Early Atlas engine in 1970 Commando

Dear Keith,

It's been done before so not too much of a job, Engine should fit in cradle OK, but there are 2 Areas that will need some work. As engine is now tilted I doubt that bolt holes for primary chaincase will line up so you could offer up commando case as use as a template to start drilling; thread is 1/4 whit I think, but if you are not a purist any 1/4 or 6mm thread would do. depends what you have taps for. There is a danger of swarf entering crankcase doing this so apply grease to tapping drill when nearly through so bits stick.

Other area to mod will be top mount, Is your Atlas head the one with large single bolt and oil feeds on top ? If so you will need to nodify commando top mount to fit, assuming you have early type rather than later box section one it should not be difficult to drill large hole and saw off sides where they foul oil pipes.

Don't worry about damaging this type of mount they are rubbish/ most have been welded as they crack. Look out for a box section one when you replace original engine. If you are near Doncaster I can lend you some Taps.

regards Martin

You will also need to change the timing cover as the earlier Commando engines with the rev-counter drive, as the engine was tilted forward had a different oil arrangement in the pressure relief valve part of the timing cover. If you read the very latest Real Classic Frank Westworth bought a Commando that had been fitted with an Atlas crankcase half and the primary chain-case did not line up with the Commando chain-case. The Commando's alternator fits in side the chain-case on a cast incasting but the Atlas engine has a bolt on casting so the crankcase half has six screw holes and not three as on theCommando's drive side crankcase has.

That would be a far better thing to do as it would not be too costly and then every thing will be standard. You would not have to modify any thing to fit your application, and it would also be far less of being problematical. The mention of an Atlas crankcase half in a Commando, Frank mentioned it in the Commando Mark 3 article in Real Classic.

I would agree with others, better to rebuild the engine.

You say quite a lot needs doing so if this includes paintwork, plating etc you'll probably be waiting a while for that so can do the engine instead of twiddling your thumbs....

Ref. rebuilding the Commando engine, assuming you have a nice warm shed, what better way to pass the time in the coming dark, damp months?

If using the Atlas engine, you will also need to look at the balance factors because the Commando iso system is very different to the rigid featherbed mounting

Hi Keith, If you go with re-building the commando engine,would you be interested in selling the Atlas one?, I'm trying to build an Atlas motor, so if anyone has bits to sell? Also what 99 parts could I use in an Atlas??

Previously keith_parsons wrote:

Hi,

I recently bought a 1970 roadster which needs a lot of work to get back on the road. To speed things up and as the engine needs a complete rebuild.

Could I tempararily fit an early Atlas engine I have, which has been completely refurbished?

I am not an engineer and do not have access to a machine shop.

I'm thinking that some of the mountings won't match up, hence the question for the experts.

Thanks Keith

Hi, As someone else stated Balance Factor will be a big issue. Commando 52% Atlas High 70's %.

I tried it the other way round fitting a Commando 750 to a Rickman Metisse and used it like that for a few years but my fillings would drop out but it kept my dentist employed.

I now have the crank balanced to a BF of 77% and the bike is much nicer to ride although changing the BF moves the vibration to another rev range, soI were you I wouldre fit your command engine.

Good Luck.

The 650 I took out of a commando meerly had a .218" steel spacer plate between the featherbed engine and the commando primary. The bolt holes orientation is not different. Put the drill away it is not needed!!!!!

You are still left with rocker oiler hook up and compatibility problem depending on whether high or low pressure system. Which also leads to head/isolastic mounting problem.

Just for temporary fitment the different balance factor is functionally irrelevant IMO.

Having seen it done and in practice observed the hack work, I'd highly recommend against it. You would need a machine shop to make a respectable job of it.

I could do a conversion like you are describing, but I won't.

IMO your time is definitely better spent building your commando engine.

Previously robert_tuck wrote:

Hi Keith, If you go with re-building the commando engine,would you be interested in selling the Atlas one?, I'm trying to build an Atlas motor, so if anyone has bits to sell? Also what 99 parts could I use in an Atlas??

Hi. I have a complete Norton engine here we'll have two one is totall rebuild, you name it it new or been done , others is a 1/2 race Dunstall built engine, if your interested could come to a satisfactory price I'm sure.

Tec Roberts