Nippy type cam

[Greig Smith]

Those who have been following the saga of the green single seater my lovely wife over revved at the Simola Hillclimb last year will know that we had to rebuild the motor, as I mentioned in my updated post on the blue supercharged single seater, the Babbitt arrived late and my supremely talented engineering friend Steven machined out 4 old 1.5/16' conrods to suit the old crank. While everything was apart we did the Forrest double oiler conversion to this motor as well. One of the things we decided was to fit a Nippy cam, one was fetched from the stores and oops, the centre cam bearing and sports rollers don't fit the standard crankcase.

Back into the store and Dad fetched a cam we bought from a chap in the car club who used to own a 7 many years ago. he said it was a Nippy cam. Unlike the others we have this one has a stock centre cam bearing which is permanently attached to the cam, there is simply no way to get it over the cam lobes and we tried...

I presume this is a built up cam on a pseudo Nippy profile.... hey ho, whatever the pedigree, in it went and boy does it deliver the goods !! Below 2000 rpm very little happens, but it arrives with a wallop and the power is there all the way till you chicken out at 6000 and change gear. Perfect for a race car. We got the motor running at 21h45 and did 6 laps of Gino's complex followed by 4 runs up the hill before something went awry with the rear axle.

Not bad for a motor that was built up and into the car on the Wednesday, towed to scruiteneering on Thursday and run up the hill on Friday. Kudo's to Dad and Steven !!

Here's the cam and the built-in centre bearing...boy are these cams noisy in an engine !! Lots of clatter and chatter from the valve gear with those ramp profiles.

Cheers
Greig

[Terrytuned]

Hi Greig the cam ring should should have a radius (lead in) on one side, we had some cams made by Newman Cams which had to be fitted with centre bearing assembled we made up a tool to help fitting the cam that held the cam ring in place. On one cam I fitted the radius was rather small managed the fit the rollers in the ring but could not get them out again,live and learn.

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[Colin Wilks]

Apologies if I am taking this thread off at a tangent, but I have a sports crankcase into which I intend fitting a modified standard camshaft (the sports cam I have does not have sufficient meat on it to modify without building up with weld, plus I'm loathe to alter an original sports cam). I had planned to simply replace the bush in the crankcase with one to fit the smaller roller bearings of the standard camshaft. Am I missing a trick?

Also, I note Terrytuned's camshaft has no oil thrower on it. The oil thrower makes fitting the tab washer a pain. Do people usually just dispense with these?

[Greig Smith]

Hi Terry

I understand what you mean by a radius or lead-in on the cam bearing, but to my eyes there was nothing like this. If you look at my third picture above, there was simply no way to get the rollers in or out that we could see. On one cam we have there is a notch filed in the bearing walls / guide on the cam to allow the rollers to be removed or installed. Nothing like this on this cam. The outer ring hits the edge of the lobes adjacent the bearing about half way along the length of the rollers. no chamfer or anything on either side of the outer or inner rings.

I was merely curious about it, we could see no way to remove or replace this bearing or rollers. Its a moot point now as its safely tucked into the crankcase of the green single seater and boy does it deliver the good with a wallop. The night we tested it around Gino's complex there was a bit of dew and the brick paving was damp with a bit of moss between the bricks so I could hang the tail out at every corner once it was on cam.

Cheers
Greig

[Ian Williams]

Greig I raced with a Nippy cam in one of my engines for several years, it produced reasonably good power and the engine certainly had a bark. However even with some very strong valve springs I had issues getting it to rev over 6K without valve bounce, although mine survived the Nippy cam has unnecessarily high lift which puts a lot of strain on the cam gear, block studs and top face of the block. I later changed to a cam ground for me by a well known UK specialist, this gave me a worthwhile reduction in lap times as well as noticeably more torque and no valve bounce, I would suggest this is a path of further development well worth exploring.