A: The rubber is there to provide comfort. Without it the vibrations will loosen your fillings and give your missus a 'good ride' on the pillion seat.

B: I'm not sure whether the frame was designed to allow the engine to be mounted solidly. I'm not a frame designer so I can't comment on whether there'd be any of those issues.

However, it is not unknown for certain racers to change the rear isolators to solid, but I've not seen it personally, nor have I actually spoken to any of these people and I've not seen any data on it. Bit of an unknown territory. Its probably best to speak to a professional frame build like Briz from Custom Cycle Developments first before you consider doing this.

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Illegitimi non carborundum

Thanx for that!

Well it won't have a pillion seat so tough shit for the missus!

My last Harley was a hardtail with solid mounted engine and even solid mounted handlebars with tape for grips and that was fine!

The rear isolators....do you mean the discs wich also secure the swinarm?

If so: those have already been changed to solids on my bike

It would be easy for me to convert the frame to solidmounted IF the same rules apply as to my Harley...as I did myself as well.

Ideally, wouldn't the crank need rebalancing to suit the dynamics of what would be a different frame?

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If your dreams don't scare you, they are not big enough.

Got a fresh engine sat here with a dynamically balanced crank!

Is it balanced to suit the properties of the frame you're proposing? EG a TriBsa will have, ideally, a different factor to a Triumph using the same motor.

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If your dreams don't scare you, they are not big enough.

You've lost me there....

I've swapped quite a few engines over in my years of tinkering but never had one balanced to suit the frame??

I replaced a knackered front isolator on my XB12S last week. 2 days later I knocked 6 seconds off my fastest lap time at the track, which I hadn't come anywhere close to for nearly 2 years. Co-incidence

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Wear the fox hat

A solid mount is not quite the same as a knackered rubber mount

I don't think those 6 seconds are coincidental though!

I agree, I only had intermittent pain

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Wear the fox hat

Dave Degens (of Dresda fame - he pioneered the early years of TriTon building, along with the chassis guru, Tony Foale, have written papers on this.
The Norton factory also changed the balance factor of their cranks on the same motors when production changed from using the 'Garden Gate' frame and went on to use the Featherbed frame.

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If your dreams don't scare you, they are not big enough.

I think that what Adam is saying is that a heavyweight Harley type frame will absorb vibrations better than a lightweight Buell frame - and have a different resonant frequency, therefore altering the Engine's balance factor to suit can produce a more harmonious running bike.
Additionally, as Mich says a Buell frame is not designed to resist the vibration solid mounting would cause as it doesn't have to normally - as a result it can be a lot lighter than it would otherwise have to be in order to stay durable.
Finally, as Buell engines give of their best at the upper end of the rev range I can't begin to understand why people ever even think of using them solid mounted

Well in my case the Buell is a custom project.

Ideally I'd like to solid mount the engine so I can alter the frame in the fashion I like wich means doing away with the rubbermount and all the rosejointed crap.

Now the average Harley frame isn't that much heavier if you take into consideration that you'd have to deduct weight for integral non-swinging swingarm

Besides: the Buell frame would be way more rigid.

I think with some good sturdy enginemounts there really is NO problem rigid mounting the engine!

It's very little to do with the gross weight of the frame. When the Rickman Bros built the Mettise, their cranks were balanced to the same factor as people had done when building TriBsa's, since the Mettise frame is similar geometry to that of a late A10 frame. This prevented cracking around the headstock. I don't know for sure, but I expect there's very little difference in weight between a BSA and a Triumph frame.

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If your dreams don't scare you, they are not big enough.

I think I should have said the weight of the bike in my previous post as it is the total mass of the bike helping to reduce vibes not just the frame. In that respect an HD is much heavier than a Buell whatever the frame alone may weigh.
Thinking of older bikes I often consider the Commando to be a cousin of our Buells as it's anti vibe system was similar in many ways. They had to mess with the resilience of the rubbers to acheive durability - which meant some vibration getting through - and "tuned" them to restrict the vibration to idling and sub 2500rpm running where it was deemed the least intrusive to riders.
Interesting about headstocks Adam - dunno about you, but I never hold the bike on the front brake whilst idling as the vibration really increases on mine.

Yea, I've always thought the Doug Hele? designed Norton Isolastics were similar to the Uniplaner system of Buell. I'll bet Erik noticed that too The later vernier adjusters worked quite for a // twin which is much harder to balance than a V.

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If your dreams don't scare you, they are not big enough.