Building a Ht Motorized Bicycle or Three.

[Theon]

The Softtail.
I got a short plug from RSE yesterday, Its an NGK BL-6H.
And it allows me to run a straight fire head on the bike, despite the limited frame clearance.
I thought best to just start with an unshaven head, to see what compression I get.
Not much more than 125 PSI, It was 150 before, so I took her for a ride, Big difference!
She's a bit of a slug now compared, didn't want to rev out, boring!
So will be measuring my head displacement on both heads, and work out how much to take off to get her back up again.

 

[Davezilla]

Really impressive work!! I'll be doing some of the same things to mine real soon, working a cylinder jug now but I need to stop until I get some copper gaskets I ordered before I can set up the port timing. So far I trued up the top deck which took shaving off .009" before it was perfectly flat, then I shaved off another .043" to give a total of .052" (about 1.25mm) removed from the top deck. This will get me in the ballpark for setting the squish later so I won't have to cut so much off when I'm fine tunnig the squish since I'm using a lathe to do the cutting and it can be quite time consuming.

Right now I'm running a pretty much stock engine with a Fred head and an expansion chamber off a pocket bike, then I indexed the piston by shaving off 1mm at the exhaust port and transfers as well as shaving off 5mm from the bottom of the piston skirt. This setup works fine while I'm breaking in the engine, power is decent and comes on at a really low rpm which is good for a safe break in, but not so good for all out performance.

I'll be reading thru this thread a bit more as well as my other 2 stroke tuning books before I do any serious cutting on my new jug

 

[Theon]

Thanks Dave,
I prefer not to index the piston, as I see it upsetting the squish band and lowering compression a little,In my opinion Better to raise and shave the jug.
I still have engine no.4 to finish, and plan to make it a little hotter,
Sub said he was sending me a reed valve, as well as one I've been working on.
And thinking to taking Mech Engineers lead with the 3rd transfer and possibly case induction.
I like Fred's heads, but more inclined to go with the Puch.
Which I should order.
Then a big old chainsaw carb!
And looking at a modified dirt bike pipe.
Probably not so much of a 'Daily driver'.
But trying to finish off a few other things first.
Stuffing the cases and making a new inlet port is my next step.
Have access to mill and lathe soon, so need to get someone to weld a bit extra to the cases, or JB weld? which maybe a good alternative.
I think if I helicoil the JB it should hold the reed and carb alright, welding would be better.
Are you using a 40mm crank? That's a big gain in my experience, it's really worth paying the extra for a balanced 40mm bottom end if your planning on building something fast.
And then tuning for revs, probably good to have a milder motor as well for running about on though.

 

[Davezilla]

You're right about the piston indexing, it works but it's more of a bandaid fix compared to actually porting the jug.

I've read Mech Engineer's post and I agree with what he has to say as well, I'll be using some of his tips in my build as well as what I got from the other books by Gordon Jennings and Bell.

How big is that chainsaw carb you plan on using? I know they work well on small 2 strokes and they don't eat up precious space.

I'm thinking about making a KX60 pipe fit mine, the math is already done and they do work well. The one I got now makes nice low end power so I'd have to modify it to make a fatter power band or to be able to rev. It does look cool tho...

I don't have a lot of free time like I'd like to have so this is ore of a toy than a daily driver for me at the moment, maybe after I get my business going I can play more than work.

I saw your method of stuffing the cases with the aluminum plates, I really like that method. those plates are thick enough to bolt on by drilling holes thru the case and tapping the plates, a few welll placed allen bolts always look cool on the outside too.

I got a lathe but don't have a mill yet, you can do a lot with a lathe but milling with it is very limited. the lathe works great for truing the crank, and you can chuck up the jug for accurately cutting off the top deck etc. These cranks have a ton of runout from the factory and truing them up some will definitely reduce the vibes as well as save the bearings.

for welding the reed cage to the case, have you heard of Alumaloy? it's basically a brazing rod for aluminum and you just need to heat it to 700F for it to work. A lot of people can't get the alumaloy to stick tho because it does take practice, and the aluminum needs to be absolutely clean, you pretty much need to keep a wire brush right there while using the stuff to keep the metal clean as it heats up, but it's some seriously strong stuff once it works. I'd recommend one of those infrared thermometers to monitor the temperature as well because temp control is the other key to making this stuff work.
Lots of google and youtube info on alumaloy and how to work it properly. this is a good second choice if you can't get it welded.

JB weld is some really good stuff, but I've made it considerably stronger by mixing in some fiberglass strands to reenforce it. then it may even be strong enough to tap threads into and helicoil.

Mine does have the 40mm crank so that's a definite plus as every little bit counts when making these things more powerful, truing them up and balancing them makes a huge difference in how smooth they run as well as extending bearing life. There's also a little more power to be had just by truing and balancing since the engine has to fight it's self less.

