Molnar flywheel for the Mk3 - anyone interested?

acotrel said:

My first race bike was a Triton with a short stroke 500 cc Triumph which was made out of 650 parts. It had a light 63mm stroke billet crank. My Seeley 850 is far superior. To race the Triton, I always had to be 120% on top of it. The heavy crank creates a difference which can be managed. The throttle response of my 850 motor is much safer, and it's power is much more usable. It spins-up just as quick as my 500 motor ever did, but it does not get stupid.
Most guys tend to follow each other in corners, usually up on the high line at full lean, and they are very tyre dependent. While they are doing that they are usually trying to go faster - a light crank does not help that process. If you watch MotoGP these days, most passing is done by slipping under other riders in tight corners. On the straights and sweeping curves, it is usually a procession. You do not see much passing when they are at full lean.

Click to expand...

I think what you're really saying is the a heavy flywheel works a bit like a primitive traction control system, because it limits the engine's ability to build revs quickly, so less skilled riders are less likely to lose rear wheel traction.

That sounds right, but it is a very primitive system, with no ability to recognise the effect of even very significant factors like different tyres, rain on the track, camber, throttle opening. With that heavy flywheel slowing down acceleration the rider's options become very limited; if the rider is on a grippy track, with good tyres, and a powerful engine, then they can't take advantage of that situation.

It feels like most people would want a very light flywheel, so they can decide for themselves when to put down a lot of power, and when to be more cautious.

Molnar knows what he is doing.

Molnar's cranks will work on the street or on the track. I have one. They won't make your bike stupid. I'm not pontificating about something I have never used. I don't race, but I could if I stuffed my engine and all my parts in a Seeley frame. Not going to happen.

If one is looking for a lighter weight crank they could also consider ordering the entire crank balanced by Molnar for your pistons, rings, wrist pins (gudgeon pins), clips, and rods. You will be glad you did.

The Nourish Commando cranks were made very heavy, heavier than stock Norton. They were and are used primarily in race bikes. They enjoy a terrific reputation.
The Maney cranks are much lighter than stock and are also mostly used in race bikes. They also have a good reputation.
My take on it is that a heavier than stock crank can win races plus be durable. A lighter than stock crank can also win races and be durable, so the crankshaft weight cannot be terribly important in racing, at this level at least.

If it's not very important for racing then it shouldn't matter at all for road riding.
You might have to alter your take off method slightly with a really light crank.

Glen

worntorn said:

The Nourish Commando cranks were made very heavy, heavier than stock Norton. They were and are used primarily in race bikes. They enjoy a terrific reputation.
The Maney cranks are much lighter than stock and are also mostly used in race bikes. They also have a good reputation.
My take on it is that a heavier than stock crank can win races plus be durable. A lighter than stock crank can also win races and be durable, so the crankshaft weight cannot be terribly important in racing, at this level at least.

If it's not very important for racing then it shouldn't matter at all for road riding.
You might have to alter your take off method slightly with a really light crank.

Glen

Click to expand...

Indeed, Dave Nourish was definitely in the heavy crank camp. Steve Maney was definitely in the light crank camp. Yet they’re both (quite rightly) highly regarded experts. A classic case of why there is never any such thing as THE science !!

I’ve used Nourish cranks, as well as Norton and Maney cranks. I have a standard ‘heavy’ Triumph crank in my T140 and one of the ‘light’ cranks in my ‘68 T120. I raced a 500cc Daytona that had virtually zero flywheel effect. And I’ve run triples with both stock and lightened cranks.

So I have a pretty broad imperial data set to draw on.

As you say Glen, both heavy and light cranks win races and both are proven to be durable. So which is best ?

IMO it is basically down to rider preference. Which in turn is also influenced by the intended use. Two up fully laden touring will likely favour a heavy crank for most people for example, whereas on the track it is much less clear which is objectively ‘best’.

I have learnt that I personally prefer the characteristics of a ‘lighter’ crank. The zero flywheel Daytona was a step too far, but as I’ve said before, even a lightweight Maney crank is still very heavy by modern standards. So a “slightly lighter but still heavy” crank seems to be my preference.

That doesn’t mean that I believe they are ‘better’ though. I’d never try and persuade a heavy crank fan that they were wrong or that they’d be better off with a light crank. All I’d ever say is to try both and choose which you prefer.

