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OHC Sportster

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jib

Posts: 570

Joined: Sat Dec 10, 2005 3:36 pm

Location: devon,england

Post Thu Jan 20, 2011 1:47 pm

Re: OHC Sportster

think i will disagree on that one DD, think the 45 and sportster have the drive chain in a better position than a bigtwin. if only for ease of changing sprockets ,and the ability to have a narrower transmision /clutch width.
of course thats only my opinion and i respect your right to have yours. regards jib
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years
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Frankenstein

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Location: Interlaken, NY USA

Post Thu Jan 20, 2011 2:04 pm

Re: OHC Sportster

No Prob, Jib, It's just one of my favorite Rants! Of course Indian did it cross wise, and look where it got them :lol: (Now I'll get Cotten after me)
DD
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45Brit

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Joined: Tue Nov 27, 2007 2:29 am

Post Thu Jan 20, 2011 2:14 pm

Re: OHC Sportster

the crucial problem with the cross-over drive as fitted to the 45 is that it leaves the stresses in the transmission supported entirely by the mounting bolts. On a conventional ( ie, single-sided ) transmission the torque from the primary drive is opposed by the torque from the secondary drive. I've seen speedway bikes come in from a race with the countershaft bolts vibrated loose, just finger-tight, and the bike is still running with the countershaft held in position by the respective chain tensions. I wouldn't try that with a 45.

A lesser problem is that it imposes asymmetric loadings in the shaft bearings ( ie the sum of the forces is tending to rotate, or slew if you prefer, the shaft in a horizontal plane about a vertical axis through the centre of the shaft ) so that wear is increased.
Last edited by 45Brit on Thu Jan 20, 2011 5:27 pm, edited 1 time in total.
Shoot, a man could have a good weekend in Dallas with all that stuff...
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Frankenstein

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Post Thu Jan 20, 2011 3:03 pm

Re: OHC Sportster

45Brit, I was trying to think of a British machine with crossover drive and nothing came to mind. Was there anyone who did it that way?
DD
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jib

Posts: 570

Joined: Sat Dec 10, 2005 3:36 pm

Location: devon,england

Post Thu Jan 20, 2011 5:01 pm

Re: OHC Sportster

hi 45 brit, youre a bit confused with your sportster description, as its a unit engine, there is no ,adverse reaction from the primary ,acting on the engine/gearbox unit's external mounting system.
i agree the 45 has a wee prob there. but as the power in a standard machine is quite low ,as long as everything is regulary checked its cool. and it had only got 2 bolts, then3.!.
where as the big twin had 4 bolts originally and then 5 to mount it.

there is quiye a few rihgt side drive conversions on the market now for bigtwins,has anyone come across one of these that has had problems of twisting,or gross torsional loading giving rise to mount failure or frame failure?

regards jib
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years
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45Brit

Posts: 1406

Joined: Tue Nov 27, 2007 2:29 am

Post Thu Jan 20, 2011 5:12 pm

Re: OHC Sportster

one of the most numerous British bikes of the post-war era - the Bantam - had a cross-over drive. The clutch was on the right side of the engine unit, and the final drive on the left. This was BSA's version of the same DKW bike which formed the basis for the Hummer.

The same feature survived on the MZ two-strokes up their final models in, I think, the early 90s. These had an engine-speed clutch on the crankshaft of the 250cc units, but the older 150cc ones were again very similar to the Bantam/Hummer, being another DKW derivative.

The 1919 "Baby" Triumph had a cross-over transmission http://www.barkshire.co.uk/bikes/images ... %20005.jpg although no clutch was fitted. I would suspect that if I knew enough about early belt-drive lightweights, there might be others.

Douglas in-line flat-twins also had a cross-over transmission, I have some photos somewhere ...


re the Sportster, yes it is indeed a unit motor so the transmission stresses are within the main castings. I have edited the original post "according". However comments about asymmetric loadings on the shafts and bearings stand.
Shoot, a man could have a good weekend in Dallas with all that stuff...
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Cotten

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Location: Central Illinois, USA

Post Thu Jan 20, 2011 7:29 pm

Re: OHC Sportster

Frankenstein wrote:No Prob, Jib, It's just one of my favorite Rants! Of course Indian did it cross wise, and look where it got them :lol: (Now I'll get Cotten after me)
DD


DD!

It is no secret to anybody with eyes that the lowly K/sportster breed borrowed heavily from Indian design, appearing as soon as Indian's self-destruction made it safe.
The '65 and later Big Twin primary falls into the same catagory.
Who can deny that many of these traits continued into modern times?

Off-hand, I can't think of any original idea that H-D came up with all by themselves, other than marketing ploys.

Anyone?

....Cotten
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45Brit

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Joined: Tue Nov 27, 2007 2:29 am

Post Fri Jan 21, 2011 1:31 am

Re: OHC Sportster

I wouldn't say that H-D have had no original ideas, although like Citroen they do tend to be different for the sake of being different

the transmission-plate style of mounting for the 1930s-and-on 4-speed gearboxes is AFAIK, unique. The ohv enclosures on the knucklehead, although very similar to the set-up developed by JAP around the same time and clearly derived from aero-engine practice, is unlike anything developed by Indian. The pressurised primary chaincase set-up on the shovelhead defies all logic for no obvious purpose, and again AFAIK is unique. I don't know of any other machine which uses the chaincase-mounted starter motor, although Norton did copy the idea of driving the clutch around the same time, for a similar purpose - ie to fit an electric start to a 1930s design.

The styling of the first knuckleheads is a modern classic, and truly original.
Shoot, a man could have a good weekend in Dallas with all that stuff...
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Frankenstein

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Location: Interlaken, NY USA

Post Fri Jan 21, 2011 9:06 am

Re: OHC Sportster

Touché, Cotten :lol: Always the worthy. I wouldn't say the K followed the Indian, well, on the road, of course they did. Harley had been making flatheads for years that couldn't keep up with Indians. :cry:
DD
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Neil74

Posts: 251

Joined: Sat May 20, 2006 9:38 pm

Location: Hudson, Florida

Post Fri Jan 21, 2011 12:00 pm

Re: OHC Sportster

bye
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