First build, hopefully fast.

[Davezilla]

Yeah fast is nice but you want a centrifugal clutch on it in theory I've got one but yet to place it so I can't reply to it's performance capability some say it works well on your setup it could be perfect but the clutch it turns should likely be locked to the pressure plate I yet to hear anyone installing one correctly at that say no more..

I had one on mine for a while and it was nice to be able to stop without grabbing 2 levers on the left hand side, acceleration and top speed were unaffected by the extra rotating mass and it was also well balanced enough that it didn't add any vibration to the engine or the bike. When set up properly it can still be bump started or pull started whichever you choose.

Here's the weak spot on these... The gear is just pressed onto the clutch bell and will separate feeling like the clutch is pulled in, the engine will just free rev basically. The way to remedy this is to weld or braze it to the bell before you install it and it should last. when mine separated I went to braze it back on but there was already too much play betwen the bell and the gear so next one I get will be welded or brazed before it's installed. I also had to put the shaft extension on the lathe and take off about .004" and re polish the shaft extension before the one way clutch worked properly.

On a stock engine it might have help up a little bit better but I'd weld that gear in place anyway.

The other thing I didn't like about it was it begins to engage just above idle but I took the shoes off and drilled 5 5/16" holes thru the sides of each shoe to lighten them up and it got the engagement rpm just a bit higher, but could have still been better. If I install another centrifugal clutch on mine I'll use the lightened shoes but I plan on lightening them even more so it starts to engage at about 2500 rpm and fully engages at closer to 3000 rpm.

I can take pics of the shoes and the original gear that was brazed back onto the bell. I can most likely get this one usable again by spending a little quality time on the lathe, but it will be faster and easier to just replace the bell assembly and weld the new one before anything evil happens to it again...

 

[LandSpeedRecord]

I am really liking the centrifugal clutch idea if I can get one that fully engages and is relatively light. That would give the ability to instal say a 20 tooth rear sprocket and still get off the line. Dave do you have any pics/links to tge clutch you used?

 

[Davezilla]

I may have a few in my Imageshack album but I'll most likely need to take more pics... I got mine from BGF on ebay and it comes with the different clutch cover and all.

After I got mine I found out that grubee makes 2 types of these, one runs wet and the other runs dry, the wet clutch has a drain/fill plug on the new cover and holds 3oz of oil, but the wet clutch version doesn't have the one way bearing so it's pull start only, the dry type has the one way bearing so it can be bump started or pull started. I'm sure of someone wanted a wet centrifugal they could buy the wet type from Grubee and use the shaft extension and bell from the dry type since the dry type doesn't have the right friction material to run wet and it'll slip, and the wet type will ruin the friction material if run dry.

Well... I was gonna post this link about the wet centrifugal compared to the dry type but it looks like Grubee quit selling the wet type... bummer, but I know how to convert them to wet by swapping out the lining materials... Another member in here and myself are currently working on making a wet clutch setup for the manual clutch so it would be Real easy to convert a centrifugal to wet just by swapping out the friction material, this may also help raise lockup speed and smooth out the engagement even more than it already is in dry form... but here's what's left on Grubee's page... scroll all the way to the bottom, just too bad they blacked out the wet type instructions... http://www.grubeeinc.com/Skyhawk Instructions.html Excellent read BTW, they explain a lot of stuff there so worth bookmarking...

 

[Davezilla]

Here's the link to the one I got from BGF... http://www.ebay.com/itm/66cc-Motor-...015?pt=LH_DefaultDomain_0&hash=item2c7c4d22e7

 

[LandSpeedRecord]

Very cool Dave, thanks for the link and info! I will have to learn and understand a bit more. I don't want to loose bump start ability although it says it is still possible. I had been looking at a few go cart clutches but that looks bolt in which would be nice. Curious as to how crazy I could get with final drive gearing with one is my main motivation. I ultimately need to have about a 21 tooth rear sprocket if my math is right. The sanctioning body has rules about assistance at the start and I think I need to be able to come off the line under power somehow and this could possibly help.

 

[Davezilla]

The typical ones like BGF sells have the one way clutch so they can still be bump started, they also have the advantage that you can kick start without having to pull the clutch in before setting the rear wheel back on the ground. I'm thinking it would be real easy to re line one of these to run it in an oil bath for smoother starts and you could further control the slip and full lockup rpm by changing oil types... auto trans fluid makes for a good crisp start with a quick lockup and motor oil can make it slip a bit longer for a hither rpm launch, then a really slick synthetic could raise the fully engaged lockup rpm even higher... or experimenting with a mix of oil and/ or trans fluid you could Taylor your lockup rpm pretty much wherever you want.
there are other factors that can determine lockup rpm as well as where it starts to move the bike etc like the weight of the shoes, oil type, cutting oil grooves and their size and shape etc...
so there are several advantages to converting a dry centrifugal to wet, and if done right it would be possible to let it stay in the powerband and tighten up the slip as the bike accelerates so running a high gear would be possible and still have decent acceleration by letting it slip up into the powerband like a high stall torque converter in an auto transmission.

