded themselves to the stud i thought it was just a bolt...

so anyway can i replace them with some stainless bolts in the correct size or should i just get studs and nuts, reason is i could get the bolts today but have to order up the nuts.
cheers

you could take the bolts and use some regular nuts as long you wait for the original if you wanna have them but you do not need them.

to use some regular bolts would work but then you have to know how long they have to be wich is kinda difficult as it is a kind of "pressfit"

I've done it before. It'll be fine as long as you're not taking the headers on and off very often, and you're careful when you do. One of the main reasons for studs is to save wearing the threads in your (very expensive, alloy) cylinder head.

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+1

+2

Sometimes OEM parts/design need improving.
Othertimes they don't (method in their madness!).

This is the latter case. Steel bolts in an Aluminium head could lead to galvanic reaction - err...rust - causing the bolts to "weld" in place. Hence a steel nut on a steel stud.

In reality, for emergencies, you might get away with a steel bolt (and copper greese?) for awhile. I have on previous bikes. Perhaps not good practice though.

thanks for the replies lads

yeah fair point about the press fit thing, anyone know where i can get these online the nearest yamaha dealer is a bit of a drive would rather order and have them posted.

what are the standard ones made of out of interest?

it doesnt really save the threads if the nuts weld themselves to the studs making it impossible to remove the nut without removing the whole thing lmao

Having the studs also makes it easier to locate the header clamps. Any Yamaha dealer should be able to order you one but Fowlers in Bristol hold good stocks of OEM parts.

Steel studs and steel nuts are not dissimilar metals so will not be subject to the galvanic reaction that would occur between aluminium and steel. However, should the nut stick to the stud then there's always the option of the stud undoing instead.

Like I said: "method in their madness"