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Heavy Twins


A technical forum for Model 7 to Mercury

Siamese exhaust


Just about to order a  stainless system for my slimline 99  (inside frame) ,from Armours, has anyone had any experience  of these.?. Do  you finish up with a nice line or a droopy silencer?.

Transmission, sprockets.


I have an 88SS and first gear seems too high. I was hoping to get someone to sort this out for me. I have a list for various models listing sprockets and gear ratios. The sprockets are listed under E C G & R. What do these letters mean  and what does overall ratio mean ?

   Thanks for any help

Crankcase breathing


What is the general consensus on crankcase breathing ?

I have a tuned 1962 650SS with a standard vent to atmosphere and central oil tank that I am rebuilding and have googled the subject on this site and also the Heavyweight Twins Compendium.

It looks like my choices are,

Silent Block - Temperature tolerance


I'm looking to have a slimline swinging arm powder coated but I do not have the facility to remove the silent block bushes

I've scanned through the forum for advice but found conflicting information, in one thread it was said this was possible without any ill effect yet in another thread someone claimed after stove enamelling their bushes were melted?

As I understand it powder coating requires ~200°C but stove enamelling is significantly less?

Any advice gratefully accepted




Hi, went to change the pistons in my Atlas, as I've found some proper low compression ones at last and found this, The engine has only done about 3000 miles since being professionally rebuilt and seemed to be running ok.

Any ideas??

oil pressure gauge


Having bought an oil pressure gauge from RGM I am having trouble fitting the banjo bolt connection to the timing cover. My Norton 650SS has a plug bolt that can be removed to allow a banjo bolt to be inserted.but as the banjo I believe was designed originally to be located local to the tappets maybe the banjo bolt is too long for insertion into the timing case. .Does anyone know if I must shorten the bolt so as to match the extent to which the plug bolt was able to insert into the timing case so as to be able to measure pressure from the timing case.


A small step backwards?


Seduced by the cherry-red Atlas on the cover of this month’s (Oct 2022) issue of The Classic Motor Cycle, I was very happy to read the 8-page feature on the bike. Well illustrated, and finishing with a road test of the bike in question, it had been rebuilt by its previous owner from a 1962 Atlas fitted with a later 1968 engine.

The article included quite a good potted history of the genesis and development of the 750, but I was surprised to read the following.

Wrong Rear Hub Bearing ?


Could someone please confirm what I think is wrong or shed some light on other theories.

I've seen a couple of other forum post on a problem similar but am not familiar with the mechanical jargon that was said. 

I believe my dominator rear hub has the wrong bearings installed. The outer hub plate wasn't sitting in the groove and noticed it was sitting on this lip. I'm sure it should be flush. 


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