Intermittent miss

Vince said:
Had that one myself years ago,a lot of bikes have a metal conduit below the rear guard to run wiring through.Thats a big rear tyre on that bike.Tyres grow at high speed as well.
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I had to run the wires externally when I relocated the upper rear suspension mounts forward because of the increased wheel travel, could run them back there now with the longer shocks.
Who is Marty referring to in his post about club rides?
 
Vince said:
Tyres grow at high speed as well.
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True, Vince, but they grow in diameter, which means they probably become a tad narrower as the centre grows. but, yes, I've relocated the wiring over the guard.

Keep at it Chris! As for vibes, I noticed when I built my 50% statically balanced 270 crank, the obvious areas of vibration stress shifted from when it ran as a 360, which makes perfect sense. the out of balance phases change completely . A lot more vibes at the upper rear, and the upper engine mounts cracked for the first time since I'd had the bike (1974). My footpegs are very solidly mounted: 12mm plate bolted at each corner in the pillion peg triangle a la Jota, and solid steel pegs with original rubbers on them ... so no issues there.

Gonna be interesting to compare with the 60% dynamically balanced.
 
Hey Quentin,
Mark and I were talking about balance factors yesterday on the twisted twins
wonder what balance factor Yamaha, KTM, Royal Enfield and others use for their 270 degree cranks ?
if I could find a cheap wrecked twisted engine of an engine type that does not use a balance shaft as well we could easily reverse engineer the crank to measure the balance factor in play

we chose 60% in discussion with Crankshaft Engineering, have asked Greg how his is going and he says it is great, no issues
May as well ask a brick wall than ask House for meaningful feed back, all he says is it seems good
Chris is the first to say his suffers

going to try and load David H's engine into Mark's SF2 this month and then we will know for certain what is going on
 
I thought that all of the modern raft of 270 motors had balance shafts.
My 270 has very different vibration characteristics in the stripped down race chassis than it had as a road bike, as subjective as it is. It is definitely better at full power/load high revs, and vibrates more in midrange when using less power, as in slowdown laps and wet races. On the road it was great up to about 6000rpm, then got pretty annoying. It seems interesting that the power/load use affects vibration, as virtually all street riding is part power this would have to be the focus. Great idea to try the motor in Mark?s bike.
 
Good thinking. FWIW when i did mine I had nothing to go by other than Mark parker's twisted BSA crank, motor shoehorned into an RGV Suzuki frame!!! He told 50% is the go but as we know a two bearing-crank on an old pommie twin is a shedload narrower than a four-bearing SF/C crank. So whether the rocking couple is contributing significantly I don't know.

A lot of the modern twisters use counterbalancing of some sort to offset the rocking couple and the fore-aft out of balance phase. Triumph Thunderbirds are 1600cc FFS and they are a 270, as is the Thruztons that Smarty races against.

At 50% mine was definitely good at 4500, the only area I wasn't really happy with was at revs above maybe 6000. I still have a quest to build a SF/C type crank with all the counterbalancing built into the middle webs, even if it means loading them with mallory on the heavy side, then neutralise the outer webs. Try to get the counterbalancing as close to centre as poss, as per the pommie twins. The guy in Canada who does loads of then for race bikes has some great shots on his website of where he adds the weight.

Yes, greg did tell me he found his bike very similar to his Guzzi and his Duke, and he had it on the track at Broady.
 
I met that Mark Parker bloke once,his brother was the drummer in The Radiator.Another mate replaced him in the band a few years later.He arrived at a mates place in Sydney on his Honda beam framed Triumph trident that's the T150v older engined.Interesting bloke. His mate eventually moved to Bemboka and they would ride a lot together. The next time had use arrive at Tathra on a Snowy Ride and while we were booking in I notice him turn up on that BSA outside the pub,but he left before I could get his attention.Both of his bikes are spectacular.
 
Yes, a clever bloke. Still posts on a Brit custom forum I think. Nearly managed to visit him in Tathra. he posted me a video of his BSazuki. If he was able to ride it to the SNowys then it must be pretty smooth, because those alloy spar frames are as light as and would suffer badly from heavy vibes. Maybe we need to convert the SF/C cranks to two-bearing mains  :LOL: :LOL: :LOL:
 
Piranha Brother 2 said:
At 50% mine was definitely good at 4500, the only area I wasn't really happy with was at revs above maybe 6000. I still have a quest to build a SF/C type crank with all the counterbalancing built into the middle webs, even if it means loading them with mallory on the heavy side, then neutralise the outer webs. Try to get the counterbalancing as close to centre as poss, as per the pommie twins. The guy in Canada who does loads of then for race bikes has some great shots on his website of where he adds the weight.
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I suspect you have a very valid point there Quentin.  Reckon the uneven firing could exaggerate the rocking couple, the sheer length of the Lav crank making things even worse.  Could well be the way to go, going to have a long think over that!

piet
 
That BSazuki was featured in a bike magazine recently. It was probably the British mag "Classic Bike" or the Oz "Old Bike Australasia" because they're the only two bike magazines that I read regularly. I'll see if I can find it.
 
sfcpiet said:
I suspect you have a very valid point there Quentin.  Reckon the uneven firing could exaggerate the rocking couple, the sheer length of the Lav crank making things even worse.  Could well be the way to go, going to have a long think over that!

piet
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There you go Red. I'll see how it works with my crank made from triple webs 3 and 5 for the inners, loaded with Mallory, and pared down SF webs for the outers. If it works, it will be the way to go in the future with the twisters. Of course, we could always find a way to incorporate balancer shafts as well!!
 
Tippie said:
Use a toothed belt to drive the generator and unbalance it (never mind the bearings) :-X
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Thought about that as well, junk the genny innards and fit a balance shaft in there.  Ideally the balance shaft would need to rotate "backwards", fit a gear next to the crank to reverse the drive?  Or cross the belt?  K?nig flat-four 2-strokes had a belt going through right angles to drive the rotary intake disc. Could also lengthen the genny shaft and fit one of those tiny Kubota thingys on the end, they don't mind which way they go round. :D

piet
 
chrisk sent these photos to my phone and asked me to post them here. Had to figure out a way of getting them outta the phone and into my computer first. Maybe I should have asked Ron how to do it in his PC thread  :D

Anyway, nice job Chris. Very neatly done.
 

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Here is my newly fitted up alternator, 12.1V at idle, 12.7 at a few revs. And no leak to earth :D
I will test it, and if it works OK, Red is going to have a billet cut down on CNC, it'll be better than my lathe, drill press, angle grinder, and bastard file attempt.

Thanks Cam for posing pictures for me. I'm almost PC illiterate since PhotoBucket did the job on me.
 
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