magneto side shaft not turning true

[breno]

Hi all has anyone had an issue where the crank stopped running true and the magneto seal begins to suffer due to the shaft kinda moving around not turning dead staight.

This problem with the shaft now not turning straight has resulted in the magento seal not really having a fighting chance in sealing properly due to the shaft oscilating.
The magneto stopped working on the way to work due to it being covered in oil..

Is there any semi-permanent fix to making sure the crank cant become untrue?

It would be great if I could just pull it out true it up and spot weld it a couple of times but I dont think I can do that coz its cast I dont really know??

This is the 2nd GT5 that has done this and I'm begining to wonder what the heck i'm doing to make it go out of wack like that.

I'm really having a bad run of luck lately any advice on a fix or a means of preventing this problem would be gr8..

 

[2door]

My first question is did you remove the magneto rotor (magnet)? The crankshaft where the rotor sets is small in diameter and can be easily bent if you pry on the rotor to remove it. This is a common problem and why we suggest a puller that does not apply lateral force to the rotor or shaft.
Second question, are you certain the shaft is bent? If it is then there should be interference between the mag rotor and the coil. If there is no sign of contact I doubt the crank is bent. Replace the seal with a new one, available from several of the sponsors here, and make sure it is driven all the way into the bore provided for it. A common condition is the seal was not installed correctly in the bore from the factory and the rotor damages it. Let us know what happens.
Tom

 

[breno]

thanks Tom.
The rotor has come off before a couple of times but it comes off easily by hand and goes on by hand in the same fashion.

The magnet doesnt touch the magneto she just clears by a whisker..

But I can can clearly see the centre of the thread moving around kinda like a ceiling fan a tad outta balance..

I can get the seals fairly easily from CBC bearings in OZ.

I'll give it a shot and replace the seals I distinctively remember though the shaft never looked the way it does now coz I checked it the last 2 times I replaced it.

This motor has done some KM's too.. I've already replaced the jug, piston/rings, small end bearing and studs.

I'd say she's probably done approx 6000km's I use it everyday doing rather big km's to work and back. Even towing a trailer with my drills and hand tools, etc. for jobs on the side.. I live in a hilly area.

This motor has seen it all to from different mods to different styles of gearing setups.

I'm currently on the 44tooth it doesnt quite have the top end speed it has had but it hauls a55 up to 55km/hr it can stretch to 58km/hr but it it feels like pulling the pin of a grenade and seeing how long you can hold it for...

 

[2door]

Breno,
Sounds like you have a handle on things and you've certainly gotten your money's worth from that little engine.
I'm surprised you found seals from a supplier. I did some extensive searching for replacements, even going through a place that specializes in metric seals but didn't have any luck. The last set I got was from Piston Bikes, one of our sponsors.
Good luck and let me know if the new seal helps or if it goes away quickly. I'm interested.
Tom

 

[breno]

I'm multitasking at the momnent trying everything I can to get the S6-S morini sent to OZ.. I want one sooooooo bad.

 

[breno]

Thanks Tom..
I let you know how it goes I've got a spare motor I might have to chuck in if the new seals dont work out..

It'll be then if I can be bothered to rebalance it and possibly try and weld it..

And hey if it dont work out meh.. I'll just get another spare motor there cheap enough..

I can justify it, as it is my only means of transport everywhere..

 

[breno]

A morini S6-S is now in the pipelines..

WOOOOOOOOOOOHOOOOOOOOOOOOOO!!!!!!

Cant Wait!!

Ill just have to lean on my dads mates to make me up a nice zorst and some brackets..


On another note the motor is out and the spare is in..

I'll be stripping it as soon as I can and getting the crank trued and welded by a friend then port it properly, reassemble and refit this motor as it has been good to me so I would rather that be in there at this point in time...

I'll be sure to post up any results and progress to let ppl know what happens when ya weld a crank and the results that follow..LOL

 

[breno]

Well I ended up pulling the motor apart and found that the two flywheels aren't straight. That was the cause of the magneto side crank shaft osilating. Now it is just a matter of getting the thing trued up and balanced properly then welded up to get rid of any unwanted top end vibration issues.
I noticed that the port matching isn't much to speak of either on the gt5 go-sickem so looking forward to cleaning that up for a smoother flow. Will also be trimming the bottom of the piston skirt on the intake side 3mm as well as many have done before.
I'm thinking of making this the gun motor if all works out u know the typical 18mm mikuni, straight intake, kx 65 pipe blah blah. Should be good ,might even chuck the shift kit back on to make the most of it. I'll do my best to post up any progress pick and let you know if there is any performance gains. Thanks for reading this far happy molding fellas.

 

[breno]

well got the 2 bearings today for the clutch shaft (sealed on 1 side rated at 15000rpm) the 2 bearings for the crankshaft (sealed on one side rated at 12000rpm) and the conrod bearings are coming in tomorrow rated at 12000rpm also. More than I should need really. just gotta lttle mill work. Cant wait to put it bak togethr and flog the out of it. LOL
I'd say the next weakest link is going to be the piston and rings. Hmm go kart shops??

