help - vibrations on old twin 650 engine

[odthing]

I have rebuilt my T120 engine on a bike that I acquired in bits. It is vibration free up to nearly 3000 rpm, then vibrates a lot. I know that there are inevitable dynamic vibes from all old twins, but it seems more than I would expect.

The new pistons are about 4 grams heavier (each) than the old ones.

I also noticed that the clutch runs very slightly out of true.

Would either of these affect it, and what else should I look at?

[Rex]

Not wishing to teach grandma about eggs etc, but have you compared it with another similar bike, or had another owner ride yours?
Trumpets (and I love 'em) do vibrate, but before worrying over-much, you need to find out if yours is more than usual.
You may wish to check engine mounting bolts as being tight AND correct, and the head steady too, in the meantime.

[odthing]

Thanks for that. I haven't had an old Triumph since the early 70's so can't really remember what it was like. Engine bolts are tight and correct, and I will recheck the head steady.

[triman65]

Hello Odthing

Yes triumph 650 do vibrate when on center stand I often have to follow it out of the garage if you go over 3000 rph. I have a 1973 Bonneville and in the mid 1960s I had a 1964 Bonneville. This also vibrated and I had to replace back number plate several times as it would snap just below the fixing to the mudguard.

[Justin_Faithfull]

As you have been told Triumphs do vibrate, but even so it is possible to alter the 'vibration period' (e.g. move the vibration up or down the rev range). If your pistons are 4 grams heavier than the originals then this will have altered the vibration period a little.
I can't exactly remember which way round it is but I think it is vertical component of vibration that the rider feels more than the horizontal component.
If your engine starts to vibrate at 3000 rpm it should reach a point at higher revs. when it starts to smooth out.
It may be worth considering having your crankshaft re-balanced.

[odthing]

Thanks for all the thoughts, Will