Gary Fisher Marlin

Ptenwal · Sep 26, 2010

Hey,

I currently have a 21in Gary Fisher Aluminum Mountain bike. It has been converted to a rigid single speed with; Surly 1x1 fork, Avid bb7 disc breaks, Continental Town & Country Tires, Sun Rhino Light Rims, and Shimano Disc Hubs .

Recently, I have decided that a motor "needs" to be added for a new project. I purchased a Grubee 66cc/80cc GT2 build kit online and the "universal mounting brackets." My hope is that the over sized down tube will not be an issue when mounting the engine. I also bought a King 34t sprocket to attach to the disc mount on my rear hub. Realistically I can't imagine this being as simple as a straight "bolt on build," but I remain optimistic. I have a lot of experience with bicycle mechanics, but zero when it comes to engines.

Does anyone have any suggestions or comments about; engine compatibility with the frame, chain alignment, the selected gear ratio I have gone with (my thought was that a smaller sprocket would eliminate issues with chain clearance). Also, Tomicog makes fixed gear cogs that bolt directly onto a disc brake hub, but the largest size available is a 20 tooth. Is this way to small for a 66cc motor and a 175 lb rider?

Thanks,

Paul

scotto- · Sep 28, 2010

Ptenwal said:
Hey,

I currently have a 21in Gary Fisher Aluminum Mountain bike. It has been converted to a rigid single speed with; Surly 1x1 fork, Avid bb7 disc breaks, Continental Town & Country Tires, Sun Rhino Light Rims, and Shimano Disc Hubs .

Recently, I have decided that a motor "needs" to be added for a new project. I purchased a Jet 66cc/80cc build kit online and the "universal mounting brackets." My hope is that the over sized down tube will not be an issue when mounting the engine. I also bought a King 34t sprocket to attach to the disc mount on my rear hub. Realistically I can't imagine this being as simple as a straight "bolt on build," but I remain optimistic. I have a lot of experience with bicycle mechanics, but zero when it comes to engines.

Does anyone have any suggestions or comments about; engine compatibility with the frame, chain alignment, the selected gear ratio I have gone with (my thought was that a smaller sprocket would eliminate issues with chain clearance). Also, Tomicog makes fixed gear cogs that bolt directly onto a disc brake hub, but the largest size available is a 20 tooth. Is this way to small for a 66cc motor and a 175 lb rider?

Thanks,

Paul

Yes, a 20t on the rear would be way too tall (too small) of gearing for any small engine to pull realistically. The 34t is pretty much on the tall side as well.....good for the top-end flats but will suffer on any hills and on take-off's from a stand still.

Nice bike, it should motorize well with minimal issues, just be sure to keep some of that braking power as it will be needed. I'd run a 44t on the rear for all practical purposes....just my opinion, of course.

bluenosegoat · Sep 29, 2010

Thats a very nice bike. You shouldnt have much difficulty with the engine install. If your engine has the larger front mount you should be all set. I prefer a 41 tooth sprocket but I also ride in the city of mesa- no hills to speak of. You might want some suspension on the front end though. I love my shocks on longer rides compared to my sons bike with the rigid fork. There doesnt seem to be much room between the rear tire and seat post tube if you might be thinking of some gears with a shift kit but you will have a blast either way. Good luck and post some pics when you are done

Ptenwal · Oct 3, 2010

After six trips to home depot...36 hours of obsessing over this build here it is.

-I had to modify the stock rear sprocket to mount on inside of my king sprocket which then mounts to the disc hub for chain alignment.
-A piece of two inch steel stock needed to be cut and drilled to make the rear down tube engine mount. Some small adjustments to the steel plate needed to be made for chain clearance.
-20 hours of labor and elbow grease.

It's really fun, and here are some pics.

bluenosegoat · Oct 3, 2010

looks great! So how do you like it? Worth the elbow grease? Just incase you werent aware you can turn the cylinder head around and make the plug face forward if things are a little tight up top. Nice looking bike for sure.

Ptenwal · Oct 17, 2010

The latest updates on my bike...

-34 tooth sprocket & top hat adapter
-Chain Tensioner
-Rear Brake (I was unable to mount the rear disc due to lack of clearance with the rotor, sprocket, and hub...In the end, it just wasn't meant to be....sad)
-Dual pull brake lever
-Seat Tube Engine Mount & Fabricated Mounting Plate
-Saddle

The ride is now incredibly solid and extremely fast...

