Valve guide fit in head

pommie john · Oct 29, 2011

How tight should a bronze valve guide be in the cylinder head?

Background: I've just rebuilt the motor ( 750 Commando) and it's smoking from the left pot. I looked down the inlet port and there's a pool of oil on top of the left inlet valve. To get oil there I can only guess it's a valve stem seal or a loose valve guide. The stem seal was seated OK and brand new. maybe I damaged it on installation, it's hard to tell.
To check if it was a loose valve guide , I got my guide drift and knocked it with a hammer. It's not too hard to make it move a mm or so with a firm hit. That's without heating the heat. They seem to be about the same left and right, but there's no smoke from the right pot.

Is that looser than you would expect?

comnoz · Oct 29, 2011

A hard hit would dislodge any guide but it sounds like yours may be too loose. That or scratches in the guide bore will allow oil to leak around the guide. Jim

GRM 450 · Oct 29, 2011

John, do you know Ron Russ? He is very knowledgeable on Norton heads and is in Brisbane. I had oiling issues from guides, bought new cast Norton guides and they were worse that the original guides. Bought a set of Kiblewhite guides and Ron fitted those, no more problems. My ph 0422 336013. graeme

pommie john · Oct 29, 2011

GRM 450 said:
John, do you know Ron Russ? He is very knowledgeable on Norton heads and is in Brisbane. I had oiling issues from guides, bought new cast Norton guides and they were worse that the original guides. Bought a set of Kiblewhite guides and Ron fitted those, no more problems. My ph 0422 336013. graeme

I have heard of him and he's well recommended, so I guess I should talk to him.

GRM 450 · Oct 29, 2011

I've got 2 spare guide seals if you need. graeme

pommie john · Oct 29, 2011

Thanks for the offer, but I've got to go to BJs for a few other bits anyway.
Are you Northside like me?

GRM 450 · Oct 29, 2011

Capalaba, Ron is at Wishart. His number is 3343 2502, ring first. Good luck. Oh and nice BM, I saw it at Morgan Park earlier this year. Graeme ps the fellow that sells Kiblewhite and black diamond valves is at Albian

pommie john · Oct 30, 2011

GRM 450 said:
Capalaba, Ron is at Wishart. His number is 3343 2502, ring first. Good luck. Oh and nice BM, I saw it at Morgan Park earlier this year. Graeme ps the fellow that sells Kiblewhite and black diamond valves is at Albian

thanks.

I'll get on it next week.

i went to Stanthorpe at the weekend. They are trying to get permission for more racing days from the council so we were invited to ride around while the council put noise meters up to see how noisy we were.
i thought it an ideal chance to run in the new motor....I spent the day cursing Nortons.

I'm confused as to why a guide might get loose suddenly. It was fine before the rebuild. I put in new Kibblewhite valves , new springs and a new PW3 cam. I've checked all top end clearances. Tons of valve to piston, plenty of spring to coil bound, and plenty of retainer to stem seal .

I'll get Ron to look at the guides. I know they are already oversize on the OD so I'll have to wait until they are out before buying new .

Cheers
John

rx7171 · Oct 30, 2011

pommie john said:
GRM 450 said:

Capalaba, Ron is at Wishart. His number is 3343 2502, ring first. Good luck. Oh and nice BM, I saw it at Morgan Park earlier this year. Graeme ps the fellow that sells Kiblewhite and black diamond valves is at Albian

Click to expand...

thanks.

I'll get on it next week.

i went to Stanthorpe at the weekend. They are trying to get permission for more racing days from the council so we were invited to ride around while the council put noise meters up to see how noisy we were.
i thought it an ideal chance to run in the new motor....I spent the day cursing Nortons.

I'm confused as to why a guide might get loose suddenly. It was fine before the rebuild. I put in new Kibblewhite valves , new springs and a new PW3 cam. I've checked all top end clearances. Tons of valve to piston, plenty of spring to coil bound, and plenty of retainer to stem seal .

I'll get Ron to look at the guides. I know they are already oversize on the OD so I'll have to wait until they are out before buying new .

Cheers
John

If the guides were fine before the rebuild assuming your new valves stems are in spec I'll bet on a bad stem seal.
I had my head done by a shop experienced in working on classic English bikes and smoked quite a bit on one side.
I figured I'd not installed rings properly so put in new pistons and rings and still smoked a bit from same side!

Pulled head and took back to shop and found brand new stem seal had split, probably at installation.
Seal replaced and I've used about a cup of oil when I changed it at 2,500 miles.

Bob

john robert bould · Oct 30, 2011

Just my two penith, I have seen the valve seals quite "floppy" and sometimes the valve on full lift will push the seal past the full valve diameter,in so much the seal edge "drops" into the collet taper allowing oil down the steam...this was the case with a 650ss.Are Commandos differant ? I machined the guide shorter and fitted Ford Cosworth seals, which have steel caps and a garter spring...well it worked :!:

pommie john · Oct 30, 2011

john robert bould said:
Just my two penith, I have seen the valve seals quite "floppy" and sometimes the valve on full lift will push the seal past the full valve diameter,in so much the seal edge "drops" into the collet taper allowing oil down the steam...this was the case with a 650ss.Are Commandos differant ? I machined the guide shorter and fitted Ford Cosworth seals, which have steel caps and a garter spring...well it worked :!:

It's something I looked at. There seems to be about 15mm distance between the top of the seal and the bottom of the retainer. The cam has 12.7mm valve lift, so I think that should be OK.

There is evidence that the head gasket was not sealing properly.
I am wondering if a leaking head gasket could cause oil to get back into the inlet port. Any ideas?

splatt · Oct 31, 2011

You havn't had your porting pineapple in there by any chance and made it to thin under the spring seat or somthimething horrible like that.
I have found over the years that bronze type guides were harder to fit than cast iron,they suck the heat up quicker, made them more vunerable to picking up in the guide bore.

pommie john · Oct 31, 2011

splatt said:
You havn't had your porting pineapple in there by any chance and made it to thin under the spring seat or somthimething horrible like that.

No. I didn't touch the guides or ports in the rebuild.

Carbonfibre · Oct 31, 2011

Fitting valve guides into an alloy head can leave the guide bores scored, which will obviously result in oil being drawn into the combustion chambers. Lining the existing guides is a far better idea, as it costs less to do, lasts longer, and there is no chance of any of the problems related to removal and refitting of guides.

Valve guide fit in head

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