Earlier 850 motor into Mk 3

Will an earlier ( non electric ) 850 motor and gearbox fit into a Mk 3 cradle ok what mods required, I presume gearbox adjuster slots ?
or do I need the earlier cradle.
I have the chance of a good early 850 motor /gearbox which would be used as a spare while rebuilding my Mk 3 .
Would the earlier 850 motor /gbox and cradle fit in the Mk 3 frame without any mods ?
thanks
sam

You may also need primary cases as mk3 has four bolts for fixing to crank case but earlier motors have only three bolts.
Then you may need to think about gear lever is on other side on earlier box an as earlier box has no provision for cross over shaft it would cause problems. One problem of on R/H as on earlier model is that rear brake would have to go on L/H as it is on pre Mk3 but that is a cable an drum system.

With the problems I have mentioned and those you have already asked about I personally would just spend the time an money on overhauling your existing mk3 even if it means it will be off the road. Your plan to put earlier motor and gearbox in will need lots of other parts (some of which you many not have).

I appreciate your reply.

The motor I'm looking at is complete with primary, I don't think it's much trouble to alter the rear disc brake actuation to the
other side ,I have a lot of brake parts from various bikes, but point taken.
I really want to know if the cradle containing the earlier motor/primary/gearbox will go straight into the Mk 3 frame without mods to the frame.
ta
sam

trident sam said:

I really want to know if the cradle containing the earlier motor/primary/gearbox will go straight into the Mk 3 frame without mods to the frame.
ta

Click to expand...

The earlier cradles (except perhaps for some late Mk2/2A cradles) don't have the twin cotter locations for the Mk3 swinging arm spindle.

Yes, that's something I knew but haven't had enough thinking time to get round it yet.
thanks
sam

trident sam said:

Yes, that's something I knew but haven't had enough thinking time to get round it yet.
thanks
sam

Click to expand...

You could get a mk2a type spindle or carefully drill an tap a thread in the mk3 spindle. I believe they are harden but it may be possible.

Hi Sam

Could you use your own Mk3 gearbox & fit the earlier engine? Just make up a primary cover race style? Don't know if the cross over shaft would be supported enough?

Chris

Hi Chris,

using right foot change wouldn't bother me, I think my stumbling block would be the swinging arm arrangement, but anythings possible with time (and money)
I'm very loathe to pass up the chance of a complete motor/gearbox in a good running order.

See you at Beezumph ?
cheers
sam

trident sam said:

using right foot change wouldn't bother me, I think my stumbling block would be the swinging arm arrangement, but anythings possible with time (and money)
I'm very loathe to pass up the chance of a complete motor/gearbox in a good running order.

Click to expand...

Wouldn't it be a whole lot simpler, quicker and probably cheaper just to spend the time, money and energy on rebuilding original engine-as that seems to be what you intend to do in the long run?

trident sam said:

Hi Chris,

using right foot change wouldn't bother me, I think my stumbling block would be the swinging arm arrangement, but anythings possible with time (and money)
I'm very loathe to pass up the chance of a complete motor/gearbox in a good running order.

See you at Beezumph ?
cheers
sam

Click to expand...

Well you could maybe get the earlier parts an use them as the starting point for a future project after you have sorted your mk3.

toppy said:

Well you could maybe get the earlier parts an use them as the starting point for a future project after you have sorted your mk3.

Click to expand...

The complete top end plus various other parts could be borrowed from the 'earlier' 850 engine, and a lot of gearbox internal parts also clutch parts are interchangeable.