Insane Vibration

Discussion in 'Frame Mounted Engines' started by LabDude661, Sep 4, 2008.

  1. LabDude661

    LabDude661 New Member

    I have been searching the forum for days now looking for an answer and forgive me if I missed a post that already discusses the issue. I got a 70cc HT from boygofast. Everything looks fine and runs fine except I have been getting insane amounts of vibration. I'm running a 44t sproket and I can only get to like 25 mph before the handlebars want to buzz out of my hands. The highest comfortable cruising speed I've gotten is about 21 mph. Was I just naive to belive that this thing would do 35 out of the box or is the vibration keeping me from going top speed? I really don't need to go much faster but it would be fun :grin:. I used an old innnertuber around the frame on the mounts and I loaded the handlebars with lead weights and I still can't break about 26 mph without pain from the vibration. I've seen a few little rubber engine mounts that might work but I wanted to know if anyone else is having this same problem. Everyone on here is talking about 35 40 mph and I'll just say it... I'm jealous!!! :yuck:

  2. Skyliner70cc

    Skyliner70cc Active Member

    If you want 35-40 mph, consider a scooter. I have no problem hitting max rpms on my BGF engine without an vibration issues. Some bike frames and mount setups are more prone to vibration than others.
  3. HI,

    Assuming your engine is running properly (not missing etc....) and is securely/properly fastened to the frame, the best thing you can do to reduce vibrations and increase speed is to get a smaller rear sprocket....It'll kill 2 birds with 1 stone....Try it you'll like it! ;-)

    Hope this helps.

  4. Skyliner70cc

    Skyliner70cc Active Member

    Is you bike an old Huffy by chance? I had a Huffy bike that vibrated like crazy and I blamed it on the engine. I swapped engines and didn't help one bit.
  5. LabDude661

    LabDude661 New Member

    Nope it's a pretty sturdy mountain bike. I'm going to try putting big hunks of car tire on the mounting points to see if that helps. I've been seriously considering getting a smaller sprocket but I want to be sure that the problem won't still be there. I don't want to cut the chain and drop more money on the problem if it's just the bike.
  6. hill climber

    hill climber Member

    my ht vibrates like crazy too, but i can get 40 plus out of it with the jack shaft and 6 gears. i dont have a tach but am a motorhead and i bet its turnnin 6000-6500 rpm maybe more. it runs smoother at the higher rpm for sure, if you can get the jetting right. by the way when i put my expanshion chamber on it smoothed out considerabley. hill climber
  7. LabDude661

    LabDude661 New Member

    where do you pick up an expansion chamber, or is it a DIY mod?
  8. Stink Bike

    Stink Bike Member

    I was getting a bad vibration at about 30 k's so I cut a spark plug lead in to 1/4 inch lengths and jammed it in between the fins of the motor.Problem solved..... and it reduced the noise.This has been the best and cheapest mod I have done to my motor.

    I still get plenty of vibration through my hands.
  9. hill climber

    hill climber Member

    it is a diy but works very well, probley doubled the power, its off a 85 suzuki rm 80, i moded the first 8-10 inches and a couple custum bends in the tail pipe before the silencer. sick bike parts has two different models for sale for the ht, one v frame type and a cruiser type. i found them in here just search expantion chamber. there is another guy selling pipes here. no coment on these. hill climber
  10. relaxxx

    relaxxx Member

    My experience has been the faster I run the motor the smoother the ride. I'm on my second frame, a cheap walmart bike with front shocks and I mounted the motor with some tire rubber and it is a very nice ride compared to my first frame. If you want to go faster than 25MPH, definitely get a small sprocket. After running a 36T I'd never consider going back to 44T. I don't understand why they even sell 70cc motors with 44T. Mt 36T climbs hills just as well as the 44T did, if not better!
  11. LabDude661

    LabDude661 New Member

    Well for some odd reason, I took off all of the dampening material that I had put on the mounts and now it's actually smoother. Of course I also changed the head studs, cleaned all the gaskets and tourqued everything to 11 ft/lbs. I've gotten a serious performance boost from making sure the whole thing is well sealed and seated. Also while re-mounting the engine this last time, I went out of my way to get the engine down in the V of the frame as far as I could get it. I think that helped also. I'm still getting some pretty serious vibration at 30 mph but at least I can cruise comfortably at 25 mph. I'll keep everyone posted on future vibration reduction improvements.
  12. 5-7HEAVEN

    5-7HEAVEN Guest

    My engine's vibration would make my hands numb at idle. It was a Mitsubishi 43cc 2.2hp engine on a rack-mount rear friction drive. When I swapped bicycle gloves for full leather gloves for safety reasons, my fingers no longer went numb.
  13. LabDude661

    LabDude661 New Member

    New update on the vibration issue. It turns out it was most likely the chain causing the problem. I got rid of the chain tensioner all together an moved the engine a bit forward using a spacer idea I saw here on another post. With the chain nice and tight (still a bit of slack) it runs so super smooth its like a motorcycle. Great ride just got a whole lot better. Oh and I replaced the mount studs with some overly strong allthread from mcmaster. I was able to torque it way down. So we'll see if that keeps her together a little better.
  14. rangerjelly

    rangerjelly New Member

    I had some vibration issues so I took an old pair of shop boots with foam soles. i cut the heels out of the boot and carved them to fit as part ofmy motor mount. It made several of my friends scratch their head at the start but the finished product ended up looking like a after markert motor mount. and more importantly the vibration is a thing of the past. (I agree with the speed statement about scooters. these bikes (in my opinion) are not for land speed records.).