Dirt Bike Dan
Member
- Aug 18, 2004
- 63
- 0
I've only been on a couple rides this summer :ahhh:
as this spring I had to replace the swingarm bearings. I ended up stripping the bike, had to weld a a tab for a motor mount back on, painted the frame, found both motor mounts were cracked. So I made new ones. The old ones were 1/4" alum. plates, the new ones I made were 5/16"(the numbers might be off, but the new ones were thicker). So I drilled into them so they would fit properly. For the swingarm bearings, I had to make my own metal bushings for the cases ($$$ for new ones), so I used a metal sleeve and cut a large nut down to the correct thickness. After I got the bike back together, it worked fine. At the end of my second ride (maybe 8-10 hours of riding after putting it back together) the bike started to shake like crazy. For most of the rpm range it vibrates much more than I ever recall. In the top end/overrev it clears up, and is much smoother. I noticed one of my motor mount bolts had snapped off, and my exhaust pipe cracked again. I replaced the bolt, but it still shakes. When I sit in neutral and rev the bike, I can see the pipe rattle and shake up to about the mid section(where theres a mounting point to the frame). The rpms also seem to hang when I rev the bike to the point the shaking/rattling smoothes out. I usually have to press the kill switch to bring the revs back to idle.
Something is obviously wrong, but I don't know where to start.
I have a couple trains of thought on it:
1. I've done a lot of reading on, and plan to make a homemade expansion chamber. (google it, as well as "hydroforming" for info). Currently, the pipe is dented, cracked, and has been repaired a couple times. In the midsection of the pipe is a patch about 2"x2", now leaking (enough to coat my knee in spooge after riding for a while). I don't know if the waves in the pipe are causing the problems...? :coocoo:
2. My motor mounts have the engine out of alignment. I would say this is the most likely culprit, but the problem only started after about 10 hours.
3. This could just be my lack of experience, but jetting/general poor state of tune? Would a lean condition make the bike rev out like that? I don't think this would be the primary cause of the vibration, but I'm sure it wouldn't help. It's still stock jetting, and it worked fine last summer (a little smokey, but not bad). I was going to tackle the jetting this summer, but too much has been going on and now I'm back to school already. When I first got the bike running (a couple years ago) it had about 180 psi of compression, now I think it is down to 165psi. Again, I don't think that is enough to be the primary cause, etc.
another random thought - when the bike clears up and runs smoothly (upper rpms), it seems almost like the clutch is slipping. The basket is likely grooved (I filed the outer basket down when I first got the bike, but i didn't do the inner...never could push the bike in gear, motor off, clutch in) The only reason I think it might be the clutch, the bike doesn't seem to pull as hard - whether that's the clutch, or just because it's in the overrev, I can't say.
Any ideas on how I should attempt to fix this?
Thanks for any replies (and reading all that^)
as this spring I had to replace the swingarm bearings. I ended up stripping the bike, had to weld a a tab for a motor mount back on, painted the frame, found both motor mounts were cracked. So I made new ones. The old ones were 1/4" alum. plates, the new ones I made were 5/16"(the numbers might be off, but the new ones were thicker). So I drilled into them so they would fit properly. For the swingarm bearings, I had to make my own metal bushings for the cases ($$$ for new ones), so I used a metal sleeve and cut a large nut down to the correct thickness. After I got the bike back together, it worked fine. At the end of my second ride (maybe 8-10 hours of riding after putting it back together) the bike started to shake like crazy. For most of the rpm range it vibrates much more than I ever recall. In the top end/overrev it clears up, and is much smoother. I noticed one of my motor mount bolts had snapped off, and my exhaust pipe cracked again. I replaced the bolt, but it still shakes. When I sit in neutral and rev the bike, I can see the pipe rattle and shake up to about the mid section(where theres a mounting point to the frame). The rpms also seem to hang when I rev the bike to the point the shaking/rattling smoothes out. I usually have to press the kill switch to bring the revs back to idle.
Something is obviously wrong, but I don't know where to start.
I have a couple trains of thought on it:
1. I've done a lot of reading on, and plan to make a homemade expansion chamber. (google it, as well as "hydroforming" for info). Currently, the pipe is dented, cracked, and has been repaired a couple times. In the midsection of the pipe is a patch about 2"x2", now leaking (enough to coat my knee in spooge after riding for a while). I don't know if the waves in the pipe are causing the problems...? :coocoo:
2. My motor mounts have the engine out of alignment. I would say this is the most likely culprit, but the problem only started after about 10 hours.
3. This could just be my lack of experience, but jetting/general poor state of tune? Would a lean condition make the bike rev out like that? I don't think this would be the primary cause of the vibration, but I'm sure it wouldn't help. It's still stock jetting, and it worked fine last summer (a little smokey, but not bad). I was going to tackle the jetting this summer, but too much has been going on and now I'm back to school already. When I first got the bike running (a couple years ago) it had about 180 psi of compression, now I think it is down to 165psi. Again, I don't think that is enough to be the primary cause, etc.
another random thought - when the bike clears up and runs smoothly (upper rpms), it seems almost like the clutch is slipping. The basket is likely grooved (I filed the outer basket down when I first got the bike, but i didn't do the inner...never could push the bike in gear, motor off, clutch in) The only reason I think it might be the clutch, the bike doesn't seem to pull as hard - whether that's the clutch, or just because it's in the overrev, I can't say.
Any ideas on how I should attempt to fix this?
Thanks for any replies (and reading all that^)
