270 degree crank

Status
Not open for further replies.
Lots of people winning lots of races and championships with various crank configurations (mostly 360 degree) :lol:

The question in my mind is, what are the advantages of a 270 that would drive someone to complicate their life? The only thing that comes to mind is perhaps different traction control - maybe.
 
The upside is you get to have a Norton that sounds like a Ducati. The downside is that it doesn't sound like a Norton anymore, and ( 360 degree) Nortons , Triumphs, Beezers are about the best sounding MC engine of all.

Glen
 
Jagbruno said:
Steve Perlinski has been using a 270° crank for quite a few years now with considerable success: he won the French Championship (VMA) and was very close to win the British Championship as well...

Just saying... :mrgreen:
Click to expand...

Are you sure about this Jagbruno? I know from speaking to him at Le Mans in July that father Bruno has just fitted a 270 crank in his bike, the crank was previously in the 750 ridden by Gary Thwaites, but I didn't know Steve had ridden with one.

If you were at Gedinne recently you may have seen me wobble around on my Rickman short stroke, in the same race Gary Thwaites retired a G50 from with a closed plug gap!
 
Dances with Shrapnel said:
Lots of people winning lots of races and championships with various crank configurations (mostly 360 degree) :lol:

The question in my mind is, what are the advantages of a 270 that would drive someone to complicate their life? The only thing that comes to mind is perhaps different traction control - maybe.
Click to expand...

That is also my thinking. There is enough to do - getting a motor with a 360 degree crank to perform, is difficult enough for most people. When you speak of traction control, the way the motor delivers it's power can have a big effect on the handling of the bike. It is an unknown until you try the bike. If you bought a staggered crank and the bike stopped making you feel confident, would you change back to the standard crank ? If you don't believe my ravings, just fit separate pipes with megaphones to your bike after riding with mufflers or a 2 into 1.
 
SteveA said:
Jagbruno said:
Steve Perlinski has been using a 270° crank for quite a few years now with considerable success: he won the French Championship (VMA) and was very close to win the British Championship as well...

Just saying... :mrgreen:
Click to expand...

Are you sure about this Jagbruno? I know from speaking to him at Le Mans in July that father Bruno has just fitted a 270 crank in his bike, the crank was previously in the 750 ridden by Gary Thwaites, but I didn't know Steve had ridden with one.

If you were at Gedinne recently you may have seen me wobble around on my Rickman short stroke, in the same race Gary Thwaites retired a G50 from with a closed plug gap!
Click to expand...

Yes, pretty sure, as I saw the engine being worked on by Bruno about 2 yrs ago in his workshop...but of course I couldn't say whether he is using that particular engine for all circuits.

Unfortunately, I missed out on Gedinne this year...but looking forward to meeting you in the future.
I will be riding my '69 Daytona in two weeks' time at the Carole circuit near Paris for the Trophées Jumeaux.
Anyone coming?
 
Yes Bruno has been racing with a 270 crank awhile. He uses Beehive springs with increased installation height to reduce tension on the valve springs and the cam chain.
 
jseng1 said:
Yes Bruno has been racing with a 270 crank awhile. He uses Beehive springs with increased installation height to reduce tension on the valve springs and the cam chain.
Click to expand...

Does that work, or do you end up with a tangled mess in the cylinder head when you find out it doesn't ?
 
jseng1 said:
Yes Bruno has been racing with a 270 crank awhile. He uses Beehive springs with increased installation height to reduce tension on the valve springs and the cam chain.
Click to expand...

Let us not confuse Bruno and Steve! Bruno owns a number of Seeley Nortons, and as Jagbruno infers, has used a number of configurations.

In 2015 when he raced in the UK and I looked at his bikes they had PVL type ignitions, which work on 360 degree cranks. At Le Mans in July he had a Boyer to cope with the revised crank. I spoke to him about it, he also showed me then a Boyer/Maney ignition he had used on 360 cranks with pick up on the crank, and we talked about those because I also have one that is not installed now!

Jim, when you mention increased installation height, surely that is done in the same way the ones you supplied to me? Any greater installation height would require longer valve stems.

To me this means that using your kit there is an increased installation height, that can also be considered of benefit when fitting a 270 degree crank.

Regardless of installation height, I shim my beehives to a given spring pressure, which I guess really only refers to 'tension' at full lift and the 'reduced tension' you refer to is at low lift?
 
With regards to the advantages of a 270 degree crank, I would be surprised if traction control was a reason on an engine developing relatively low power unlike the big bang V4 honda engines a few years ago. The 961 Commando, Hinkley Boneville, TDM Yamaha and it's siblings all feature a 270 degree crank but also include balance shafts. The 961 Commando is not that smooth so it's not the be all and end all of vertical twin vibration.
 
Fantastically good looking crank! I have mine, also a 80,4 mm 270 degree unit, made by Geoff Collins
at Offsetcrank in Canada. He takes old Triumph T140 units, saws them i two pieces, retards the
drive side 90 degrees and welds them to a new centrepiece ( I believe it is newly made ). It does
not look half as good as this one but Geoff assures me it will work fine at 8500rpm with a 50%
balance factor and <8 kg weight. Other ingredients are a JS2 (270 degree ) cam kit, longer R&R connecting rods,
FA head with ports modified by Comstock, also containg his valves and springs. My biggest worry
are the 38 mm Gardner carbs that this motor had to inherit from another project - arte they going
to be TO big ?? Only time will tell - plan is to fire this thing up early next year. Follow my frequent
mishaps and far in between successes on www.myseeley.net.
 
