Commando motors in Featherbed frames or other frames

Hi All,

I switched from a 600 cc Dominator to a 1972 750 Commando engine in my Featherbed slimlime chassis a few months ago. I got plenty of advices from this forum and from other guys who had done it.

I used 8 mm 4G / 2017 alloy (I don't know to which grade it corresponds in US - UK standards) to build the gearbox and engine plates. I designed them so that the engine is "as low and as forward" as possible. I was a bit concerned with the possibility of re-using standard Commando exhaust pipes and being able to take off the cylinder head whilst keeping the engine in the frame, but all went well.

The most complex issue was with adapting the central and side stands to the new plates. Lots of drawings / measurements / cutting & welding but no unsolvable problem.

Re: the solution to keep the vibrations within acceptable range (ie keeping only the good vibes!), I started with the most attractive one (Featherlastic) but the guys who did that in the US (Mike Harcourt, Randy Ullery, Ron Fraturelli) could not help me and I felt not able to make it properly on my own and starting from scratch.

Then I considered having all the moving parts carefully dynamically re-balanced but I opted eventually for Jim Schmidt's longer rods / lighter pistons / standard camshaft package and I am very satisfied with the result. From my experience, vibrations are lower than when I had a 500 cc / single carb engine. The engine power curve is very pleasant and fits exactly my type of riding.
Furthermore, Jim is very reactive and very helpful.

With about 4000 miles of experience with that engine now, no broken plate neither loose nut nor any damage caused by vibrations.

L.

Nice report, L. Any chance of pictures showing the details?

Ken

Ken, I was just looking at the 2007 version of your bike. I think when I find some money again I will have to build one of those, it looks so correct. I notice you ended up with a two into one exhaust system, I love the one on my Seeley. Your bike looks simple, functional and deadly - I could really do some damage with that.

Is there any video of it racing ?

L, Tritons often run balance factors up to 80% and spin to 8,000 RPM. Your motor has a heavier crankshaft and if it is balanced to 72% is probably swinging a bigger counterbalance. When my Seeley 850 is idling it actually rocks backwards and forwards due to that balance factor. As soon as I start to ride it the roughness disappears . You obviously could not sell a production road bike which did that, to commuters who had the choice of buying a Honda CB 750. However the problem is minor and certainly not intolerable. If I was buying a British big twin in the 70s, I would have expected it to be rough low down in the rev range. The trouble was that the market had changed and customer expectations had become based on what the Japanese could supply. My feeling is that Ken's 2007 racer is brilliant. It is worth bearing in mind that one definition of the word 'quality' is - 'fit for purpose with obvious attention to detail'. Ken's bike fits that perfectly. The 'purpose' is road racing in a particular class, 'attention to detail' - it is perfect. So I suggest you have to think about your intended purpose for your bike, compromise bikes often suit neither purpose very well.

acotrel said:

Ken, I was just looking at the 2007 version of your bike. I think when I find some money again I will have to build one of those, it looks so correct. I notice you ended up with a two into one exhaust system, I love the one on my Seeley. Your bike looks simple, functional and deadly - I could really do some damage with that.

Is there any video of it racing ?

Click to expand...

Thanks, Alan. I kind of like the looks of it myself. The exhaust is a Steve Maney item, which I liked for it's good mid-range power, more useful on many tracks than top end power. For long tracks like Daytona I liked the twin megaphone exhaust better. This shot shows the Maney exhaust in more detail.



Sorry , no videos. The ubiquitous Gopro cameras hadn't been invented yet back when this bike was raced regularly. Best I can do is this shot of me on it back in '93. It still had the Rickman forks (later outlawed by AHRMA for the class) and Axtell megaphone exhaust system.



Ken

Ken, Do you still own the bike ? Just looking at it gives me the urge. I'm really sad that you have no video of it racing, I'd love to see it being used in anger, it is a most inspiring bike. If I'd had that in 1970 I'd have really blitzed my main rival. Everything about it looks perfect.

About that exhaust - mine is similar however goes under the motor. I used the Maney configuration on my 500cc Triton and ended up with a second degree burn on my ankle from one race. My boot heated up and I couldn't get away from the heat. It looks at though my exhaust system has skinnier header pipes. I've matched their ID to the exhaust stubs ID. My tail pipe has the same cross sectional area as the sum of the headers. I've advanced the 850 cam 12 degrees to compensate for the pipe, so it is very loud however it really works well.

Ken,
I was wondering if you could tell me what gas tank that is. Sure looks very nice.
Thanks
Jeff

The gas tank looks like it is a Lyta, They are still being made, I found one years ago on a Suzuki two stroke racer, bought it and used it on my 500cc Triton. They were the good gear on Manxes in the early sixties. All the A graders had them.

