Author Topic: 90Plus camshaft  (Read 3616 times)

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Offline Froggy

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90Plus camshaft
« on: 27 Sep 2010 at 08:45 »
Can anybody advise me on how to identify which camshaft is fitted to my '51 90Plus without completely stripping the motor? Can one tell with a timing disc and the opening/closing timings of the valve gear.

If splitting of the engine is necessary, are the camshafts marked? (The Duggie is fitted with an engine  number 382 greater than the original with which the motorcycle was first registered in  March '51 and I am therefore unsure whether it is a 1951 or '52 engine, perhaps someone can help with that?)

Has anybody any information regarding the best cam profiles for road and for racing?

I believe that early 90's used a tappet clearance of 25thou but later camshafts used a lesser clearance (and consequently, less clatter!) How do I know which clearances to use with any of the varying camshafts?

Hope you can help,
Regards from a new Douglas owner
Froggy

Offline eddie

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Re: 90Plus camshaft
« Reply #1 on: 27 Sep 2010 at 12:26 »
Froggy,
             Most of the camshafts used on postwar Douggies were marked between the cam lobes to identify the type of cam fitted. Touring models had a cam marked with a 'T', sports machines were marked up with an 'S'. The situation is not quite so clear with the Plus cams. Original Plus cams had a narrow groove machined around the flange that butts up to the front camshaft bush. From what I am lead to believe, the first cam (later referred to as the number 1 cam) may not have had any marking. The number 2 cam had a very harsh profile which the followers had trouble staying in contact with - even with triple valve springs. The later number 3 cam was marked with a '3' and was more like a high lift 'S' cam. As you say, early cams (nos. 1 and 2) should have .025" tappet clearance whereas the number three cam ran with .010" clearance.
           Hope some of this helps,
                               Regards,
                                       Eddie.

Offline coles1933

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Re: 90Plus camshaft
« Reply #2 on: 29 Sep 2010 at 17:49 »
The following may help you to determine which of the possible cams you have without splitting the cases  Normal mark valve timing inlet opens 22 before tdc  closes 6 4 after bottom dead centre   exhaust opens 58 before bottom dead centre  closes 28 after top dead centre    plus series quoted from page 44 of manual  55  btdc inlet opens  83 abdc closes  exhaust opens 83 btdc  closes 55 atdc   The actual S lift at the cam follower will be around 0.186" the rocker ratio of 1.5 to 1 gives you around 0.30" at the valve  The T cam has a lift of 0.150",  0.225" at  the valve   Other relative information that might be of interest  to you cam base circle  1.00" standard  down to 0.965" for the LDMCC supplied cam  I modify both standard and S and 1and 2 cams to give o.340" lift at the valve and similar valve opening to the original  80/90 plus figures  If you are interested i have graphs of most of the lift figures for T, S, and 90plus and Joy cams  and keep stocks of reground high lift cams for sale on a service exchange basis  John Coles

Offline coles1933

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Re: 90Plus camshaft
« Reply #3 on: 30 Sep 2010 at 06:39 »
The following are proven and might be of use to you You also asked about racing cams for your 90 plus .  Joy cams have special profiles available ( joy No. 323B)  These profiles are best set advanced 1 tooth from standard setting and then give the following figures 57/56  68/70  75/78 with a lift at valve of 0.30" if you come by some of these ( about 300 per set) make sure you check both cams for angle balance as you may find some variations  I have graphs of these if you are interested you may find they are only available to the person who has paid for the development, just ask if so regards coles1933

Offline 90minus

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Re: 90Plus camshaft
« Reply #4 on: 23 Apr 2012 at 17:55 »
Hello everyone,
Does anybody have any timing figures for Plus No 3 cams?
Regards etc