Author Topic: DIY cams  (Read 2969 times)

arthur lewthwaite g50d

  • Full Member
  • Hero Member
  • ***
  • Posts: 1045
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

  • Full Member
  • Hero Member
  • ***
  • Posts: 1045
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

  • Full Member
  • Jr. Member
  • ***
  • Posts: 85
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

  • Full Member
  • Full Member
  • ***
  • Posts: 215
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

  • Full Member
  • **
  • Posts: 199
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

  • Full Member
  • Full Member
  • ***
  • Posts: 215
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

  • Full Member
  • Hero Member
  • ***
  • Posts: 2211
  • Alchemy in Grenoside
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

  • Full Member
  • Full Member
  • ***
  • Posts: 215
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

  • Full Member
  • Hero Member
  • ***
  • Posts: 2211
  • Alchemy in Grenoside
Re: DIY cams
« Reply #23 on: May 23, 2020, 08:03:46 PM »
My mistake. I remember the conversation now
Winners never qui

Ron Herring

  • Full Member
  • Full Member
  • ***
  • Posts: 215
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


Ron Herring

  • Full Member
  • Full Member
  • ***
  • Posts: 215
Re: DIY cams
« Reply #25 on: July 26, 2020, 04:31:54 PM »
Gary,
  I hope you're still making progress with your cam grinding equipment.
You are probably well aware that copying from an existing cam is one thing, but working out an original design is something very different, and the difficulty is multiplied when two lobes are on the same shaft.
Some years ago I was very much involved in producing cams for the Speedway fraternity, the GM engine in question featured a single overhead camshaft. Lobe separation was critical for performance, and I made up a vernier adjustment that enabled testing to confirm lobe separation for production manufacturing.
I attach two photos,  one shows a lobe being machined up using a rotary head and milling cutter in the lathe. Another shows a finished prototype in aluminium, for test purposed.
I have somewhere a photo of the vernier adjustable GM camshaft, and will try and find it to include in a future post

Ron Herring

  • Full Member
  • Full Member
  • ***
  • Posts: 215
Re: DIY cams
« Reply #26 on: July 27, 2020, 11:42:42 AM »
Grinding is only one way whereby cam profiles may be created.
 For some years now I have been designing/producing cams using a milling proceedure.  Where only a single cam lobe is required the process is fairly straight forward, albeit much simplified and faster if a CNC mill and competent operator are available.
Photo's attatched show a single camshaft after milling is completed, still in the machine vice, and a batch of completed cams.
Where two lobes are on a single shaft, as the GM cams in the picture, one lobe is machined, then the camshaft replaced end for end in the jig and the second lobe machined. The hole in one cam is for locating purposes

Ron Herring

  • Full Member
  • Full Member
  • ***
  • Posts: 215
Re: DIY cams
« Reply #27 on: August 17, 2020, 11:17:08 AM »
I am busy with a project, and an aspect of it makes me think it is worth mentioning as a natural addition to this thread.
 Every cam opens and closes valves by means of a cam follower of some kind. Pushrod engines with flat base followers are very straightforward, as also are bucket followers in DOHC engines.

The problematic followers are those where a contact pad of a radius profile is used.

All too often a used radius follower will have some wear after considerable use, and if such a follower is not correctly and accurately re profiled, it will most likely cause premature wear of a new cam, not a very happy prospect!
The difficulty in re profiling the follower is to first find out what the radius should be, and most important, the exact location of the radius centre.
The project I am working on has such a follower, and I am fortunate in also having the correct data for the follower radius and location, but of seven followers that I have checked, anly one is correct to drawing.

The margin of error admittedly is small in most cases, although the location of the follower radius being 20 thou out  may not be too significant in a road going engine, for racing one should strive for something a little better, so I have some work ahead to produce followers either closer to the original specification, or to my own design.

Andy Guy

  • Full Member
  • Hero Member
  • ***
  • Posts: 2211
  • Alchemy in Grenoside
Re: DIY cams
« Reply #28 on: August 17, 2020, 09:51:12 PM »
Ron

Reddich or chennai?

When it comes to manufacturing parts and jigs to the closest possible tolerance I amaze myself with how much more time I can spend to produce scrap. :)
Winners never qui

Ron Herring

  • Full Member
  • Full Member
  • ***
  • Posts: 215
Re: DIY cams
« Reply #29 on: August 21, 2020, 05:08:57 PM »
Andy
  Reddich unfortunately.

 Currently looking at the feasibility of manufacturing a follower with a roller contact for the cam. This will of course mean a new valve lift design, but it will keep me occupied during the next F1 debacle (a better alternative to F1 is watching paint dry!).

You could of course make roller followers for your AM.