Modified Cam Followers

[Steve Jones]

A young friend, prominent in VSCC events in his Ulster, has built a vernier valve-time adjustment mechanism. So far he reports that results are inconclusive.

I suspect your young friend (who I know well) is being his usual modest self, Tony . However, I have a similar arrangement and have set it to that which the well known supplier of the modified cam suggested. It would be difficult to come to a conclusion about its benefits without comparing it with the same engine with standard timing and that would mean much dismantling and re-assembly.

Steve

[Austin in the Shed]

I read all the forum entries about go faster tweaks and remember a visit to one of our suppliers some years ago where he had a stack of Seven crankcases nearly as big as my RN saloon, most were cracked on the NS in line with the camshaft. He thought the cause was high lift camshafts, flattened tappets and double valve springs. We are bombarded with adverts for new cars which can do 0 to 60 mph in around 4 seconds but I don't know where these cars are because when I drive my bog standard RN saloon I have to be careful not to ram the guy in front when setting off from the traffic lights. How do drivers accelerate their modern cars so slowly, it's more like gathering momentum?

Several nippy crankcases I’ve seen have cracks between the bell housing and the case,3/8”” lift cam maybe?

[Alan]

It’s not the lift,as such, it’s the acceleration as the valve opens. Theoretically at least the acceleration at opening with flat tappets is infinite. It probably isn’t quite but you get the idea. Nippy cams, likewise, have very sharp ramp angles. I agree with Dave. My trials car, when I did such things in the 70s/80s was on a standard cam with 3/4 radius tappet blocks. It was quite successful. My advice would be to sort out the inlet/exhaust manifolds before you even think of the camshaft, but when you do, talk to Paul Bonewell and listen to his advice.

[Steve Jones]

................... talk to Paul Bonewell and listen to his advice.

I'd second that.

Steve

[Charles P]

I bothered to measure a handful of cams and plot the duration, lift, acceleration and jerk (the derivative of acceleration) on charts using some clever software. If I can find them on my laptop I’ll share one or two.
What it did tell me is that Paul Bonewell’s cam grinds are very clever at minimising the valve train loads whilst giving very much improved breathing. 
And never use a standard Nippy cam.

[Ruairidh Dunford]

               

[Nick Lettington]

Was that from an engine you are stripping for refurbishment Ruairidh or something in your rogues gallery?

[Ruairidh Dunford]

I recalled someone asking about them, perhaps it was you?

They were in a box of spares - would you like them?

[Nick Lettington]

It was me who asked if anyone had ever tried it. Interesing that Chapman's design made them concave. I would like them Ruairidh, like those cast wheels,  but I'm trying to quit the habit.

[Ruairidh Dunford]

They will be sent south next week…