Road test 1973 refers to preload on top mounts

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kommando

kommando

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This is a transcribed road test from 73 on what must be a MK1 850, when talking about the isolastics its says.

The 850 vibrates quite a bit at engine speeds below 3000 rpm, but this can be all but taken away by putting a preload on the top motor mounts. This is done merely by installing the proper thickness washer under the allen screws in the top mount. This will be done by the factory on later machines but for those of you who buy an early model, your Norton dealer should have the necessary information by the time this test is printed.

http://www.motorcyclespecs.co.za/model/ ... 0%2073.htm

Seems like before they added the suspensory spring on the MK3 but before they came up with the spring they had this other idea, anyone recognise this mod, not that I'd use it but out of interest.
 
kommando said:
anyone recognise this mod,
Click to expand...


Service Release N3/51, May 1973

EXPLANATION:
It has been established that residual engine vibration can be minimised, particularly at low engine R.P.M. by taking particular care in the method of assembly of the head steady to the cylinder head, and to the frame engine steady rubber mountings.

ACTION:
Place the machine on the centre stand. Remove the fuel tank. Remove the cylinder head steady. If not already fitted, fit the box section head steady 064179 (see Service Release N3/38) utilising a flat steel tank washer 014999 1.25 in. (31.75mm) O.D. x .328in.
(8.33mm) bore x .080in. (2.031mm) thick under the head and spring washer of each of the two outer engine steady to head socket screws.

The flat washers locate the head steady in its most forward slot location. Assemble finger tight only.

Offer up and assemble the two engine steady side plates and studs, washers and nuts onto the frame engine steady rubber mountings. Some pre-loading may be necessary due to the new forward location of the head steady. Tighten up the two lower side plate stud nuts. Tighten all the remaining screws and nuts progressively and in sequence, which will then pre-load the engine steady rubber mountings, with those nuts being tightened last.

Important Note:
For optimum engine vibration insulation, it is recommended that the stipulated 0.010in. (0.25mm) Isolastic mounting clearance is set to provide 0.005in. (0.13mm) per side when at rest, without any side load pressure being applied.

The above procedure will ensure that the engine will be provided with the correct support under riding conditions.
Click to expand...
 
Thanks for that, wonder if it actually works, will look at the box section head steady and see if it makes sense.
 
Already updated my 750 to box-section head steady many moons past when I restored mine due to original being cracked/unwell. Plus it was almost free at a swopmeet. Very interesting post, will re-read when sober and investigate. Then drink more if successful. Man, I love this forum and my Commando, am I sick?
Cheers, Martin
 
Important Note:
For optimum engine vibration insulation, it is recommended that the stipulated 0.010in. (0.25mm) Isolastic mounting clearance is set to provide 0.005in. (0.13mm) per side when at rest, without any side load pressure being applied.
Click to expand...

Wow! Would be really nice to be able to go down that rabbit hole. So many ways for a Commando isolastic to get out of kilter. It is challenging enough to get a reliable feeler gauge reading on an isolastic on one side only. Not saying not to strive for this.
 
When I installed my DIY heim joint headsteady on my early 750, I got the parts and also installed the 850 spring. Reason was, I never put the covers on my iso ends and I noticed that the front iso bolt while the bike was on it's tires was about 1/4" below center, the engine weight was pulling it down. The spring pulled it up to near center, but I had to tighten the spring up as much as I could. Noticed it also brought the rear iso back closer to center than before where it was a bit forward. I did notice that the idle vibration nearly disappeared, didn't do much on the road that I could tell.

Comnoz uses a valve spring under the engine, same effect, get the engine weight off the isos.
 
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