Guide to valve clearence ?

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GRM 450

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Hello, what is the recomended clearence between the valve guide and the valve stem? I can't find it in the manual. I can find the guide tolerence, but want to be sure.

This is a picture of one of my inlet valves, and I'm assuming this is oil leaking through the guides?

Guide to valve clearence ?


Thanks Graeme
 
0.002'' is a good starting point for a new guide and valve, manual suggests up to 0.004'' which is alot for a inlet, I have seen valves that look alot worse
 
.002 is WORN out in my book... IMO this spec is for ease of factory assembly... yes the bike will run but thanks for guide seals...

.0008 intake valve will not slide from it's own weight unless bone dry....ie has no oil on it and cleaned with solvent
.0012 exhaust valve will barely slide if oiled
These # are only a guess for a few simple but technical reasons

That's how I've been doing them for the last 20 years
 
When I finished pressing in new guides they were buttery smooth. I thought this was ideal. I was wrong. Once the motor got hot, these got tight. I ended up bumping a valve and had to go back in to replace. I purchase an adjustable reamer from the local tooling outlet and brought it out to spec.
Once pressed in, they get a couple thou tighter. You will also have to dress the valve seats with seat cutter if you are changing the guides. I got one on line and turned it around for what i payed for it to another needy person
Google "Neway Valve seat cutter".
 
If you’re going to fit a guide at .0002-.0008 than the cutting of the seat must be even more concentric to the guide than those numbers. It’s hard to do in your shop at home. When they wrote the specifications most bike shops could not hold that concentricity so they opened the specification to a working clearance (worn out). If you aim at .001 clearance with a system that has no solid spindle support for the tool while it cuts the seat than you could have problems on the road at speed.
When its done right as Dave describes wear is staved off by the lack of rocking. When you start with .002 the rocking has a good start and will get worse much quicker.
 
dynodave said:
.002 is WORN out in my book... IMO this spec is for ease of factory assembly... yes the bike will run but thanks for guide seals...

.0008 intake valve will not slide from it's own weight unless bone dry....ie has no oil on it and cleaned with solvent
.0012 exhaust valve will barely slide if oiled
These # are only a guess for a few simple but technical reasons

That's how I've been doing them for the last 20 years
Click to expand...

The advice is good , but take your cell phone because you will more than likly be pushing it home on the first full power blast.
STD valve size, .310-.311 roughly , std 5/16 guide, .3125, fixed reamer, will probably cut .3135++, an adjustable reamer, will cut to any size but more than likly hour glassed.
To tight for cast iron guides,
 
Thank you all,
Another question, or 2
Can I use 4 inlet guides with oil seals to keep oil out of the smaller clearence guides?

And what is the best way to promote valve rotation?

graeme

(Mk3 Head)
 
I just bought 4 new cast iron guides .002" over OD. First over size.

But the hole for the valve in the new "Norton" guides is bigger than the guides I just removed.

Are these "pre worn out" to save me the trouble of wearing them out myself? I appreciate the manufacturer taking the trouble to do this for me, but I would prefer to wear them out myself.

Where do I get decent guides from?

graeme.
 
Graeme, if the guides are still tight in the head take it to a recon shop and get 4 guide liners fitted, and get the seats cut at the same time.
 
splatt said:
dynodave said:
.002 is WORN out in my book... IMO this spec is for ease of factory assembly... yes the bike will run but thanks for guide seals...

.0008 intake valve will not slide from it's own weight unless bone dry....ie has no oil on it and cleaned with solvent
.0012 exhaust valve will barely slide if oiled
These # are only a guess for a few simple but technical reasons

That's how I've been doing them for the last 20 years
Click to expand...

The advice is good , but take your cell phone because you will more than likly be pushing it home on the first full power blast.
STD valve size, .310-.311 roughly , std 5/16 guide, .3125, fixed reamer, will probably cut .3135++, an adjustable reamer, will cut to any size but more than likly hour glassed.
To tight for cast iron guides,
Click to expand...

I fit all my valves at .001 intake and .0015 exhaust. Of course I would never use cast guides. I have found DLC coated valves with Ampco 45 guides outlast cast guides 2 to 1. Jim
 
Of course I would never use cast guides. I have found DLC coated valves with Ampco 45 guides outlast cast guides 2 to 1. Jim

Sorry Jim, but can you explain the above please. I have never heard of these before.

DLC coated valves ?

Ampco 45 guides ?

graeme
 
GRM 450 said:
Of course I would never use cast guides. I have found DLC coated valves with Ampco 45 guides outlast cast guides 2 to 1. Jim

Sorry Jim, but can you explain the above please. I have never heard of these before.

DLC coated valves ?

Ampco 45 guides ?

graeme
Click to expand...

Dlc coating is a hard vapor deposit known as "diamond like coating" It is what is on Black Diamond valves from KPM [Kibblewhite Precision Machining]. Ampco 45 is a work hardening bronze used in KPM and a few other guides. It is tough to get a good valve fit. Reaming gives a poor finish so they need to be honed to size. When they are fit correctly they wear very well. Jim
 
Hi Jim; I had just bought a set of KPM guides and valves , and as the valves were 7.98mm stem diameter, and the guides ID smallest , we had ordered a bronze guide reamer( (7.95mm) from Cylinderhead supply , we intend to start the job on the lathe with a tool , then fit the guides and finish with the reamer ........any advise???? that will go onto the Seeley with JS rods.pistons /Bsa tappets /JS cam. Now the 750 head is beeing machined ala 850 to fit onto maney ally jugs.....absolute beginners in tuning , but my buddy was a tool maker before retiring.
 
I would not finish the guides with a reamer. It will leave a poor finish and cut down on guide life. You can hone to size with a Sunnen hone or next best thing would be to ream to just under valve size and then finish with a brush hone. Dynodave's fitting by feel [above] is good. It is difficult to get an accurate measurement with gauges. Jim
 
Thank you gentlemen for your advice,
I have found a Kibblewhite dealer in Brisbane, so we will go with your recomendations.

Thank you for your advice.

Graeme
 
Hi thank you Jim, i had a look to sunnen and ask them a question about their products , though we thought , we are following your second suggestion, idest to ream undersize before fitting and then when fitted slightly hone with a brush (or an old valve with some grinding compound ) while we are in the job what kind of tolerance do you use for the guide OD (I don't know the english mechanical term for that negative tolerance!!),have a nice day , here in Britanny the snow is falling..........
 
marinatlas said:
Hi thank you Jim, i had a look to sunnen and ask them a question about their products , though we thought , we are following your second suggestion, idest to ream undersize before fitting and then when fitted slightly hone with a brush (or an old valve with some grinding compound ) while we are in the job what kind of tolerance do you use for the guide OD (I don't know the english mechanical term for that negative tolerance!!),have a nice day , here in Britanny the snow is falling..........
Click to expand...


Don't use lapping compound on the stem. You will end up too loose and the compound can become embedded in the bronze. A brush style guide hone is cheap and readily available. Use it to remove the last .001. I like the intake to just be able to slide out under it's own weight when clean and dry. Slightly looser on the exhaust. Synthetic motor oil for prelube on the valves.

I fit the guides at around .002 to .0025 in. interference- except the intake guides on a RH4 head. I go not tighter than .0015 to help prevent cracks. Head at 375 F. and guides cool.

We had snow last weekend but it's sunny and 50 today. It's desert climate here so we will drop to the teens as soon as the sun goes down. Jim
 
Hi Jim, all copy loud and clear , will tell that to my buddy tomorrow morning...........Pierre
 
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