PS:

I really want to convert an MSR fuel bottle into a gas tank so I can lose the hideous tear drop can...Does anyone have any suggestions or ideas about how that could be accomplished?

Could I just screw on a brass fitting and attach the fuel line to the shut off control? Or does a gas tank need to be vented?

Thanks,

Paul

bluenosegoat · Oct 17, 2010

A fuel tank does need to be vented otherwise no fluid would flow---like turning a bottle of water upside down- if there is no air to replace the liquid coming out the liquid wont come out-- maybe a straw is a better analogy? Anyways nice looking bike! I agree bummer on no rear disc but most of the stopping force is in the front (like on a car) anyways but sure would've looked cool. Now you need an SBP pipe if you think your bike is fast now! Hold on!

Where did you find that chain tensioner? Very nice compared to the kit's
ps:I like to drill and tap a bolt into the chainstay to make sure the tensioner wont eat spokes

Ptenwal · Oct 17, 2010

Do I really want to go faster?! The thought of hitting the pavement at 30+ mph still keeps my riding style relativity conservative. "Catastrophic engine & mechanical failure" is quite a disturbing thought to me... Thanks for the gas tank advice. If nothing else, I would like to get something smaller to streamline the look.

The chain tensioner is from a local bike shop (DMR STS)... Typically it would mount where a dérailleur attaches on the bikes drive side. Check out Jensonusa.com, They are one of the best bike parts suppliers. Also, I really don't want to drill into the frame...I moved the tensioner closer to the bottom bracket. If it does get pulled inward, the rubber wheel will contact the rim, hopefully preventing the lose of any spokes...

bluenosegoat · Oct 17, 2010

The expansion chambers out there let the little 2 stroke develop the power they are supposed to not to mention sound like a 2 stroke should. I hear you though on the speed! I have scares from a 37mph crash on chewed up asphault in 115 degree weather! Nothing like crashing into a cheese grater! I just like getting my all from what i have. I have a rock crawler that will idle in low and you cant hardly see it move but it has 413 hp if you want it!
Right on with the chain tensioner, I've gotten parts from Jenson usa before but never thought to look for chain tesioners- thanks! I dont know if drilling the frame creates that much weakness since you are filling with a tapped bolt that is tight but ....... better rubber than spokes thats for sure! I look forward to see what you do for your fuel cell.

Ptenwal · Oct 18, 2010

Sad news.

So I'm riding along and things are great. Then I notice the engine making an unusual rattling noise. I'm about a 2 miles from my destination when the dreaded sound of metal clanking, snapping, and hitting the pavement breaks. I stop and give everything a once over. Bolts are tight, chain is taught, wheels are intact, breaks work, and the engine is secure. (HMM!? Mildly unsettling, but mind you, I've got places to be!) I hop back on and proceed to ride cautiously to my destination. The ominous rattle still plaguing my ears...

The bike sits for 2.5 hours and I decide to try and nurse her back home. 1/2 a mile into the the ride I lose all drive / throttle power. Needless to say I did not want to stop and tear the engine apart in the middle of DC, so I peddle the remaining 8 miles UP HILL to get the bike home. Along the way, I experiment and release the clutch a few times to see if I can get the motor started up...The drive sprocket seems to turn freely with or without clutch action. (If I wanted to peddle, I would have ridden one of my other three bikes!)

After doing some research I think I might have broken a woodruff key...Hopefully, this won't be a horrible problem to fix. I've only put 65 miles on the bike and It's left me stranded twice! I enjoy working on it, BUT riding it is even better.

Should I disassemble the entire clutch to make sure everything is in its correct place? If so, could someone please post the address of the Manic Mechanics Clutch Diagram to this page for easy reference?

Thanks, everyone on this site is extremely helpful.

