SBP shift kit performance mods

[jon.karak]

I consider the shift kit the most valuable component on my motorized bicycle. It allows me to take advantage of the power band of the engine, better fuel economy, manage hilly terrain better, and allows for future full-suspension bicycle upgrade. It also steps the RPM down to emulate the normal range of human cadence, thereby keeping performance within the normal standards of bicycle engineering.

I use my bike as a commuter, so durability and dependability are on the top of my list. The following are a few mods that have helped improve the performance of my shift kit, and I would recommend them to anyone who installs one on their bike.

1) Improved upper jack-shaft bracket: (see pictures here)

• The upper bracket is reinforced with a slender aluminum block
• The unit resists deforming and twisting around the seat stay
• It prevents the engine from yanking the jack-shaft out of true
• Not sure if the part is is production, but it couldn't hurt to ask the gang at Sick Bike Parts

2) Weld deck spacers: (see pictures below)

• Welding spacers to the engine mounting deck ensures that the 2-pieces of deck mesh together flush
• This prevents creeping engine misalignment
• I used a couple of steel bolts

3) Weld pair of engine stops: (see pictures below)

• This prevents the engine from getting pulled rearward by the force of the primary chain
• Maintains perpendicular positioning of the engine
• Creates adjustment for primary chain tension
• Requires a bit more fabrication => welding angle-iron and some fine-thread hardware

4) Replace #415 primary chain with #410 chain:

• Because #415 primary chain is oversized, the extra distance between inner plates (3/16" versus #410's 1/8") makes the stock shift kit more tolerant of misalignment
• Rather than use oversized chain to compensate for a sloppy system, I prefer to reduce/eliminate the slop
• This allows me to use more appropriate size #410 chain, which is the same as the intermediate chain. This also means that I don't need to keep three different types of chain for one bike, and I can cut a bit of weight too
• There is no difference in tensile strength between #415 and #410 (link)
• So if #410 chain is good enough for the intermediate chain, then stands to reason it is good enough for the primary

5) Reinforce seat-tube:

• The stock muffler clamps that connect the shift kit to the frame are designed to "seat" firmly on an automotive muffler. When used on a bicycle, they can easily crush steel (Chromoly) tubing
• This damages the structural integrity and strength of the tube
• It also makes it more difficult to adjust tension of intermediate chain
• At the time, I did not follow the suggestion in the installation manual to insert a seat post deep into the seat-tube. The next time I put this kit together, I will.

6) Small spacers for engine mounting hardware:

• The engine mounting deck has 5/16" slots, but the hardware that secures the engine to the deck is less than 1/4" wide
• Eliminating the gap between these two dimensions eliminates the possibility that the engine could shift laterally
• I haven't found anything commercially available that would provide just the right amount of spacing. Shoulder bolts would theoretically be the best solution, but I haven't found them in the right size either
• Having resolved the other issues 1-3, I'm not as concerned with this one, but I'm still looking for the right parts

7) Access hole for oil changes:

• Cut a small notch in the engine mounting deck directly below the oil drain
• Replace the plug with a right angle elbow
• Add a small length of tubing
• Keep the tubing secured and out of harms way. If it ever gets damaged, you are liable to lose all of your oil, and that could put you engine at risk of a catastrophic failure.
• I haven't tried this fix yet, but I plan to once the season is over

If you have tried alternative solutions for improving the performance of the Sick Bike Parts shift kit, or have some better alternatives, please share your wisdom.

 

[The_Aleman]

hey Jon, I like your style! That's some nice overkill. I have the original SBP 4-stroke mount with none of the improvements of the newer one. My humble opinions:

1) SBP has already addressed this with an improved jackshaft bracket. I battled this ever since the first time I pulled the "go" trigger hard in first gear and found out my 4-stroke can do wheelies(!) if I pull and pedal.

2) This is nice for peace of mind, but I haven't had any problem with deck alignment. Still, I wouldn't complain with this improvement. Great idea!