Acotrel,
I haven't seen 1 decent copy of an original Lyta tank, ever. I'd certainly love to find one for my own wideline.
Jeff

There was a guy making them at Kinglake near Melbourne, Australia. I think he might still be there, however the bushfires went through so I cannot be certain. I'll ask around and if he is around, I will let you know. His tanks looked slightly taller but still close to the original to me.

P.S. Just spoke to a friend, and he says the guy is still around somewhere and he was talking to him recently - charges $1000 for a tank regardless of what it is - takes a week's work. I will find out where he is.

John's Classic Bike Tanks
Kinglake West, Victoria, Australia
phone 61-3-5786 5198

http://classicbike.com.au/cms/links/19- ... urces.html

wilkey113 said:

Ken,
I was wondering if you could tell me what gas tank that is. Sure looks very nice.
Thanks
Jeff

Click to expand...

It is an original Lyta. I visited the gentleman who made them on a business trip to England back somewhere in the late '80s, and had him make the one shown, plus a short circuit tank for a Manx I was planning to restore and race. His name was B.G. Hichisson, and he built the tanks in the "garden shed" in back of his home in Dartford. He gave me a great tour of the shop, and explained how he came to be in the business in the first place. He learned the trade in the service, Royal Air Force, I think. After the war, he started making tanks for race bikes, and rapidly became popular with racers, including some of the factories. He told me that when the demand for special tanks died down he'd quit for quite a while, but with all the interest in classic racing at the time, had gone back to making them again. He had patterns for tanks hanging from the ceiling with some very famous names on them. He welded them with an oxy-hydrogen flame, because it was a bit cooler flame than oxy-acetylene, and didn't have the yellow glare that makes gas welding aluminum so difficult. He was a really pleasant fellow, and I really enjoyed the visit. I really doubt if he is in business today. He'd be getting along in years if he was still around.

There are several people now making similar tanks and calling them Lyta or Lyta Style tanks, but I wonder if the quality is up to the originals. They were really beautiful.

Ken

I think I must have a critical eye. Most of the Lyta copies I've seen in recent years look a bit too peaky at the top. I know how they looked in the old days on the A graders' bikes. I know I'm getting on a nostalgia kick, however it is about 'attention to detail' and most people don't seem to know what the detail looked like. I know the old days can never be recreated, however I feel we should try to have our bikes at least look authentic, if we are doing the historic racing thing - otherwise they just become 'paddock bikes' of the sort used for scrub bashing by grubby little kids.
Ken, I absolutely love your bike, it looks like the real deal. I recognize it.

You'll get to see this one soon Ashman. The primary chain guard is at the welders right now getting covers on the clutch and alternator. The it's done.




I bought the rolling chassis in 1984 and was given most of the engine by a friend. I made the engine mounting plates myself and had always assumed it was a 750 Commando. Only recently did I check the engine number to find it's a '64 Atlas. I knew the engine came from a rigidly mounted frame in a drag race bike, so I just ran it and never checked the crank balance. It's nice and smooth. It supposedly has all the wrong parts in the oil system: low pressure pump, scrolled rocker arms, vent holes in the conrods, but it's been raced for decades and never had a major failure. My only worry is that maybe the fact that on the race track it's screaming it's nuts off so always has good oil pressure. Now I'm going to use it on the road maybe it will be a problem if I'm just cruising along?

Looking good John and look forward to meeting up with you.

Ashley

John, that is a great looking bike...just wondering what the tank is? Looks really neat on your featherbed!

Nice indeed John. Can you tell us a little bit more about the triple clamps, exhaust headers and megaphone mufflers?

I think that with the normal yokes on a featherbed frame with 24.5 degree rake, it is difficult to make the bike steer quicker and tighter than beyond being fairly neutral. I'd be interested to know how much offset is there on those fork yokes, and how the bike steers under power - whether it inspires confidence or feels vague ? What size wheels are you using ?

Jagbruno said:

John, that is a great looking bike...just wondering what the tank is? Looks really neat on your featherbed!

Click to expand...

The tank was hand made by a guy called John Pearson in the UK. He was well known for making alloy tanks... he made the Gus Kuhn pannier tanks on their BMW endurance racers.
It was many years ago and I don't know if he's still around.

Dances with Shrapnel said:

Nice indeed John. Can you tell us a little bit more about the triple clamps, exhaust headers and megaphone mufflers?

Click to expand...

The triple clamps are solid blocks of alloy. They were on there when I bought the bike as a rolling chassis. They are obviously hand made. I'll take a photo later to show them better.

Jim Cray ( who mainly tunes BMWs ) made the headers . He made them the same way most of us do by buying mandrel bends and welding them together to get the shape you want.

The megaphones are copies of Supertrapp megaphones. I used to have a pair of stainless Supertrapps but I had a big crash and damaged them quite badly so I cut them open, pulled the baffles out and got a local fabrication company to roll up a pair of megaphones to fit the baffles into. Only thing is that they couldn't do it in stainless for some reason so I had to paint them.