Ariel Owners Motorcycle Club

Simon.Gardiner wrote: ↑Fri May 19, 2023 9:39 pm

simon.holyfield wrote: ↑Fri May 19, 2023 3:42 pm ''''Will it do any harm if I leave it for a while longer?

Simes, exactly how loose is it (eg wobbly, finger-tight) ?

SG

No wobble, but I can push it in with no tools...

Not so much loose as not very tight!
I'd say you could probably get away with that for a bit - unless maybe it was tight once but it's becoming less tight of it's own accord.
Might be worth checking the OD - I've just run a mic over some NOS NH/VH cast-iron guides, they're all for a nominal bore-in-head size of 0.625, nearly all are 0.625 + somewhere between 1/4 thou and 3/4 thou (ie oversize by less than a thou) except for two - one that is 1 thou undersize (probably why it's in the spares box) and one with an oil-hole (so for an open-valve head?) that seems to be 1.5 thou oversize.

I've never had a problem with valve guides becoming loose in an iron head - so far!

SG

I wouldn't run it with a guide loose in the head. It will get worse and the guide will be very hot since it's not cooling as it should The original bronze one is very eroded so something's "different" there.You certainly get much more trouble with alloy heads, but they cool better and allow higher compression ratios.Inevitably you need to make oversize OD guides to fit properly what you have. They should be an interference fit always. Nev

nevhunter wrote: ↑Sat May 20, 2023 12:53 am I wouldn't run it with a guide loose in the head. It will get worse and the guide will be very hot since it's not cooling as it should The original bronze one is very eroded so something's "different" there.You certainly get much more trouble with alloy heads, but they cool better and allow higher compression ratios.Inevitably you need to make oversize OD guides to fit properly what you have. They should be an interference fit always. Nev

OK. Given that I'll need to make a new one, what material should I use? The exhaust guide is cast iron which seems to be readily available as 'meehanite'.

Despite spending 35 years as a mechanical engineer in a oil & gas industry, I'm not very familiar with cast iron!

I think I'd give cast Iron a go. Keep the bore and OD concentric. Try to BROOCH the surface of the guide bore in the head to a truer shape with a rough surfaced turned CI blank of an appropriate size. Assemble guide with the head hot and some oil on the guide to stop it picking up. Should go in tight, but not eyewatering tight. Try to start it straight. There's more metal on one side so try to address that when brooching. Nev

Posts with discussion about cast-iron inlet guides moved to this topic (might be getting confusing having them in a thread about alloy-head exhaust valve guides).

SG

admin wrote: ↑Sun May 21, 2023 2:16 pm Posts with discussion about cast-iron inlet guides moved to this topic (might be getting confusing having them in a thread about alloy-head exhaust valve guides).

SG

Good idea!

I have some that with thumb-push fit and others that I didn't fit: I was worried about damaging the head because, hammering them in would have required excessive force. I could look for the guides and try to find one with oversize. A thou makes a big difference here.

Do you have some guides knocking about Volker?

Simes - what's the exact OD of your inlet guide?

SG