25SA Renovation

[dave higgins]

Rob, wearing a nuns outfit to often is a disgusting habit, now lets get back to the project...

[ADickerson]

Thanks all for the very amusing and off Topic diversions, it certainly helped to take away the attention away from my lack of progress on the project recently. In heating his Shed it seems that Stuart is putting the Winter Fuel payments to good use.
My next task is to produce a cylinder base gasket/packer! Now the original Villiers part was mild steel, but I am wondering if I should use a similar material or go to Tufnol, as used on the Griffons as it helps to keep the heat from passing to the crankcases? Can anyone advise which, if any, I should plump for?

[John Wakefield]

Adrian
You need to let heat transfer to crankcases. So I advise you to use the steel spacer. The more heat you can disperse from the cylinders the better. As I have said before the finning on the 2T/3T barrels is non existant between the barrels.

[dave higgins]

Hi adrian, tough one that, an engine will perform better on cooler damp air, which a tufnell spacer will help create, but at the possible risk of over heating the top end.
But the barrel temp rising may only be a problem, if it induces seizesure, high barrel temperature is not necessary a bad thing, providing the friction materials can take it.
I don`t know if there is an inherent problem with the pistons picking up due to hot spots between the barrels, but i would imagine a method of testing to see how hot it really is going to get, is the way to go.
Its a shame you cannot thin out some of the finning, which may cause problems on some of the damper circuits, the close finning may have served the cooling purpose well on the road, at higher speeds, but i would imagine taking out every other one, will stop clogging & aid better air flow around the top end, on the mx track.
Radiating the heat out & along the fins is only good when you have plenty of airflow around to remove it. just a thought, dave.

[Stuart Baskill]

Originally Posted by ADickerson

Thanks all for the very amusing and off Topic diversions, it certainly helped to take away the attention away from my lack of progress on the project recently. In heating his Shed it seems that Stuart is putting the Winter Fuel payments to good use.
My next task is to produce a cylinder base gasket/packer! Now the original Villiers part was mild steel, but I am wondering if I should use a similar material or go to Tufnol, as used on the Griffons as it helps to keep the heat from passing to the crankcases? Can anyone advise which, if any, I should plump for?

If you race in January and February overheating shouldn,t be a problem

[ADickerson]

Nice one Stuart, I'd better get a move on then!
Interesting, if opposing views otherwise and I'm grateful to both contributors for their thoughts. I'd being trying to weigh up the benefits of each but can come to no clear conclusion. So, to assist heat transfer I've resolved to making one from Aluminium, while on the opposite tack I'll make another from Tufnol to see which might have the best effect. I accept there are no fins on either of the inner transfer ports but as the exhaust gases presumably shouldn't penetrate beyond the piston at BDC then each could be cooled by the incoming fresh mixture! I am also aware that the "fresh" mixture might not quite be that, as it will no doubt be a mix of fresh gas and those that have been circulating around the crank for several revolutions previously!
Now, where's the YAG Laser! Sorry, I mean bandsaw and files.

[Gr11mpy]

Notice that there's a 2T engined BSA C15 for sale on e-bay.... Interesting pipes.

[Mike48]

Interesting what a differencethe base gasket material can make. A local club member in Brisbane has just fitted a tufnol? base gasket/spacer in his Grifon - he had been using, I believe an aluminium one. He took it out to our first club meeting of the year today, temp 31selsius in the shade. Engine seized after a couple of laps. First time I believe. There might be something in top end heat needing to escape through the crankcases.

[ADickerson]

Originally Posted by Mike48

Interesting what a differencethe base gasket material can make. A local club member in Brisbane has just fitted a tufnol? base gasket/spacer in his Grifon - he had been using, I believe an aluminium one. He took it out to our first club meeting of the year today, temp 31selsius in the shade. Engine seized after a couple of laps. First time I believe. There might be something in top end heat needing to escape through the crankcases.

Thanks for posting Mike, good to here news of Greeves from Aus. Seizing a Griffon can't be a very pleasant experience. Haven't experienced the same here with mine, even with a Tufnol base gasket. But then again, thankfully, I've never ridden it at 31 degrees in the shade!
With all the finning that's available on a Griffon, I think I'd be inclined to suspect another reason for the failure!

[Punchy]

thanks for your comments Dave re your solutions to stop overheating on the barrels they're really appreciated.

We have got an alternative solution, there is a nice little german twin engine that has plenty of space between the barrels and with some jiggery pokery we're sure we can get it to fit. We have sourced a heavily tuned version from Druid who has breathed on it, I always wanted an engine to run on pure John Smiths Oops I mean alcohol. it may even be close to matching that rather attractive looking beastie on the front of this months LL
Punchy