 

[LandSpeedRecord]

I was planning to make clutch pucks out of really good material and pedal assist the motor up to about 25 and hope it had enough bottom end power to pull from there. While another bit of enigineering, trial and error with the centrifigul set up is daunting with everything else to do it is a better idea than mine no doubt. Right now I'm in the process of building a balanced, helicoiled, bottom end with OEM Honda bearings I found to fit the crank. Using whats been learned with sand drag Banshee's to make the power I think I can spin 9,700+rpm with a 21 tooth rear sprocket and the 700c wheel. Then hopefully get the little China girl to hold together all the way thru the traps at Boneville. I don't know if anyone has ever pushed one of these motors this hard. It will be fun if nothing else.

 

[LandSpeedRecord]

I re packed the bearings with slippery grease, installed the 36 tooth, tried 3 different jets. Went out and ran it about 15 minutes holding it wide open to progressively higher speeds. Then broke another rear motor mount as the GPS was passing 46.3 and had to pull in the clutch and pull off the road. the motor flexed far enough down to bend the carb.

 

[Rudz]

You need Bikebobber.com mounts, machined billet aluminum

 

[LandSpeedRecord]

Yep! I talked back and forth with him a bit in another thread. I had grade 8.8 hardware and double stock plates on this one. I really need the bikebobber mounts but i also need to look closelly and see what is wrong here. It should not have broken the really good hardware and the double brackets that were blue lock tighted in. I had probably riden between 3 and 5 miles and just had the motor all the way warmed up and checked the mounts before riding.

 

[cannonball2]

Shifting is not allowed?

For inspiration if you haven't seen it and for those who haven't, heres Budfabs 50cc Bonneville run. Love hearing the little 50 winding up. https://www.youtube.com/watch?v=mYINrhTNiyM

 

[LandSpeedRecord]

Shifting is allowed, it's just finding a system with near zero frictional losses to be worth it. Thats a great video, i love the small diaolacement motors and streamliners. It's incredible how fast some of them are.

 

[LandSpeedRecord]

 

[cannonball2]

You can run a BMX chain to cut some loss there. I have found them plenty strong. An internal hub may work. The fixie hub I m using in a build is a 1:1 lock up in high. Would add some small losses but being able to gear higher overall would be worth it.

 

[LandSpeedRecord]

I am curious about that fixie hub. Most of what i have read on here warns the internal hubs arent strong enough. The two speed fixie you are talking about might work though. I will look into that one, that. There are a couple BMX chains i have been wanting to try, tha KMC 510 is an awesone chain in nickel and the all half link chains look super strong.

 

[cannonball2]

The SA fixie is a 3speed. 3rd is 1:1, 2nd is 75% and 1st is 62%. The advantage is 3rd being 1:1(locked ) the power flow is straight through the hub being less power consumptive than through a gear set. It also very strong with a beefy clutch. Besides the engine being geared high isnt going to be able to dump a bunch of torque on it anyway.

If the 1st ratio was set at or close to what the tallest gearing the bike could pull as a single speed then the other gears are over drives. Do you have a target top speed?

 

[LandSpeedRecord]

There are 4 classes I could possibly run at Bonneville. The records in those I believe are 52, 56, 73, and 99 miles per hour. I am testing on pavement guessing the salt will knock between 15 to 20% off my top speed. Right now I am at the point of adding steering stops and a steering dampener before I go any faster. The hub you are talking about sounds like a good option and it's not the one I thought it was. Do you know how you shift it?

 

[LandSpeedRecord]

I found the hub. Looks like it's cable shift and I would need to run a jack shaft and freewheeling crank. It would be a clean way to have multi speeds if it will hold together. I need to figure out about how much power it can take.

 

[LandSpeedRecord]

Better yet, if I could run that hub AS the jack shaft I could change the reduction going into it and have a gearing range right where I need it. Probably one of my best options if I could make it work like that.

 

[cannonball2]

Heres my build thus far. Plan to finish the engines drive tomorrow and will post some completed pics of that. I don't know if this will fit all bikes. The driven chain line is closer on the inside. Im using 3rd as my highest ratio(10t/40t) and gearing down from there for lower speed ranges. You would want to do the opposite. In this configuration it nixes the need for the jackshaft, its complexity and its frictional loses. You can make quick ratio changes using only the splined hub driven sprocket in minutes provided you have premade chain sections. Just something to consider. http://motorbicycling.com/showthread.php?t=58233.