 

[breno]

Well all welded up crank fitted brand new jap bearings, match ported the motor and made the transfers slightly bigger, trimmed the skirt on piston intake side so it doesn't block my efforts I put in with intake I made 1 sided sealed bearings crankshaft new seals n gaskets. Pending 18mm carb n kx65 zorst but it can wait for now. Took pics n have all bearing sizes if anyone is interested.
Next post will b performance results with the upgrades on the motor alone.
Happy moddin$

 

[breno]

So far hmmm.. Possibly more vibration in motor from 40 - 48km/hr (but only minor it could just be a placebo affect) haven't gone past there yet as the new bearings fitted made the crank a little tighter than when I started to turn the crank by hand it does turn smooth though. I'll be ridding around all 2morrow to try and set it in. 1st rebuild/build so hopefully it all goes well.
in the afternoon I'll wind it out and c how it turned out if I'm not impressed with the crank balancing I'll just throw new flywheels back on it can only be better than where I started.

 

[breno]

Past 48km/hr and it feels like it going to throw a leg outta bed.
Cranks coming out again to check for trueness and put the new spare flywheels back on.
I'll post up pics soon to show wat not to do to the flywheels..lol

 

[Venice Motor Bikes]

, trimmed the skirt on piston intake side so it doesn't block my efforts I put in with intake I made

It's not a good idea to trim the piston skirt because it changes the port timing. (unless you're talking about the sides of the piston where the transfer ports are?)

 

[breno]

nope I was talking about the intake side of the piston...DOH!
I have made the piston flush with the top of the intake port at TDC.
What will it cause in lame mens terms to the port timing?
I have spare pistons to place in if need be until I eventually get it right..
do you mean trimming the piston on the top or bottom of the sides??
(i'll do a search)
I cant picture it right now, might make more sense when I pull it apart again..

I'm not to fussed about pulling it apart and putting it back together its about 40min for me to strip and just over an hr to refit I'm sure at this stage I can only get quicker LOL dont have much choice.. hmmm

I'm yet to determine if the vibration at 45km/hr upwards is coming from the drive shaft as it was slighly bent I can get a spare.
I plan on replacing it to help rule that out.

On another note here is a couple of pics of what I have done to my grenade havent got any pics of the porting or piston but will get sum next time I crack it..

I'll keep trying and posting progress and pics as I go down this learning path.
I plan on using the same zorst and intake mods the whole way through to make it easier for a performance measurement its easy to tell when she's cracking and i've also been using my mates bike as a reference from the start he is also a MB nut but doesnt ride too much anymore coz he got his license back..

 

[breno]

does anyone want the bearings sizes and conrod type of the GT-5 go sickem?
Happy to post them up if anyone needs them.

 

[breno]

some posts of piston trimming on the intake side I found..
http://motorbicycling.com/f13/piston-skirt-openings-24992.html
http://motorbicycling.com/f13/custom-clutch-bar-piston-skirt-trimming-8609.html

 

[Venice Motor Bikes]

I made the same mistake when I modded a engine last year... I thought it would let more air in if the piston skirt wasn't blocking the port, but what actually happens is when the piston travels back down, some of the fresh intake charge is forced back OUT the intake port because the piston skirt doesn't close the port fast enough!!

 

[Goat Herder]

I made the same mistake when I modded a engine last year... I thought it would let more air in if the piston skirt wasn't blocking the port, but what actually happens is when the piston travels back down, some of the fresh intake charge is forced back OUT the intake port because the piston skirt doesn't close the port fast enough!!

I did this only once to a old original Kings bushed motor. It ran great after I did it. I had a noticeable gain all around low and high end. Here at 5500 above sea level I needed all the air I could get.

All the motors I have come across lately the port is no where ''nearly'' as blocked as that King's motor was. So I have left them alone for the most part because on them the piston skirt has been barley visible at TDC

I don't think any of the motors come blocked off like that old original Kings did now.

Not to confuse things because its a different motor but..http://i137.photobucket.com/albums/q208/foureasy/DSC01136.jpg

http://motorbicycling.com/f13/hybrid-chinese-motors-performance-tuning-14204-13.html

 

[breno]

I understand what you mean.
For now I will clean up the filter cover (no filter ) and keep my eye out out for additional blow-by it does seem to have more of a chugging sound coming from the carby too so that could be what your talking about.

As it stands at this point in time though, the plans in order are to replace the drive shaft with a newbie then pull the crank out and throw the new untouched flywheels back on.

It did run fine before with the other flywheels before I tampered with them but yeah turns out my experiment was a fail but ya get that..

Thing is though before I played with the flywheels and got the bent crank I noticed the motor when I was running the 44tooth sprocket would run really quite after 52km/hr almost sounded like a sewing machine but I wasnt sure if that was the quite before the storm or if that was normal..since the bent crank (which could be from low end torque or high end rpm) i'm playing around with it as I would have just junked it if I didnt try as it wouldnt have worked properly anyway.

Once the vibrations are gone crank back to its old self and the drive shaft is replaced/straight then will I know how the piston skirt trimming worked out providing the crank turns nice and free with the jug off.

My plans are to let the motor rev further past 8000rpm kinda smooth and safely with the 36 tooth I will just have to play with it until I get a good or grenade result.

 

[breno]

Thanks for the link GH and some xtra PE.
The piston skirt blocked the intake path by approx. 4mm I will have to take a pic of before and after to show what I mean. I shaved a roundish 3 mm shape (3mm at the deepest part). The skirt would have blocked the intake path by approx 10-15%.
Is that the average it should be??. I'll post up a pic tonight to better my explanation.
Thanks to venice and GH for your advice and personal experiences I am a little in the dark..Ive always done things 1st time round the hard way mind you but ya gotta learn somehow. Cheers

YouTube - trued crankshaft
this is definately something I will have to do before I even think about it going back in
I likes it alot..
Might have to do some more homework on this balancing of the crank its too too early to give up and revert back to standard. thanks again for the link