Acotrel and Steve A

When I say increased installation height on the Beehive springs I mean they have the thinner street bottom washers instead of the thicker racing bottom washers. This gives you spring pressure in the same range as stock springs. But the beehive springs in the stock pressure range will still rev to 8000 because the springs, retainer and BSA type lifters are so much lighter than stock. The thicker racing bottom washers give more pressure and a safety margin for those with short strokes and missed gear shifts etc. The beehive springs are really the best option. I’ve checked into conical springs and the rising rate is too high – the pressure over the nose is increased in relation to the pressure on the seat (not a good idea).

The 270 deg crank works well because one piston is accelerating when the other piston is deaccelerating. This means the crank doesn’t have to speed up and slow down each revolution. Some report more torque.

The 270 deg crank also splits the big Norton out of balance jerk into several smaller portions which is good but it causes more strain on the cam chain because two valves are opening at once. Its a trade off but I think the newly designed smooth ramp cams help close the gap.
 
On naming it 90 or 270 degree crankshaft: If you consider that the cylinders fire at 90 degrees
after each other it is a 90 degree crank. If they fire with a 270 degree lag then it is obviously a 270 degree
crank - although the two are identical. Cams and ignition vary though - of course.......
 
jseng1 said:
Acotrel and Steve A

When I say increased installation height on the Beehive springs I mean they have the thinner street bottom washers instead of the thicker racing bottom washers. This gives you spring pressure in the same range as stock springs. But the beehive springs in the stock pressure range will still rev to 8000 because the springs, retainer and BSA type lifters are so much lighter than stock. The thicker racing bottom washers give more pressure and a safety margin for those with short strokes and missed gear shifts etc. The beehive springs are really the best option. I’ve checked into conical springs and the rising rate is too high – the pressure over the nose is increased in relation to the pressure on the seat (not a good idea).

The 270 deg crank works well because one piston is accelerating when the other piston is deaccelerating. This means the crank doesn’t have to speed up and slow down each revolution. Some report more torque.

The 270 deg crank also splits the big Norton out of balance jerk into several smaller portions which is good but it causes more strain on the cam chain because two valves are opening at once. Its a trade off but I think the newly designed smooth ramp cams help close the gap.
Click to expand...

I have often thought those beehive valve springs look very good, but because I always keep the revs below 7000 RPM and I don't use a radical cam, I have not even lightened and polished my valve gear. Once you go above the normal rev limit, everything becomes much more expensive. What I really love about the 850 Commando engine is it's TORQUE characteristic. I run very high overall gearing and work at making the engine pull harder, while using a close ratio box to keep the crank spinning at max torque. If you don't use the close box and race change but wait while the heavy crank spins up, everything happens much slower.
 
Jim, that is a beautiful crank. Looks like the counterweights have been welded on - just like on my
offsetcrank from Canada. BUT, your looks a lot better. Can you have more made and offered for sale?
 
I believe that MAP already supplies 270 degree cranks. There is another issue with cranks which relates to the way power is delivered and the recovery of the tyres after every power pulse. With my standard crank, I know what to expect. The 270 degree crank for me, is an unknown and might become an expensive exercise. The biggest off-putting factor is the cam problem. Even with a standard crank in a Norton, moving lobe centres means you need to buy another cam. If the changed balance characteristic means a higher rev limit and thus more power and torque with reliability, then it is probably worth doing.
 
acotrel said:
I believe that MAP already supplies 270 degree cranks. There is another issue with cranks which relates to the way power is delivered and the recovery of the tyres after every power pulse. With my standard crank, I know what to expect. The 270 degree crank for me, is an unknown and might become an expensive exercise. The biggest off-putting factor is the cam problem. Even with a standard crank in a Norton, moving lobe centres means you need to buy another cam. If the changed balance characteristic means a higher rev limit and thus more power and torque with reliability, then it is probably worth doing.
Click to expand...

I personally believe the 'tyre recovery' thing is a total Red Herring, especially on our old Nortons, they just don't produce enough power for the tyre to need to recover from !
 
SteveA said:
moppedog said:
Jim, that is a beautiful crank. Looks like the counterweights have been welded on - just like on my
offsetcrank from Canada. BUT, your looks a lot better. Can you have more made and offered for sale?
Click to expand...

Read 6th item from bottom!

http://www.jsmotorsport.com/products.asp
Click to expand...

Yes I am offering them. A regular one piece 360 deg 89mm stroke crank is being made now. The counterweight on the 270 deg crank was welded on to ease the machining but there will be no welding on the 360 deg crank as below.

270 degree crank


An offset crank can be made one piece as below but the machining is a little more complicated and expensive.

270 degree crank
 
jseng1 said:
Yes I am offering them. A regular one piece 360 deg 89mm stroke crank is being made now. The counterweight on the 270 deg crank was welded on to ease the machining but there will be no welding on the 360 deg crank as below.

An offset crank can be made one piece as below but the machining is a little more complicated and expensive.
Click to expand...

Jim, I am most impressed. Will you provide a Mk3 version as well?

Do you have weight and moment of inertia (I_max) figures for both versions featuring an 89mm stroke?

Cheers, Knut
 
What is the price of the one-piece standard crank ? I really like the thought of that. With my motor, I am always waiting for the big bang.
 
Status
Not open for further replies.

Similar threads

grandpaul
New Commando 270 degree
Replies
17
Views
1,329
Stu Bodycote
Stu Bodycote
acotrel
  • Locked
270 degree crankshaft
2
Replies
29
Views
8,516
acotrel
acotrel
J
  • Locked
270 degree crank
2
Replies
35
Views
3,889
Hobot
Hobot
RoadScholar
  • Locked
76 degree offset crank
2
Replies
27
Views
4,547
Matt Spencer
M
Back
Top