Twin Pocket Bike Engines Build

[5-7HEAVEN]

I'm vacationing in sunny Arizona and will return to this project of mine in a few days. I am missing it, being gone almost a month.

I bought two of these engines today. They should arrive in a week or so:
http://www.ebay.com/itm/49CC-2-STRO...ash=item41b5865991:g:120AAOSwDiBZKSF3&vxp=mtr

I have this: pipe at home:
http://www.ebay.com/itm/2-stroke-43...501869?hash=item541e4b43ad:g:MwEAAOSwBLlVQ8v8

If that doesn't fit, I'll buy these:
http://www.ebay.com/itm/Mini-Pocket...m2a196cdfc6:m:mueuCeIYc4TEERdpwowERDA&vxp=mtr

I might need a few spare coils like these, just in case:
https://www.ebay.com/p/stock-replac...-mta1/1742287653?iid=172467392426#UserReviews

 

[5-7HEAVEN]

Tony, yes the CY46 engine is FAST on flat ground with friction drive, and a dog going uphill.
With a shift kit and 15:1 in 8th gear, my bike was fast on flat ground and climbed steep hills from a standstill like a mountain goat.
If it weren't for its undependable clutch, I'd still be using the CY46 engine.

 

[5-7HEAVEN]

I'm still gathering parts for the build. It's a slowww project.
For kicks, I bought a shiny chrome $20 timing chain cover for a small-block Chevrolet engine. It'll serve as a chain guard for both engines (The big-block Chevy timing cover I was going to use was okayyy. However, it was heavier and wasn't shiny chromed).
I'm cutting up an old steel bed frame to fab motor mounts for both engines. I found it at the curbside trashpile. I was supposed to buy one on Craigslist Sunday morning. The seller postponed the sale to Monday at 9am. I was walking my dog at 6am that Monday and stumbled upon the free bed frame.
Lucky timing.

 

[5-7HEAVEN]

I trial-fitted the exhaust pipes I had on hand.

The best fitting ones were the SBP expansion pipes. They cleared the proposed motor mounts on both engines, allowing the Cag powerplants to mount in a horizontal "spoon" position, instead of horizontal "face-to-face".

I've used the SBP pipe on a CY46 5hp engine with a shift kit. It produced sufficient power. The amazing part was that it quieted this loud engine to the sound level of a 1957 Singer sewing machine. I swear I could hear the piston ring scraping the cylinder wall at idle speed.

 

[5-7HEAVEN]

I bought this China Girl poo poo pipe to trial fit onto my pocket bike engines:

http://www.ebay.com/itm/49cc-80cc-2...ash=item27f239a693:g:sxMAAOSwWKtUucEP&vxp=mtr

The pipe is cheap, clean and simple. My friend Rick had it on his CY46 4.5hp engine. His best time was 53mph on the flats.

That's more than enough for my build.

 

[5-7HEAVEN]

Time for a major engineering change.

While assembling and disassembling the bottom bracket, T8F chainring sprockets, freewheel and bolts, it dawned on me....
This chainring assembly is massive and HEAVY!!!
I was going to use TWO 72t solid sprockets(no lightening holes) and two 9" diameter stainless steel(SS) discs 1/16" thick. The SS plates form a "sprocket sandwich"(chain guard) with the lower engine's 8" chainring sprocket. This should prevent the inside 72t sprocket from chain jumping either way and wreaking havoc.
Also on the bottom bracket shaft is another "sprocket sandwich"(chain guard). It is a 24t chainring, 4" in diameter, with two 5" diameter SS discs 1/16" thick, one freewheel, one sprocket adaptor and a spider adaptor, along with five M5 bolts and 25 nuts and washers.
And of course the pedals and arms.
Even if I trimmed the excess weight off the 72t sprockets and 9" SS discs, the assembly's mass and two engines' torque might be enough to shear off or bend the M5 thru-bolts, creating mass destruction.
I had intended to drill all holes to accept M6 or maybe even 1/4" bolts. Maybe that wouldn't be able to prevent damage.

