Author Topic: 2 3/4 HP  (Read 343 times)

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Offline Red

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2 3/4 HP
« on: 12 Aug 2021 at 14:31 »
I've just started work on a 2 3/4 HP I acquired a while back. I'm refitting the valves and in the parts book it refers to a "Copper asbestos Washer behind Exhaust Valve Spring" part no 482D. There were no copper washers on my engine. Are these always fitted and do they go between the end of the spring and the valve guide seating? Any guidance will be appreciated. Thanks

Roy

Offline Jonathan Hewitt

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Re: 2 3/4 HP
« Reply #1 on: 12 Aug 2021 at 18:55 »
I have also just started ( yesterday in fact ) on my 2.3/4 engine and there were no washers of any kind under the springs. I have bought the valves and guides from club spares. The inlet guides that I removed were made of phosphor Bronze whereas both inlet and exhaust club style are cast Iron. The valves removed are very much more convexed than the club replacements ,not that this will make a great deal of difference I feel
    hope this helps
Jonathan

Offline EW-Ron

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Re: 2 3/4 HP
« Reply #2 on: 12 Aug 2021 at 22:39 »
The beauty of cast iron guides is that they will run with little or no lubrication
- the carbon in the iron provides the lube.
Whereas bronze NEEDS some oil - or you have to run quite big clearances to prevent seizures.

Very wise choice by the club by the sound of it ...
Can't help on the washers side of things - what year is this.
Hopethishelp.

Offline cardan

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Re: 2 3/4 HP
« Reply #3 on: 12 Aug 2021 at 23:10 »
Hi Roy,

I wasn't aware that Douglas used copper/asbestos washers under the exhaust valve springs. It seems a little weird as washers of this type - because of their 'crushabilty' are usually used where a seal is required. The common application is under the valve cover bungs.

That said, many early engines used a spacer of some kind between the very hot part of the cylinder adjacent to the exhaust valve and the spring itself. This was often made from very thin pressed steel, shaped to keep the spring maybe 3-6mm away from the cylinder, to try to minimise heat transfer to the spring. The problem with most copper/asbestos washers is that the copper usually surrounds the asbestos (at least on the inside), and because copper is an excellent conductor of heat I'm not sure whether it would do a good job of isolating the spring from the cylinder heat.

I wonder if part 482D was a "sandwich" of copper/asbestos/copper, with the two copper sides not joined.  At least something like this might help to keep the the spring a little cooler. It would be fun to see an original!

All my waffle can possibly be ignored - modern valve springs can probably take the heat without sagging, even without a spacer.

Leon

Offline Red

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Re: 2 3/4 HP
« Reply #4 on: 13 Aug 2021 at 08:39 »
Thanks all for the repies.

Like Leon I think they could only have been fitted to try and protect the exhaust valve springs from the worst of the engine heat. The fact that most engines these days don't seem to have them fitted suggests that they are of no real importance, probably because we are unlikely to give the bikes any serious use. One other member has sent me an email saying that he has recently acquired a couple of scrap barrels and the remains of these washers were still in place. I will try to get some further details from him.
By the way it is not an item stocked by club spares

Roy