Valve Timing.

[Wagger]

Posted this here for information and interest. No problem to solve, but interesting discussion will develop, I'm sure.

When I started with cars I was used to timing BMC A series camshafts with crankshafts. On those, the keyways point at each other for correct timing. My first rebuild of a Triumph SC resulted in me doing the same. After running in, it was gutless, especially on hills. I then consulted the manual and realised my error. The camshaft was retarded by two teeth! Correcting it took a couple of hours and was very worth while, obviously.

I rebuilt several Triumph motorcycle engines in my teens and twenties. All 350 or 500cc. They had two camshafts and three key camwheels. Very few people now know how to use them. They allowed setting cam timing plus or minus 5 degrees of 'Nominal'. They also used tappets with differemt radii to obtain more valve overlap. My mates who raced them spent forever playing with the settings. This was the forunner of variable valve timing. Some settings resulted in engines that produced more power at high rpm, but were pigs to get started.

In later years a pal planed 20 thou off the head of a single OHC engine. Unfortunately, he did not realise that the rotation of the cam is retarded by the chain (slack side) by twice that distance that side of the sprocket. Only fitting a thicker gasket allowed the engine to run nicely, negating what he hoped to achieve. Plus the fact that it was  9.5:1 compression engine before he bothered. Five star fuel was essential. Anything less and the thing was undrivable.

I always wondered why more manufacturers did not produce twin cam engines. Riley did it in the block with short pushrods until the demise of their super engine in the Pathfinder. Some of you will know of others. It would be interesting to know.

[Pete Lewis]

were Triumph the only  ones to have the 4 hole 1/4 tooth indexing adjustment by simply moving the fixing holes ??

Pete

[Wagger]

20 minutes ago, Pete Lewis said:

were Triumph the only  ones to have the 4 hole 1/4 tooth indexing adjustment by simply moving the fixing holes ??

Pete

 

21 minutes ago, Pete Lewis said:

were Triumph the only  ones to have the 4 hole 1/4 tooth indexing adjustment by simply moving the fixing holes ??

Pete

There you are Pete. Not many people knew that. How many actually did it? Tinkerer's paradise or downfall.

[Wagger]

Yes Mathew, I discovered, by accident, that lowering the gearing made my 350cc Triumph bike faster. One tooth less on the gearbox sprocket and it did 90 in top and 84 in third, Before changing it, third was faster than top because it would not pull full revs without a following gale.

The best solution is a moderately tuned big capacity engine in a small machine. Much less fiddling about. Took a few years to learn that though.