help with bad vibrations

[ky 2stroker]

we need some help in figureing out how to re-do the engine mounts in my brothers 500cc drag blaster. a couple weeks ago I got some rubber grommets and put in the front and lower motor mount holes and it helped alot...........for about 30 seconds untill the vibration eat right through the thin rubber. theres some pics of what it currently looks like. we put a +3 swingarm on it and it fits the look pretty good. in the pic with the head stay motor mount, it is fully rubberized (the black piece that is bolted to the head) and works pretty good. our main problem is with the lower and front mounts. they are pretty solid and welded good, but they are gonna come off when we re-make a new rubberized mount setup. if anybody has any ideas or suggestions please post em.

[Paulie B]

What a beast. I've been waiting to see more of this quad since those vids you posted a while ago.
I don't see anything you can do with those mounts other then cut them off where their welded and then rubber mount them to the frame.
It's gonna take some thought and maybe you will have to do what the CR500 guys do and break down and have the crank balanced.

[ky 2stroker]

we kinda got some ideas from the "cr500 in a 250r frame" thread about trying an engine cradle that connects the front and bottom mounts to one main rubberized mount to the frame. heres some pics I found from the thread. or maybe just one heavy duty rubber mount for the front and just leave the very bottom mount un-bolted. but im not sure how much stress that would put on the cases like that.

[Paulie B]

Those are good looking ideas.
I know were talking apples and oranges here but I never had my front mounted.
My vibes were very manageable at 426cc's as they are now @ 406cc's.

[ky 2stroker]

if its not any trouble, could you get some good pics of your engine and mounts? it could probably help us out alot. and this might be a shot in the dark, but I think a majority of the vibration is coming from the state of tune of the motor itself. it basicly runs like a bitch. its got a rigged up honda three wheeler kick starter (a 93' wr500 kickstarter is impossible to find unless you buy a new oem), but it does no good to try and kick start it, and we also got clearance issues with the kicker and frame. we always have to pull start it with another bike to get it running, then you have to keep it revved up to stay running while its vibrating the hell out of your ass, feet and hands. the throttle response is half ass sloppy and rough. but once you get going through the gears and revvin it out to a point where the exhaust sound changes and smooths out, it pulls like mad on the topend and it just hauls the mail. what it really needs is a new carb........a 38mm air stryker. then we could probably get the jetting pretty dialed in to where it idles and revs a little better. but the topend is not in the best of shape. I remember a long time ago when we first pulled the head, I remember there was quite a bit of piston/cylinder wall clearance. and so far ive only found one place to order wiseco pistons for up to 2mm over stock. and i;d rather not waste what bores it has left untill it comes time for porting the cylinder.

[atomicsaladbowl]

you should break that sucker down and balance that crank, any other ideas of mine would be killing the problem where it actually is by adding rubber to all contact points of the rider and the actual quad, maybe some cushier gripes or, they make these pars that have rubber springs to make the handle bend when you get to much air or bottom out or somethin, and maybe some rubber on the pegs? i dunno vibrations from that sucker must be real rough. good luck solvin it, paulie i would wanna see a closeup of your mounts too if you got time.

[Paulie B]

Yeah the whole vibe thing is weird. My motor at 426cc's vibrated LESS then it does now at 406 even after I had the crank re-built and trued. I think a new carb will help out alot for you as well as the normal 490 fixes like head work or running 2 base gaskets. I've seen various piston kit on Ebay for that motor.
Anyways here's a pic for ya.

[flotek]

paul yo u had a more balanced bore to stroke ratio before and thats probably the reason it self balanced the rotating weight better

[Paulie B]

Since were on the subject, is went a different route and rubber mounted almost everything on my bike except the motor. The seat, tank, exhaust, silencer, rear plastic, and handle bars are all rubber mounted.
Denny is there some formula for a balanced bore/stroke combo or is it one of those things that just worked out for me last time?

[flotek]

im sure theres some kind of rotating mass enertia formula that illstartes why it favored less vibes, i dont know it off the top of my head