Bronze valve guides

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bruce.carrad
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Bronze valve guides

Postby bruce.carrad » Tue Feb 13, 2018 8:28 pm

Has anyone used a bronze valve guide in an iron head? I believe the expansion rate is different to cast iron so may not be compatible, perhaps. Would like to know from someone who has more knowledge than me as I need a replacement exhaust guide for a 1937 500 head. I have a lathe and some bronze so here's hoping.

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Re: Bronze valve guides

Postby paul.jameson » Tue Feb 13, 2018 9:19 pm

I am sure it has been done but if it was a success we would know about it from the time when bronze guides were still available and cast iron ones were not. I suspect that the difference in expansion will eventually lead to the guide coming loose. Why not simply buy a cast iron guide from Drags and fit that? For a 1937 head, the only thing which matters is to use a 3 plain ring piston rather than one with an oil control ring so that you still get some oil past the rings to lubricate the guide.
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Re: Bronze valve guides

Postby nevhunter » Tue Feb 13, 2018 9:32 pm

Agree with Paul. Cast iron is still the best in an iron head. Your valve material can sometimes be a problem, Stainless of some varieties can gall rather than wear well. Hard chrome plated stem or nitriding is a help. and the correct running in the guide, clearance with a good finish on the wear surface. Nev

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Re: Bronze valve guides

Postby bruce.carrad » Tue Feb 13, 2018 10:13 pm

Thanks for the advise chaps, much appreciated. Bruce

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Re: Bronze valve guides

Postby Ian.Taylor » Wed Feb 14, 2018 3:56 pm

Last September I bought a 1931 Norton Model 20 to go with my 31 VF.

my 31 VF has as you know a line comes off the crankcase to the inlet track to feed the Valve Guide with oil mist. The Exhaust is lubed by the small amount of oil going past the 2 or 3 compression rings.

1931 Norton in comparison uses a piston with 2 compression rings and 1 oil control ring. This was originally fitted to Norton that year .
The Intake & Exhaust have NO lubrication at all. You just lube the stem before a ride.
As far as I'm aware Norton guides did not wear out that fast . This head still has the original guides in it although now worn.
The replacement Guides recommended by a UK Norton singles engine builder to use in the ol gals is Colisbro guides NOT iron as I had thought he would have suggested.

My thoughts on the NO lubrication to In or Exh on the Norton was, why then can't we use an oil control ring on our Black or later Ariels. If Norton didn't seem to have a problem then why would Ariel?

Also the Norton Heplex 4245 6:1 piston also requires .007 clearance just like the Black Ariels

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Re: Bronze valve guides

Postby pappleton » Wed Feb 14, 2018 7:07 pm

Maybe pertinent or not, but in a Triumph twin with an alloy head I have used CI guides. The reason being that the bronze guides were wearing faster than I thought they should, also galling the valves. By replacing with CI the problem was solved. When I first rebuilt my VH alloy head I made silicon bronze guides, at that time I couldn't find guides at all, and the worn ones in the head were bronze. Seems to point to the fact that the valve material plays a big part in this as Nev says.
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Paul Appleton '53 VH plunger, '53 VHA rigid - in many boxes, '58 H.D. pan/shovel rigid

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Re: Bronze valve guides

Postby nevhunter » Wed Feb 14, 2018 10:16 pm

Nearly all engines in the 20's didn't use oil rings . Oil rings are a big contributor to engine friction, more heat and loss of compression where the ring sealing suffers . (total loss systems and low volume pumps and hot running engines) They became more common in the late 30's . Ariel used them after fitting the larger oil pump in the late 40's. I wouldn't see the rings as being the main factor in exhaust guide wear. You can add a bit of two stroke oil if you wish to the fuel to achieve the same effect. I do this on many bikes I run. It helps the tank, carb slide and the engine as well.
The biggest problem is unhardened stainless steel valves and the type of cast iron used. Grease nipples where fitted are effective. Stainless steel is notorious for being difficult to lubricate. If there's any sign of galling on the stem you are not going to get any real life out of the guides. Chroming of the valve stem is common on quality car engines.
Just as an aside, the Single ariels don't work well with a high volume pump. They don't scavenge well and run hot and oily due to the sumping and oil drag. I've run a W/NG fairly hard since 1997 and the engine never blows smoke and has the original type 3 comp ring no oil ring piston with the original small pump. It's never had any engine work in that time except for rare tappet clearance check and oil changes.. The piston should have the usual relief under the bottom ring with the small holes drilled. THAT has been common practice since the mid 20's . Nev

