G12csr rev counter?

[Don Madden]

I have a photocopy of an article Mike Duff wrote on his experience as one of the riders in the Thruxton event, I think 1962, the other was New Zealander Hughie Anderson.

As AMC did not have an official race program, they built & tuned the bike but supplied it the Arter Brothers of Kent, who entered it.

The rules allowed only minor modifications, (at least visible ones), & the machines were required to have operating lights & standard brake systems, except racing linings were allowed.

The engine produced over 64hp, (yes, 64hp), on the race shop dyno, more than any other production racer built then.

The team immediately left all others behind, including Phil Read & Brian Setchell on the factor Norton 650 & gained a "commanding lead" at half way until the mag acted up, causing several laps lost to repair. They got back on the track, passed everyone & re-took the lead.

Then the overtaxed front brake failed due to overheating, followed by the rear & when their boots wore out from dragging they had only engine compression left to slow down. They rode the last two hours with no brakes & were left well down in final results. Read & Setchell won.

Cheers, Don.

[alan humphrey]

dave I was aiming for standard trim as i have no idear what mods were done to the marshals bikes,i would have prefered to do it as it left thruxton heading for the TTs but i have aqiured motorcyle mags and a vidio of the 61 TTs but to no avail ,no sign of mine or any other matchles marshals bike . From what you and rick say about the race kit i think i might leave it aloan as it does not seem to have much benifit apart from frightning the life out of me. If anyone out there has any info on factory marshals bikes could they please let me no.
don one of the bikes in the same batch as mine was sent to arters,also one was marked "surtees" . thanks to you all regards alan

[arsey30]

Don,
I spectated at Thruxton in the early sixties, a 31CSR won the 1960 race, and also the Oulton park 1000km in '63
Duff/Bill Smith were 4th in '63 at Thruxton on a 31CSR

64hp is amazing, but Jack Wlliams was Chief developement engineer at the time, so maybe he turned his attention to the motor as the directors would not allow him to further develope the G50 and 7R.
Arters later sponsored his son Peter on Nortons.
Peter rode a G15CSR in the Castle Coombe 500 in 1965 and it was then sold on to a customer.
I can confirm that bike looked pretty standard, as the owner rode to my house to buy some standard parts from my own G15CSR, as I had fitted some Dunstall parts.

Dave.

[wilko]

I'll bet it had special headgaskets and a billet steel crank!! If only we knew what goodies they fitted internally! If they were standard bits i might take mine out now and go for a good fast fang!!

[Don Madden]

I agree about the head gaskets & the engine probably had bigger studs, too. However, the later nodular crankshaft is very strong & somewhat flexible & may well take the abuse. Ed Crowell builds & races them bored & stroked to 750cc but uses Carillo rods. He uses copper wire fitted between the cylinder spigot & the head recess to hold compression.

Cheers, Don.

[Rick.Edwards]

If you've got loads of money then Nourish will build you a one piece billet crank,when i discussed it with them 3 years ago it was 750 pounds+vat and you HAD to supply Carrilo rods.10% deposit and the rods and he'll start i think he said around 6-8 weeks for completion.Would have loved to have had one of these cranks made.

[Adrian Pancaldi]

Hi All, I was running the race kit cams on my G12 along with twin carbs. I ran copper head gaskets with an "O" ring around the oil metering jets and 3/8 studs, kept the 8.5:1 pistons. The noddy crank can take a little abuse. Though it's a case of the next weakest link... I hit a false neutral at high revs and demolished the engine when a follower let go , I think that the pushrod may have popped out and did most of the damage, chicken or the egg(?).
I would build that engine again though with different conrods , either later followers or new ones made from better material and upgrade the valve springs.
Regards

Adrian

[bailequaile]

Speaking of Speed Kits. I have always felt that the twin carbs and rev counter make the bikes look much more balanced and like the' Sports' bikes they were at the time.

The parts can be hard to come by but they are out there if you search. I found the twin carb manifolds + carbs, rev counter, cams and instrument bracket online over the last two years.
The bike will probably be a pig to run but it will look good and that's what matters to me:) I like to restore to the standard that I would have had the bike in if I'd been a contemporary of it. I'm sure most young fella's at the time would have opted for the Speed Kit if available.

[alan humphrey]

I see where you are comming from bailequaile, but in those days we would have put on clipons or ace bars also rear sets.but this is not what i am trying to acheave,(sounds good though) iam trying to get the bike back as near as i can to when it left the factory as a marshals bike. thanks for the thought though regards alan

[mdt-son]

I found the engine on my '63 bike with full speed kit [10.5 pistons, twin carbs, cams, hand controlled mag] was not much less flexible than my standard '61 bike.
The factory told me the power increase was only about 48bhp to the standard 46.
Acceleration was better but top speed about 5mph extra [110 against 105]

It will require more than 2 additional hp to increase top speed from 105 to 110 mph.
Under equal testing condition, gearing, and assuming the quoted power at crankshaft of 46 hp is correct, the required power to reach 110 mph is 53 hp at the crankshaft.

If gearing is equal, the rpm at 110 mph will be higher than at 105 mph of course, this is normal for a race engine. There will usually be a margin to maximum permissible rpm, but no further gain from peak hp as the power curve branch usually drops steeply.

-Knut