Author Topic: A65 competition rocker arms  (Read 3539 times)

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Servodyne

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A65 competition rocker arms
« on: 08 October, 2018, 17:44:50 »
Hi all.
I recently came across a pair of special inlet rocker arms for an A65 the other day and was wondering where they were developed and if they are still available, as I would like a pair for the exhaust valves.
They differ to the standard ones in as much the adjusters are directly over the push rods and have curved pads over the valve stems.
Any information on these would be greatly appreciated.

JulianS

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Re: A65 competition rocker arms
« Reply #1 on: 08 October, 2018, 19:48:17 »
The rockers are a Devimead mod. You will see them mentioned in the 1972 article below.

SRM now own Devimead.

I think the rockers will be quite rare, I have a 1985 Devimead list and they are not on it.

Servodyne

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Re: A65 competition rocker arms
« Reply #2 on: 08 October, 2018, 20:51:19 »
Fascinating stuff, many thanks for that. I'll keep my eyes peeled at Stafford for some exhaust rockers. It seems a much better set up than the standard and gives an easier life for the valve stems.
It was common practice on many old car engines to have the adjusters directly over the push rod with a curved pad over the valve stem that it's a wonder BSA never introduced as standard on the A65 engine, seeing that the removable rocker box cover gives ample access to adjust them.

Cyclops

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Re: A65 competition rocker arms
« Reply #3 on: 09 October, 2018, 11:51:47 »
An interesting post, but looks like the rockers in pic 1 need shimming to centralise the hard pad over the valve stems.

morinipete

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Re: A65 competition rocker arms
« Reply #4 on: 12 October, 2018, 20:36:49 »
Les Mason got the idea for these off a draughtsman called Paul Rideout, who did most of the drawing for the final 1968 Daytona 500 racers (Les Mason drew up the frame). The change not only reduced the reciprocating mass but having the curved feet it also made for an initial slower lift and closure of the valve, so making for less stress all round. Oddly they never used this set up on the works bikes, as the Production Racers had standard sets (BSA didn't cheat, unlike Triumph!) while the open class racer used by Tony Smith and subsequently Bob Heath had eccentric rockers, a bit like on the later B25. So instead of two long rocker shafts, four short ones. So lighter still than the ones shown above (which are very nice though). Why didn't it go on the ordinary production bikes? If it cost 1p more, it wasn't going to happen. Ron Mason was the one at Devimead who did all the welding up, etc. All the actual end-feeds too. If anyone's interested it'll all be in a forthcoming book (but don't hold your breath, it's still a year off, the speed I'm going at  :o).     

Cheers

Pete

Servodyne

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Re: A65 competition rocker arms
« Reply #5 on: 13 October, 2018, 19:35:45 »
Cheers Pete, a good bit of background information there.
The only reason I'd be using them is for stress reduction as you mentioned. Curiously though I'm wondering if Devimead ever produced these rockers for the exhaust valves, as the info posted by Julian clearly shows only the modified rockers on the inlet. The exhaust ones look standard. I had thought that if you had this type on rocker on the exhaust, the adjusters would be very close to the top of the rocker cover. 
Look forward to reading your book for more little gems of information.

morinipete

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Re: A65 competition rocker arms
« Reply #6 on: 14 October, 2018, 18:53:43 »
Hi again,

Yeah they did them for both inlet and exhaust. They weren't special bits, just the original bits welded up and machined. PS. Could I use your photos in the book? They're way better than the low res ones (example attached) I have at present!

Cheers

Pete

Servodyne

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Re: A65 competition rocker arms
« Reply #7 on: 15 October, 2018, 09:43:49 »
They weren't special bits, just the original bits welded up and machined.
[/quote]

Funny you should say that. I was thinking along those lines for the exhaust rockers. The threads for the devimead adjusters is 5/16 UNF so I'm hoping that there will be adjusters out there that will have a 5/16 ball end on a 5/16 UNF thread.
No problem using the pics, I'll look forward to seeing them in your new book. Is it going to include anything about the A70 by any chance because that's what these rockers are for.

Cheers

Jim

morinipete

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Re: A65 competition rocker arms
« Reply #8 on: 15 October, 2018, 10:32:55 »
Well on the A70 it's an odd one. It's the one everyone denies any involvement with!

By 1970 everyone inside the factory knew the short stroke was the way to go. It was easier to get a big engine using an A10 crank - Vincent, Brown, Norman Hanks and Mick Boddice all did it - but the short stroke was better in engineering terms and would have been cheaper to produce. Les/Dave Mason worked on this - all un-officially of course, like everything else good at BSA! - while the A70 seems to have been Clive Bennett's baby. Bennett probably saw what the sidecar racers were doing and thought; "That's the way to go then" instead of asking them; "If you were going to produce a 750, how would you go about it?" But that seemed to be standard management practice in BSA. The management never consulted the shop floor.

Dave Mason put Les Mason's first short stroke A65 in a Rickman frame and used it to beat Phil Haslam to the MCRC Open Class Championship. If you don't know of Phil Haslam he was the fast  one. The one destined for stardom (but was unfortunately killed, passing on the mantle and his bikes to Ron). Les offered the engine to BSA to bench test and was told he was only a draughtsman and should eff off! Mal Carter - the Haslam's wide-boy sponsor - of course came round and tried to make them an offer they couldn't refuse, to buy it! A bit sad that a Yorkshire second hand car dealer saw more in it than the management at BSA! But then there wasn't much chance of Lionel Joffe being seen at a race track!

