1959 engine and gearbox sprockets

According to Bacon, for a 1959 88 dommie the engine sprocket is 20T, Clutch 42T,gearbox 19T,and rearwheel 43T. for a 1959 99 Dommie a 21T engine sprocket is standard, others as per an 88.Just to confuse matters , my 1960 Workshop manual shows 20T for the engine sprocket of the 99.

To the best of my knowledge, engine sprockets size is 19T for an 88, 20T for a 99, 21T for 650 & Atlas, all with 21T gearbox sprocket. Try running an 88 or 99 on a 21T engine sprocket and you will find it faster in 3rd than 4th.

Gordon.

Previously wrote:

Hi Andy,

You did not state which 1959 model you have. However, (for once!) I agree with Gordon. I place more faith in my (genuine) Norton handbook than in anything written by a third party, Bacon or otherwise, and, this confirms Gordon's figures.

Regards, John.

In support of Roy Bacon, my copy of the Norton Spare parts list for 1959 specifies a 21T engine sprocket (part No T2180) for both the 88 and 99 of that year , cost £1/3/8. Sprockets with from 17 to 23T are offeredd for twins. The use of the 21T sprocket gives a top gear ratio of (42*43/(19*21)= 4.53:1. The Road test on the 99 dominator on 'The Motorcycle' for the 1958 model, reports that the top gear ratio is 4.53:1. The maximum speed obtained in 3rd gear was 91 mph and in top gear only 93 mph, with a best one way speed of 96 mph. with a moderate side wind. However the top speed in the lower gears involved reving the engine until valve bounce occurs. This is generally considerd to be a bad idea with aged engines.

Previously wrote:

To the best of my knowledge, engine sprockets size is 19T for an 88, 20T for a 99, 21T for 650 & Atlas, all with 21T gearbox sprocket. Try running an 88 or 99 on a 21T engine sprocket and you will find it faster in 3rd than 4th.

Gordon.

I think there may a typo in the above. Most of the twin engined, road going bikes used a gearbox witha 19 tooth sprocket.

It wasn't until the Commando arrived that the option of a 21 tooth item really became an option.

Another point to bear in mind is the gearbox type fitted to the bike. Post Laydown Gearbox (1956) but pre 1960 bikes most likelyhad an AMC 1 gearbox with a 24 toothmainshaft output gear. After this year, the AMC 2 was fitted and this had a 23 tooth gear. This difference of one tooth makes a big difference to the gap betweenthe first and top gear ratios. In the AMC 2 box the first 3 gears are now raised and the previous large gap between 3rd and top closed up.

The AMC 2 gearbox is a much better to use with the later engines. They have the power to pull away despite the higher first gearing. Earlier lowered powered twins will struggle a bit unless the engine sprocket fitted is no greater than 20 teeth.

Or...................you fit a smaller gearbox sprocket and then have fun and gameswith the rear chain.Checkout the attachment for internal gearing of Norton Boxes.