Here's Plan B:
Change all the running gear from T8F (pocket bike) to the much smaller #25H chains and sprockets(also pocket bike stuff).
The 24t chainring drive sprocket and chain will remain 3/32" size.
If the #25 chain is strong enough to be standard issue on pocket bikes, they should be able to handle each individual engine's torque. The lesser inertia with lighter components should also help prevent breakage..

More researching.....

 

[5-7HEAVEN]

Plan B - #25H Running Gear:
engine sprockets
http://www.ebay.com/itm/FOR-25H-CHA...ash=item33cf89ff5f:g:DbkAAOSwq1JZKID2&vxp=mtr
chains
http://www.ebay.com/itm/3-Feet-25H-...ash=item4b0de89bbf:g:~SYAAOSwiONYOg01&vxp=mtr
rear sprockets
http://www.ebay.com/itm/25H-55T-54m...ash=item3d2206c1b6:g:j6QAAOSwARZXo~81&vxp=mtr

6" SS discs
http://www.ebay.com/itm/1-16-0625-S...234721?hash=item2ee5d1e8e1:g:U3IAAOSwLVZVqZSZ

5" SS discs
http://www.ebay.com/itm/1-16-0625-S...461172?hash=item2ee6ba3f34:g:U3IAAOSwLVZVqZSZ

The new gear ratios are similar to the original T8F running gear. Originally, 1st gear and 8th gear were 46.36:1 and 15:1(like a 37-tooth sprocket), respectively. New gear ratios will be 43.29:1 and 14:1(like a 34-tooth sprocket).
The new 7th gear ratio is 16.55:1, like a 40-tooth sprocket.

 

[5-7HEAVEN]

I've learned that the M6x80mm bolts holding the pocket bike engine's cylinders and heads are its weakest link. The short bolts loosen up under the engine's vibrations, allowing the gases to blow by between cylinder and engine block.
Sooo, I ordered M6x100 STUDS to replace the cylinder bolts.
The longer studs allows me to bolt an extra nut on them, inside the engine block. Outside the block will be another nut and lock washer. At the outer end will be lock washers, nuts, then Nylox nuts. And Lock-Tite.
Studs:
http://www.ebay.com/itm/M6x100mm-Stainless-Steel-Double-End-Threaded-Stud-Screw-Bolt-5Pcs-Z3K2/122483028065?_trksid=p2045573.c100507.m3226&_trkparms=aid=555017&algo=PL.CASSINI&ao=1&asc=41375&meid=5e0ec7a2b0a74fd4ba36ff0169736263&pid=100507&rk=1&rkt=1&

 

[5-7HEAVEN]

I picked up bed frame rails to fab engine mounts.
They were tough to cut and drill holes, to fit onto my bike.
They were also heavy. so I bought two of these:

http://www.homedepot.com/p/Everbilt...teel-Angle-with-1-8-in-Thick-801477/204225769

I'd also tried angle iron in 1"x1"x.125" and 1.5"X1.5"X.125" size.
They were also too heavy. The .75"X.75"X.125" steel was light, strong and rigid. I cut them oversized and bolted them onto my frame. When the engines are perfectly aligned, I'll trim the excess and weld them onto the frame.
Bolted between the engines and iron mounts will be 3/8""X5"X6" aluminum plate.

 

[5-7HEAVEN]

The .75" angle iron mounts MIGHT not be strong enough, once I start drilling engine mounting holes.
Soo, I'll weld on 4"X5"X.125 steel reinforcing plates, then bolt on .250" adjustable aluminum engine plates of the same size.

 

[Tony01]

Bed frame rails are made of some of the worst steel out there. Believe me I tried using em... For a license plate mount. Cracked no matter how many times I welded it. You want real metal like the stuff sold at osh or hd.

Although bed frame rails do see some vibration in use under a mattress it isn't enough to crack them...

 

[5-7HEAVEN]

Yes, I bought iron from HD.

