New project, need some opinions

acadian said:

from our event last weekend, Pete McKenna's bike upright in a slimline frame

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I like this bike, it looks honest and correct. One of my mates said to me 'at least your bike looks right'. What I did not tell him was, I could not have built it an any other way. What I have learned about this type of bike has come at the price of pain. It took a year until my chromo clavicular joint had a enough scar tissue to stop hurting. I had to use my left hand to put my right hand on the steering wheel of my car to drive to work.

jseng1 said:

The big end of the stock rod weighs 343 grams. The big end of the JSM long rod weighs 326 grams.
Total weight of stock rod 420 grams Total weight of JSM ultralight long rod 401 grams, std JS long rod total weight 431 grams

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I went by LCRKen's measured weights, that was 390 g total weight for the stock Norton rod, and the same 431g for your std long rod.
The 389 gram stock 850 rods that went into my 920 almost matched Ken's 390 gram number, so I think it's a good one.
Many of the numbers in your " Correction Post" appear to be incorrect.

Re the country of Manufacture mention- China etc,
MAP pistons are listed as manufactured in U.S.A.

Glen

acotrel said:

If I was going to go a step further with my 850 motor, I would buy Jim Scmidt's long rods and 12 to 1 comp. pistons. His pistons probably have slightly domed crowns to get the comp. But I doubt the crowns would be high enough to be adverse. I would also buy a programmable ignition system, and work on developing a curve for more torque. It is easy to get more power by revving the motor higher. But with a Commando engine, that is probably the wrong way to go. What I found with the 850 engine is it took longer to learn how to use it properly. It did not really go until I used close ratio gears to ride the torque. With close gears, the power never drops out the bottom. It stays between 5,500 RPM and 7,300RPM. The overall gearing becomes much higher.
With my first race bike, I had the opposite problem. I was always looking for ways to help it pull harder at low revs. It desperately needed 6 gears, and I never had much money to spend on bikes. I liked that bike, it was a thrill-a-minute, but deadly.

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Flat top raised crown pistons in an 850 set up with a .040” squish clearance will give you around 10.5:1. So to get 12:1 you would need domed pistons, how much dome would require some calculating, but as you say, it’s unlikely to be big enough to cause any flame path issues.

I built (3) 880s using the JE dished pistons with gapless rings, all very similar with ONE exception - the one different one used the Megacycle 560-00 cam with radiused lifters.

That was the only Commando I've ever been able to wheelie on simple throttle application.

No 750 I built could ever do that, had to pop the clutch.

worntorn said:

I went by LCRKen's measured weights, that was 390 g total weight for the stock Norton rod, and the same 431g for your std long rod.
The 389 gram stock 850 rods that went into my 920 almost matched Ken's 390 gram number, so I think it's a good one.

Re the country of Manufacture mention- China etc,
MAP pistons are listed as manufactured in U.S.A.

Glen

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Yes I checked a complete Stock Norton rod and it's 395 gms (rather than adding up the big and small ends I had written down and will have to go through again).

MAP also says that they are the manufacturer of the pistons. But MAP doesn't make pistons. Tell me what you can about the actual name and location of the MAP piston manufacturer.

MAP also says they are the manufacture of their rods. Their description says "Finite element analyses design by High Cotton MotoWorks..."

About "High Cotton" that provides the MAP rods

“Started a small vintage motorcycle parts business based in Chongqing China. Responsible for all of the design/engineering work. Also responsible in directing other purchasing agents in the procurement of the vintage motorcycle components. Have designed and supplied US based distributor with forged connecting rods and various intake manifolds. The connecting rods were designed complete with FEA analysis. Manifolds were designed using CFD analysis. Looking into expanding into the procurement of specially design crankshaft and cylinder heads. Parts are being sourced from different suppliers around various parts of China.”

Not an 850 engine, but having used stock rods and pistons, JSM and MAP log rod and pistons sets in a 750, I'd say it is hard to tell much difference between the long rod sets. However, both long rod sets are better than a stock engine with all factory parts and a factory crank balance. An engine with stock rods and pistons, a "rebalanced crank", and a spicey cam is pretty hard to beat though.

All of those configurations started out quiet and all of them ended up being noisy Norton.

My preferred setup was with the JSM parts, but the bore was +.040 and the pistons higher compression.

Forgot to mention JSM rods are a little longer than the MAP rods and the pin moved up in the piston to compensate. JSM rods are an improved design IMO, but I'm no closet engineer.

JS wrote - "MAP also says that they are the manufacturer of the pistons. But MAP doesn't make pistons. Tell me what you can about the actual name and location of the MAP piston manufacturer.

MAP also says they are the manufacture of their rods. Their description says "Finite element analyses design by High Cotton MotoWorks..."



Note that the MAP pistons for stock rods are listed as " Manufactured in USA"
I take that to mean they are manufactured in the USA.

MAP long rods are not listed as manufactured in the USA. They are listed as manufactured by MAP. I would take that to mean they are not made in USA, but likely made in somewhere in Asia.

Glen

Sometime around 1972 I acquired a bent Commando, maybe a 1969 or '70, along with a 1964 or maybe '65 Atlas with a blown engine. With no knowledge or expertise of any kind, armed with nothing but basic tools I did the obvious. I simply bolted the Commando engine into the Atlas. I can't remember what I did about the top head steady, but for the rest I just used the Atlas engine plates so my engine was vertical. I had no idea or concerns about oil pickup. The first iteration I used the Atlas primary components, but the clutch slipped quite regularly. I then took the Commando primary and drilled three new holes to suit the vertical engine. I epoxied the originals and went on with further hacking. I created quite the buzzing anvil with no rebalancing of any kind.
Since Ashman built a smoother runner, I have to suggest you follow his lead. My contraption had a 19 tooth sprocket and accelerated really well. However, I recall burning out lights constantly, and at some speeds it was very difficult to keep your feet on the footpegs. At least once I suffered a broken bracket that was holding a muffler on. It was at least 1/8" thick. It was all I had for transportation for a time. Unfortunately I let the oil get low and broke a connecting rod and put a hole in the cases. I still own the frame and much of the engine, including the cases with the hole welded up.
If I ever finish my long suffering and neglected '72 Commando project I plan to lay out all my remaining parts and see if I can build another viable bike. Best of luck with the project!!

For people who were around British motorcycle in the 1960s, a lot of things do not present real problems. Read Phil Irving's book 'tuning for speed'. One thing I would say - if you are fitting a vertical twin motor into a featherbed frame, the wheel size determines where the motor needs to be. If you are building a Domiracer type bike which has 19 inch wheels, the motor needs to be as far forward as possible. If you must have 18 inch wheels - the motor an inch further back might be better. The latter handles pleasantly , but cannot be as fast in corners with a lighter front. With 18 inch wheels and the motor forward, the bike can be tiring to ride, even if it corners better.
A 500cc Domiracer with 19 inch wheels should be a real goer - with 750cc, even better. I wish I had thought about it in 1966