Cylinder head centre studs worn through valve guide 'chamber'

[Jeremy Wilton]

Having lapped my 500s valves I noticed irregular wear patterns in the valve guide chamber. But only in the two inner inlet passageways (nearest the middle)... It seems that the cylinder head studs have worn 4mm deep 1mm wide holes through the metal next to the oil passageways that lubricate the valve stems? The wear is only on the two central valves (those with the studs rubbing up closest to the Valve guide 'chamber'. Has anyone come across this before?
Having looked at a spare Alpino Head, sure enough, I can see a dull area in the passageway that shows that the metal is thinning in this head too! It hasn't worn through - but it will...
Now from what I can work out, there won't be a great deal of pressure in the holes, they're only linking up the cylinder head stud 'holes' to the inlet valve cam and bucket chamber... what to do?
Leave as is - or plug with araldite - can't weld them as it's right at the base of the valve guide chamber - anyone have any ideas about this?
Cheers
JW

 

[piranha-bro2]

No direct experience, but check out Loctite's Epoxy Weld - I've used it on my Keihin FCR conversion and it sets very hard, can be filed, machined, drilled and has a high operating temp.

 

[mauricejota7604]

I can't imagine a head stud wearing away at the head they shouldnt be moving if correctly tensioned are you sure they are not oil drain holes so any oil building up in that chamber drains down the stud cavity into a groove machined into the bottom of the cylinder then back into the crankcases?

 

[Jeremy Wilton]

Thanks for the replies - I will probably use the epoxy weld...
There's definite wear, next to the drainage bore holes... It's only the inner studs and they're definitely the culprit - (you can look down the stud hole and see the gap) - Have looked at another 500 head and there's discolouring to the metal in exactly the same place.. What I need to know is this going to put pressure in the stud 'passageway'... I suspect there isn't going to be a big build up - it's only the cam bucket going down that'll give pressure?
Anyhow, I suspect I'll have to live with this...

 

[sfcpiet]

As the centre studs do not carry oil to the head and cam bearings, there is no need at all to close the holes.  Oil is transported up the corner studs only, supplying the outer bearings with oil (see oil gallery at the cylinder base).  The centre needle bearings cope quite well with what they get splashed with.  With the opening to the stud bore, this will simply fill up with oil, surplus will then run down the drain holes proper.

I'm suspecting you might have found a simple casting flaw that has broken through, the follower bore is extremely close to the stud bore at this point.  Casting flaws are not at all uncommon in Laverda engines, especially in the heads...  I've seen oil creeping out of the engine number frame on a OR600 engine!

piet

 

[Jeremy Wilton]

Yup - having looked at lunchtime - you're right mate - it looks like a casting flaw. I suspect that over the weekend having jet washed the head (at one point squirting the hose into the valve guide chamber) it's burst through the flaw... as I said I had a look at another head and there was definitely 'discoloured' metal in the chamber in exactly the same spot as mine.... I don't think I need worry...
Thanks for the help chaps!

 

[sfcpiet]

Reckon if it had been vital, the engine wouldn't have made it to where it is today...

piet