MKIII style headsteady well sprung

geo46er · Oct 25, 2011

Greetings,
In the current thread "Can a Norton engine to made to run without vibration" Jim "Comnoz" said, "The rubber biscuits in an isolastic mount are about as close to hanging in space as you can get without doing away with gravity.". So I was wondering what would happen if someone used an MKIII style headsteady with a couple really stout springs, strong enough to take some serious weight off the iso biscuits. I know last time I checked my isos it was clear that the bottom of the biscuit was somewhat compressed. I know that there is probably not enough room under the tank for the size spring it would actually take to suspend the engine. I was wondering if anyone has ever tried a good stiff spring(s) and what were the results?

GB

swooshdave · Oct 25, 2011

Isn't the headsteady spring suppose to suspend the engine?

grandpaul · Oct 26, 2011

In theory, the Mark III headsteady spring, properly adjusted, results in the two rubber bisquits being neutrally loaded.

comnoz · Oct 26, 2011

grandpaul said:
In theory, the Mark III headsteady spring, properly adjusted, results in the two rubber bisquits being neutrally loaded.

In theory yes, in practice no.

Brian Slark told me once that the original design for the isolastic mount used a stainless steel mesh spring of some type instead of rubber to suspend the engine. He said it worked very well but was to expensive to produce. I have not seen this setup and don't know how it was done. Jim

cash · Oct 26, 2011

In theory yes, in practice no.

It works well for me and a few others.

Cash

swooshdave · Oct 26, 2011

comnoz said:
grandpaul said:

In theory, the Mark III headsteady spring, properly adjusted, results in the two rubber bisquits being neutrally loaded.

Click to expand...

In theory yes, in practice no.

Brian Slark told me once that the original design for the isolastic mount used a stainless steel mesh spring of some type instead of rubber to suspend the engine. He said it worked very well but was to expensive to produce. I have not seen this setup and don't know how it was done. Jim

Because the headsteady spring is adjustable (I think it is) then you could get the spring to take the load and result in a neutral balance. I suspect this could be validated by handing the engine from the spring with no isos installed. Correct?

comnoz · Oct 26, 2011

cash said:
In theory yes, in practice no.

Click to expand...

It works well for me and a few others.

Cash

I can't say I have researched it much but I do know that on both of my MK3s the front isolastic sacked out and was hanging low after a couple years even with the spring. The adjusting stud broke off on my injected bike recently. It had been tightened about as tight as it would go. I simply removed the remains and couldn't tell the difference in vibration so I did not bother to fix it. Jim

grandpaul · Oct 26, 2011

swooshdave said:
Because the headsteady spring is adjustable (I think it is) then you could get the spring to take the load and result in a neutral balance. I suspect this could be validated by handing the engine from the spring with no isos installed. Correct?

Yes. You should be able to pull the front mount bolt with ease.

rx7171 · Oct 26, 2011

When I look at the springs that I got with my Dave taylor head steady it is hard to imagine they are capable of really carrying the full weight of the front half of the engine.
I suspect they are more to help adjust the resonant frequency of the moving engine through adjusting the tension on them with the adjusting nut.
The net result is most of the weight of the engine is carried by the rubber of the isos.
Has anyone investigated the load capacity of these springs at various extensions?
In addition since they are angled at maybe 45 degrees the vertical component of the force that lifts the engine will maybe be half of the springs actual tension load.

JMHO

Bob

xbacksideslider · Oct 26, 2011

Does the spring pull at the right angle to take all of the load off of all of the isos?

It's complicated. The weight of the frame/seat tank pushes down onto the engine/trans/swing arm/wheel by way of the two isos and the head steady while the front wheel/forks carry some of that weight directly.

So, what is the spring doing? I can envision the top of the rear iso as an axis for the engine/trans/swing arm lever that transmits a down load onto the front iso and that is what the spring then offsets.

grandpaul · Oct 26, 2011

I can tell you this: on my '75 Mark III 850, when it's adjusted right, I can pull out the front iso bolt easily, and re-insert it just as easily.

rx7171 · Oct 26, 2011

grandpaul said:
I can tell you this: on my '75 Mark III 850, when it's adjusted right, I can pull out the front iso bolt easily, and re-insert it just as easily.

Then it does carry the engine weight. Thanks

Bob

rick in seattle · Oct 27, 2011

A very robust discussion of the MK3 head steady is at

mk3-head-steady-adjustment-t8299-15.html

The 0.5 inch spring extension provides a total (two springs in parallel) of 145 lbs of tension along the jug angle (be sure to attach the spring exactly as shown in the manual to preserve this angle). This approximately unweights the cradle, as others have stated on this post. New springs are cheap and available.

comnoz · Oct 27, 2011

Well I bought new parts to fix mine when it broke, including a new spring, guess I will have to make the time to install it. Jim

MKIII style headsteady well sprung

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