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Author Topic: 100cc classic production build  (Read 477 times)

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Offline roflhat

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100cc classic production build
« on: November 04, 2019, 04:03:52 PM »
Hi everyone,

starting a thread for my P-PC 100cc build. Trying to keep it both simple and cheap, I've always wanted to attempt a record at Bonneville so this is hopefully what I'll be doing it on.
Bought the bike last month on ebay, and by a stroke of luck a friend was down in Wales with a van and was able to collect and take it up the Isle of Lewis for me free of charge. Here's the bike as I got it, hasn't run in likely over a decade but is in nice overall condition


Stripped a few bits off, indicators, luggage rack etc. Some other jobs, front brake was locked on, changed the front wheel bearings.


Allowed to change the handlebars so I got a clubman style set, needed some sanding to get the new throttle roller on there


How the bike sits at the moment, haven't had it running yet still waiting on a couple parts.


Sure I'll have plenty questions as I go along, any input welcome

Still need to get new tires, wheel balance, steering damper, a kill switch with cord

cheers

Offline Stan Back

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Re: 100cc classic production build
« Reply #1 on: November 04, 2019, 05:07:49 PM »
Great-looking little bike!

I'm not a bike guy (although I had a CB100) -- what year is it?

What class would it run at Bonneville?  And what's the record?
Member of the San Berdoo Roadsters -- "California's Most-Exclusive Roadster Club".
Celebrating 67th anniversary of racing on the salt.

Offline donpearsall

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Re: 100cc classic production build
« Reply #2 on: November 04, 2019, 05:09:53 PM »
Good Luck! I hope you get to come over and set a record. Which Bonneville sanctioning event are you planning for? SCTA (Speedweek, etc)  or AMA (BMST)? I see that the SCTA record is open so that is guaranteed. BMST is 52.7 MPH. Easy-peasy!  What are your plans to make it go fast?
Keep posting.
Don
550 hp 2003 Suzuki Hayabusa Land Speed Racer

Offline donpearsall

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Re: 100cc classic production build
« Reply #3 on: November 04, 2019, 05:27:08 PM »
Also- make sure you measure bore and stroke and verify the engine is indeed stock. There are overbore limits that could possibly disqualify you.

Don
550 hp 2003 Suzuki Hayabusa Land Speed Racer

Offline Sumner

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Re: 100cc classic production build
« Reply #4 on: November 04, 2019, 05:55:56 PM »
.... I see that the SCTA record is open so that is guaranteed. BMST is 52.7 MPH. Easy-peasy!  What are your plans to make it go fast?
Keep posting.
Don

Suppose to run 70+ stock...

https://www.cmsnl.com/gp100_model13377/info/

Good luck with the bike and sure hope you make it over,

Sumner
« Last Edit: November 04, 2019, 06:12:59 PM by Sumner »

Offline roflhat

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Re: 100cc classic production build
« Reply #5 on: November 05, 2019, 02:13:07 AM »
Thanks everyone! It's a 1980, class allows pre 1981
The AMA record was 35.949mph although I believe it was beaten in 2018, around 50mph as Don says.
Original top speed of the GP100 is meant to be around 70mph but I will have to see what it does now. Going to rebuild the engine, make sure everything is in new condition. Not allowed to do too much for this class, going to fit a narrower front tire, then just play with the jets and different sprocket sizes. I've heard you lose 20% ish power and compression at Bonneville so will no doubt have to adjust again if I get there.
Spoken to George Kronkite who set a record on a Suzuki TS400, after all his tuning his record speed was identical to the original top speed of the bike. So around 70mph would be a nice target for me
Will also be going on a diet myself, I'm around 75kg at the moment.

Not sure whether to go for Speedweek or BMST, from what I hear Speedweek is a great spectacle with awesome machines but busy. AMA sounds good too, and I like the idea of having a target speed to beat

Offline RaceEngineer

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Re: 100cc classic production build
« Reply #6 on: November 05, 2019, 09:15:32 AM »
Roflhat,

SCTA (Speedweek) does not have a Production Classic class, only AMA (BMST).  At an SCTA meet, with the bike your building/planning, you would have to run in Production Production .  The current record is 82.8 mph set in 2003.  AMA rules are online.  SCTA rule book can be purchased for $10 (go to the home page of this forum, then SCTA)    Welcome to the LSR family.  Hope this helps..

Offline donpearsall

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Re: 100cc classic production build
« Reply #7 on: November 05, 2019, 11:24:47 AM »
The low handlebars and narrow tire are good for a bit of speed. Remove the turn signals of course. Get tires as smooth as possible, not knobby ones.  Run as high tire pressure as possible. Make sure the brakes do not drag.  Wear tight fitting leathers. Practice your tuck and get as low as possible. Elbows and knees in.

