270 degree crankshaft

've been having a discussion with a friend about fitting a 270 degree crank to a Commando engine and the matter of secondary balance has come up. I'm wondering if any of you guys have built a motor with this type of crank ? Secondary balance is something of which I know very little. Found this article interesting :

https://en.wikipedia.org/wiki/Engine_ba ... 29_balance

Nourish Engineering will make, and balance a billet 270 crank for a Norton. Dave worked out his own balancing solutions some years ago for these.

Phil Irving covers the topic in Tuning for Speed if I recall correctly.

A racing mate / rival made a 270 Norton crank and fitted it into a Triumph engined Seely. It was a quick bike, but not quite as quick as my Triton which had a 360 Norton crank.

My Tritons crank was dynamically balanced and I don't believe the 270 was any smoother.

Moral of the story for me is: by all means, play with a 270 crank as an engineering exercise if that's what floats your boat, but as an amateur development engineer, I'd say that there are probably other, more beneficial ways to spend ones energy improving the bike.

All only IMHO of course.

Nourish Engineering will make, and balance a billet 270 crank for a Norton.

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The New Nourish Engineering does not seem to be up and running properly yet, buyer beware for the moment.

Suggested reading .......found in my Cranky Cranks folder.....
1. Vic Willoughby's 'Smoothness by Degrees' Vic willoughby's View on the 90 degree rephased crank. The ONLY hint i have as to where it was published is that it is marked XS650 Club of Australia.
2. 'Not so Cranky Cranks'. Well -nigh 30 years ago a neglected Phil Irving brainwave shows what could have been done with the parallel twin. My copy was published in Motor Cycle Sport. September 1990.
3. Dont know where the hell you would find it but at one time a missive ' Why 76 Degrees' appeared which was rather interesting aqnd looked at Phil Irvings 76 degree crank idea......
4.Triumph rather tha Norton but still applies... '76 degree Twin Triumph'. The copy I have is marked ........................http://home.iprimus.com.au/toota/vtwin.html

I built a 920cc engine with A 90/270 Crankshaft, then stuffed it into my Atlas. Their is some benefit in a non isolastic frame, but even so, had I known about JS Motorsports lightweight components, I probably would have gone that route. In a Commando, what's the point? Light weight components is money better spent. Just my opinion...
Mike B.

Some of the classic sidecar racer guys have/had 76 or 270 degree cranks.
One in a BSA A65 comes to mind, with a suitably large dellorto twin choke, and taken out to 850cc.
It looked to have some serious mumbo, and they claimed it gives more 'jump' out of the corners.

I've never even seen a good summary of counterbalancing the primary balance in a 76 or 270 degree crank ?
Presumably taking it in for a dynamic balance would soon sort it out, but the basic process doesn't get a lot of press.

Bruno Perlinski from Lille in France has fit a 270° crank in his son Steve Seeley racer. Steve has just won the British championship with the bike. Steve is an outstanding pilot...but the bike clearly works.
:mrgreen:

Jagbruno said:

Bruno Perlinski from Lille in France has fit a 270° crank in his son Steve Seeley racer. Steve has just won the British championship with the bike. Steve is an outstanding pilot...but the bike clearly works.
:mrgreen:

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I was communicating with Bruno about that bike - he has all my parts in it and one thing he was working on was keeping the beehive spring pressure down around 80 lbs pressure on the seat for the JS2 cam - thats less than (or equal to) stock valve spring pressure. He wanted this because with his previous engine build with a 270 degree cam he broke a cam chain and there was damage. The problem with the 270 degree cam/crank is that one of the intake valves and one of the exhaust valves are opening at the same time. This means that the stress on the cam chain is doubled and the cam flexes twice as much. There is also accelerated wear on the tension adjuster. Its a serious problem with high RPM racers and a screaming 9000+ RPM 500cc that I know of needed a gear driven cam. The 270 cam is a nice idea - as long as you can keep the cam chain together. But there's a price and its a lot easier and more effective to reduce the stress and vibes by going to the lighter weight pistons etc.