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Re: Bronze valve guides

Postby john.whiting » Thu Feb 15, 2018 1:28 am

norton singles have a pressure oil feed to the back of the cylinder and are/were notorious for smoking.Many JAP singles used a steel valve guide with a bronze liner...with the warning that only plain cast iron was to be used without guide oil feed.,if seizure was to be avoided........chrome plating has been made obsolete by black melonite,but to my knowlege only Matchless used chrome valve stems in bikes.....every make bike engine is/was different and rules applying to one motor dont apply to another.......panther 600s dont have any oil feed passage in the crankpin,and rely entirely on a squirt from the cylinder base...from an oil pump that doesnt do much more than lube the rockers.....yet some owners have blocked off the cylinder hole,without problems.

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Re: Bronze valve guides

Postby cmfalco » Sat Feb 17, 2018 5:30 pm

paul.jameson wrote: the only thing which matters is to use a 3 plain ring piston rather than one with an oil control ring so that you still get some oil past the rings to lubricate the guide.
I have to wonder if this should be regarded as an old wives tale. For what it's worth I searched the web and all I could find were unsubstantiated assertions that oil in the combustion chamber was beneficial in any way. One thing we do know is oil reduces the octane of the fuel, which is a bad thing. I will be running a modern piston with oil control ring in the 1928 Black Ariel I'm presently rebuilding so I would greatly appreciate references to any credible evidence that oil in the combustion chamber lubricates the guides.

Oil leaking past the rings on the intake stroke wouldn't reach the intake valve stem because air is flowing the wrong way, and it wouldn't reach the exhaust stem for the same reason; plus the exhaust valve is closed on the intake stroke, anyway. Oil that leaked past the rings and vaporized from the cylinder wall wouldn't reach either stem on the compression stroke because both valves are closed. Both valves remain closed on the expansion stroke.

Finally, on the exhaust stroke, the intake valve is closed but the exhaust valve is open. However, the valve lift is only a few tenths of an inch while the guide is ~2" long so any oil that survived the heat of combustion would only reach the bottom ~10% of the valve guide leaving the other 90% untouched. Further, in engines with worn guides oil leaks down the guide into the combustion chamber so any oil that made it into the bottom 10% of the guide would be pushed back out by the relative pressure difference, not sucked up.

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Re: Bronze valve guides

Postby paul.jameson » Sat Feb 17, 2018 8:00 pm

I ran my RH350 engine with open valve gear for over 20 years covering about 30,000 miles in that time. The longest trip was 468 miles in a day on the London-Edinburgh run. Typically, I got about 1000 miles from an exhaust valve guide but the minimum was 50 miles to wear which was unacceptable for further use. As Singles Spares Organiser at the time I was able to use, almost exclusively, new old stock valve guides.

At one stage I fitted an 89 carb from a 500 instead of the 76 carb for the 350. This resulted in a lean spot about 1/2 open which resulted in a spate of dropped exhaust valves. In consequence, I got through quite a number of pistons and I have at least 2 still in the workshop, complete with exhaust valve heads embedded in the top of them. Eventually I went back to a 76 carb, having found a replacement body, but my best piston was by this stage somewhat battered where I think 3 valves had broken at the collet groove and dropped onto the piston head. Not pretty, but the piston still worked. It was a slipper type with oil control ring. Then I found another slipper type, virtually identical except for the fact it had 3 plain rings (and was new, and hence undamaged). I fitted this piston. Thereafter, for something like 10,000 miles, there was no need to replace the exhaust guide.

Throughout, I had the oil feed to the inlet guide from the crankcase behind the cylinder. Inlet guides didn't seem to wear.

I fitted a 500cc engine with open valve gear but a piston with an oil control ring. Within 500 miles the exhaust guide (and valve stem) was wrecked. At that point I fitted an enclosed valve head and have had no further problems. One day I will re-fit the open valve head. Before doing so I will change the piston to a 3 plain ring type.
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