Also get a NON O-ring chain as the O-ring type eats HP.

Don
550 hp 2003 Suzuki Hayabusa Land Speed Racer

Offline roflhat

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Re: 100cc classic production build
« Reply #8 on: November 05, 2019, 11:54:43 AM »
Thanks for all the help and information, I am writing this all down in a file as I plan this project.
Looks like I will aim for the AMA event, most likely 2021.
Does anyone know the differences between P-PC and P-CG? I've just been looking at the rules and can't see much of a change in the rules there. Both records are held by the same guy, on probably the same bike or at least the same make.

I don't own any leathers at the moment so will do plenty of reading before investing, ideally want almost a lycra suit!
Is there a rule of thumb as to how narrow a tire I can fit on my rims? standard front tire is 2.50r18, rear 2.75r18

Online Doc B.

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Re: 100cc classic production build
« Reply #9 on: November 05, 2019, 12:29:08 PM »
Biggest difference between PC and CG is that a CG motor can use any fuel delivery (bigger carbs, switch to fuel injection), while PC has to stay with stock carbs.

Leathers - a road race style suit with lycra panels and perforation is legal at BMST. But if you ever plan to run at an SCTA event the suit cannot have any perforations. You can usually pick out an SCTA racer by their very expensive, vintage looking custom Vanson or Bates leathers. You don't need new leathers, but you need good quality, protective leathers. The salt is very unkind to skin. Dainese, Alpinestars, Spidi etc. one and two piece suits will work.

Re tire size, manufacturers will often have a chart that specs the minimum and maximum rim size for a tire. I've had good luck finding Heidenau tires in skinnier sizes. They are mostly rated for speeds below 112 mph, but that will not be an issue for you. I run a Heidenau K40 2.50-18 front on a 1.4" rim.

Offline Stainless1

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Re: 100cc classic production build
« Reply #10 on: November 05, 2019, 02:06:44 PM »
75 kg... what's that in Stones?  OK just kidding...
Well you have a goal... you can set an AMA record or you can try to be the fastest 100cc production bike in the world...
Ya know if it came from the factory with a fairing... it would be legal....
Don't know if any did, just clarifying the rules
Have fun  :cheers:
Stainless
Red Hat 228.039, 2001, 65ci, MSA Bockscar Lakester with a little N20 
MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.

Offline donpearsall

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Re: 100cc classic production build
« Reply #11 on: November 05, 2019, 03:36:50 PM »
Yes, Like Stainless said, you can go for the American Motorcycle Assn record at BMST, or go to BMST and get the record certified by by the FIM, which is International. FIM has specialized rules so check that out too.  SCTA is regional, not national or international.

Don
550 hp 2003 Suzuki Hayabusa Land Speed Racer

Offline rgdavid

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Re: 100cc classic production build
« Reply #12 on: November 06, 2019, 02:08:28 PM »
Are you aloud to tune the moter and use an expansion chambrer in your class ?
You can do a lot to thise little gp disc valve moters for allmost no money,
« Last Edit: November 06, 2019, 02:10:15 PM by rgdavid »

Offline comet

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Re: 100cc classic production build
« Reply #13 on: November 07, 2019, 03:50:47 AM »
hello ROFLHAT
welcome.
The build should be a lot of fun. Good luck with it. The BMST event is AMA and FIM sanctioned. You would just need to choose which sanctioning body you want to race under. AMA rules and regs are linked under the BMST website, I am not sure about the FIM rules, but there are some differences so check out which are relevant to you. FIM is a bit more critical I think its fair to say. Speedweek is certainly more of a spectacle as you say, but BMST is a bike only event so you will find the course might be a lot less abused and dare I say it, in better condition. Plus the waiting times will be less at the BMST event.
Whichever event you choose to race at, good luck with the build, it'll be very interesting to see how it goes.

Cheers
John

Offline roflhat

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Re: 100cc classic production build
« Reply #14 on: November 07, 2019, 11:06:22 AM »
Thanks for all the replies, might look into doing the P-CG at the same time using one of these Smartcarbs.

Looks like I'll do the BMST event, will keep an eye out for a decent set of used leathers. Going to have a measure of the rims and then look further into tires too. Think I'm pretty limited to what I can change aerodynamically on the bike, but will try and make sure my helmet and my own positioning on the bike is decent

Not allowed to run an expansion chamber, the whole bike has to pretty close to standard, can tune the engine a wee bit but all needs to look standard