How does a cylinder head sound?!

[Guest Nogbad]

A very interesting article. Thanks for the link.

[big J]

Given that in a 4 stroke engine each cylinder fires only every second revolution of the crank, I can't see it. Was the engine set up as a sort of "big bang" split single with the power strokes closely following each other?

 

The standard BSA configuration was like every other Brit parallel twin with both pistons rising and falling together but with firing strokes 1 revolution apart.

86202[/snapback]

 

Yep,dead right.It went really well,I had welded a pair of ally pipes onto the head so that twin carbs could be used as the two firing events were so close together and I didnt think a single carb would work. A spitfire cam was cut up and made to work with the welded crank.It was great fun and had a few guys scratching their heads cos it went "da-dum da-dum" at tickover.I used to have great fun lying to old giffers about it's provenance. BIAS engineering consultantancy.(Built In A Shed)Smoother than any of my other flashes/rockets, I've owned 8 altogether and this was basically built out of bits I had left.

[Guest ratchethack]

This discussion brings to mind the practice of "twingling" (twin --> "single") the crank of the formidably powerful (at the time it was The 250 Power King) Suzuki X-6 Hustler, circa 1966. No mortal human racer on the local dirt tracks had access to a dyno, but it was discovered that by dismantling the 180-degree pressed-up crankset of the 'Zuke, and pressing it back together with the crank throws in-line, that the new torque curve dramatically transformed the formerly ultra-peaky 2-stroke twin power delivery into a "big single-stomping" winner for dirt-track racing.

[mike wilson]

No messing about with chopping a cam up and just a little fiddling about with the ignition system, too. Two strokes are wonderful machines.......

[pete roper]

see what I am up against? tag teaming guys that know everything about d i c k.

Just for your information there is a whole other world out there, and it is not all about d i c k.

86159[/snapback]

 

Dave! C'mon. How about a sense of humour transplant? Please!

 

Pete

[dlaing]

Dave! C'mon. How about a sense of humour transplant? Please!

 

Pete

86621[/snapback]

I guess it is no coincidence that your name is peter

Your Penis humor is very funny, you just can't here me laughing over the internet....I need more smilies, I guess

[mdude]

There are people cutting and re-welding the cranks of old XS650 Yamaha parallel twins to make them fire like V-twins.  The theory, at least, is that with staggered crankpins the pistons are never stopped at the same time, a twice-per-revolution event with a parallel twin, and that itself reduces vibration quite a bit.  A better explanation is available here:  http://www.sense.net/~blaine/270.html

 

Yamaha did the same thing themselves with the TRX-850 sport twin (sadly not brought to the U.S.).  They had a single balance shaft, like the TDM-850 from which they were derived, and I never heard of the TRX being particularly nasty.

 

Also, FWIW, some of the new Bonneville variants are set up the same way, the America and Speedmaster, I believe.  They use a single counterbalancer, as does the standard new Bonneville (and Thruxton), and don't vibrate much at all.

86207[/snapback]

 

My wifes Laverda 668 (same as the later 750) has the same engine arrangement, cant seem to find how big the offset is, and one balance shaft. I picked it up from the mechanic after a small rebuild yesterday and it is sooo sweet running and completely without any vibrations as long as it is kept on the boil above 3500 rpms. Lovely smooth power delivered with a hard metallic cackle up to 8500 rpm. Rock steady chassis...

(FYI its engine was opened and examined and there was no signs of wear at all at 20.000 kms. This mechanic, who works on all kinds of sports bikes japs or others, reckons its one of the best mediumweight sportbikes ever built.)

 

The only snag with this arrangement it that the engine is prone to sudden stops, this happens when one decelerates and then pull in the clutch. If you do this with the engine in the wrong place in the firing cycle, it dies instantly. Happened two or three time with the Laverda.

[Steve G.]

My wifes Laverda 668 (same as the later 750) has the same engine arrangement, cant seem to find how big the offset is, and one balance shaft. I picked it up from the mechanic after a small rebuild yesterday and it is sooo sweet running and completely without any vibrations as long as it is kept on the boil above 3500 rpms. Lovely smooth power delivered with a hard metallic cackle up to 8500 rpm. Rock steady chassis...

(FYI its engine was opened and examined and there was no signs of wear at all at 20.000 kms. This mechanic, who works on all kinds of sports bikes japs or others, reckons its one of the best mediumweight sportbikes ever built.)

 

The only snag with this arrangement it that the engine is prone to sudden stops, this happens when one decelerates and then pull in the clutch. If you do this with the engine in the wrong place in the firing cycle, it dies instantly. Happened two or three time with the Laverda.

86632[/snapback]

It was unfortunate the Zane Laverdas stopped production. The chassis and hardware on these machines was top shelf equipement. Nothing but the best. Ultimately, the companys downfall was the engine, through excessive warranty claims. The early 668 engines did have a solid reputation as having a limited life, with big ends the weak link, as this engine shares it's lineage with the old Breganze 500cc Montjuic engines, which did extremely well at 500cc. A move to 750cc, and a liquid cooled head cured many of the mechanical issues, but not only had the damage been done financially, but this engine was not able to compete performance wise against the 600cc jap bikes, although it was more than a match against the Ducati 748.

Ciao, Steve G.