 

[5-7HEAVEN]

Don't you just hate it when the vendor sends you the wrong parts?
They said in 3 different parts of the ad "#25H sprockets".
They sent me #40 sprockets.
Not even close. #25 chain has about 1/4" pitch; 40 sprockets have 1/2" pitch.
I was gonna use 9-tooth/55-tooth sprocket combination in #25H.
Apparently the 9t/25H sprocket doesn't exist; it's a misprint.
Now I'll be shopping for 15-tooth/89-tooth sprocket combo in #25H drive.
The projected 8th speed of 15t/89t will be akin to a 33-tooth sprocket. Seventh is like a 39t cog.
With the 9t/55t, final drive would've been 34-tooth sprocket. Seventh gear would have been like a 40t.

Close enough.

 

[5-7HEAVEN]

After hours and hours of searching, I found and bought 3 sets of 15 tooth and 89 tooth sprockets on ebay.
Now 1st, 2nd and 3rd gears will be likened to sprockets having 103, 78 and 69 teeth. Low gears come in handy, as will the matching 7th and 8th speed of 39t and 33t sprockets.

 

[5-7HEAVEN]

The chrome China Girl poo poo pipe is a perfect fit for the bottom pocket bike engine. The top engine's angle iron frame mount's obstructing the pipe, needing rerouting at the head pipe.

 

[5-7HEAVEN]

A major change in the engine line up:

Harnessing modified Cag engines in a daily driver is asking for trouble.
Sooo, I'll install a stock, 2.5hp pocket bike engine topside for now. The 4hp Cag will find duty as the bottom engine and have a shorter connecting chain.
This way, it'll be easier to work the bugs out of my new build. The stock engine does yeoman duty as the main power plant to get to and from work. The beastly engine will be the back up.There are 12 road passages along the trip, where brute power will be sorely needed. When I get to those areas, I'll start up the second "twin".

 

[5-7HEAVEN]

Both engines' cranks will be spun-started by a cordless Milwaukee drill, which fits into my "man purse".

It'll be interesting to see if I can start one or both engines while I'm coasting on The Blue Twins.

Update: The top(stock) engine's throttle will be controlled by my right hand.
That way, I can fiddle with the throttle, whilst I stick the cordless drill into the flywheel socket on the left side of the engine.

 

[5-7HEAVEN]

My second poo poo pipe arrived, as did a completely stock pocket bike engine.

It's a good thing the motor mounts are still temporarily bolted on.
The top engine needs to be raised 1.25" off of its motor mount, in order to make room between its exhaust flange and motor mount to fab exhaust head pipe bends. Raising the top(stock) engine this amount leaves .25" clearance between the bike's top tube and the top engine's spark plug boot.

Both engines use the same China Girl pipe. The top engine has exhaust clearance problems, but the bottom engine does not.

Why is that, one might ask?

It's because both engines' sprockets cannot be on the same vertical plane with its corresponding chain ring sprocket on the BB. The bottom engine's sprocket aligns with the chain ring sprocket in the middle of the BB. Because the outer chain ring sprocket is 1" from the middle sprocket, the top engine must be extended 1" further outward, deeper into its motor mount. There is no way to clearance the 3/4" x 3/4" angle iron mount without weakening it substantially.

.

 

[5-7HEAVEN]

The vertical distance between the top engine's sprocket and the bottom bracket(BB) is 14".

Because pocket bike engines are short in height, the bottom engine is mounted 3.5" above the BB.

That's VERY low.

However, there's almost 8" distance between the BB and the bottom(highly modified) engine's sprocket.

The chainring sprockets I'll use have a 3.75" radius. Lots of room to run the chain.

I'm using offset crank arms. They have .75" clearance on both sides of the bottom engine.

Yanking two engines' pull starts was not something I was looking forward to. Sooo, I'll be using electric drill starts on both pocket bike engines (I have a separate thread on "Cordless Drill Starts".

By removing the engines' pull starts, I gained 1" clearance on the bike's left side.

 

[5-7HEAVEN]

I'm cutting off the radius bends of a spare bicycle handlebar to use to fit the CG pipe onto my top(stock) pocket bike engine.

This is a true test of spatial intelligence.

I have great respect for craftsmen who fabricate custom headers for automobile engines.