Interesting details, Jim. Never thought about that aspect. Sounds like the perfect place for a center cam bearing mod, and maybe an IWIS chain. Don't know what you could do about the tensioner wear, except maybe regular replacement.

Ken

When my friend started discussing this idea, I dismissed it because of the cost and difficulty of changing cams to find the best race grind, as well as getting an appropriate ignition system. However I can see advantage in the idea if the improved balance means the Commando engine could safely be revved to 8000 RPM. My feeling is that the Commando's limitation is it's potential to destroy itself when revved too hard. With my own bike, I feel fear and trepidation when I see 7,500 RPM as I race-change up through the gears. It is not just a matter of reliability. The higher the engine revs, the more power it delivers. My major worry is the weight of the 850 pistons hanging on aluminium conrods, however Jim Schmidt has the answer to this. I think that when we fit thicker crankcases we are simply doubling resistance to destruction, whereas the effects of the internal accelerations in a motor due to imbalance are a squared relationship as the revs rise. So fitting thicker cases will probably never be a real answer.

jseng1 said:

He wanted this because with his previous engine build with a 270 degree cam he broke a cam chain and there was damage.

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Wonder what brand of chain that was with ?

Haven't I seen a warning that modern day chains aren't necessarily as good as a genuine Reynolds chain from back then ??
(doubled load notwithstanding).

Clearly someone has not read the Norton Owners Club Commando Service Notes booklet and the section on the rediculous loads put upon the cam chain... NOT helped when people go and fit6 higher / quicker lift cams. It was selected for use with the cam fitted as standard to the motor in the 1940s NOT for use with the rediculous high / quick lift cams later employed. It is yet another example of a RAMIFICATION. Luckily some of us olde farts still have a stock of real 'Made in England' Renold cam and magneto chain and rivit links to suit ..the ones with a shoulder on the pins to locate the side plate correctly unlike the crap available for many years....

We experienced broken cam chains and adusters with the USS Norton 500 twin when deploying a 180 degree crank. Fixed that with a gear drive cam. Then we began to break the small timing pinion on the crankshaft.

From my experience, a 180 or 270 crank is introducing greater problems, particularly with the valve drive. We went 180 degree crank as a solution to crank durability but in reality, with the improved materials available for a crankshaft, the durability issue is solved. In my opinion, vibration is better addressed with lighter reciprocating components, better balancing and/or an Isolastic system.

I'll throw my 2 cents in, just based on my experience with the rephase process. I bought a junk Yamaha xs650 2 years ago for like 125 USD. Got it running and used it around town during my first year of law school. Vibration at interstate speeds was very bad: 35 min and your hands were numb, an hour and you can't feel the clutch lever anymore. no isolastics obviously but it had clip ons so I'm sure that didn't help. it was fun but started running pretty badly, lots of burning oil, and i ended up rebuilding it. somewhere along the way, i decided to make the motor a project and ended up with a pretty hopped up rephased yamaha.

first thoughts: when i got back on it and year and change later, it was so much faster than before that i only really noticed the jump in power from unrelated engine modifications. first interstate ride i remember thinking the vibrations were still pretty bad and i know i was frustrated. i did notice some difference but i remember thinking that the vibrations didnt change

Last month, i did 500 miles with two friends, one with a 70' bonneville and one with another xs650. we trade off during rides often and i have to say, there is no comparison. my bike has WAY lower vibes. that being said, it is pretty expensive to do, and if i hadn't ridden a bike with a standard crank after, i would have still been thinking mine was bad. it does help, but vibes are not gone. i see people all the time on the 650 forums claiming it eliminates vibration which is total nonsense.

I've got 8500 miles on the rephrase motor without any issues, so it seems to hold up, but time will tell

Adding to my comments above regarding introducing other problems with a rephased crank and cam on a Norton twin, I have heard there may be traction benefits upon acceleration with a rephased crank. This would be applicable in dirt racing, dry lake bed or (playa) land speed trials or on asphalt where you are leaned way over, at the margins of your traction and pouring on as much throttle as the system will handle.

