MY buddy found me a GX390 off a power washer and I knew I had the beginning of my next project. I purchased a Motovox MBX10 rolling chassis and a complete Doodle bug DB30 from Ian at Motovox. Decided to put the GX390 on the MBX10 and away we went.
Mocked up the engine in the frame and decided we needed to stretch it 6 inches. Started by cutting out the original engine plate and the front tube and foot pegs. Stretching the lower part of the frame was easy. Took some heavy walled pipe and cut it into two 8 inch pieces. Machined 1 inch of each end down in the lathe so it would fit inside the existing frame tube. Used those to fill the gap in the lower frame. The top frame tube was more of a challenge. After cutting it apart just ahead of the seat mount we stretched it and tried to decide how to piece it back together. Decided that there was no easy way to fill in the gap and make it look good. Decided to cut the top tubes off at the neck and fabricate new ones. Bent up new tubes to match the original lines of the frame and tacked it all together.
Reassembled the bike to check how everything lined up and it all looked ok. We stripped the frame again and did the final welding. The seams in the tubes were plug welded and then the perimeter of the tubes were Tig welded. Where the upper tubes met the neck it was Mig welded. There will be gusseting going in to tie the new top tubes into the neck and into the existing lower tubes. The area in frt of the seat where the tubes were seamed will be reinforced also, have to decided on what I'm doing for a fuel tank first before we weld that in.
Purchased bearings and drill rod from McMaster to use for the jackshaft. Fabricated a jackshaft tube out of some heavy walled pipe with the ID machined to accept the bearings. Fabricated the saddles from a piece of 3/4 flat stock. Cut a 12" piece of drill rod and machined a keyway slot. The final dimensions for the length jackshaft will be determined once we decide where the engine is going to be. Cut 1 1/4 inches off the crank to narrow the whole package so it wouldn't stick out to far on the right side.
Decided to run a one piece engine plate from just head of the rear tire up to the front frame tubes to tie the lower frame tubes all together. Made a pattern for the plate and cut it out 1/8 inch stock with the plasma torch, bent it up on the 35 ton press. Due the the downward angle of the frame we angled the plate up so the engine sit's level.
That's were it sits for now. I'll take some more pictures and up date the post as the project progresses.
Mocked up the engine in the frame and decided we needed to stretch it 6 inches. Started by cutting out the original engine plate and the front tube and foot pegs. Stretching the lower part of the frame was easy. Took some heavy walled pipe and cut it into two 8 inch pieces. Machined 1 inch of each end down in the lathe so it would fit inside the existing frame tube. Used those to fill the gap in the lower frame. The top frame tube was more of a challenge. After cutting it apart just ahead of the seat mount we stretched it and tried to decide how to piece it back together. Decided that there was no easy way to fill in the gap and make it look good. Decided to cut the top tubes off at the neck and fabricate new ones. Bent up new tubes to match the original lines of the frame and tacked it all together.
Reassembled the bike to check how everything lined up and it all looked ok. We stripped the frame again and did the final welding. The seams in the tubes were plug welded and then the perimeter of the tubes were Tig welded. Where the upper tubes met the neck it was Mig welded. There will be gusseting going in to tie the new top tubes into the neck and into the existing lower tubes. The area in frt of the seat where the tubes were seamed will be reinforced also, have to decided on what I'm doing for a fuel tank first before we weld that in.
Purchased bearings and drill rod from McMaster to use for the jackshaft. Fabricated a jackshaft tube out of some heavy walled pipe with the ID machined to accept the bearings. Fabricated the saddles from a piece of 3/4 flat stock. Cut a 12" piece of drill rod and machined a keyway slot. The final dimensions for the length jackshaft will be determined once we decide where the engine is going to be. Cut 1 1/4 inches off the crank to narrow the whole package so it wouldn't stick out to far on the right side.
Decided to run a one piece engine plate from just head of the rear tire up to the front frame tubes to tie the lower frame tubes all together. Made a pattern for the plate and cut it out 1/8 inch stock with the plasma torch, bent it up on the 35 ton press. Due the the downward angle of the frame we angled the plate up so the engine sit's level.
That's were it sits for now. I'll take some more pictures and up date the post as the project progresses.
