MBX10 Project engine plate
Tacked the engine plate in the frame and determined where we wanted the engine and jackshaft to sit. Took our measurements and then pulled the plate back out. Set the plate up in the mill and cut the adjustment slots for the engine and the jackshaft. Also cut a slot to allow the chain to pass thru from the jacksaft to the wheel sprocket. Cut some lightening holes in the sides of the plate for looks more than anything else. Cut holes in the very frt of the plate to allow the tube for the foot pegs to pass thru.
Reinstalled the plate and welded it in. Made sure we thoroughly welded it where it straddled the splice we made in the lower tubes, this baby aint coming apart! I'll post more pictures as the work progresses.
Tacked the engine plate in the frame and determined where we wanted the engine and jackshaft to sit. Took our measurements and then pulled the plate back out. Set the plate up in the mill and cut the adjustment slots for the engine and the jackshaft. Also cut a slot to allow the chain to pass thru from the jacksaft to the wheel sprocket. Cut some lightening holes in the sides of the plate for looks more than anything else. Cut holes in the very frt of the plate to allow the tube for the foot pegs to pass thru.
Reinstalled the plate and welded it in. Made sure we thoroughly welded it where it straddled the splice we made in the lower tubes, this baby aint coming apart! I'll post more pictures as the work progresses.
I have done this on 2 Honda cranks and they were both threaded 3/8x24. I don't know if it is the same on a clone. I chucked up a 3/8x24 bolt in the lathe and center drilled it with a 3/16 bit. Threaded the bolt into the crank and used a 3/16 bit to drill a pilot hole to the correct depth in the crank. Took the bolt out and used a 21/64th bit to drill out the crank for tapping. Be careful to keep the bit straight so you don't bugger up the existing threads. Cut approximately 1 inch off the crank. Tapped the hole using the original threads that were left in the crank to start the tap and guide it straight. Go easy and use plenty of lube, you don't want to break the tap off in your crank! It actually taps fairly easily, the outside of a crank is hard but the inside material is fairly soft. After I had the hole tapped to the full depth using the starter tap I used a bottoming tap to clean the threads up all the way to the bottom of the hole. I then cut another appriximately 1/4 inch off the crank. Champhered the hole and then ran the tap thru again in case I buggered up any threads when I champhered it. I didn't cut it all off all at once because I wanted to save some of the original threads in the crank to use as a guide.
I could still shorten the crank another 3/8 of an inch or so to bring the clutch in even further but I don't know if it's worth it. If you don't have access to a lathe and you need a pilot made I could drill one for you and drop it in the mail. Let me know.
I could still shorten the crank another 3/8 of an inch or so to bring the clutch in even further but I don't know if it's worth it. If you don't have access to a lathe and you need a pilot made I could drill one for you and drop it in the mail. Let me know.
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Send me a PM with your info and I'll make one up and drop it in the mail to you.
I'm using the original Motovox throttle. I modified a 10/32 coupling nut in the lathe so I could attach it to an existing hole in the original hand throttle plate and have a place to hook up the throttle cable. I took the original wave washer out that keeps tension on the hand throttle and replaced it with 2 washers I turned out of nylon in the lathe so the plate can move freely. I can take a picture of the setup I'm using and post it tomorrow. Very simple and it works great for about $1.50 in parts and a little lathe time.
I'm using the original Motovox throttle. I modified a 10/32 coupling nut in the lathe so I could attach it to an existing hole in the original hand throttle plate and have a place to hook up the throttle cable. I took the original wave washer out that keeps tension on the hand throttle and replaced it with 2 washers I turned out of nylon in the lathe so the plate can move freely. I can take a picture of the setup I'm using and post it tomorrow. Very simple and it works great for about $1.50 in parts and a little lathe time.
Motovox MBX10 GX390 Throttle linkage
A fellow Forum member asked for an explanation of how I made my throttle linkage so here it is.
I started with a 10/32 coupling nut in which I drilled a small hole towards one end large enough to insert the throttle cable thru and secure with a short screw. Make sure the hole is close enough to the end so the screw intersects the hole and you are able to tighten the screw down against the throttle cable to retain it. I found some 10/32 screws at the hardware store that had a 1/2 inch of thread with a larger head to act as a shoulder. Turned the other end of the coupling down in the lathe to form a shoulder. Turned it down just enough so it fit thru the existing hole in the throttle arm without any slop. Turned down two nylon washers to ride on the shoulder of the coupling nut to act as a bearing surface. Put one washer between the coupling nut and the throttle arm on the top and the other underneath. Made sure the washers were thick enough so the coupling nut didn't rock around when tightened up but still was allowed it to rotate. When you install the screw to secure the coupling nut to the throttle arm use a dab of blue Loctite to make sure it doesn't come loose in the future.