Saying all this I've talked to both Dick Mann and Dave Aldana and they loved the A70 as a flat tracker. Dick Mann used it for the final races of the 1971 season, when he won the AMA title, and said when they got the A70; "It was like cheating." But you do have to ask yourself, as the USP of the A65 was that it was a short stroke motor - the only British big short stroke motor - why with the A70 did they revert to a 1950s bore/stroke ratio? Mind you, I've never ridden one. They could be the Dogs do das :)

So yes, they'll be stuff on the A70 but not too much on the technical development history of the engine, as all the factory people I've interviewed (and it's 40+) have denied any involvement. And this includes Peter Brown, who was the main A65 development engineer! I think that speaks volumes.........................       

Cheers

Pete

Servodyne

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Re: A65 competition rocker arms
« Reply #9 on: 15 October, 2018, 10:59:34 »
More fascinating stuff.
I'm having to use an A10 crank in my engine, as mine came without one, so I'll have to see how that works out. I've retained the timing side bush design utilising an outboard thrust washer to control end float and hopefully contain high oil pressure.
Unfortunately it looks like I may run foul of the law using an A10 crank as the attached A70 service bulletin states that it is illegal for use!!!
Happy days
Jim 

morinipete

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Re: A65 competition rocker arms
« Reply #10 on: 15 October, 2018, 11:58:44 »
If you're going that route look at Triumph T140 pistons. They have the same gudgeon pin size (the T140 effectively used the same con rod as the late A65s) and if memory serves me correctly you then need to just skim 1mm off a standard barrel. I've never done it myself, but there will be others who have. Standard BSA A65 pistons will obviously be sticking way above the barrel top, unless you're lucky enough to have some genuine A70 ones!

With T140 pistons this will bring in over 750cc, but that's not a problem unless you're racing it.

Servodyne

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Re: A65 competition rocker arms
« Reply #11 on: 15 October, 2018, 16:52:54 »
I did look at T140 pistons but there is a 2mm deficit in height from the gudgeon pin to the top land so I ended up buying a genuine pair from Bantam John at great expense.  Ray Fisher at Brit bits was selling them for £50 a pair this time last year until someone mentioned it on Brit bike forum, then they were all gone within a week. He'd had loads of them for years and no one wanted them apparently!
Even with A70 pistons there's still a 20 thou shortfall from reaching the top of the barrel due to the 1mm difference in the A10 stroke, but as you can see from the photo they come far enough up the bore to give a decent compression ratio.

robertc72

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Re: A65 competition rocker arms
« Reply #12 on: 13 February, 2020, 18:50:28 »
A fascinating item, so when is the book due out? And years ago someone suggested to me that the T140 was developed from the A70
I am surprised that no one wanted to talk about the A70, or denied involvement. My knowledge is very limited on the subject apart from a new A70 being in NZ for many years that no-one could afford to buy. And I had the privilege of meeting Wilf Harrison in 2004 when he came to stay with Rod Coleman, and was our guest of honour at the BSA National Rally I ran for the NZBSA Owners Club. As Export Manager Wilf was away a lot flying around the Commonwealth securing orders, so missed out on much of what was happening at the factory. He said he came back from one trip to find Jofee was planning to re-arrange the factory, and change to the 71 range. Wilf said he wrote to Jofee and pleaded with him not to change everything. Wilf said, our customers like the looks of our bikes , BSA and Triumph. Give me a 600cc A50 and a 750cc A65 and I will convince the distributors they are new bikes, and it will give us a few years to introduce the New Range of Bikes - He never said, but I believed he meant the Bert Hopwood modular bikes - The Paper Tiger

On the A70 flat track engines, they would have been superb with the longer stroke giving that extra torque kick coming off the turns. I am just a fan and people are still talking about the XR750 engine compared to the modern ones, and the power pulse. 

DAVE BRADY

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Re: A65 competition rocker arms
« Reply #13 on: 13 February, 2020, 19:27:10 »
Hi,

I have a set of the eccentric rocker shafts but no head that they fit.  See "What is this?" Star and Garter, page three, 16th Dec.  Also I have set of the rockers that I will use when I get my 750 (A70 crank) A65 back together.  As well as making life easier for the valve stems there is, in theory at least, the possibility to use the curve to make micro alterations to valve timing and valve lift by altering the curve.

Dave.
« Last Edit: 13 February, 2020, 19:50:58 by DAVE BRADY »

DAVE BRADY

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Re: A65 competition rocker arms
« Reply #14 on: 22 February, 2020, 17:07:44 »
Here is another part to do with the competition rocker arms.  The adjusters that operate on the push rod rather than the valve.  Quite an intricate thing for what it is.  It looks like oil gets in to it from the hollow adjuster and keeps an oil film in the top of the push rod.  I am wondering if the viscosity of the oil could cause the ball shape to not fully separate from the push rod and allow a slight telescoping of the adjuster resulting in less impact on the parts and maybe quieter operation.  Not cheap to make though.

Dave.