Yeah, I'll definitely have a spare emgine or 3 once I build a high reving one, even the best builds are subject to grenading when ya least expect it when running nearly twice the rpm they're built for. I'm thinking around 5 hp is good for all around use as a compromise between reliability and all out performance as well as still being almost double what these put out stock.

 

[Theon]

I do have some aluminium brazing rods here somewhere, and have managed to get them to do certain repairs, but they make me a little nervous, there seems a very fine line between them working and everything just 'dropping'. Fine for things that were stuffed other wise. I was told to draw around the repair with white chalk, when the chalk starts to discolour, the alloy is about to drop.
I was thinking the JB didn't have to actually hold the thread, more support it, if I drill through the case and use a countersunk head 6mm Stainless bolt from the inside, and use the JB with a helicoil to 'support' it?
But I have an old set of cases for my welder to practice welding on first, he sounds fairly confident he can do what I want. But JB would be cheaper and easy for me to do. I'm sure he'd charge me $50 at least by the time he'd done both cases.
And the 40mm stroke have a two fold benefit, slightly more displacement as well as a significant torque increase. Plus my 40mm cranks have had very good balance and have been quite true, happy doing 9000 RPM. And after lightening the piston even more!
Chainsaw carb is a 'Tilly' from an old 'Muckoluck' 19mm choke and 21mm throat.

 

[Theon]

The Softtail.

Has got the Raliegh's old 'Screeming Roo' Barrel now, with the twin pocket bike carb manifold.
Just going over the carbs again before I mount them.
It now has a polished but unshaven center fire head, with 1mm squish running a .5mm copper head gasket. Netting 125 Psi compression. While I was at it, I borrowed all the lighter piston and wrist pin from the Phantom, and the Phantom got all the heavier stuff.
And the pocket bike got the RT back.
I've had this crank/barrel combo doing 80 Kph, and 9500 RPM before any serious vibration set in. However this exhaust is different.
I've ordered a couple of Hi comp Puch heads, and the Softtail will be getting one.

 

[Theon]

The Goat.

Is getting Discs, BIG Discs!
Exhaust clearance is working out tight but neat.

 

[Theon]

Engine No.4,
Fits nicely in the Old Mongoose, Or at least it will after I open the front engine mount up to suit the frame, the Vee is a little off, but so are most bikes, and will be corrected in the engine mounts with the die grinder. I havn't really done much on it other than a trial cut of the reed opening in my old cases, every week, something comes up and I havn't had a chance to see my folks, or use the mill.
But I'm getting a little curious about water cooling the head.
It's just that here in the tropics, it's pretty warm most sunny days, and with the mods I've already been doing to my bikes, I've found heat a problem. This maybe able to be 'remedied'
a little with adjustments to the timing via an adjustable Cdi, But I figure if I'm planning to make more power than I have been, I'm going to need better cooling.
I'm curious to any suggestions here,
But I was thinking that a standard straight fire head, machined round, with a bit of a lip, level the fins off a little, and drill them for cross flow.
A couple of pieces of alloy tube, The larger being 100mm diameter either ID or OD and a couple of mm thick with a height of around 35 to 40mm. The smaller tube around 30mm for the sparkplug and tube spanner.
Drill out the 8mm head stud holes to a depth of a few mm from above and fit 8mm ID tubes, with a little JB weld or an O ring.
Then either machine up a top for it with o ring seals, or better slill get the whole thing welded up.
Inlet and outlet drilled and tapped with 14mm barbs.
Then when done shave as much as I can from the head, and give it a squish band. Wouldn't give huge compression, but probably just enough.
I've got a nice little radiator from a DT 200, then I just need a water pump.
For this I see a cut to the cases above the clutch flywleel and mounting a 20t crank bevel gear to a plate using the clutch cover bolts and supported be the sprocket cover bolt.
There isn't really enough room for a pump there, but then run a small chaincould be ran to a larger sprocket and running a small pump, is there a pump like what I'm needing that anyone can suggest?

 

[Theon]

The Mongoose.
Today I got the motor mounted to the mongoose, with perfect chain length on the motor side, and needing an idler only on the pedal side.
I will likely make a sprung tensioner at some stage, but don't need it yet.
I also got the rear hubs worked out on both bikes, with both my chains running true, also clearance for the 203 disc, brake caliper, chain, tyre, pedal cranks, expansion chamber, ect on the goat.
I like the way the carb sits 'down draft' and matches the angle of the seat post. I will need to get a big foam filter for it .
I also borrowed a KTM 50 pipe to take a few measurements from and see if it is worth buying something similar to mod.

