commando motor in gpz 1100 unitrac frame

bobnorsaki

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Jan 7, 2022
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i previously discussed the fabrication of a solid axle for my MK III rear wheel. but no response. so again. cut the stub off the stub axle, drill a 17mm hole in the stub. obtain the axle from an 83 PLUS gpz 750 and cut to length then thread each end to use the norton nuts. I used this axle because the MK III rear is in an 83 gpz swingarm. much wider than the commando. to proceed, the motor is mounted in a gpz 1100 frame at the front. at the bottom (think rob north commando) and at the top and the using plates attached to the cradle. not easy. now to the forks. 75 commando forks are attached to the gpz headstock by changing the bearings to fit the gpz and the triple clamp. the norton triple clamp is lengthend to match the headstock. last but not least is the front wheel. offset is ancient. a triumph disc brake hub is modified by changing the bearings to match another axle from a 750 gpz. the wheel has no offset. brake rotors from a kz400 are reduced to 10.7 dia and 4 holes are drilled to match the triumph hub. the fork sliders are reamed to fit the axle. another disc brake slider is fitted in the reverse position. all along the plan is to have a double disc front using norton calipers. the setup is similar to those on slippery sam. by using the modified triumph wheel the calipers do not interfere with the spokes. I have a slippery sam double disc setup on my 73 T150V. PS I didn't get much response on mt rear wheel solid axle and I don't expect much from this blurb. nevertheless it can be done. and I have a monoshock triple disc commando. cheers
 
Hi Bob, the reason for no replies is probably that no member here uses a GPZ chassis or has similar needs. Your project sound intriguing though. Please share some images.

One of the many engineering shortcomings of Norton is the rear wheel design.

Modifying the Mk3 dummy axle by enlarging it and allowing for a 17mm through axle is the obvious solution. The sprocket will have to be altered. A larger dummy axle requires the swing arm plate to be modified. A similar design was used by AMC, Jawa and others, and it's a mystery to me why NV didn't do a proper design when they redesigned the rear end for 1975 models. The idea of a dummy axle is clever, but the design should not rely on a threaded joint serving as a bearing support. It's basic knowledge, threads are stress risers when subjected to bending loads.

A wider swinging arm would be nice, allowing wider tires to be fitted, but its a bigger challenge affecting the final chain drive as well, thus not on my list of priorities.
How did you plan your project - trial and error, or proper planning by use of CAD etc.?

- Knut
 
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bobnorsaki said:
i previously discussed the fabrication of a solid axle for my MK III rear wheel. but no response. so again. cut the stub off the stub axle, drill a 17mm hole in the stub. obtain the axle from an 83 PLUS gpz 750 and cut to length then thread each end to use the norton nuts. I used this axle because the MK III rear is in an 83 gpz swingarm. much wider than the commando. to proceed, the motor is mounted in a gpz 1100 frame at the front. at the bottom (think rob north commando) and at the top and the using plates attached to the cradle. not easy. now to the forks. 75 commando forks are attached to the gpz headstock by changing the bearings to fit the gpz and the triple clamp. the norton triple clamp is lengthend to match the headstock. last but not least is the front wheel. offset is ancient. a triumph disc brake hub is modified by changing the bearings to match another axle from a 750 gpz. the wheel has no offset. brake rotors from a kz400 are reduced to 10.7 dia and 4 holes are drilled to match the triumph hub. the fork sliders are reamed to fit the axle. another disc brake slider is fitted in the reverse position. all along the plan is to have a double disc front using norton calipers. the setup is similar to those on slippery sam. by using the modified triumph wheel the calipers do not interfere with the spokes. I have a slippery sam double disc setup on my 73 T150V. PS I didn't get much response on mt rear wheel solid axle and I don't expect much from this blurb. nevertheless it can be done. and I have a monoshock triple disc commando. cheers
Click to expand...
I'm intrigued why you would use Norton lockeed calipers?
And reduce the diameter of the front brake discs?
And Norton forks?
It's basically the complete opposite to what I have done with my commando
I'd be very interested to see some photos
I'd like to see the frame setup,it sounds very interesting
 
I have built a mono shock T140V bonneville using an 83 gpz 750 frame. I am in the process of building a mono shock triumph T150V in an 83 gpz 750 frame. I want the mono shock norton to have as many norton parts as possible. this includes the brake calipers. as for using kz400 brake rotors they have four bolts like the triumph. to fit in the norton forks they have to be the same diameter as the norton rotors. and yes I do it because I can. I am older than biden. and yes I still ride. motorcycles are a great hobby. cheers
 
bobnorsaki said:
I have built a mono shock T140V bonneville using an 83 gpz 750 frame. I am in the process of building a mono shock triumph T150V in an 83 gpz 750 frame. I want the mono shock norton to have as many norton parts as possible. this includes the brake calipers. as for using kz400 brake rotors they have four bolts like the triumph. to fit in the norton forks they have to be the same diameter as the norton rotors. and yes I do it because I can. I am older than biden. and yes I still ride. motorcycles are a great hobby. cheers
Click to expand...
Are you solidly mounting the commando engine?
 
That GPz1100 is a big bike. I had a couple and a KZ1000. Liked the bikes but the Suzukis of the era handled better IMO. But whatever you got and are gonna do, that's cool of course, more power to ya! I sorta of feel that motor will be dwarfed by that frame tho. In the day I liked Kwaka style and Suzuki performance and handliing (circa 1982 or so)
 
All i ever heard here was the commando engine having/using a balance factor, suited for the unique isolastic rubberized setup of the Commando frame.