Paul

http://motorbicycling.com/f30/animated-view-motorized-bicycle-clutch-assembly-8939.html

PR3C150N · Oct 19, 2010

Where did u get the procket from?

bluenosegoat · Oct 19, 2010

Thats a real drag! I had a smiliar situation with my engine. Started making a clicking grinding noise. Very strange as all seemed well. Once the clutch cover was off I finally noticed the small pinion gear (the one mounted to the crankshaft) had a crack in it! It was just a hair line crack and not easy to see but it happened right at the key way. Fortunatly no other damage was done (also fortunatly there are no hills in Phoenix for the pedal ride home!) easy fix but made me very wary of the reliability factor. 2.000 miles later (knock on wood) no problems!
I keep at least two motorized bikes for myself at all times though- gotta have back up- as they are my main source of transportation for now and I have to be at school on time to get my daughter!
Hope your not to discouraged and the problem is easy to remedy. I dont have the link to the clutch tear down but there is great info from Norm on how to properly adjust and maintain the clutch I think in a sticky.

Ptenwal · Oct 20, 2010

After taking the cover plate off of my clutch, I found the woodruff key sitting in the bottom of the housing. I went to the local hardware shop and surprisingly found a match. However, upon installation I noticed the same cracking issue on my pinion gear, in the exact same spot you described! Hopefully BikeBerry.com ships quickly so I can get back to riding...

Ptenwal · Oct 27, 2010

Replaced the pinion gear and woodruff key, and now my bike is up and running again! I still notice a squeaking noise while idling and slowing down. I think the noise is coming from the left side drive sprocket, any suggestions?

PS.

There has to be a more durable design than a woodruff key? Honestly, something the size of a fingernail clipping taking a motor out of commission seems ridiculous! Just a thought...

PPS.

Took a suggestion and replaced the throttle grip with my matching red grips, and it looks nice. For anyone interested; HAIRSPRAY is a much better alternative to DISHSOAP. It lubricates for the installation, and dries quickly for a lock tight grip.

Paul

purethief · Oct 27, 2010

trying to figure out an inexpensive rear mount option like yours for my seat tube. cant quite figure what you got going on there. did you make that plate or buy it?

Ptenwal · Oct 27, 2010

I used an 1" 5/8's or an 1" 1/2 exhaust hanger that I picked up at Autozone for $3. That attaches to a 2" steel plate that I cut and drilled to fit the U-bolt and engine mount bolts. I notched the chain side of the steel plate to be the same width as the stock engine mount to allow for chain clearance. By flipping the stock engine mount around I gained a flat surface to mount to the steel plate which then mounts to the exhaust hanger, which attaches to the frame. Also, replace the stock engine mount bolts with longer 50 mm bolts. If you have a drill, hacksaw, and file you're good to go...

WildAlaskan · Nov 5, 2010

i am so jealiouse i want a disk brake bike with enough room to mount a motor

Goat Herder · Nov 5, 2010

WildAlaskan said:
i am so jealiouse i want a disk brake bike with enough room to mount a motor

http://motorbicycling.com/f23/scsws-rear-disc-brake-rear-hub-10509.html

http://motorbicycling.com/f23/new-full-suspension-scsw-boxer-7689.html

This a way of doing it that I am found of.

Other folks have put a disk combined with the sproket on the left side

Somebody did it here but I'll be darned if I can find it now?

You can run a J shaft then put the disk by itself on the left side

Go Kart Brakes - Drum, Disc, Band, Scrub

http://motorbicycling.com/f3/rear-sprocket-disc-brake-wheel-12511.html

http://motorbicycling.com/f3/sprocket-adapter-disc-brake-11396.html

Dug through here..
disk brake and sproket combined - Google Search

WildAlaskan · Nov 5, 2010

This a way of doing it that I am found of.

Other folks have put a disk combined with the sproket on the left side

Somebody did it here but I'll be darned if I can find it now?

You can run a J shaft then put the disk by itself on the left side

maybe i should have clarified i wish i could afford a disk brake bike with a jackshaft expansion chamber muffler dellorrto carb and high comprssion head

Ptenwal · May 30, 2011

500 + miles and running well. Recently replaced the clutch pads, air filter, pedals, gas line, and tightened up the wiring and cables. Thinking about upgrading the exhaust, but I'm not sure if it will look right on the bike.

I've worked over almost every conceivable way of mounting a rear disc brake, and have yet to accomplish dual disc breaks. A larger rotor does not have the clearance with the chain stay. Also, the spacing between the break caliber and chain & sprocket is very tight (non existent.) I think my only option is a jack shaft...seems like a lot of complications just for a break upgrade.

Cheers,
Paul

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