crank balancing :Gt750 kettle

[Shox Dr]

A good mateof mine has a Gt750, that vibrates, stripped all the aux parts off the motor and it still vibrates, so the crank looks to be the culprit.

Has anyone got recommendations for a good (very) crank rebuilders. Speaking to 'tigler' today and he heard PJ Motorcycle engineers in Wolverhampton 2smoke specialists: any comments either way? Or suggestions

 

[AndyStobbs]

Used to buy parts from PJ when I had aprilia's. Bit far from me to have any rebuilds done there, but spoke to Paul once or twice on phone and on a forum he used to frequent. Very clued up bloke. Not sure if they've got the gear to dynamically balance a shaft, (always thought that to be very specialist) you would have to phone them though.

 

[Wallace]

Might not need balancing just truing up if it's a built up crank. I would rebuild it whilst out as a matter of course and replace the bearings & seals.

 

[Pete.]

Agreed, if you're having the crank trued might as well have it rebuilt. Vibration need not be the crank though. A loose mount, worn rubber or many other things can make an awful buzz.

 

[MrFluffy]

Thats a built up crank with solid conrods. To balance it you have to press it apart, push it back together with weights instead of the conrods, balance the assembly on a rotating balancer, and then pull it apart again and rebuild with the conrods back on.
I say pull, it involves a decent sized press to get them in pieces. They're also a interference fit on the crankpins between webs etc, so theres a element of wear each time theyre disassembled.
Chris Applebee has a video of youtube showing them balancing a pressed together crank, but I dont think even he has found a way to do the job without having to take it apart a few times...
If anyone has a method to dynamically balance the crank without removing the conrods and replacing them with weights, I'd be interested to know it too.

I am midway through pulling my z1 crank apart and reassembling it with gsx1150 rods and retruing, its not a little job. My goal there is a straight true crank and weldments/pins on each web to get it to hold together under severe (drag) use.

 

[Shox Dr]

Pete, that's the only thing he has not checked: the mounts.

So IF it is the crank is at fault, then whoever carries out the work needs to dynamicaly balance it by splitting and rebuilding with suitable weights in place of the con rods. So it makes sense to balance the con rods and pistons?

What questions do I need to be asking potential machine shops

 

[chris-law]

A good mateof mine has a Gt750, that vibrates, stripped all the aux parts off the motor and it still vibrates, so the crank looks to be the culprit.

Has anyone got recommendations for a good (very) crank rebuilders. Speaking to 'tigler' today and he heard PJ Motorcycle engineers in Wolverhampton 2smoke specialists: any comments either way? Or suggestions

I took my cr500 crank there and they did it while i waited , that bike vibrated your teeth out but i think thats just a big single thing , a lot of bike shops send there cranks there .
I once used a place in essex that does dynamic balancing on a zx7rr and they did a great job .
They used to advertise in motorcycle news

 

[chris-law]

Note to self read all post before posting

I had my crank and rods done by chris appleby , the guy mrfluffy talked about , he did a great job on my bike

 

[Chipper]

Same here, he welded and sorted one of mine, was about 10 years back but he had a top rep.
There's always Stan Stephens too, for stroker stuff.

 

[normspanners]

I have used DAVE BROOKS engines In CREWE they did a good job for me balancing a flywheel and twin plate clutch assembly for me that reved to 10000rpm.

 

[stuvy]

Iv used PJ in the past they are really good and dont add the price up as they go along which is good

send my best to tigler mate

 

[superls]

if its just dynamic balancing you dont really need a bike or even an engine specalist, my uncle works for an electric motor rebuild/refurb/rewind company and they have a dynamic balancing machine there

 

[MrFluffy]

Pete, that's the only thing he has not checked: the mounts.

So IF it is the crank is at fault, then whoever carries out the work needs to dynamicaly balance it by splitting and rebuilding with suitable weights in place of the con rods. So it makes sense to balance the con rods and pistons?

What questions do I need to be asking potential machine shops

As someone else has already pointed out, usually when the crank causes horrible vibration, its gone out of index or alignment somehow.
Because they are pressed together, under heavy extreme loads the cranks can twist and thw two halves become misaligned. In which case, the trick is to pull it apart, inspect the bearings as thats the only time you get to see them and reassemble it. If you are going to be abusing the bike, its a good idea to get the crankpins welded into the webs while thats been done or if its really extreme use, pinnned at the same time, but be warned once you have this done, getting it apart without ruining the crank is a nightmare and some consider a welded crank unrebuildable. So if its for a quick resto with some gentle happy canters round the scenery afterwards, it may work out better to not weld it unless the fits have been destroyed on the crankpins by too many rebuilds. A good engineer will mic up the pins and holes in the webs and check the interference while its in bits for inspection. Its a bit of a specialist job, I'd take it to somewhere that knows the job to be honest as occasionally theres improvements to be had here and there that make a lot of difference (gpz1100 crank without the steel thrust bearing setup etc).

I'm not going to bother with balancing my crank once its welded and trued back up. Just push it together, weld it, hit it with big lead hammers till its true, then drill and pin it, then weld over the pins then hit it with more hammers... A pleasant job it is not.
If you can find him, and he isnt booked up for the next 10000 years because he's so much in demand, Dave Branch is the man for crank rebuilds on built up jap cranks. Yes the same dave branch from speed dreams on the telly the other week

Ive spoke to Chris Applebee on the phone about doing a crank for me a few years back, and he seemed a knowledgeable chap and you can actually find his videos on youtube of him doing gt750 cranks so he knows them well, but since then someone who I KNOW has a lot of hardcore expertise in the field has said some rude things about his work. So, dont know if I can recommend or not.