rapido 250 vibration problem

[tavspeed]

hi all,have got a very unpleasant vibration on my newly built rapido,i am running rapido 250,tmx 35,scorpion exhaust,mec eur 60mm crank,li 150 box,16 tooth sprocket,it has been set up on scootereroticas dyno by dan ,who has done a excellent job and would highly recommend ,the vibration starts at about 50 mph in fourth gear and although not unbearable you wouldnt want to be riding 80 miles on it.couple of theories,crank slightly out of true,the piston felt heavy so could be this,on building the engine the big end of the conrod touched the backof the casing,so had to relieve the casing,just wondering if at high revs the conrod is hitting the casing would this be possible,i.e conrod expanding stretching enough to catch casing,i am using indian flywheel from my old engine which was fine,is there a way of lightening the piston without drastically weakening it,any other rapido 250 users having this problem and what are your engines like for smoothness,cheers all.

[bazman]

Could you describe the vibrations ie are they constantly there or come and go in regular intervals? Only reason i'm asking is i've got the same problem , put it down to front end , had new springs, bushes , disc links and bearings fitted...guess what still there Engine revs out freely and flywheel does not spin eccentrically, so don't think crank is out, can tightening the engine pivot bolts too tight maybe contribute to this?

[tavspeed]

they start at about 5000rpm and are high frequency,so i am thinking they they are related to a fast moving engine part,piston,crank or flywheel,bike is unchanged from last year apart from new engine,i have af indian long engine mounts fitted at the moment,but bike is lovely to ride until it hits this point in the rev range,then it vibrates in all the gears at the same revving point.

[Lamaddict]

I had a Rapido 250 which was smooth through all the rev range. Could be crank/ flywheel related

[J1MS]

What engine mounts have you fitted.... mine was almost unrideable over 5500 rpm on my SX ....when it was Dynoed I was told I might have a twisted crank ....a strip down proved the opposite....In the end I Changed engine mounts for the newer style Indian ones that smoothed it out compeletly....

[sydduckett]

Mate had the same problem with the smaller rapido about 200 odd miles after complete rebuild. Turned out it was top and bottom bearings on steering colum. Tightend both and prob was sorted. apparntley this can often happen after they have bedded in?

I must point out i know f*** all about mechanics and just happened to be there

Sef

[RAP 200]

Darren here from The Lambretta Club Of South Australia,i have a rapido race 200 which runs a 58 stroke mec crank,the vibration starts around 48 mph and stops around 52 mph and is very intense ,my friend has same crank in a standard gp 200 and has the same problem, we have worked out that the early mec cranks have more big end float ,have no big end shims,and have a narrower big end eye thus causing it to vibrate at aprox 5000 to 5200 rpm ,i intend to bin this crank and fit the later type ,they dont make this type anymore ,must be a reason

[tavspeed]

hi all,think i will try some more engine mounts,take the easiest option first,the ones i fitted came from af but have been kicking around in my garage for ages,so dont know if they are the earlier type or the softer later ones,the last reply about the mec cranks is interesting,although mine is a 60mm which if anything should make the engine smoother,can anyone recommend a good engine mount,and where to get them,cheers all.

[sean brady scooters]

by all means try new mounts..........and dont overtighten engine pin nuts............
and also check everything else that could possibly give bad vibes..........
but ........what i find interesting here is why your thinking that a 60mm crank should make your engine smoother.....?
to lengthen the stroke and to fit a bigger /heavier piston on the end of it is a sure fire way to limit revs and increase vibes...............