DIY cams

[Gary Abbott]

And photo of en36 bar, cam blank and finished cam

[Andy Guy]

That's classic racing alchemy Gary. Turning rusty bar into usable parts. Brilliant.

[arthur lewthwaite g50d]

andy i have turned a rusty motorcycle into an even bigger heap of rust by leaving it against the  back garden fence for ten years,now thats classic alchemy. cheers arthur.

[wayne scholter]

Tasty piece of work there Gary BWD!

[wayne scholter]

Forgot to add - now time to get hold of some Johnson cams to copy!

[Ron Herring]

Gary
 your effort to grind up a cam as a copy of an existing (master) profile looks pretty good from what can be seen in the photo. Unfortunately you probably chose to copy the worst sample that ever was made for the Gold Star.

The checking duration for the 65-1891 profile was 325 degrees at a lift of 0.018 thou.  There are very few that match this spec. All to often cams will be found to have more duration, and one particularly bad case that I measured had 20 degrees less.

It would be interesting for you to check both the master and your copy, A/ to see just how well the copy matches the master, and B/ how well the cams relate to the BSA Gold Star specs

The cams 65-1891 and 65-2442, correct to spec, are superb cams for the Gold Star, and your vernier provision will be a major factor is enabling a far more precise setting than a stepped key and the 65-2891 exhaust version allows.

[Andy Guy]

Ron

As you say these cams are superb for the bsa. Is that in standard bore and stroke combination, would you advise them for say, 90mm bore and possibly a different rod ratio?

Thanks

[Ron Herring]

Andy,
  standard bore, 90 mm or even more, the cams are still good, Same goes for rod variations, all combinations will work well.

[Andy Guy]

Thanks Ron

[Gary Abbott]

Thanks Ron,

I must admit I had assumed the 65-1891 cam I had would be good.  It’s an original bsa cam in good condition but I should have checked.  On the Dyno  in back to back tests it did gave the best power output on my 90bore engine over an absaf exhaust cam and a 2446. 

Just building a cam measuring bench so will check it carefully and the copies made.  The measurement bench will graph the cams for easy comparison.  Although I guess I need to ultimately measure in the engine to confirm the affect of rockers etc.  I have Absaf ratio rockers fitted. 

[Ron Herring]

Gary
  for your measurements to be meaningful you really need a designated cam measuring system such as CamAnalyser,  or CamProPlus, but to some extent it depends on whether you intend to measure just one or two profiles, or perhaps begin to collect and analyse a number of cams for possible future use.

Bear in mind that if you copy a cam size for size, should there be an error on the master, that error will be copied faithfully. The old Berco and Van Norman cam grinding machines copied from larger than liffe masters, often 5 :1, sometimes greater. If the master contained an error, it was diminished by the same factor when grinding the cam

I cannot comment on the Absaf rocker ratio's I have never had such a rocker to examine

[Kerry Wilton]

Many, many years ago, in amongst a pile of BSA (mostly Gold Star) stuff my father bought, was what seemed to me tobe a 'master' cam, clearly intended to be mounted in some sort of machine to reproduce the profile. As Ron H says, it was significantly larger than the actual cam to be produced - the master was approximately 7-8" across. I gave it to a friend in the engineering world, who bought a GS from me about 15 years ago, and was racing his own at the time.

The 'master' had '2446' engraved in it. I could probably get it back if anyone needed, though the recipient in in New Zealand and notoriously slow at answering emails!

[Ron Herring]

kerry
  here is a picture of a master cam mounted on a Churchill cam grinder. Note the follower in contact with the master is based on the diameter of the grind wheel, but is enlarged by the same factor as is the master cam.
The master your father had would have been intended for use in a similar fashion

[Gary Abbott]

thanks Ron and Kerry

I did think about making a 3:1 grinding bench but concluded that making the master could be my main source of errors given the limited machining equipment I have. But perhaps calculating the cam profile from scratch and writing the g code for a master to be made by a suitable engineering company would still be the way to go.   

hopefully the measurements from a selection of original cams and my copies will confirm.

The measurements bench I am making is based on this......

https://shamwerks.com/CamWerks-DIY

Andy pointed me at it.   I am just wrestling with the Java code.  20 years since I did any Java development but one of my ex work colleagues who is a Java developer has kindly offered to help if needed. I am hopefully building in some improvements over the shamwerks bench hence the Java adjustments.

Ron... thanks for the links ,  I will also check the software.  I see they are either free or relative low cost. Maybe worth comparing them to see how good Shamwerks software is .

Kerry..  2446 was used as the clubmans exhaust cam amongst other BSA engine configs.  I would be interested in it,  if your friend is Ok to part with it.  Happy to cover postage and maybe some purchase costs if reasonable.


Regards Gary

p.s.  just got the cams I made back from hardening.   A finishing grind pending and then measurements. fingers crossed they are oK.  I am having fun making them so not too disappointed if version 1.0 is not usable.

[Ron Herring]

Gary
 you can make your own masters provided you have access to a lathe and a rotary table. Dave Nourish made all his masters for his engines this way. It's a tedious time absorbing procedure, but if you have the time and patience you can make your own masters.
The machining is usually done by locating the x and y co ordinates of the profile as the master is rotated on the rotary table.
For a measuring table I used a Myford lathe bed, headstock, saddle, cross slide and tailstock. The rotary and linear encoders are readily available from Heidenhain and Ono Sokki. I could have made a much smaller table, but some camshafts are so long (RR Merlin) that the tailstock has to be removed and a fixed steady placed to support the shaft end.(see attached)
You may end up on a sort of roller coaster ride that you can't get off. Cam design is an absorbing topic