As MichealD & Eddie have said it's how "you" ride. My 960 is all Maney! It's all about the drive out of corners, I know Steve has tried & run lighter cranks. My 750 Maney engine runs standard crank & rods with Steve's steel flywheel. It revs like a good un. It's fun to ride but a totally different thing. Too light is another matter & requires riding skill I dont have! With my sons we raced CB350K4's 11,600 revs, the best engine didnt like you to drop the revs when you changed gear. It was like racing a 2 stroke. ie abuse lol, fun when I got used to it but not me.
My triples are standard or 6lb of the crank. I ran a full Peckett engine with 11lb of the crank at a wet Snetterton. Possibly one of the most miserable meetings of my life. Like riding on a knife edge. I always remember Chris Chapman saying" that's the beauty of it Chris, controlling the slides, playing with the throttle. No thank you! I will take the heavy crank "most" of the time.

worntorn said:

You might have to alter your take off method slightly with a really light crank.

Glen

Click to expand...

Sounds about right

Street wise: If geared high taking off with a lighter reciprocating mass of parts spinning around is a little different. If geared low like stock gearing it doesn't make a lot of difference with a Molnar crank. They aren't excessively light weight. I think they are a good compromise weight wise if a person is looking for a "new crank" and doesn't want to pay AN prices. If nothing else the placebo effect should be worth it.

Sun is shining. More riding less typing.

OP here.

Those of you interested in a group order for flywheels suitable for the Mk3, please pm me with your name and complete address. Given a sufficient number of participants, the order will be placed forthwith and no later than August 15th.

Thanks,
Knut

When I first fitted the TTI gear box , I did not realise the change direction was inverted. I rode the bike around the pits at Winton in which I thought was 2nd gear - it was probably 5th. Because the bike did not accelerate, I got frustrated and took a handful of throttle and dropped the clutch - the fence was about 150 metres ahead of me. I went very close to hitting it. I would have expected to motor to stall with such high gearing. When I raced the bike with the Manx cluster with the very high first gear, the only good start I achieved was when I revved to motor to about 6000 RPM on the start line - I was afraid of blowing the Norton box apart and getting hit from behind. I actually like the heavy crank, I just work with it and let it do it's thing. I still have not raced with the 6 speeds close ratio, and I need to do that. It is on my bucket list, for when I get my glasses. The last time I raced, I was almost blind. You don't really need to be able to see the ends of the straights as you enter them. My mate rode my bike at Winton, he had only one eye and that had 40% vision.

acotrel said:

When I first fitted the TTI gear box , I did not realise the change direction was inverted. I rode the bike around the pits at Winton in which I thought was 2nd gear - it was probably 5th. Because the bike did not accelerate, I got frustrated and took a handful of throttle and dropped the clutch - the fence was about 150 metres ahead of me. I went very close to hitting it. I would have expected to motor to stall with such high gearing. When I raced the bike with the Manx cluster with the very high first gear, the only good start I achieved was when I revved to motor to about 6000 RPM on the start line - I was afraid of blowing the Norton box apart and getting hit from behind. I actually like the heavy crank, I just work with it and let it do it's thing. I still have not raced with the 6 speeds close ratio, and I need to do that. It is on my bucket list, for when I get my glasses. The last time I raced, I was almost blind. You don't really need to be able to see the ends of the straights as you enter them. My mate rode my bike at Winton, he had only one eye and that had 40% vision.

Click to expand...

Shift pattern has to be specified when ordering a TTi gearbox. Maybe not when you bought it, or if it was a used gearbox.

I don't think about the gearbox since installing and getting accustomed to the TTi 5-speed. It is nice. Of course it is new, so that might have something to do with it. My AMC gearbox was very long in the tooth. I don't miss it.

Personal thing, but I can't wear the new-fangled extremely light weigh frame with light weight lenses glasses and ride. They bounce around too much on my nose and head and drive me nuts like I'm riding underwater. I have a stiffer suspension that is more at home on smoother surfaces than a typical street or public road surface. It is tolerable but stiff, which I like if riding like I'm 28 years old again. I'm using my heavier framed glasses. Big difference for me.

I also really like being able to see approaching corners on the street. I would probably want to be able to see them on a race track as well.

I was wrong about the lighter crank and higher gearing making a difference leaving stops. I was a little lean in the low speed air circuit previously (not Amals, FCRs). Richened the low speed air circuit on the carburetors up 1/6th of a turn and no problem with launches. It would be even better with a torquey 850.

How about that for going off topic and getting slightly back on topic, but going into the wall?