Crankshaft balancing and pistons

[Martin736]

Hi Guys,

I'm going to send my crankshaft off for an overhaul next week (the bike's been stood for 16 years) and was wondering if it's worth getting it balanced? Anyone had it done? Was it worth the extra (£85)?

There was some vibration when I last used it, I thought it might have been the pistons when I stripped it as it looks like they're two different makes (two have 70.5 on the top and one has 0.5) but I weighed them in work today and there was only 4g between them (enough?)

On the piston front, I was thinking about getting a set of these:

http://www.ebay.co.uk/itm/130787708247? ... 1423.l2649

They look like very good value but are they any good?? Anyone tried them?

Thanks in advance.

Cheers,
Martin.

[Martin736]

JUst realised I've posted this in the wrong place! Whoops...

[mark.read3]

Hi Martin
Opinions will vary regarding crankshaft balancing. My view is , save your money.
The pistons are good as well, used them in two of my bikes now with no problems. Only thing is ditch the small end circlips and use genuine suzuki ones

[Martin736]

Thanks for the advice, I must admit it does seem a lot of money. It would pay for the pistons! Good to know the pistons are OK, thanks for the heads up on the circlips!

Cheers,
Martin.

[gunnar]

It depends on how much out of balance your moving parts are before you decide to strip things down.
A badly vibrating GT750 is such a waste. You will miss out on the hidden Ferrari you got, even get wear on unexpected stuff such as the air box rubber bushings..
While a turbine smooth bike is a joy for its owner.

The GT750L I worked on ironically had such magic smoothness before I began restoring it. I could ride it and forget I was in third gear only to by chance notice the rev counter was at redline. With a less balanced engine you will get a clear signal in the handlebars of misdirected energy long before reaching redline. So I suggest spending some time on this topic can be rewarding unless you already are on the proverbial turbine bike. And if so I suggest you think twice about tearing it apart.
If you insist then one simple way to not upset things could be to make note of the weight of all parts and make sure to put thwm back in the same way with replacement piston/rod units trimmed to the same weight as before (hoping to preserve its characteristic). In my opinion making sure this is done as best possible unleashes the best in a GT750. All these bikes will have some lower rev area where they will vibrate, say at 2500 rpm or so, and that is perfectly normal. But a fortunate engine will smooth out as you come to 4000 and above. To accelerate up to red with no increase in vibration is all the joy, while a bike where vibration increases in handlebars so you dare not take it to redline should be in for some treatment. The energy should go out the wheel, not wasted in other directions. These bikes have so much to offer if refined in this department. Hope I conveyed some of what I tried to communicate.

[Martin736]

Thanks for your thoughts, in the end I had the crankshaft balanced as I know I would kick myself if it vibrated after rebuilding the engine! And although £85 is not an insigificant sum of money it's going to be a small part of what I end up spending....

I've got new pistons and will be weighing them before I fit them so hopefully all will be good in the end. The main reason for stripping the engine was to get the crank seals replaced as the bike had been stood for so long but as it happens one of the main bearings was on it's way out so I'm glad I pulled it apart.

Thanks again for you input and have a great Christmas!

Here's to a smooth future!

[piggbandit]

ih mate if u are haveing the seals replaced surely the crank will be balanced , i use pj engineering in staffordshire,done my 380 £300 cant fault them,bike is as smooth as silk its not worth it get the crank done rite.as for cruzinimage pistons used in 380 and 550 top value,but use suzuki circlips.