Yeah the 4 studs that hold the head & barrel together! lost count how many times this things been down now! so could all that torqing have stretched the studs that much? is there any measurement for the length of them? could they be replaced with stainless steel ones perhaps?

Yer. Steel stretches the more its torqued down but sounds like you've been over zelous to snap it or maybe not tighened it down properly.

You'r meant to tighten them bolts down diagonally, a bit at a time. This is crucual or you will snap one or warp the head (Nightmare)

DO NOT use stainless steel as its not strong enough. You need High tensile steel and the only way to be sure is to get them from Yamaha.

You must stop riding the bike and get this stud replaced asap. Check the head base for warpage using a steel rule laid across it..

I cant stress how crucial it is to have the head equally bolted down correcty with the stress spread over the 4 studs.

Tell me your using a torque wrench ???

Personally I would:

a) Remove the head and check the head and barrel surfaces are completly flat and immaculatly clean. No burs or old gasket traces. This is crucial. Be very very careful and precise about cleaning the mating surfaced. DO NOT use a screw driver, use a craft knife blade CAREFULLY to scrape it then clean it.

b) Fit a NEW gasket

c) I would get 4 new studs but you can get away with 1 if your cheap ;)

d) Using a quality torque wrench, torque the head down a bit at a time, diagonally. DONT OVER TORQUE.

c) IIRC, there is a bolt or two on on the outside to hold the head on. These go on after the main nuts.

Yes i,m using a torque wrench, yes i know the studs have to be tightened in sequence, you say i could get away with just replacing one stud!! surely if the problem is stretched studs, all 4 need replacing!! the stud was not broken when i built the engine back up. cheers : T

Ideally you need 4 new studs but you dont have to if your on a budget. Im guessing Yamaha will screw you for it so maybe get some from somewhere else if you can find out the grade of the steel (deffo not stainless though) I recommend you do though change all 4 if they are old and stretched.

If the stud snapped after you rebuilt it then it was probably too tight and snapped during heat expansion. This is when a sense of "feel" comes into play when working with worn, stretched components etc.

Get 4 new studs and 4 new nuts and washers while your at it. And a new gasket.

Perhaps test your torque wrench too. Cheap ones are shite from day one and if you drop them they can go out of sync. They're meant to be stored with the spring un wound too. (just incase you didnt know, i dont mean to sound patronising)

Keep us posted, ed

no problem, everything has been assembled & torqued up correctly, i,ll order some new studs this week & give it another shot. more news to follow(good i hope!)

Get a new gasket too and make sure the surfaces are MINT...

No point doing half a job..

Good luck