I removed the wave washer and nylon washer that was under the throttle that added tension to the arm and discarded them. You don't want the wave washer to bind the arm, you want the arm to be able to move freely so the throttle doesn't bind. I chucked up a piece of nylon in the lathe and drilled a hole in it that was large enough to fit over the shoulder on the throttle bracket that the arm pivots on. Turned the nylon down to 1 inch OD and cut off two washers to act as bearings using a parting tool. Put one washer on the bracket, installed the throttle arm and put the second washer on top of the arm. You may want to put a dab of grease on the washers. Reinstalled the arm retainer and secured it with a new locking nut. Snugged the nut down enough so the arm still has free movement.
I have this used this same setup on another GX390 to adapt the hand throttle to cable activation and it has worked great so far. I used the existing cable retainer that came on the throttle bracket to secure the throttle cable. I guess you could make up a threaded piece to hold the cable so you could fine tune the adjustment of the cable but I found no need for it. You can cut off the extra part of the hand throttle linkage if you feel the need. Hook up a return spring and you are ready to go. Hope I haven't bored you with my long winded explanation, just wanted to make sure I explained it as best I could so others could duplicate it.
A fellow Forum member asked for an explanation of how I made my throttle linkage so here it is.
I started with a 10/32 coupling nut in which I drilled a small hole towards one end large enough to insert the throttle cable thru and secure with a short screw. Make sure the hole is close enough to the end so the screw intersects the hole and you are able to tighten the screw down against the throttle cable to retain it. I found some 10/32 screws at the hardware store that had a 1/2 inch of thread with a larger head to act as a shoulder. Turned the other end of the coupling down in the lathe to form a shoulder. Turned it down just enough so it fit thru the existing hole in the throttle arm without any slop. Turned down two nylon washers to ride on the shoulder of the coupling nut to act as a bearing surface. Put one washer between the coupling nut and the throttle arm on the top and the other underneath. Made sure the washers were thick enough so the coupling nut didn't rock around when tightened up but still was allowed it to rotate. When you install the screw to secure the coupling nut to the throttle arm use a dab of blue Loctite to make sure it doesn't come loose in the future.
I removed the wave washer and nylon washer that was under the throttle that added tension to the arm and discarded them. You don't want the wave washer to bind the arm, you want the arm to be able to move freely so the throttle doesn't bind. I chucked up a piece of nylon in the lathe and drilled a hole in it that was large enough to fit over the shoulder on the throttle bracket that the arm pivots on. Turned the nylon down to 1 inch OD and cut off two washers to act as bearings using a parting tool. Put one washer on the bracket, installed the throttle arm and put the second washer on top of the arm. You may want to put a dab of grease on the washers. Reinstalled the arm retainer and secured it with a new locking nut. Snugged the nut down enough so the arm still has free movement.
I have this used this same setup on another GX390 to adapt the hand throttle to cable activation and it has worked great so far. I used the existing cable retainer that came on the throttle bracket to secure the throttle cable. I guess you could make up a threaded piece to hold the cable so you could fine tune the adjustment of the cable but I found no need for it. You can cut off the extra part of the hand throttle linkage if you feel the need. Hook up a return spring and you are ready to go. Hope I haven't bored you with my long winded explanation, just wanted to make sure I explained it as best I could so others could duplicate it.
Motovox Project, MBX11 frt end
Installed the MBX11 sprung frt end and it looks pretty neat. Mocked up the fuel tank in a couple of different configuarations. Installed it both on top of the backbone and underneath, also tried it mounting it cross ways in frt of the engine. Looked too much like a St. Bernard carrying a brandy keg mounted crosswise in frt of the engine. Decided to mount it under the backbone but the issue of where to put the filler neck came up. Could fab a new fuel bung that had the fuel filler mounted on the side of the tank but didn't think that looked good. Decided to bring the fuel filler up thru the middle of the backbone. Figured out how to modify the backbone with a piece of tubing that allows the filler to come up thru the middle of the backbone. Won't compromise the strength and makes for a clean look. Will work on that next chance I get.
