Vincent Racing Calendar

[vibrac]

Methanol: best thing we ever did was to go back to petrol.
Hi

 

[Bill Thomas]

Another regret of mine, Was not trying Methanol with 12 to one pistons, On the L/ning I was only on 9s because the petrol was so bad by then, I found out later that a lot of the Lads were using Av Gas, But I thought that was cheating ?.
Methanol on 9s did't feel any better, I only tried it for one 1/4 mile Sprint. Cheers Bill.

 

[litnman]

Has anyone else had issues with cams showing cracks like this?

 

[greg brillus]

Are they in a road bike or a race engine........?........If it was a race engine, one scenario I can see after what happened to me on the weekend is if the engine suffers a valve bounce/overrev, where the piston clips the valve, the load through the valve train down to the cam which is not that strong. It happens on the inlet cam lobe because the inlet valve is larger and therefore heavier. I'm Not 100% certain about it, but it seems likely that this is what smashed the cam in my racer this weekend just gone after the springs let go (three springs in total) two on the rear inlet and the inner spring from the front inlet........

 

[Robert Watson]

Yes indeed. When I first spotted it I was cleaning things up and tried to wipe the dog hair off the cam that had obviously come from the rag I was using...... Not a dog hair at all.

We ground down through the outer face and did a hardness test on it and it had been hardened all the way through making it too brittle. I still have somewhere and will try and find it a post a picture.

 

[litnman]

Greg,
One came came from a race engine with big valves. I don't know the history of the other one. Not sure I would trust welding them, but seeing how welded up cams hold up, maybe it's worth a try, at least for a mild non-racing engine.

 

[ClassicBiker]

I just replaced the Mk IIs in my Shadow as they and their followers were quite worn. It was used before my father bought it in 1978 as an ice racer at one point by the previous owner(s), it has only been used lightly on the road since then. I didn't look to closely at the old cams when I replaced them, but they are still sitting on my bench so I will look tonight and get back to you.
Steven

 

[roy the mechanic]

In most piston/valve events I have seen there is most times a bent pushrod. If the one involved is still straight, the cam must have been particularly weak. Think, the power to break it had to be transmitted by said 'rod.

 

[Bill Thomas]

If you look at Johns cams, I think there are some faulty ones that are too Brittle, They should never do that. Cheers Bill.

 

[clevtrev]

The rod is in compression, the bent rods usually occur when it jumps out of the cup, the bend is at the point of leverage, i.e. the bottom of the tube.