Cannonball DIYs a CG

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cannonball2

Well-Known Member
Oct 28, 2010
3,682
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Colonial Coast USA.
So the box engine is basically finished. Overall Im impressed with the quality. After much discussion with Map, Dave z and others I have concluded it is a GT5 engine. Basically means its a 38mm stroke long rod(114mm as measured) engine. Here is the thread, lot of good informative discussion on engine type.
http://motorbicycling.com/showthread.php?t=57810

Heres the basic build. I built this engine to be basically stock only machining was to match the transfers and clean ridges/flashing from all the ports. Bearings are SKF both crank and clutch shaft. All fasteners replaced with 1/4 20 hex heads. Head and cylinder trued, no raise in compression. Intake manifold matched to the port, slight trimming top and bottom, both trued, run with no gasket but yamabond 5. This crank had some side play, set clearance to .002 using shims. Replaced wrist pin caged roller with high quality unit, and lighter moped wrist pin. Cylinder stud/nuts replaced with hex bolts tightened on double hardened gr8 washers. No/never use lock washers! Chinese use them for some reason, I believe spacers to keep dumb acorn nuts from bottoming-doesn't work all the time. Installed bent/long clutch arm. The cases run no gasket but are sealed with Yamabond. Since they are so well sealed and the SKF bearings have such good seals I added ATF to the clutch shaft case to smooth clutch action. Replaced drive sprocket to run BMX chain, I really like those chains compared to the bigger ones.
I guess that's about it. As discussed this engine does have the bigger nicer drive gears, which has a taller gear cover. If you wind up with one of these, DONT buy an after market CNC cover it wont fit!
Doesn't look much different than normal in the pics. Notice the bigger gears. The bag is all the stuff I didn't use. For you Noobs DONT think your new engines head is loose because you see daylight around the gasket its usually normal on a stock head. Also unless it just wont fit the proper position for the plug on a slant head is to the rear, it adds less heat to the pistons already hot exhaust side. I didn't know this until recent reading on tuning.
 

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cannonball2

Well-Known Member
Oct 28, 2010
3,682
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Colonial Coast USA.
Pic of the normal head gap. I think the Box O Engine is a good experience if one has basic skills. It costs as much as an assembled engine but then you have to factor in the time to disassemble it to inspect it. You are going to do that right? Plus you assemble every bit of it save the clutch main shaft which came together. Once done you know what/where every bit of a CG engine is. Its a blank slate also as to what you want it to be. Just be advised there are NO instructions provided. But its all here on the forum. I enjoyed the build. Will report soon on how it runs.
 

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cannonball2

Well-Known Member
Oct 28, 2010
3,682
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Colonial Coast USA.
Going to mount this engine today. Will run initially on the NT carb. I bought and identical engine that I will run also next.

A word of advice. I would as has been stated a zillion times on the forum at least remove the head and jug and clean the bottom end to be SURE there is nothing in the case. I found that the common slight misalignment of the cylinder studs, unless held into alignment on jug installation will shave a bit of aluminum from the jug which is free to fall into the case. All of the engines I have were this way. Aluminum particle contamination. Using head bolts eliminates this problem, as well as holding the studs straight and working the jug down slowly. Two things that don't happen in the CG factory.

I also advise filling the engine with a fluid while the jug is off(I just use gas) to check for case/seal leaks. If there are any you will have a poorly running/no run engine depending on how bad the leak is. My last engine was damaged in shipment to the extent that fuel began leaking from the clutch side on cleaning.
I found a crack at one of the screw bosses where the engine took a hard knock, it was basically invisible. Glad I found it then instead of later, or never!
JB Weld took care of it.
 

cannonball2

Well-Known Member
Oct 28, 2010
3,682
221
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Colonial Coast USA.
Well got blown out of the water on swapping the GT5 box motor on to the test mule bike that was built around a Flying Horse motor. You wouldn't think it but These engines are all a bit different. First thing the supplied mounts wouldn't line up exactly. After fighting with that I got everything all hooked up and the dang exhaust wouldn't fit, hitting the frame. I guess that the difference in the placement of the port on the GT5. Not gonna mod the exhaust a third time. This engine will just have to wait and have the 3sp bike built around it.

Check out these mounts all the same right? Wrong. Two came with the GT5s and they are even different. Only the mount on the right would work with the FHs mounts which are welded to the frame. Makes you wonder if any two of these engines are truly the same.

Have to add at this point that I pleased with the Klotz R-50. After about 100mi of usage I found it has left a nice oil film through out the engine what will just wipe off. I have moved from 32:1 to 40:1 with this oil.
 

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Intrepid Wheelwoman

New Member
Oct 29, 2011
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Hauraki District, New Zealand
Something I noticed with my China Girl engine that's pretending to be a Villiers engine, - it has an undrilled boss on the clutch cover that looks like it was intended for an oil level plug. Anyone else have an engine with a clutch cover like mine?

 

mapbike

Well-Known Member
Mar 14, 2010
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Central Area of Texas
No I don't recognize the cover and I dont recognize the carb on your CG there either.

Iteresting though since we have a couple people on here currently working on a possible wet clutch setup for our CG's.

Just wonder if the centrifugal clutch would still grab and hold if it were to be a wet setup..??????
 

Intrepid Wheelwoman

New Member
Oct 29, 2011
2,830
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Hauraki District, New Zealand
The engine was made to the special order of a trader here in New Zealand. He's no longer importing MB engines and parts though as he's moved onto agricultural machinery.

The carb is the one Villiers made in house for their two stroke engines. Brilliantly simple and very reliable :)

I wouldn't like to say whether or not the centrifugal clutch would still work or not if it was wet and I'm too much of a cowardy custard to want to find out in case I break my nice engine.
 
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cannonball2

Well-Known Member
Oct 28, 2010
3,682
221
63
Colonial Coast USA.
There were two versions, one a dry clutch and a wet version.
Yours must be obviously a dry version since the boss isn't drilled.
I believe the wet version has cork shoe faces.
 
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