 

[Davezilla]

Looking good with the new mods.. That dual pocketbike carb manifold looks sick and it should flow plenty good enough.
I've been toying with the liquid cooling idea hear too since I live in a rather hot climate. there's one on Arrow's page that has a liquid cooled head on their site http://www.arrowmotorizedcycles.com/index.html then click thru the slide show pics at the bottom part of the page. It looks like a solid aluminum head that has a small inlet and outlet on the top of it for the coolant to pass thru with a small dirtbike radiator on the side of the frame, but I'm not sure how they're circulating the coolant, probably with a battery operated pump hidden under the tank on the frame, but can't really tell from the pics.
You may be able to fab up a pump that's engine driven and fit it under a centrifugal clutch cover by using that space for the pump instead of a centrifugal clutch.
You could probably liquid cool a puch head by putting it in a lathe holding the head by the spark plug hole and shaving the fins down until you got a round pattern and welding an enclosure to it. You would have to decide whether to keep the top fins or to cut them off as well, then add some fittings to the enclosure and route to a small dirtbike radiator. The other option is to use some aluminum round bar stock and cut in your own combustion chamber then route out the top for the liquid to pass thru and put a shouolder on the outer edge and cut a groove for an o ring, then use another piece of round bar stock to route out and cap off the bottom piece, the o rings will seal in the coolant and you could place the inlet and outlet fittings wherever they would work best for your setup.
If you wanted to liquid cool the jug as well, you could just lathe off the fins until you got them round, wrap in aluminum sheet or tubing with about a 3mm wall thickness and weld in place to seal off, of course, drilling thru the fins etc to allow coolant flow, then put an inlet and outlet fitting so the coolant would flow thru the head into the jug, and back to the radiator.

I'm just throwing ideas out there that could work, but it may be even easier to find a jug that's already liquid cooled from a small dirtbike or scooter that had the same 47mm bore. I was reading a little on some older posts and saw where someone put a Puch jug on this engine by using a longer rod and a spacer with excellent results, but that also got me thinking we could do the same with a liquid cooled setup if we find one that has the same bolt spacing and close to the same bore size.

 

[Theon]

Your right Dave, Puch head could be a better platform for building a WC head.

 

[mech_engineer]

My opinion is that you need to make an 45 angle with the carb respect to the intake like this "Y"

 

[Theon]

The Softails inlet has two curved sections meeting in a Y.

 

[Theon]

The Goat.

I ordered a couple of those spin on disc adapters,
beware, the cheaper ones are for scooters?, and come with a slightly different PCD.
I however made one work for the purpose I needed, and am left with two that are possibly useless.
I am using a double sided(flip flop) hub, both threads are 35mm.
So a 17t freewheel sprocket on the pedal side,
On the motor side, I have a home made 5mm alloy spacer, the 39t sprocket, the 7.5mm 'scooter' spin on disc adapter and then a 203mm disc.
This is all aligned, tightened and then drilled and bolted with 6mm bolts through the steel hub flange.
I'm still trying to decide which pocket bike caliper to go with, Ilike the bigger one, but the smaller one may allow me to go to a 44t rear sprocket, which Kinda sounds like fun.

 

[Theon]

Got the exhaust to clear everything just.

 

[Davezilla]

how much modifying did it take to get the pipe to fit and clear everything? I saw the pipe in your other post and it looks like a better idea than what I was originally planning on using. I don't mind doing a little welding and cutting etc... but the less the better on that thin metal... it's the more time riding, less time welding thing...

 

[Theon]

The Pipe is made from scraps, a bit of 3" exhaust, A bit of bike frame, a bit of scooter header pipe, and a few different front fork sections and probably some old handle bars for a stinger.
It was originally designed to go above the motor on the Old Raleigh,
It was a pretty 'lucky' fit really, and took a bit of panel beating around the crank quite well as the 3" pipe is strong. It took a couple of goes to get everything to line up right, and I have no idea regarding the math.
But I'm starting to believe pipe building is more art than science.
I like the idea of going it the easy way this time with the KTM pipe.

 

[Davezilla]

ah.. I thought you got that KTM pipe to fit in there that quick and easy... I was thinking "damn that was quick...
Ok, I might get a little negative feedback for this one, but have you seen how some of the chain driven Harleys just use the rear sprocket as the sprocket and the brake rotor by sliding the caliper over the sprocket just past the teeth? I was thinking that could be done on these sprockets as well if the caliper can open up enough and reach past the sprocket teeth. It may not work with smaller sprockets and will not work with the ones with the teeth offset to one side, but a 40 tooth ot larger flat sprocket should be fair game.
The benefit is less rotating mass and a disc brake, but the drawback is that the sprocket could possibly warp if it heat soaks from going down a big hill or racing, and I wouldn't recommend it if using a rag joint.

 

[sublunacy]

i just saw a watercooled head yesterday. i will look again for you.

have u tried a piston port w high duration yet? it seems a good idea if no hills.

 

[Theon]

I Usually run 155 exhaust duration on a piston port for a bit of fun up top.
No hills here, but low to mid are still O.K. fun starts around 6000.
but keep to 150 duration for my other bikes, which I find fairly even through the revs.