Featherlastic commando

But, wasn't this all already done with the Atlas? :roll:
Fritz

bad_friday said:

But, wasn't this all already done with the Atlas? :roll:
Fritz

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Not 100% sure if I have read you right here or completely misunderstood you.

The Atlas engine in the Featherbed frame was angled slightly backwards :!: ( Of all things)
Also there was a discussion that the guy who balanced the cranks just drilled holes in the crank randomly :!: :shock:

Bernhard said:

…The Atlas engine in the Featherbed frame was angled slightly backwards…

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Of course, it was rigid mounted. But, it's nearly the same engine. Isn't it?
Fritz

The 850 engine has more cubes, of course.
One of the torquiest motors in recent british motorcycling...

Yes, and the Atlas was renowned for shaking itself to bits and giving the rider numb arms due to the vibrations.

The 650SS, although a smaller displacement engine, was widely regarded as being an all round better bike to ride.

gtiller said:

Yes, and the Atlas was renowned for shaking itself to bits and giving the rider numb arms due to the vibrations.

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Not all of them though. ?

There has been much chitchat recently that AMC apparently contracted out the crank balancing,
and the man doing it may have been somewhat haphazard shall we say about how it was done.
So only some of them were correctly balanced.

Even when they were new, some owners claimed theirs was smooth, and others were shockers.
Or maybe the correct word there is 'vibrators'.

Several owners here have recently reported that their 850-in-featherbed wasn't anything like that,
reported in the past day or so, in other similar threads....

texasSlick said:

........Then, there is the problem of the rear chain getting stretched if the engine is allowed to move due to vibration, but the swingarm is rigidly mounted to the frame........Slick

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+1.....this is not such a problem if you are just putting around, however if you get on the gas and then shut the throttle, then get on it again etc...it becomes a problem. the engine / gearbox movement has been noted to be "unsettling".

Hi All,

When I decided putting a 750 Commando engine in place of the 600 cc 99 in my Slimline chassis, I considered different solutions to cope with the vibrations issue.

The sexiest one was to build a Featherlastic but after a few mails with Bob Cox and Mike Harcourt, I gave up because there was no way for me to build or buy the Iso cradle and plates etc...

Finally, I opted for Jim Schmidt's longer rods and lighter pistons (plus a few other parts: camshaft and tappets) without changing the standard balance factor and I'm very pleased with the result. Almost no vibes or very slight ones up to 5000 rpm, a bit more between 5000 and 6000 but quite acceptable (clear image in the mirror & comfortable riding).
You don't feel the vibes in the footrests neither in the handlebar or seat. They are transmitted by the fuel tank only so it's not really annoying.
No crack nor loose nut or other sign of damaging vibrations after about 10 000 miles of use.
Carburation and timing settings are very stable.

And there are other testimonies here or in other forums to illustrate how good Jim's products are.

Hope it helps.

Laurent

So, just to be clear, you used the standard Commando balance factor ?
Is this engine upright or inclined ?

And fitted Jims lightweight pistons and rods - and rebalanced it still at the standard factor.
Or just fitted the lightweight bits and left the balance untouched.

If you replace the stock rods and pistons with Jim's lightweight kit, and don't rebalance the crankshaft, the BF only changes by a few percentage points. When I did the calcs using the average weights I've measured over the years for stock parts, compared to the weights of one of Jim's 750 kits I bought quite a while ago, the BF only changed from the stock 52% to 56%. The weights of the stock parts varied some over the years, and so might Jim's kit, so that's not a precise calculation, but probably accurate within 1% or so. Probably not enough to notice. That's actually kind of convenient, because you can get the lower force from the lighter reciprocating weights without the bother of re-balancing. On the other hand, if you were doing this to a Commando engine, and then mounting it in a featherbed frame, I'd think you would want to re-balance the engine to a higher BF anyway. But then that's what this thread is trying to sort out, isn't it?

Ken

Hi Rohan and All,

The engine is tilted forward as in a Commando frame.

I did not re-balance the crank after fitting Jim's parts. As Lcrken explains, the impact of Jim's rods and pistons on the BF is a matter of a very few percents only and Jim told me not to bother about it.
And he was right.

Rohan : I sent you a PM yesterday night about the UXG 126 Deluxe dommie.

Laurent

Hi Laurent, it is a small world.

Google these days snaffles and collects pics, and will show them in a search.
Anything shown here goes straight into googles' collection.
Along with everything else they hoover up from everywhere. !
Cheers.