The BSA A7-A10 Forum

Technical (topic titles must be descriptive) => A7 & A10 Engine => Topic started by: stev60 on 14.04. 2018 08:29

Title: valve Guides
Post by: stev60 on 14.04. 2018 08:29
 Fitting new valve guides to a spare A7 head, has anyone used phospher bronze or steel guides as to the original cast type and any problems.
Steve
Title: Re: valve Guides
Post by: Triton Thrasher on 14.04. 2018 09:29
Don’t think I’ve heard of steel guides.

I find that cast iron lasts longer than phosphor bronze.  The modern super aluminium bronzes may be different: I don’t know.
Title: Re: valve Guides
Post by: muskrat on 14.04. 2018 10:24
G'day Steve.
Stick with CI for a CI head and pB for alloy heads. I know that later on they fitted CI guides to alloy heads but more of a cost cutting exercise than performance. 1-1/2 to 2 thou" interference fit.
Cheers
Title: Re: valve Guides
Post by: stev60 on 14.04. 2018 22:04
Thanks for that I will go with CI,   
Title: Re: valve Guides
Post by: chaterlea25 on 14.04. 2018 22:13
Hi All,

Last week I was asked to give an A10 iron head the once over,
It had been fitted with PB guides, The guides had squeezed tight onto the valve stems and on the exhaust side were easily pushed out with finger pressure  *problem*

PB will expand more than the iron which is why I believe they then were compressed inwards  *????*
Anyway the head guide bores are bang on size so its getting cast guides, new valve seats, valves and springs

BSA  fitted cast guides to alloy heads, the head I got for my RGS had iron guides in it, three of them were really tight, one less so

John
Title: Re: valve Guides
Post by: stev60 on 15.04. 2018 20:11
I wondered about the different expansion of PB and cast iron  when the head warmed up, I noticed steel ones on ebay, but no indication of what type and the question wasnt answered
Title: Re: valve Guides
Post by: muskrat on 15.04. 2018 20:44
Cast Iron Stevo not steel. https://tinyurl.com/osvpurs
Cheers  *smile*