3) I like what you did here. It's overkill and possibly unnecessary, but that level of fine-tuning can't be bad at all. When the primary JS chain is loose, it causes drivetrain oscillations at high drivetrain speed.

4) My SBP kit didn't come with 415, it had 410 (BMX) chain at all points. I now run 410H, also made by KMC. It's a HD version of 410. When I wear this stuff out, I'll be switching to half-link chain.

5) I put a cork-stuffed shortened seatpost all the way down the seat tube to prevent seat tube deformation. A piece of conduit might work even better, with enhanced mount stability. Lots of 2-stroke builders use that method with great success.

6) This might be unnecessary, those wide slots offer a lil bit of extra drivetrain fine-tuning. I run fender washers between engine and mount and lockwashers on underside of mount. My engine doesn't move, even tho 1 of the bolts has stripped out and is missing.

7) This is rendered moot because it's very easy to make your own remote oil drain. Even if this access hole existed, it's not as handy as having a hose with a petcock to drain oil easily into a container. Well, unless that remote hose went down the access hole....

Thanks for posting, Jon!

 

[jon.karak]

In my opinion, its never a bad idea to shed weight. Even though there are suitable work-arounds to add on a remote oil drain (like installing a Drainzit kit), it still adds weight.

Removing a bit of material from the mounting deck--maybe about the size of a nickel--reduces weight without any practical reduction in strength. If that were done as part of the manufacturing process, then the buyer has more options to customize their bike. And more customization means more sales for SBP.

A simple drain could be an elbow and some tubing. But I think a really slick solution would be 90-degree miniature valve, similar to a outdoor garden-facet but with a 6mm allen head instead of a big cast-iron knob. A fully developed version could even be sold separately, or as a fully integrated "delux" shift kit.

Besides, producing parts with less material theoretically would also save the manufacturer money.

 

[jon.karak]

And speaking of weight, I would spend money on a kit that reduces weight by using lighter materials. I would love to see a shift kit machined out of Aircraft aluminum. Even if the engine mounting deck and the upper bracket had to be a bit bulkier, there is enough dead-space that could be put to good use. It could be done without making the overall kit any bigger.

...or even Titanium.

 

[MotoMagz]

Jon,nice right up and work.I too have not ever had the motor move on my 4 stroke shift kit.I have had the thing start to move downward on me.Then I saw something OcScully had done to his set up.Since I added the shims the moving has stopped .....See photo below

 

[spad4me]

These parts work very well together.
They are my standard setup for a shift kit

8 feet of compression-less shift cable housing from a local bike shop.
a seven speed mega range free-wheel from amazon
Amazon.com: Shimano 7-spd Megarange Freewheel, 14-34: Sports & Outdoors
a seven speed sram twist shifter with adjuster on the handle end from amazon.
Amazon.com: Sram MRX Comp Twister Mountain Bike Shifter - Rear: Sports & Outdoors
a Shimano mega range seven speed derailuer with pulley and adjuster from amazon.
Amazon.com: Shimano RD-TX51 Tourney Mega Range Rear Derailleur 6/7 Speed Hanger Mount Black: Sports & Outdoors
plus freewheel remover silicone lube fuss and bother

Both the twistshiftcontroller and the derailuer have a cable end adjuster making small adjustments very easy.

I have not missed a shift since I started using this setup.
I know the derailuer is out of stock for now they sellout all the time.
I make my own shift kits with some sick bike parts, some thats dax parts, and others parts. For a fraction if what they sell for.

 

[reclaimer]

Old thread I know. I ordered up one of those RD-TX51'es, a mega range freewheel and bb adaptor. Moving my shift kit from my lts to my roadster. Will post up results in a week or so.

 

[The_Aleman]

Cool, Reclaimer! You might want to make your own thread about that. I also have an RD-TX51 that I plan on 4-stroke, shift-kitting soon.