Loose valve guide

Previously simon_ratcliff wrote:

Previously Jonathan Soons wrote:

I bought an Atlas head with a missing valve guide....The guide measures .499". What should the oversize guide measure? I am guessing .501"?

Depends what size the hole in your head is.

The mechanics will read the symptoms and know exactly what I am talking about. If this were a crude slab of alloy like a Triumph head I would just get it hot and bang in a .503" (.004" oversize) but the Norton head is a convoluted affair with its own pitfalls and I don't know how careful I should be.

Previously simon_ratcliff wrote:

Previously Jonathan Soons wrote:

The mechanics will read the symptoms and know exactly what I am talking about. If this were a crude slab of alloy like a Triumph head I would just get it hot and bang in a .503" (.004" oversize) but the Norton head is a convoluted affair with its own pitfalls and I don't know how careful I should be.

Any 'mechanic' who knows what they're doing would first check the hole for concentricity and any taper and then measure the hole diameter and detemine the guide o.d dependent on the required interference fit.

I trust the factory to have got all that right. The guide just loosened up a little (not enough to have gone oval). No damage. Perfect shiny hole. Measured the hole with a .499" valve guide (I just happened to have one handy). Fits tight but can be tapped out.

Anyone know the required interference fit for a Norton head?

P.S. Forgot to say, new valve seats perfectly with guide in place. Just lucky.

Previously simon_ratcliff wrote:

Any 'mechanic' who knows what they're doing would first check the hole for concentricity and any taper and then measure the hole diameter

A quick note on procedure: When sitting at the Norton dismantling bench, pondering a cylinder head, boxes of used parts on the shelf within arms reach, I could consider standing up and going over to the tool drawer under the lathe, a full 150 feet away and rummaging for the Starrett small hole gauges. But wait. Right here is my box of scrap bronze which I am sure will come in handy one day. What are the odds one of these old valve guides is a close fit? And what are the odds I always walk around with a micrometer in my pocket? Sometimes you just have to trust yourself.

Anyone know the required interference fit for a Norton head (exhaust side)?

Previously anna jeannette Dixon wrote:

Previously David Cooper wrote:

I could not find any data when I did mine in 2005. I put the guide in at nearly .004" bigger than the hole. It seems OK. Gas mark 4 (180C) for about 20 minutes and a stepped drift. I see the oversizes available are +.005", +.010". Whether you'll get a +.005" into the hole I leave for others to speculate - sorry. David Cooper (Franks's book says "at least the temperature of boiling water")

Well I made one at .503" using the same measuring tool so we will see how that goes. Thanks

Previously martin_freeman wrote:

Dear Jonathan,

I have looked in commando manual and external diameter is given as 0.5015 - 0.50 inches, I then measured 2 spare new guides I have and both came out at 0.501. Which throws up 2 possibilities checking your micrometer reads Zero when closed removes one, with would leave you with an undersize guide. I would expect guide to be around 0.002 bigger than hole - which worked well with Trident - I turned down Bsa A10 guide to fit as it was in period when nothing was available locally and well before internet.

This leaves you with either trying STD guide of known provenance at 0.0015 or going for smallest oversize you can find.

Unlike many I agree with one of your earlier responces - heat head in oven and have guides and the stepped drift you are using in freezer well before you need them.

regards martin

I got the info from the manual but I could not make any decision based on that. I can't take credit for the oven technique. I don't do that. I use a roofing tar propane flame thrower which heats the whole head in under a minute. As soon as all the water has boiled off I know I am up to temperature. I do this on top of fire bricks so there is no time wasted moving the head (or crankcase) around. People who play around with a blow lamp and spit once in a while just have too much time to waste.

Previously anna jeannette Dixon wrote:

Hello Again I must say this is not a good idea why you may ask , well your cylinder head expands too quickly and it then has a tenancy to go out of shape, , you need to heat your cylinder head slowly with a even heat the only way too do this is in the oven and its the safe way too , leather welding gloves at the ready you have to be careful not to get burned !! in all mechanical operation you may under take safety always comes first, !! have fun yours anna j

Previously barry_carson wrote:

Hi jonathan. dont know if this will help you at all.

Baz

Yes Barry, this pretty much clears it up. It looks like .002" is the maximum interference in aluminum alloy. I will go with that.

Previously David Cooper wrote:

Nowadays I'd check temperature with an infrared thermometer cheap from Maplin.

If I use one of those then I won't seem like the hot metal wizard who can divine temperature with his bare eyeballs. Also I might not melt any alloy crankcases.

Previously David Cooper wrote:

It does warn somewhere not to exceed 200C (gas mark 6 or thereabouts) or the alloy heat treatment will be affected. That's a long way from melting it! But there's a thought - I wonder if anybody has ever identified an engine problem caused by previous owner accidentally softening the head by overheating it? I doubt it! But anyway: - don't cook your cylinder head as if it were the Christmas turkey!

But I don't use the flame thrower on turkeys. It is an idea though.