More weights

I weighed my friend's 71 750 frame yesterday. The bare frame weighs 26 pounds 8 ounces.
I then weighed my new to me Mk3 850 frame. Much has been written about the massive weight of these bikes, and of course it's bunk. It's the same old bike with a few pounds of strength added in key places plus an estart.
The bare MK 3 frame weighs 27 Pounds 2 ounces, just 10 ounces more than the 71 750 frame.

worntorn said:

...The bare MK 3 frame weighs 27 Pounds 2 ounces, just 10 ounces more than the 71 750 frame.

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Commandos are a nice light bike. Whach gonna build with that "new to you" MKIII frame, Mister? :mrgreen:

Slowly gathering parts right now CJ. Hoping to do a Superleggera Commando, but I'm not sure how Super or how Leggera it will be.
The front fork is going to be a Showa Big piston from a 2013 Gixxer 600. I have the same fork on the Thruxton R and really like how it works, plus it is a lot lighter than the stock Commando front end.
The Big Piston fork has anti dive technology so that even when the brakes are banged on fairly hard, dip is minimal. Anti-dive forks were tried in the 90s then abandoned due to excessive weight and complexity.
Showa seems to have figured it out, this is one of the lightest fork sets built today. As far as handling the bumps, Triumph claims it out performs the high end Ohlins, that is why they put it on the front of the R and Ohlins shocks on the rear.

Not too sure about the rest of the bike other than it will be a 920 with MK3 crankcases and crank.

Glen

worntorn said:

Slowly gathering parts right now CJ. ....Not too sure about the rest of the bike other than it will be a 920 with MK3 crankcases and crank ......Glen

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I look forward to seeing your creation take shape :mrgreen:

worntorn said:

I weighed my friend's 71 750 frame yesterday. The bare frame weighs 26 pounds 8 ounces.
I then weighed my new to me Mk3 850 frame. Much has been written about the massive weight of these bikes, and of course it's bunk. It's the same old bike with a few pounds of strength added in key places plus an estart.
The bare MK 3 frame weighs 27 Pounds 2 ounces, just 10 ounces more than the 71 750 frame.

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I don't think anybody ever claimed that the frames accounted for any significant weight difference between a Mark 3 850 and a 750. Does anybody have any credible total weights, either wet or dry, between the two?
This source: http://www.motorcyclespecs.co.za/model/ ... 3%2075.htm
says the 750 weighed 440 pounds and the Mark 3 weighed over 500 pounds.

Stephen Hill

The 500/440 numbers are wonky in that there isn't sixty pounds difference between the bikes, but that is par for the course.
At the moment I have most of an 850 MK3 in bits and my friend has all of a 71 750 in bits so we spent some time yesterday recording weights of various items.
Other than the added weight of the start and drive, there isn't much in it, just a few ounces here and there, all used for added strength or rigidity.
For example ,the 71 swing arm weighs 7 pounds four ounces and uses 1 3/8 tubing, unbraced at the crosspiece. The early 850 swing arm had gussets added to the cross piece. The MK3 swing arm with 1 5/8" tubing and large rectangular cross looks huge and heavy next to the 71 swing arm. Actual weight difference is only 3 ounces.

My fully assembled MK3 weighs 448 with oil and battery but no fuel. We will weigh the 750 in the same state when it is complete. I'm guessing it will be in the 415-420 range.

I suspect the "overweight" reputation of the Mark 3 came from a combination of things, including:
-the added weight of additional components
-reduced power from larger gearbox sprocket, restrictive airbox and exhaust, and change in internal gear ratios
-going head to head with lighter and/or more powerful Japanese bikes of the day

Stephen Hill

So is this frame weight without the engine/trans plates, Isolastics and swingarm. Did the frame have the head bearings installed when you weighed it? Just trying to get a concise picture of this.

I always thought of a Commando as light and well designed.

I seem to recall the Colin Seeley Mk2 frames weighed in at about 23 lbs and I think that included the swingarm but doubt it included the engine plates as the plates varied from engine to engine

The head stock bearings are in place, other than that both frames are bare, no isos etc.


Stephen- agreed, the heavy and slow rep likely does come from the way the bike was factory equipped. The quiet mufflers alone sapped a lot of power. The weight was blamed and much exaggerated numbers were floated about. It appears the weight dif is hardly a factor. I don't expect any of the owners of earlier bikes will feel any noticeable on road decline in performance after adding an estart.


Glen

Also, the difference in frame rake between the 750 and 850 might give the "heavy" theory weight.

Pun intended.

Hi Glen

In 1976 when I brought my new 74 850 Commando there was only 2 74s left in Brisbane but there were a few newer 75s I decided to go with the lighter 74 kick start Norton as by the brouchers the Mllls were 45 lbs heavier, I still have these brouchers but are now framed and hanging on my shed wall, I went with the 74 because being lighter and $400 cheaper at the time, being 17 years old money was tight in them days.

45lbs really not much differance, the extra weight being down low on the bike, the handling would be much the same, I was also told at the time that the ES was more of a kick start helper, press button and kick at the sametime, but we all know there are a lot of upgrades to the ES system to make them work better than when they first came out from the factory.

Ashley

gortnipper said:

Also, the difference in frame rake between the 750 and 850 might give the "heavy" theory weight.

Pun intended.

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If you use an anti-dive front end, won't that affect the way the rake changes as you brake into corners and alter the handling ?

If you are braking going into a corner, yes, but once you are in the corner, not many riders brake on the front. Gp riders trail brake to load up the front suspension but they have anti everything on their bikes. Anyway, who mentioned anti dive?

Stephen Hill said:

Does anybody have any credible total weights, either wet or dry, between the two?
This source: http://www.motorcyclespecs.co.za/model/ ... 3%2075.htm
says the 750 weighed 440 pounds and the Mark 3 weighed over 500 pounds.

Stephen Hill

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Can only speak for my own MK3. As weighed on a NASCAR scale at New England Motor Speedway - 475 LB with about a gallon short of a full Roadster tank, But with original tool kit.