YPVS vibration

[giggsey999]

Hi all, my freshly re built pv engine starts and runs lovely, it is crisp and sounds really nice, the only prob is that it has a vibration mainly on over run but also when slowly increasing the revs. So far I have checked the flywheel is seated and tight, I can't feel any movement in the flywheel end of the crank, I have run it with the flywheel cover off and it looks true and with my finger on the end of the crank it seems OK. On the clutch side again can't feel any movement in the crank but there is movement in the clutch basket, it appears to be in the primry/clutch basket bush,there is rotational movement in the basket,about 5mm,that I know I can fix with new rubbers but can't see that it would vibrate, today I even took the clutch pack out and ran the engine to see if it reduced the vibs but no, still the same. Has anyone else had the same prob, could it be the ware in the bush do you think, it's all I can find so far. Could the crank itself be out of balance. The bottom end all looked good when I re built it, all the bearings were smooth and quiet, no play in the big ends, the top end is all new, re sleeved bores, new pistons. I think the problem may have been there before the re build as the engine mountings had extra rubber washers fitted, I didn't think about it at the time but maybe someone was trying to hide the vibs. So that's where I am with this bike, its 2 steps forward, 1 step back, I just want to ride the thing. Can you get the primary/clutch basket bush, I can't find any, don't really want to spend another £325 on a new basket nd it's not that. Any thoughts and ideas would be appreciated, I'm about ready to set fire to it. Cheers

[midlifecrisisrd]

You don't want to hear this but I'd suspect the crank

At the stage where the engine is stripped I just either get them rebuilt or buy a new one

In my opinion if you can spin the bearings and they run on for a second or two then they are shagged

Also any noise at all spinning them and they are toast

Did you measure the big end side float or con rod small end deflection?

They can also twist or have slightly bent rods if tried to start with a flooded crankcase after parked up for long periods

Don't think there is enough weight in a clutch basket to cause vibes

When the clutch is engaged the plates and inner drum tend to support it

You have got the tie bars fitted and the 2 engine mount vibration dampers fitted?

Steve

[giggsey999]

Hi Steve, yes tie bars and dampers fitted, all bearings were good, tight and quiet, there is no play in the outter bearings and can't feel anything through the flywheel. If the crank has to come out the so be it, just want to be sure it's nothing simple first.

[giggsey999]

Big end side float was well within spec, didn't check small ends.

[kostas]

I believe I have the same problem with you.
When I close the throttle at high speed I can feel the bike / engine vibrate.
If I pull the clutch it stops. My engine was rebuild with reconditioned crankshaft.

I tend to believe that the rubber engine mounts have turned to concrete which in turn does not help.

[giggsey999]

Mine is the same, clutch in or out, in gear, out of gear, which I suppose would suggest the crank is the prob in my case.

[midlifecrisisrd]

When you say no play there should be some on the bearings

When the crank is out you should be able to waggle the bearings a little. Not up and down but they should not be tight.

I remember the first time I thought a timing side bearing was a bit knackered. Bought a new one but never fitted it as it was slacker than the one fitted lol

Steve

[Tobyjugs]

I had a crank which was i think 6 degrees out of sync.
I never felt any vibrations, my tuner could hear it pinking on one cylinder when it was on the dyno bank, and told me to check it.

If your crank is out its easy to check with a degree wheel and a DTI through the spark plug hole. Just find TDC and mark it on the timing disc for both cylinders, i wouldn't worry about it if it's half a degree out. I think you can download a print out from Zeel to stick on a cd to make a timing disc. It might be a bit harder to get the right size DTI.

[giggsey999]

When I say bearings were tight I mean like new, not tight tight.

[donkeychomp]

Where do you feel the vibration? Through the bars, footrests? Why so sure it's the engine? Could be something so simple you're over thinking the problem.

Either that, or the crank

Alex

[giggsey999]

Definitely from the engine, shakes the whole bike.

[mannanan]

Hmmm… do you know the history of the crank itself. How many miles, has anyone rebuilt it previously, if so whom. Sorry, but even without those answers, I still suspect the crank is the culprit.

[giggsey999]

No, don't know any of that, it looked good, all bearings felt as new, had made in Japan on the rods so was told it should be decent quality, so took a chance on it. Will get it out tomorrow.

[giggsey999]

So the crank is out, still looks OK to me although the flywheel end bearing is a little worn but not enough to cause the vibs I had, so what now, new one or re build, I would think most of the engineering shops that could do it are very busy, 6 to 8 weeks I bet,that's the summer gone, what about exchange, I think norbo does re built exchange cranks, anyone used them?

[Yogi]

Grampians generally do a crank in 3 days return 👍

[stirling11]

These 350 engines do shake a little, it's in their make up, no counter balance shafts to smooth them out and only two cylinders that fire pretty much opposite each other

Tie bar rubbers maybe ?

The 350 pistons are also heavier than what the original crank was designed for, as a 250

Could it be you are chasing something that isn't normal ?

Is there someone close that could have a look and listen ?

If it's a really heavy vibration then I'd have to agree on the crank, unbalanced pistons could be a culprit too, it would be fairly rare for this to be the case but you never know, now you have the crank out take off the pistons and weigh them

HTH