Moved on to figuring out how to install the frt brake caliper. Going to use the mechanical rear caliper and mount it on the frt fork. Installed the MBX rear wheel with the rotor attached on the frt fork. Machined down a couple of spacers to center the wheel in the forks and found the rotor mounting bolts barely clear the down tubes on the fork. The bolts cleared but am going to change the rotor mounting bolts to low profile button head socket bolts to gain some extra clearance. The fork down tubes are aluminum so decided against trying to weld a bracket to the down tube. Came up with a couple of different ideas on making a bracket that bolts to the existing bosses that are cast into the down tubes for mounting the frt fender. Came up the layout of the bracket and mocked one up out of cardboard. Started fabbing one style of bracket out of steel but ran out of time. Will make up both styles of bracket and decide which one works best Will pick it up again next where we left off.
Installed the MBX11 sprung frt end and it looks pretty neat. Mocked up the fuel tank in a couple of different configuarations. Installed it both on top of the backbone and underneath, also tried it mounting it cross ways in frt of the engine. Looked too much like a St. Bernard carrying a brandy keg mounted crosswise in frt of the engine. Decided to mount it under the backbone but the issue of where to put the filler neck came up. Could fab a new fuel bung that had the fuel filler mounted on the side of the tank but didn't think that looked good. Decided to bring the fuel filler up thru the middle of the backbone. Figured out how to modify the backbone with a piece of tubing that allows the filler to come up thru the middle of the backbone. Won't compromise the strength and makes for a clean look. Will work on that next chance I get.
Moved on to figuring out how to install the frt brake caliper. Going to use the mechanical rear caliper and mount it on the frt fork. Installed the MBX rear wheel with the rotor attached on the frt fork. Machined down a couple of spacers to center the wheel in the forks and found the rotor mounting bolts barely clear the down tubes on the fork. The bolts cleared but am going to change the rotor mounting bolts to low profile button head socket bolts to gain some extra clearance. The fork down tubes are aluminum so decided against trying to weld a bracket to the down tube. Came up with a couple of different ideas on making a bracket that bolts to the existing bosses that are cast into the down tubes for mounting the frt fender. Came up the layout of the bracket and mocked one up out of cardboard. Started fabbing one style of bracket out of steel but ran out of time. Will make up both styles of bracket and decide which one works best Will pick it up again next where we left off.
Maybe you can do something like this.
Fuel Tanks and Mounts
Fuel Tanks and Mounts
Fuel tank position
I plan on dropping the rear fender down to gain some clearance (so it doesn't melt) and running the exhaust under the seat. Putting the fuel tank in the rear isn't an option. Of the 3 frt mounting possibilities I think under the backbone looks best. It puts the tank out of the way and you won't have to worry about sliding forward on the seat and crushing your cajones.
I plan on dropping the rear fender down to gain some clearance (so it doesn't melt) and running the exhaust under the seat. Putting the fuel tank in the rear isn't an option. Of the 3 frt mounting possibilities I think under the backbone looks best. It puts the tank out of the way and you won't have to worry about sliding forward on the seat and crushing your cajones.
GX390 fit
The 390 was too tall to fit in the Motovox frame with the stock parts installed. You can see how high the air filter sticks up above the frame even with the air box removed. I removed the air cleaner, tank and exhaust and was able to wedge the engine into the frame with a shoehorn but that left absolutely no room to move the engine forward or back for chain adjustment. The rear wheel on the Motovox is fixed so you cannot move the wheel back to tighten the chain, you must move the engine forward. Decided that a 6 inch stretch would leave me plenty of room to move the engine forward and backward as needed and also give me room to mount the jackshaft.
The 390 was too tall to fit in the Motovox frame with the stock parts installed. You can see how high the air filter sticks up above the frame even with the air box removed. I removed the air cleaner, tank and exhaust and was able to wedge the engine into the frame with a shoehorn but that left absolutely no room to move the engine forward or back for chain adjustment. The rear wheel on the Motovox is fixed so you cannot move the wheel back to tighten the chain, you must move the engine forward. Decided that a 6 inch stretch would leave me plenty of room to move the engine forward and backward as needed and also give me room to mount the jackshaft.