Engine offset ???

A

Andy Higham

Joined
Apr 16, 2025
Messages
85
Country flag
With the chain adjusters set equally, the rear wheel is over to the left of the rear loop.
The frame is Mk3, the front iso is also Mk3. The gap between the front iso side plates and the frame tabs is equal each side. So the front of the engine is central?
Where the swing arm passes inside the frame, the gap on the left is about 4 - 5mm less than the right. So the rear of the cradle is offset?
I haven't measured accurately yet, but i would guess the rear wheel is more than 4-5mm out of centre in the loop.
It appears the engine centreline is diagonal to the frame centre line !!!!!

What I am thinking is, shorten the rear iso abutment so the rear of the cradle can move over to the right and fit a spacer in between the frame and adjuster in the left. This will bring the engine/cradle/swing arm parallel and central to the frame.
My next job already in motion is building a new rear wheel, with everything in line I can true the rim in situ to ensure everything is in line.

An added bonus would be a couple of extra mm between Z plate and swing arm for brake cable clearance.

I would welcome thoughts and comments please
Andy
 
Andy Higham said:
What I am thinking is, shorten the rear iso abutment so the rear of the cradle can move over to the right and fit a spacer in between the frame and adjuster in the left. This will bring the engine/cradle/swing arm parallel and central to the frame.
Click to expand...

The cradle, therefore engine, gearbox, primary and front end of the swinging arm should be approximately 1/8" to the left of the frame centre line. The head steady and both Isos are also built with that offset. The swinging arm isn't symmetrical.
 
If as you say the front Iso is a Mk3 unit then the threaded vernier adjuster must be at the right-hand end.
 
I don't have any dimensions but the tube of the Mk3 Iso should be shorter than pre-Mk3 on the adjuster side. Are you sure you don't have two adjusters? The abutment should have one hole in it for the grub screw.
Is that the clip on the 'abutment' as it should go on the adjuster side.
andover-norton.co.uk

Andover Norton - SPRING CLIP for isolastic mount - 06.4723

SPRING CLIP for isolastic mount
andover-norton.co.uk


andover-norton.co.uk

Andover Norton - FRONT ISOLASTIC ADJUSTER COLLAR R/H (VERNIER MK3) - 06.4665

FRONT ISOLASTIC ADJUSTER COLLAR R/H (VERNIER MK3)
andover-norton.co.uk
andover-norton.co.uk

Andover Norton - FRONT ISOLASTIC ABUTMENT L/H (VERNIER MK3) - 06.5514

FRONT ISOLASTIC ABUTMENT L/H (VERNIER MK3)
andover-norton.co.uk

The head steady is offset therefore the front Iso must also be or the engine would lean over when it was bolted up.
Engine offset ???
 
See photos above adjuster and abutment fitted.
I wonder if something has been transposed front to rear?

I am going to order a set of stainless from RGM then put it back in.

Why is the engine offset to the left? It can't be for chain line. It puts slightly more weight over to the already heavy side
 
Andy Higham said:
I wonder if something has been transposed front to rear?
Click to expand...

Front and rear Mk3 adjusters are the same but the abutments are not but that isn't a rear one in your pictures. AN refers to the adjuster as "front" but this is incorrect as it's front and (LH) rear.

Andy Higham said:
Why is the engine offset to the left?
Click to expand...

I don't exactly know but it's not uncommon on British bikes Trident, Bonneville, etc.
 
1up3down

Post in thread 'ISO-cradle-frame alignment'

Well, this is copied from NOC list notes from the above link.

Am I correct that at the bottom paragraph the conclusion is that the adjusters should be on the SAME side?





Commando wheel offset - the definitive answer
I have the definitive answer as to what is offset, how much, and which way!

I set up a 1973 850 on the frame table and verified it was straight. I then put together a dummy engine and installed it with new isolastics, new washers, Hemmings adjusters, and a Norvil head steady. I put both adjusters on the left side, checked the swinging arm in my fixture and then...
 
Andy Higham said:
Why is the engine offset to the left? It can't be for chain line. It puts slightly more weight over to the already heavy side
Click to expand...
On the featherbed framed bikes the rear chain was very close to the back tyre, limiting the width that could be fitted. With the Commando this limitation was eased slightly in the simplest and, most importantly, as cheaply as possible. That was achieved by moving the whole engine, gearbox, engine/gearbox plates, swinging arm pivot, back wheel hub and brake assembly and primary & rear drive trains 3/16” to the left hand side. The swinging arm legs were made asymmetrical to keep the rear suspension units upright. Finally, in order to put the back tyre into line with the front tyre, the back wheel rim was offset 3/16” to the right hand side. Job done.
 
Besides everything @L.A.B. told you. If you have a pre-MK3 frame, you should not have a MK3 front ISO mount or vernier internals. Some people modified the mounts before the vernier kits were available for pre-MK3 so there are at least three front mount possibilities. When you buy the front ISO kit from AN, notice this comment: "ISOLASTIC KIT FRONT VERNIER for COMMANDO 750 850 1968 to 1974 *YOUR FRONT ENGINE MOUNT MUST BE UNMODIFIED - CALL IF NOT SURE *"

Since you have a hybrid, then most if not all components must be hybrids. In the end, everything must be sifted and then the rear wheel laced to compensate. All a good reasons to use the stock components for the year being built! I've thought many times about using a MK3 cradle and then told myself - don't be stupid - too much work! I don't know what cradle you have - has cotters but you are using the earlier end caps and thru bolt so the wrong spindle (I guess).

Also, what is the point of questioning why everything was designed off center - it was. @hybridracer just gave a good explanation that I didn't know (or need to know).
 
Andy Higham said:
The frame is Mk3, with the seat lock brackets adjacent to the shock top mounts, The front iso is Mk3, The engine is Mk2

From being a small child I was always encouraged to ask WHY ?
Click to expand...
I don't think the engine matters. But didn't you say you have a drum rear brake - whole bunch of differences there. Do you have a pre-MK3 swingarm - you said no center bolt so it sounds like a Mk3 cradle. If a MK3 swingarm, off the top of my head is not readily compatible with a pre-MK3 rear wheel (could be wrong).

Asking why is fine:

However, ask why we don't now how high is up will hurt your head from a small child - still hurts mine!

Asking why it is presumed that a black hole has a singularity, but the event horizon width can be thousands to billions of miles across hurts because why doesn't the black hole collapse to nothing with a singularity at the center. Don't even start studying black holes if you want the answers to why?
 
I have a Norvil electric start cradle with a Mk2 swing arm.
I have just measured at the rear iso, outside of frame gusset where the long bolt goes through to the outside of then cradle plates, just below the iso
Left 65.6mm Right 64.4mm
So the engine is all but central at that point

I have ordered a complete set of Mk3 stainless adjusters caps and abutments from RGM, they should arrive early next week. Then I can compare and see how it all lines up
 

Similar threads

jseng1
Norton Desaxe cylinder offset
2 3 4 5
Replies
96
Views
5,523
mdt-son
M
Jonez69
Installing completed engine assembly into the frame, Will this work?
2
Replies
25
Views
954
ilikevelos
I
R
1977 T140 with offset rear wheel
Replies
5
Views
133
L.A.B.
L.A.B.
Fast Eddie
MAP offset rocker buttons in a T140
Replies
8
Views
182
Fast Eddie
Fast Eddie
Jonez69
1974 Commando swinging arm rebuild question ( Complete engine rebuild happening as well )
Replies
12
Views
822
Rockithound
R
Back
Top