920cc with 270 crank

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HanaAna

HanaAna

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Just disassembled my Commando engine and thought I'd share same info/pics just in case if someone finds it interesting. Been riding with it two summers now and decided to go back to 360degrees with the crank. First of all it was not me who build this engine in the first place, so I was not aware what to find inside. I'm pretty happy what I did find. JS2 cam with BSA lifters for one. I did know about needle bearings with the cam and "vessel" underneath the cam to keep it oiled. Pistons are modified gixxer 81mm. Rods I'm not sure what they are, but they look solid.

The reason I want 360 crank is because, since I'm not racing, I want to make this bike more driveable on the street. On open roads this setup was really nice but obviously the shakes were quite disturbing on lower revs in the city (< 3500 rpm). 270 flywheel weight was 8.44 lb. I have flywheel that I think is the original, weight 11 lb.








 
You have a pretty fancy 'Thunder Muffin' there which someone bestowed time, effort & $$$ in. I'll wager she ran damned well when given throttle and room to breathe.
 
jbruney said:
You have a pretty fancy 'Thunder Muffin' there which someone bestowed time, effort & $$$ in. I'll wager she ran damned well when given throttle and room to breathe.
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Yep, she ran really well on the open road! Too bad I have no dyno data. I’ll definetely do a dyno run on the next setup. I did not push her to the revving limit because I wasn’t ready for the worst case scenario ... only 7k rpm when she really started to fly ;-)
 
A 270 crank ‘should’ be smoother than a 360. The difficulty is in knowing what and how to balance it properly.

Personally, I prefer a 360 as it’s easier to balance and it sounds like a proper parallel twin !

What else you got in there? What head and carbs etc?

Do please keep us posted...
 
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Some very nice work there
What breather does it have at the moment?
When you go 360° I'm guessing you will alter the breathing?
 
Fast Eddie said:
A 270 crank ‘should’ be smoother than a 360. The difficulty is in knowing what and how to balance it properly.

Personally, I prefer a 360 as it’s easier to balance and it sounds like a proper parcelled twin !

What else you got in there? What head and carbs etc?

Do please keep us posted...
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A "parcelled twin" what's that then?
 
Fast Eddie said:
A 270 crank ‘should’ be smoother than a 360. The difficulty is in knowing what and how to balance it properly.

Personally, I prefer a 360 as it’s easier to balance and it sounds like a proper parcelled twin !

What else you got in there? What head and carbs etc?

Do please keep us posted...
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Yes I agree with you there, but in the lower rpm I think it is quite challenging, especially with Commando iso's? Head looks like pretty much standard except lightened rocker arms. There is an Microsquirt EFI system with Keihin TB's.

 
baz said:
Some very nice work there
What breather does it have at the moment?
When you go 360° I'm guessing you will alter the breathing?
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Breather is off timing case going to oil tank. I'm hoping this is enough with 360 also, we'll see...
 
Theoretically, with a 270 degree crank you should be able to rev much higher with safety and use much bigger inlet ports. But I would not like to try it It would probably change the torque characterristic to something more difficult to handle. - "Because I can; is never a good reason for doing anything, - but if you do not try, you never discover. It all costs money.
 
acotrel said:
Theoretically, with a 270 degree crank you should be able to rev much higher with safety and use much bigger inlet ports. But I would not like to try it It would probably change the torque characterristic to something more difficult to handle. - "Because I can; is never a good reason for doing anything, - but if you do not try, you never discover. It all costs money.
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I agree. I felt no vibration above 4k rpm and round 7k rpm where I placed the rev limit there was even less vibration ;-D. So I'm pretty sure 10k rpm would not be a problem. But because I'm sissy I wasn't ready to blow the whole engine.
 
kommando said:
Does the sensor run off the sprocket looking at an area off the chain teeth, is it one tooth or a missed tooth that sets the sync.
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There is a crank sensor on the primary belt side looking for the missing tooth and cam sensor on the timing side looking for one signal to make the sync.
 
kommando said:
Yep, reed valve and off the sump if possible so nearer to the blowy bits.
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Can you share ideas how to do it properly on Commando engine? I once tried in the middle of the sump on Triumph, thats where you can lock the crank, and it was a disaster. Blowing oil out.
 
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