Author Topic: DIY cams  (Read 1426 times)

arthur lewthwaite g50d

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Re: DIY cams
« Reply #15 on: May 19, 2020, 08:47:36 PM »
back in there late i990s there was an article nonworking out a cam profile on paper from a genre point you drew out 360 lines ,1 degree apart.and then marked to on this lines dots for your cam profile,when done you made a master out of gauge plate from this,you made master say ten times bigger than cam,nowadays you could draw ,and then transfer to cad and cut on cnc,

arthur lewthwaite g50d

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Re: DIY cams
« Reply #16 on: May 19, 2020, 08:51:13 PM »
meant to say centre point of circle,with 1deegree line radiating to from centre like protector.

Gary Abbott

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Re: DIY cams
« Reply #17 on: May 19, 2020, 11:17:00 PM »
Hi Ron and Arthur,

Thanks for thoughts and comments.  Much appreciated.

I am making v1 of the  measurement bench from a basic cnc mill linear rail with pillar bearing/coupling.    A small lathe bed would be good and regretting I sold an old boxford lathe now.

I can change the grind bench to 4:1 and will look to that for v2.

I am off to the dyno on Friday with a new build 90bore goldstar engine and hopefully will get chance to try one of my DIY 1891 cams.  The engine currently has a 65-2446 fitted.

Here is a pic of a hardened cam and a hardened cam after final grind.   The ruby 46 grit wheel gave a reasonable finish and basic measurements are ok.  Will measure in detail on bench.

Regards Gary

Ron Herring

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Re: DIY cams
« Reply #18 on: May 20, 2020, 12:45:48 PM »
 The Gold Star cams were designed by Jack Amott, who pre war had worked and raced Rudge machines.
The design method used at Rudge was very much simpler than the proceedure described by Arthur, and attached is an example dated 1927 for Amott's 4 valve special.

Kerry Wilton

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Re: DIY cams
« Reply #19 on: May 20, 2020, 01:54:32 PM »
Will see what can be done to get hold of the 2446 'master'. It did look very similar in size to the Churchill version in the photo in a previous post.

I recall reading (the usual legend, I'm sure), that Jack Amott was a cam wizard with his designs subsequently proven to be well ahead of their time. Also read about Amherst Villers (I think) filing cam lobes by hand for a small sports car he was working on in the early 30's..with no small amount of success!

Ron Herring

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Re: DIY cams
« Reply #20 on: May 23, 2020, 11:26:23 AM »
There's an interesting story that Phil Irving tells in his autobiography, of how Gold Star cams came to be used in the Repco Brabham engine that he was designing. Phil was well advanced with the engine design and had thoughts on using Gold Star cam profiles, but Jack Brabham said not to worry as he was obtaining some special cams. When the special cams arrived Phil Irving measured them and found they were Gold Star profiles.

The Repco Brabham engine had pushrod driven valve train, so Phil had seen the potential for Gold Star cams if he could incorporate them in the overall design, and with his background in motorcycles would have been well aware of how a Gold Star so equipped could perform

Jack Brabham went on to win a World Championship with the engine, so it says something for the effectiveness of Jack Amott's design work.

Andy Guy

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Re: DIY cams
« Reply #21 on: May 23, 2020, 04:51:56 PM »
Was that the engine some time ago which ran huge Amal Gp carbs but as part of a fuel injection system?
Winners never qui

Ron Herring

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Re: DIY cams
« Reply #22 on: May 23, 2020, 07:15:18 PM »
Andy
  first a correction to my last post. The Repco Brabham started off with a pushrod block, but was subsequently modified  to accept new design cylinder heads that featured in line valves actuated by a single direct acting camshaft via the usual bucket type followers.
Page 545 in the Irving autobiography contains first mentions the Gold Star cams.

The engine with massive GP carbs was the Vanwall. The carbs were used purely as a means of air control only, the fuelling system was by injection

Andy Guy

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Re: DIY cams
« Reply #23 on: May 23, 2020, 08:03:46 PM »
My mistake. I remember the conversation now
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Ron Herring

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Re: DIY cams
« Reply #24 on: June 22, 2020, 02:28:40 AM »
A point I would raise re the measuring of existing cam profiles.
If the camshaft has a centre at each end of the shaft, one would assume that to mount the shaft on these centres is the right way to measure.
Unfortunately the camshaft doesn't run on the centres, but on the bearings , and it is often found that the bearing is not true to the centre.
Faced with such a situation the correct way to measure is with the shaft mounted on the bearings, this is how it will be running in the engine