OOPS..cock up. The bit regarding the cam chains was NOT in the Commando Service Notes written by an NVT Qual;ity Engineer / Service Engineer but in an artocle written by the same Gentleman published in Motor Cycle Sport January 1977 pages 27/28. It was headed ....... 'VICIOUS CIRCLE. A cautionary tale, in which it is shown that in engineering at least nothing is as simple as it seems. The following story is based on a series of events which took place not long ago, at a motor cycle manufacturer somewhere in Europe. Only the names have been omitted to protect the guilty'.
The relevent bit reads........ ....It did not go unnoticed that this mileage was the distance at which the mains failed in many cases, and that failure of the advance unit happened much more quickly with the super-sports camshaft. That was because of the fierce nature of the new cam which driven by as it was by chain, used to thrash about within the slack allowed by the chain adjustment. This too, was giving problems. Many engines seemed to be wearing their camshaft chains excessively, and this fault was compounded by the difficulty of regulating it. To do this the timing had to be disturbed and the complete timing cover removed. Dealers were suppossed to adjust the chains at the first service but you can imagine how many of them did so. The torsional vibration of a 4 lobed camshaft driven by a slack chain is tremendous, especially when it is remembered that the cams were not evenly spaced and so for two periods in each turn of the cam (4 at low speeds where inertia effects are less) the cam is actually trying to turn the engine because of the pressure of the valve springs on the downside of the ramp. Mistake No 7.
Dont suppose many have ever read the Motor Cycle Sport article ! ALL Commando owners really should do so.
Just thought I had better correct my error before someone does it for me.. Personally I blame finding the Service otes the other day and having a quick look... I did notice the bit on the CORRECT oil toemploy within the primary chain case.......Castrolite. A nice thin SAE 10-40 straight engine oil. Shame it is no longer available so Castrol told me a few years ago..... I believe either Morris or Silkolene flog a straight 20 in quart pots.....
I still have unused gallon cans of straight 10 and 20 ......and all belts were designed to be employed DRY aqnd that includes AT10 belts!!

J. M. Leadbeater said:

Dont suppose many have ever read the Motor Cycle Sport article ! ALL Commando owners really should do so.

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It's been posted here several times in the past so you might suppose wrong.

Hortons Norton said:

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J. M. Leadbeater said:

I did notice the bit on the CORRECT oil toemploy within the primary chain case.......Castrolite. A nice thin SAE 10-40 straight engine oil. Shame it is no longer available so Castrol told me a few years ago..... I believe either Morris or Silkolene flog a straight 20 in quart pots.....

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Please, for crying out loud, NOT AGAIN! :roll:

Dances with Shrapnel said:

We experienced broken cam chains and adusters with the USS Norton 500 twin when deploying a 180 degree crank. Fixed that with a gear drive cam. Then we began to break the small timing pinion on the crankshaft.

From my experience, a 180 or 270 crank is introducing greater problems, particularly with the valve drive. We went 180 degree crank as a solution to crank durability but in reality, with the improved materials available for a crankshaft, the durability issue is solved. In my opinion, vibration is better addressed with lighter reciprocating components, better balancing and/or an Isolastic system.

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Here's a view of a JS2 270 cam for BSA lifters - Bike Bruno P is using. He went to lighter spring pressure (80 lbs on the seats with the Beehives) and Jwis chain. You can see an intake and an exhaust lobe nearly aligned - both lifting valves at the same time - more strain on the chain and wear on the tensioner.

jseng1 said:

more strain on the chain and wear on the tensioner.

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The proper technical term is - "it beats the living sh*t out of everything".

jseng1 said:

Here's a view of a JS2 270 cam for BSA lifters - Bike Bruno P is using. He went to lighter spring pressure (80 lbs on the seats with the Beehives) and Jwis chain. You can see an intake and an exhaust lobe nearly aligned - both lifting valves at the same time - more strain on the chain and wear on the tensioner.

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Makes sense.
The new Norton 961 has a 270 degree crank.
Dreer had originally designed a spur gear cam drive, but it was very noisy, so he decided to go back to the chain drive.
According to a technical person that was once at the new Norton UK company, early on, the new 961 Commando prototype had cam chain problems.