Hitchcocks Forum

I have bought a new 1992 500 valve set and found my valve guides in the head to measure 16.5mm externally and the new guides sold as 0.020 oversize only measure 16.43mm so they are undersized. My head must have had bigger guides fitted previously? So now I seem to have a problem as our hosts say the ones I have are the biggest they do although they were quite shady and would not give me their guide dimensions? Do any of you know of other bike guides that could be adapted to fit my head to save having to make new bigger guides from scratch and a block of phosphor bronze? HARVEY

A standard valve guide OD is 0.627" (15.93mm)

So a plus 20thou guide come to 0.647" (16.43mm)

So from the book, Hitchcocks are right and that's the biggest oversize.

I can only imagine someone has made some oversize guides at sometime and either worked to the drills/reamers they had or drilled oversized to remove damage.

If you do have new guides made, they need 2-3 thou driving fit and the valve seat must be cut to the new guide (not just lapped)
Knowing where you are, there are shops in Hull who could do this (Alex Carr would probably do it)
If you have access to a lathe it's not a hugely difficult job to make the guides (but the seats would need to be cut) Reamers would also make the job more accurate. Fozzy bronze would be the stuff to use.

Ian Myers engineering has the head and like you say I think it will need bigger guides making sadly. There seems to be all sorts of different phosphor manganese bronze materials but I've no idea which is the most suitable or where to find some bar for Ian to machine. H

Hi, oversize .040 guides available on ebay. Vince

Try these guys, Mallard Metals, http://www.mallardmetals.co.uk/products ... rvices.htm They have lots of types of phos bronze bar for sale and I'm sure they could advise what to use.

REgards, Mark

It appears that PB104 is the spec for the job, but is there an expert in the house:-
http://www.holmedodsworth.com/materials ... 453k-bsb24

Also PB can be a bit of a pig when it comes to keeping a size. It may be necessary to ream the valve bore hole in situ after fitting the guides into the head. (Again expert opinion welcomed.)

If you're keeping the bike, why not get a quote from the Cylinder Head Shop, Louth, Lincolnshire for a pair of Colsibro power guides which will probably outlast the rest of the engine. Far superior to phosphor bronze in this application. 01507 328590

I have in the past with this problem turned down the guide and shrunk a brass sleeve over it then turned it down to suit, but you need the finished sleeve thickens to be around 3/32 to 1/8.

Foot thickens read thickness, predictive text baa.

Bloody hell I give up