Predator 79 Transmission Options?

Status
Not open for further replies.
Wed. Nov. 18, 2015

I got my GTC Jackshaft Kit yesterday and did a trial fit. Boy is it going to be tight on space. Still can't quite tell if it will work but it's close enough for me to go for it.

I might have been able to save myself $55 by ordering part #1056 instead of #1055 but it's not clear if the plate alone includes the bearings. I won't be able to use the shaft or sprockets so that's $55 for just 4 bolts (one should be shorter btw). The kit came with a 17t and 10t sprocket both #35 chain. That's too bad because I can't use either one. Also, the kit did not come with any chain.

The 17t needs to be replaced with a 33t. I'd like to replace it with something larger but it's getting very close to the exhaust. A 33t is 4.2" dia and a 44t is 5" dia. I had better go with the 33t to stay on the safe side.

The main issue with the included 10t is that it's for #35 chain also, but since it will connect to the SBP Jackshaft, it needs to be 1/8" (1/2" pitch). Another issue is that "c-type" does not have locking screws and there is not enough room for a lock collar. The shaft it came with has a stop at the end but I'll probably need to use a different length shaft. There is NO extra space between the GTC & SBP jackshaft sprockets (if I want to do a cool "tight" setup).

There are some other issues when I try to put the SBP 9t sprocket on the GTC shaft instead. Namely, the integrated b-hub is too wide and if I flip it around, I don't have spacers small enough to clear the chain! If it were only 0.65" thick (not 0.875") perhaps it might clear. Another option is to find a 9t c-type sprocket (without set screws) and either find a real small lock collar to use or perhaps just weld the sprocket to the shaft (or, use a shaft like the GTC one with the built-in stop at the end).

Here's what I found and ordered...


- - - - - - - - -

Tritan #35 Sprocket [35BS33HX] 3/8" Pitch, 5/8" Bore, 33 Teeth, 4.2" dia,
http://www.globalindustrial.com/p/m...35bs33hx58-38-pitch-58-finished-bore-33-teeth

MowForce # 9322 Go Kart #35 Roller Chain C-35 36" w/Master Link
http://www.globalindustrial.com/p/o...go-kart-35-roller-chain-c-35-36-w-master-link

#35 J35-60 Chain Tool
http://www.globalindustrial.com/p/motors/sprockets/Roller-Chain/35-60-chain-tool

AZ8555 (x2) - One Piece Locking Collar 5/8 ID x 1 OD x 3/8 W
http://www.mfgsupply.com/az8555.html

AZ2180 - "C" Type Sprocket for #40/41 Chain, 9 Tooth, 5/8" bore
http://www.mfgsupply.com/az2180.html

- - - - - - - - -

IMG_2409-SM.jpgIMG_2410-SM.jpg
 
Wow, not much room! You could replace the SBP 17T with a #35, that would also allow you a little more reduction, and it lets you keep the 10T #35 the GTC plate came with.

Toothcount * pitch \ Pi = roughly the diameter of a sprocket at chain pin. Therefore the SBP 17T is ~2.7" (17 * 0.5 / 3.14). A 22T #35 is 2.62", a 23T is 2.74".
 
UPDATE

I welded the engine bracket together so I could grind off the raised nub holding the two pieces together. This allowed for the motor to sit flat and also gave me a little extra room. This allowed me to fit the SBP 9t on the end of the GTC jackshaft.

The 15t cog for the rear wheel showed up and I got it installed. I was concerned that it wouldn't fit because it wasn't the correct part number but apparently all 15t and smaller cogs are flat instead of dished so it fit fine and wasn't too difficult to install. Since it is flat the chain is now misaligned by 1/8" or so. I will have to move a couple shims in the bottom bracket which should be quick and easy.

I received the 40t sprocket as well and installed it. I had to lengthen the main drive chain a few inches to get it to fit.

It might have been a good idea to use #35 chain to attach the GTC jackshaft to the SBP jackshaft but there probably isn't enough room there anyway. Anyway, I have 3 of the 4 chains installed now and everything is looking pretty good! I'm waiting for another 9t and #410 chain to connect the SBP jackshaft to the 48t pedal sprocket.

I still haven't fired this thing up. I forgot to connect the plug wire and had to take everything apart and remove the engine to put it on. Hopefully I won't have to do much maintenance that will require engine removal, once it's all finished. I suppose it goes with the territory though, I DID want everything very tight.

While waiting, I installed the throttle assembly along with mirrors, bell, and kill switch.

