Mk3 engine 750 frame

Chris · Feb 12, 2010

Hi
I read the earlier post's but other than "its wider" they were not that helpful. So!
I am working through my options ie frames engines etc & one of those options is to put my MK3 Competition engine into my 750 flat tracker.
So front mount? the same? Cradle & swinging arm from a MK3?
Or as per Ludwicks fabulous bike make my own engine plates & swinging arm?
Of course dreaming may not lead to practical matters but I would like to keep my options open?
Thanks
all the best Chris

Danno · Feb 12, 2010

I have a '75 850 Mk III Engine and trans in a '71 Commando frame. I used the vernier isolastics, Mk III headsteady and swingarm, and it was a straight drop-in with no issues. If your tracker uses a stock frame or one intended for any Commando motor, there shouldn't be a problem. If it's a non-stock tracker frame such as Redline or Trackmaster, Isolastics and Norton swingamr will likely not be compatible.

Holmeslice · Feb 12, 2010

Chris,

The MKIII Crankshaft is wider by about 1/8", thus the cases are wider, but the engine mounting boss widths are exactly the same as any other Norton Twin and will fit right into a stock Commando frame/engine plates. I had trouble when trying to fit the MKIII motor into a Featherbed using "off the shelf" alloy plates because the curvature of the wider cases would foul against the bottom frame rails, where 750 cases would've just missed.

HTH,

-Kenny C.
NYC
www.nycnorton.com

RennieK · Feb 12, 2010

The cradle has 2 locating bolts for the swingarm spindle. The swingarm itself is quite different with the box end and the diameter of the tubing seems to be considerably thicker. I've ben comparing photos but have never had a markIII swingarm to properly compare. The disc brake hub and sprocket are quite a change so the distance between the forks could have changed also. The markIII cradle swingarm seems to be an improvement and more robust. Still, if money was no object a set up like Ludwig's would be the best option as it weighs almost 1/2 and should be stronger.

Chris · Feb 13, 2010

Hi
Thanks for the replies.

Hi Danno stock commando frame Spondon wire disc rear wheel with homemade mounting plates. I will look out for a Mk3 s/arm, or follow Ludwik.

Hi Kenny I ran a commando featherbed for a short while. Half nut on the front engine plate & threaded my gearbox bottom mounting boss with an M10 thread & used 2 short bolts to hold the gearbox. It makes it easier to remove the box than trying to jack the lot up to try & pull the bottom bolt out.
Hope you have a great season. Got to say I love my MK4.

Hi Renniek Go to say if I find a MK3 s/arm I will remake the rear disc set up again. I cant weld but I will have a look for some alloy!

All the best Chris

Danno · Feb 13, 2010

Chris said:
Hi
Thanks for the replies.

Hi Danno stock commando frame Spondon wire disc rear wheel with homemade mounting plates. I will look out for a Mk3 s/arm, or follow Ludwik.

Hi Kenny I ran a commando featherbed for a short while. Half nut on the front engine plate & threaded my gearbox bottom mounting boss with an M10 thread & used 2 short bolts to hold the gearbox. It makes it easier to remove the box than trying to jack the lot up to try & pull the bottom bolt out.
Hope you have a great season. Got to say I love my MK4.

Hi Renniek Go to say if I find a MK3 s/arm I will remake the rear disc set up again. I cant weld but I will have a look for some alloy!

All the best Chris

I have a spare Mk III swingarm f/s if you're interested. It would require blasting and painting.

Chris · Feb 13, 2010

Hi Danno
Thanks for the kind offer but you are the wrong side of the pond! My poor old mum gets tired of bringing stuff back from the states for me.
Especially as she needs a frame of her own to get about with!
A couple of years ago she brought me back a couple of brand new Daytona rods & was all ready to dump them in the trash because airport security would not let her on the plane as they did not know what they were. My mum didnt iether she just kept saying they are just old bike bits!
And they are! Its a great hobbie that takes over your life.
all the best Chris

Mk3 engine 750 frame

Chris

Danno

Holmeslice

RennieK

Chris

Danno

Chris

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