ET: Engine (Twin) ET35 to valve guide clearance
- Thread starter nkt267
- Start date
No Vic. I know someone else with a similar, if not identical, set up and it meant lots of machining of the cylinder head.
Norman, you will be right about this piston type found on other engines but as far as I know it was a design from Norton´s Manxes. To be open, would I try to modify a standard Vincent head for this piston - no way ! The heads seem to be quite flexible anyway under high stress so machining them for Manx pistons would call for desaster unless you´d go for awkward welding add-ons to compensate for lost material on top of the combustion chamber. . . . Or have new castings made for them.
The very black coat on the shirt will be graphited most likely, common on modern truck and car pistons. Did not like to have graphite in my engines as this is a bit abrasive knowing from my trade as toolmaker and from machining graphite electrodes for spark eroding. So I got special MoS2 bake-on paint for the BMW pistons for having less piston clearances in alu barrels when having car pistons in bikes. See the blueish colour as no graphite in it.
Vic
can of ultrafine MoS2 powder and grease :
The very black coat on the shirt will be graphited most likely, common on modern truck and car pistons. Did not like to have graphite in my engines as this is a bit abrasive knowing from my trade as toolmaker and from machining graphite electrodes for spark eroding. So I got special MoS2 bake-on paint for the BMW pistons for having less piston clearances in alu barrels when having car pistons in bikes. See the blueish colour as no graphite in it.
Vic
can of ultrafine MoS2 powder and grease :
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If you can put BMW parts in a Vincent, then I can put Norton Manx parts in one!
It was the late Ian Hamilton that came up with this design. He was copying the Manx because that was where all the dyno work was going. It is a very old design, but it seems to do the trick.
I last saw it in 2017 when I installed it in an engine that went to David Tompkins, which he has been racing ever since.
A dyno run last week showed 39 BHP at the rear wheel with a Megacycle Mk2 cam.
David
Davidd, I don´t mind having all sorts of components in my bikes, no matter where they come from or if someone else does same. The B-Rapide engines have Alfa Romeo pistons plus 4mm compression plates under cylinders now. The pistons in my photo are Porsche cast iron cylinder types and go in the BMW alu pots so I coated them for less cold clearance . . . . after I had to hone the BMW cylinders a bit oversize because of seizures at both sides . . . . . ahmmm, because I forgot to fill in any oil again when I changed all oils on the bike, engine, gearbox, swing arm, rear bevel drive. But no oil in the engine so it lasted 17 kilometers (11 miles) from home till I felt the seizure and stopped. Sent my lady back home to get some liters of engine oil with the car and filled the engine at last . So I laid the flat twin on both sides to soak the pistons, kicked it and got home with no morte troubles. But the nice set of pistons were scrap.
I looked at the piston photo you posted , Manx type. The installed piston in the cylinder does not look as dramatic as the special high skirt new piston. But anyway, you´d have to machine the Vincent head a lot to clear this piston - unfortunately just at places you´d NOT like to have weaker than standard. I learned in the forum that Vincent heads tend to be somewhat flexible in the middle and weakening this place seems no good idea for durable use, racing allright, I´d think. Is there somebody with pictures of a Vincent head showing this mod ?
Vic
I looked at the piston photo you posted , Manx type. The installed piston in the cylinder does not look as dramatic as the special high skirt new piston. But anyway, you´d have to machine the Vincent head a lot to clear this piston - unfortunately just at places you´d NOT like to have weaker than standard. I learned in the forum that Vincent heads tend to be somewhat flexible in the middle and weakening this place seems no good idea for durable use, racing allright, I´d think. Is there somebody with pictures of a Vincent head showing this mod ?
Vic
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This is not a Vincent head but my friend had a project to make his two-valve pushrod Norton head into a four-valve. He machined out the combustion chamber and welded in an aluminium billet and then machined in the four ports. Likely you could not do this with a Vincent head but it does show that there are possible ways of changing a combustion chamber shape. We have a saying here, "There is more than one way of skinning a cat." (Apologies to cat lovers.
)P.S. It does work and the engine is in a Featherbed frame and on the road.
Has anyone welded the head up and changed to a "modern" bathtub shape using flat top pistons ?
Would this actually strengthen the head while giving better combustion ?
Would this actually strengthen the head while giving better combustion ?
Yes I know of an owner in UK who has done exactly that on a road going bike and the bike flys and it has also been proven as reliable in the last 20 plus years of use with these modified heads. As far as I know he's not on this forum though and is a private person hence no name, but one of his other modifications has been greatly discussed on this forum over the last few years.
I think the clues are there, he also did a really nice Alternator conversion in place of the ESA I seem to remember, I think it is Ducati based.
So the long exhaust might NOT be better for a standard Bike ?, .
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