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78 R100/7: A flywheel from the Bay Area?

K

kmkahuna

Guest
I just cracked open my 78 R100/7 clutch assembly and this is what I found beneath it.
The bike is a white slash7, with a sport fairing on it, and two other fellow airheads seem to think this might be a San Jose BMW work from the 80s or an old B&S trick flywheel...
I am pretty sure I'm the third owner for this bike, and will follow up with hopefully, the original owner this week.
Sure was a bit of a shock, after reading all the books regarding flywheel removal: the original flywheel has none of these holes...
 

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Trick flywheel indeed. .. .. that thing has more holes in it than any other lightened wheel I've ever seen.

Your scoot must accelerate like a scalded dog! Any noticeable problems at idle?
 
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Lmo1131 said:
Trick flywheel indeed. .. .. that thing has more holes in it than any other lightened wheel I've ever seen.

You scoot must accelerate like a scalded dog! Any noticeable problems at idle?
Click to expand...

Lew, other than a 2 minute test ride, this bike has been in my garage being torn into neatly organized pieces. I would say during those two minutes my impression was like the other airheads I test drove: felt like the bike was on a solid rail going straight ahead. The other big impression was the distinct lack of a front brake (I normally ride an 96 R850R)...I do remember at idle thinking about that sewing machine analogy, so after the warm up, it was sitting there in the parking lot, ticking along.
I'm pretty sure the flywheel is free of defects: I'm just very curious about the history.
 
DennyPink said:
Hi Kurt;

Look at the 1 o'clock position on your flywheel, looks like two broken starter ring teeth.

Denny Pink
Click to expand...

Good eye, Denny. That is a nice little morsel of grease and clutch dust on the tooth.
 
lostboy said:
Shame about the ring gear.
Click to expand...
Look closely at the pic -- that is grime/crud on the casting boss in *front* of the flywheel (it's throwing a shadow from the flash onto the flywheel). Same thing at the bottom right of the flywheel housing.

The teeth are fine.
 
kmkahuna said:
Who is Reg Pridmore, Lostboy? This bike was owned by a guy up in San Clemente in the mid 80s...
Click to expand...
Seriously?

Reg Pridmore was the Brit who put BMW on the map in 1976, winning the first U.S. superbike championship on a (highly modified) R90S.
 
mneblett said:
Seriously?

Reg Pridmore was the Brit who put BMW on the map in 1976, winning the first U.S. superbike championship on a (highly modified) R90S.
Click to expand...

Thanks for letting me know, Mark. Just read up on him, and it's fascinating. I'm a relative newcomer to the bike world, so I don't know all the history; since I joined the San Diego Antique Motorcycle club last year, I'm learning quite a bit, and my neighbor Marc Lemieiux is a walking motorcycle encylopedia.
The wiki says that Reg lives up in the Ventura area now. I'd just be very interested in finding out exactly what happened to this flywheel and why.
 
kmkahuna said:
Thanks for letting me know, Mark. Just read up on him, and it's fascinating. I'm a relative newcomer to the bike world, so I don't know all the history; since I joined the San Diego Antique Motorcycle club last year, I'm learning quite a bit, and my neighbor Marc Lemieiux is a walking motorcycle encylopedia.
The wiki says that Reg lives up in the Ventura area now. I'd just be very interested in finding out exactly what happened to this flywheel and why.
Click to expand...
Sorry if the tone came across harsh -- not my intent! I need to remember sometimes that not *everyone* was watching AMA racing at Daytona in 1976 :D

If you get a chance, there's a TV series called "Twist the Throttle" (I believe on the Discovery or History channels) which takes an hour to go through the history of each motorcycle manufacturer. I've seen episodes on BMW, Honda, Suzuki, Kawasaki, Ducati, MV Agusta so far. Reg Pridmore is in the BMW episode talking about the AMA superbike period -- definitely worth watching, not only for him, but for a pretty good newbie's overview of BMW Motorrad's history since the 1923 R32.
 
mneblett said:
Sorry if the tone came across harsh -- not my intent! I need to remember sometimes that not *everyone* was watching AMA racing at Daytona in 1976 :D

If you get a chance, there's a TV series called "Twist the Throttle" (I believe on the Discovery or History channels) which takes an hour to go through the history of each motorcycle manufacturer. I've seen episodes on BMW, Honda, Suzuki, Kawasaki, Ducati, MV Agusta so far. Reg Pridmore is in the BMW episode talking about the AMA superbike period -- definitely worth watching, not only for him, but for a pretty good newbie's overview of BMW Motorrad's history since the 1923 R32.
Click to expand...

I watched "long way round" last year, and chuckled quite a bit at the GS phenomenon: I never really see those things with anything but road dust on them, and my introduction to the dirt bike world has been on a CRF230F: small, agile bikes seem to be the way to go in the dirt, vice the gigantic 1200GS's out there, but as I said, I'm a beginner, and I'm probably missing something....If I had as much money as Ewan McGregor, why not?
I will look up "twist the throttle" Mark: I'm sure my neighbor Marc can quote the entire series verbatim...
Here was a good history lesson: last year's ride to the Guy Webster Museum in Ojai..
http://guywebstermuseum.shutterfly.com
 
I just had to throw these in. Icons, Reg Pridmore (#163) and Steve McLaughlin (#83) at Daytona in 1976

Pridmore.jpg


And this classic; R90s doing a barrel roll; the result of a failed pass at Laguna Seca in 1976.

upside.JPG


Pridmore operates CLASS a rider's school based in Santa Paula, California, about 20 miles northeast of Ventura. They use tracks across the country: Willow Springs & Streets of Willow: Rosamond, CA; Laguna Seca: Monterey, CA; Infineon Raceway: Sonoma, CA; Gingerman: South Haven, MI; and VIR: Alton, VA.
 
Clymer Service manual

I think you are a lucky man as this is one improvement I will also do when I change my clutch.


My manual published in 1978 has "High Performance How-to" secrets from Reg Pridmore page 184 shows a flywheel very similar to yours. The most outer holes are not drilled as close together as to what I say on your picture.
Paraphrased: Here's what they say are the benefits you now have:

Stock flywheel weight 10#, can be reduced to 5.2 to 5.3#
Reduce Engine Inertia
Engine Torque will not suffer
Rev more rapidly
Decelerate more readily
Improved acceleration throughout the power band
Reduction in driveline strain
Longer engine life
Easier to shift will lessen the "clunk"

Doesn't affect flywheel's lifespan
Pridmore has been installing these for over (5) years with no failures even on full-on road racers.
 
What they might have left out is that with the lower inertia, power pulses and imbalances will be more noticeable, especially for a non-balanced engine. The heavy inertia of the original flywheel tends to dampen those pulses out.
 
Lmo1131 said:
I just had to throw these in. Icons, Reg Pridmore (#163) and Steve McLaughlin (#83) at Daytona in 1976

Pridmore.jpg


And this classic; R90s doing a barrel roll; the result of a failed pass at Laguna Seca in 1976.

upside.JPG


Pridmore operates CLASS a rider's school based in Santa Paula, California, about 20 miles northeast of Ventura. They use tracks across the country: Willow Springs & Streets of Willow: Rosamond, CA; Laguna Seca: Monterey, CA; Infineon Raceway: Sonoma, CA; Gingerman: South Haven, MI; and VIR: Alton, VA.
Click to expand...


Geez... I wonder how many valve covers they went through weekly
 
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