Next, I need some fuel line, a filter, a gas can, and engine oil. Time to see if this thing will fire-up and if stuff starts spinning (without exploding or killing me)! ...a very exciting time.

IMG_2415.jpg
 
Looks like a really sturdy setup. Only thing I would've done differently is I wouldn't use such a tiny rear sprocket; it means there's a huge amount of torque pulling the axle forwards- wearing the right hub bearing extra fast and pulling on the bicycle chain super hard. If you used a larger rear sprocket (I'd go for ~36t), you could get away with less primary gear reduction (maybe even eliminate a jackshaft), while having a higher fraction of the chain tension going towards spinning the wheel (more leverage) vs. pulling the axle inwards.

I say this because I built a 5 speed bike with a 140cc 2-stroke lawnmower engine, and in 5th gear (3500rpm=around 40mph), when I look down the chain is moving at a ridiculously slow speed- like if I lug the engine I can follow a specific link with my eyes. Which means there's tons of axle/chain torque. My 5th gear sprocket is 15t- same as yours, but my wheel is 20" and I assume yours is a 26"... which is worse because more rotating torque is required.

Now I don't really think it will be much of a problem for you with the 79cc (2.5hp?) engine and centrifugal clutch. But my bike could do wheelies in first gear from idle without even popping the clutch, and had a top speed something like 60mph (don't want to test it and die/throw the rod/explode the flywheel since the engine is ungoverned). And if I was doing it again I would definitely go for larger rear sprockets, to take some strain off the components. I broke a brand new 3/32" Z-chain twice, each within 5 minutes. I've been having no problems with wide 1/8" chain however the side plates keep on shifting outwards on the pins (luckily the pins are extra long, unlike the flush-cut pins on the 3/32"). There's also 3 missing teeth on my 1st gear sprocket (not a problem), and I broke the rear freewheel twice before welding the sprockets directly to the hub. Some of these problems might've been more caused by my shifting system, but it just shows how much force there really was on that little bmx chain.
lawnmower bike shifting.jpg
This is my chain/shifting setup, which would take 5 paragraphs complicated to explain lol. Basically all the extra tensioners/guides/etc. are needed because the rear cassette is welded right to the hub. It's extremely dangerous (the wheel locked up many times during the refinement stage)... I probably wouldn't do it this way again. I was also rushing when I was making it and I started it before I had a welder- so I was stuck with all these crappy no-welding-required designs.

lawnmower bike.jpg
here's the whole bike by the way

(end ramble) But like I said I don't think it will be a problem with your setup; or at least not any time soon. And I see that you're trying to make it with pre-existing components anyways. What you could do though, if it ever actually becomes a problem, is use a disk brake hub and bolt a larger sprocket to the disk brake flange.
 
Thanks for your input Keatonx! Your ride is pretty crazy looking. :)

I hope rear torque is not a problem for me. I just replaced the rear 18t with the 15t and the front 30t with a 40t in hopes that it would REDUCE the amount of torque on the hub. ??

I'm getting ready to fire it up and try it for the first time. I'm still waiting on a missing gear so it might be next week before I test ride it.

The engine chain is a #35 and the other 3 chains are 1/8" #410 BMX chains. I hope they can handle it.

The wheels are indeed 26" but the tires are 29" x 3" fat bike tires so that probably makes a bit of difference.

I DO want a good amount or torque though. Most people are looking for speed but I'm more concerned with hauling capability. It's a big & heavy steel frame bike, it has a good size motor, I'm up to almost 220lbs, and I'm getting a little trailer to haul around my 80lb dog. I believe that 15 or 20 mph is about as fast as I would ever want to go while pulling the trailer & dog. Without the trailer I think ~35mph is fast enough for me. To go faster I'd just get another regular motorcycle.

I'm getting pretty excited. I ended up spending way too much money and time already so I just hope it was worth it.
 
Hey Cold, looking good!

Make sure you don't forget to install the brace on the jackshaft mount between the 2 sides - that brace was put in the SBP jackshaft to help eliminate mount twisting.
The early SBP jackshaft mounts did not have that brace, and mounts often got twisted - causing increased jackshaft and bearing wear. I had to replace mine with a newer model.

Also, for the RHS jackshaft - the 9T output to the outer pedal crank - you may want to use a full halflink chain on that. That will help you get the exact length you need.
I recommend KMC HL710L. Keep us posted!
 
Status
Not open for further replies.
Back
Top