Billet rod for 49cc/53cc engines

[Will'smotobikes19]

To those of you that don't know cast aluminum is actually quite porus and holds up at lower rpm in gas engines however it can shatter in certain circumstances. If your rod has broken or just looking to increase power a billet aluminum rod is reccomended for most engines that go karters/ minibikers use. In the M.B. world this holds true even for a small 49cc motor. Since I don't have a spare HS rod or GXH rod I made some calculations from measurements I saw on some pictures. The listing says it is For a GXH50 so could have the 36mm over 35.8mm on huasheng rod. (slightly higher compression).

The piston pin thru hole is 11mm (not pictured).

If you wanted to build a high rpm motor could use the measurements to make one out of 6061 or 7075.

Idea is to use the Honda flywheel and coil with this rod but would give strength to a stock motor.

Center to center of the thru holes would be 61.75mm or 61.8mm (not sure which unless the vernier was exactly on the outer edge and not loose.


Vernier reads 48.8mm inner edge to edge

Vernier reads 14.9mm +- a thousandth perhaps.

Drilling location:

1/2 of 14.9mm=7.45mm
(Could also be 7.5mm if bore is 15mm)
1/2 of 11mm=5.5mm

5.5mm+7.45mm= 12.95mm
5.5mm+7.5mm= 13mm

48.8mm + 1/2 of bore can indicate drill location

48.8mm+12.95mm= 61.75mm
48.8mm+13mm= 61.8mm

Further measurements could be taken from a stock rod but don't have one.
I also believe the bottom rod bore would be drilled after splitting the cap by cutting/machining so the ID is the same on both halves.

Most rods have an interlocking rod cap so V grooves or a step will have to be machined or filed by hand. Not sure about this process as I've never done it.
I had an idea that after cutting the centerline of the bottom rod bore you would hand file or machine the aluminum to fit together (easier to explain in person). Measurements must be made either way to calculate so the bottom bore is still around 14.9mm.


A rough sketch

 

[Wrench]

I see the H/P brain is thinking because ya can't shave the head on a HS 49cc for higher compression.
So your thinking Stroking a HS 49cc But ya think it's worth the trouble?
Your only talking .2mm = 1/64"= .0078" Not gonna make much difference.

The cyl base gasket is probably 1/32" thick. Just use a 1/64" thick base gasket and it's almost the same thing.
You'll have very slightly higher compression if that's what your trying to accomplish. The piston will be .0078" closer to the head @ TDC

If ya could shave the head I would suggest to shave it as much as ya can
I've found ya gotta shave at least .040" of a small 4 stroke engine head to notice a slight difference.
If ya can shave .060" to .100" or a little more off the head then it make's alot of difference. ( I'm talking Flatheads)
Now put in a bigger intake valve and ya got something.

Actually I wouldn't try to do speed mods to a HS 49cc cause it can't handle it and will just blow

Maybe all's ya really need is a shift kit to get the power bands ya want That would be my choice for a HS 49cc
Or it's time to upgrade to a predator 79cc 4 stroke

 

[Will'smotobikes19]

I was just scrolling through some old posts on the other forum and that's what they were saying about rod differences. The one piece cylinder does limit it some. Could port and polish the exhaust to match the flange port intake a little. The one piece cylinder is a good idea in some ways as you don't have a possibilty of blowing the head gasket or base gasket and it has about a 3 piece crankcase bolted together at an angle. Mine is just RTV sealed. I had a 79cc once I actually like the 49cc better. If I was going that size I'd probably go 118cc or a 100cc kawasaki FJ100 or something (my neighbor has one sitting around). As for the 49cc clutch seems more reliable, smaller engine at 11.4lbs and fits into legal stuff category more.

 

[mark20]

hmm, i wonder if you could find some bigger valves and grind a custom cam for it, possibly a scooter qmb 44mm piston big bore?

for power, the compression is pretty damn good for it (id guess about 10:1) id say intake and bigger carb and a cam with a custom exhaust will make the most difference.

i know you can fit Predator 212/gx200 carb on there will little modification (on the stock airbox) increasing the overall carb size.

 

[CrazyDan]

I posted the numbers agk gave me that they ground their cams to somewhere. Putting in bigger valves would be tricky with the 1 piece head/cylinder/middle case section. The grubee site says my 144f (the 53cc) has a 7.4:1 c/r . I don't have the means to do any milling so if anyone makes something, I will be buying it.
Edit: found the email from agk. "We didn't make any adjustments to the timing and I found a note that said our cams were .172" lift although I think I remember doing some at .175" lift as well."
I promised to mention that these numbers are AGK's (affordable go karts), they did the r&d on this. I didn't have any part in this, just begged him to not let the cam grind they found to work best die just because it wasn't profitable to produce.

 

[Will'smotobikes19]

Didn't really think of the cam one could be machined with the taller lobe perhaps the good thing is it's just one cam lobe. Activates both valves (most have 2 lobes so I see the confusion). The gear is indeed nylon so would increase sturdiness to make a custom cam.

Sometimes it has so much compression cold that it lifts the whole bike when I pull the starter so compression seems fine.

 

[mark20]

hmm, i wonder if you could 3D print the gear and lobe out of abs or carbon fiber? Does anyone know what kinda plastic honda uses for there gears?

 

[CrazyDan]

Didn't really think of the cam one could be machined with the taller lobe perhaps the good thing is it's just one cam lobe. Activates both valves (most have 2 lobes so I see the confusion). The gear is indeed nylon so would increase sturdiness to make a custom cam.



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Sometimes it has so much compression cold that it lifts the whole bike when I pull the starter so compression seems fine.

That cam with the sintered metal lobe is unobtanium. I tried to buy it and a plastic cam came in, seller gave me half my money back when I complained. If you can find a seller with the sintered metal lobe I'm gonna be all over it.
The lobe isn't made taller, the circle is made smaller.

 

[Will'smotobikes19]

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Type C but there's no selector probably do the same thing and give a nylon.

 

[Will'smotobikes19]

I just thought if you were making a CNC rod you could add to the length a little maybe getting 9.0:1 or 10.0:1 along with the cam and honda flywheel. It would be like a stage 4 50 lol.

Here is how to do the fly and coil:

[How-To] Ungovern HuaSheng 142f

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