When solid mounting,, as in the prior Atlas frame/model, a diff balance factor is used for more suitable vibes., Then there is upright or slanted forward positioning to decide on. The upright Atlas is known as a shaker, whereas a member here who went with (~40 yrs now ) the Commando forward angle/Atlas balance factor & Atlas type frame, reports barely noticing vibes.

Not sure if a mismatch of frame/engine balance factor, can also result in frame integrity issues, other than

a Commando setup, with miss adjusted isolastics, can result in frame cracking.
 
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On a whim, I went to the CAT (Caterpillar) hardware desk in San Antonio and purchased a hardened bolt for my rear axle on the Dreer monoshock prototype bike. +/- $20 if I remember correctly, but it's been 14 years. This is an all-OEM '75 rear hub assembly, except the axle & stubs. I sliced the threaded end of the stub axle but retained the sleeve spacer.

commando motor in gpz 1100 unitrac frame
 
bobnorsaki said:
i previously discussed the fabrication of a solid axle for my MK III rear wheel. but no response. so again. cut the stub off the stub axle, drill a 17mm hole in the stub. obtain the axle from an 83 PLUS gpz 750 and cut to length then thread each end to use the norton nuts. I used this axle because the MK III rear is in an 83 gpz swingarm. much wider than the commando.
Click to expand...
Just a fwiw, there is also a substitute/upgrade 1 piece norton rear axle out there, not sure if for the 75 disc wheel deal.
 
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bobnorsaki said:
75 commando forks are attached to the gpz headstock by changing the bearings to fit the gpz and the triple clamp. the norton triple clamp is lengthend to match the headstock. last but not least is the front wheel. offset is ancient. a triumph disc brake hub is modified by changing the bearings to match another axle from a 750 gpz. the wheel has no offset. brake rotors from a kz400 are reduced to 10.7 dia and 4 holes are drilled to match the triumph hub. the fork sliders are reamed to fit the axle. another disc brake slider is fitted in the reverse position. all along the plan is to have a double disc front using norton calipers. the setup is similar to those on slippery sam. by using the modified triumph wheel the calipers do not interfere with the spokes. I have a slippery sam double disc setup on my 73 T150V. PS I didn't get much response on mt rear wheel solid axle and I don't expect much from this blurb. nevertheless it can be done. and I have a monoshock triple disc commando. cheers
Click to expand...
That would be a 1st/1 & only front stock Norton/lockheed double front caliper setup i'm aware of. Also, a 1st triple stock Norton/lockheed caliper usage. albeit not with a norton frame

Major also is the 1st/1 & only commando engine/gpz1100 frame/swingarm combo.
 
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bobnorsaki said:
I have built a mono shock T140V bonneville using an 83 gpz 750 frame. I am in the process of building a mono shock triumph T150V in an 83 gpz 750 frame. I want the mono shock norton to have as many norton parts as possible. this includes the brake calipers. as for using kz400 brake rotors they have four bolts like the triumph. to fit in the norton forks they have to be the same diameter as the norton rotors. and yes I do it because I can. I am older than biden. and yes I still ride. motorcycles are a great hobby. cheers
Click to expand...
I never even considered the Japanese front end calipers fouling the spokes on an adapted Britbike wheel, thankfully none of mine did, by using Dreer VR880 front hubs designed for better clearance (narrowed hub flange spacing, but still structurally / geometrically sufficient))
 
bobnorsaki said:
I have built a mono shock T140V bonneville using an 83 gpz 750 frame. I am in the process of building a mono shock triumph T150V in an 83 gpz 750 frame. I want the mono shock norton to have as many norton parts as possible. this includes the brake calipers. as for using kz400 brake rotors they have four bolts like the triumph. to fit in the norton forks they have to be the same diameter as the norton rotors. and yes I do it because I can. I am older than biden. and yes I still ride. motorcycles are a great hobby. cheers
Click to expand...
It is excellent that you are using as many Norton parts as you can.

Since you are using a wider swinging arm, have you considered moving the engine and transmission further to the left and increasing the back wheel rim offset to the right in order to fit a wider tyre?
 
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bobnorsaki said:
i previously discussed the fabrication of a solid axle for my MK III rear wheel. but no response. so again. cut the stub off the stub axle, drill a 17mm hole in the stub. obtain the axle from an 83 PLUS gpz 750 and cut to length then thread each end to use the norton nuts. I used this axle because the MK III rear is in an 83 gpz swingarm. much wider than the commando. to proceed, the motor is mounted in a gpz 1100 frame at the front. at the bottom (think rob north commando) and at the top and the using plates attached to the cradle. not easy. now to the forks. 75 commando forks are attached to the gpz headstock by changing the bearings to fit the gpz and the triple clamp. the norton triple clamp is lengthend to match the headstock. last but not least is the front wheel. offset is ancient. a triumph disc brake hub is modified by changing the bearings to match another axle from a 750 gpz. the wheel has no offset. brake rotors from a kz400 are reduced to 10.7 dia and 4 holes are drilled to match the triumph hub. the fork sliders are reamed to fit the axle. another disc brake slider is fitted in the reverse position. all along the plan is to have a double disc front using norton calipers. the setup is similar to those on slippery sam. by using the modified triumph wheel the calipers do not interfere with the spokes. I have a slippery sam double disc setup on my 73 T150V. PS I didn't get much response on mt rear wheel solid axle and I don't expect much from this blurb. nevertheless it can be done. and I have a monoshock triple disc commando. cheers
Click to expand...
 
Depending on the trail on the steering, the bike can have less lean in corners and need less tread on the road. I would always have the motor as far forward as possible. When you accelerate, you tend to lift the motor - if the front end is light, the feel of the bike can cause you to back-off.
 
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