Bent output shaft...

Firestorm

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Joined
Mar 27, 2019
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14
Evening all,

After a successfull 80 or so miles on the new engine and with break in going smoothly I seemed to be living the dream as far as motored bikes go.
Not one issue with anything engine wise and had mega power too.
Went for one of the best rides ever and on the way home I ended up hearing a noise I didnt want to. I could tell it was the gears so stopped engine and decided to pedal home to be on the safe side. There were no issue pedaling, it was free and smooth.

- Head off first to make sure my lovely mildly broken in bore and piston/rings were ok. Top stuff there. No issues at all :)

- Next, come round to the clutch side and slowly take off the cover thinking I would see horror. Nope, not one single gear tooth gone or broken :)

- Further inspection reveals that the little screw holding the flower nut in place had come unstuck and then allowed it to do what it wanted in there while engine was running and it decided to get itself run through the little drive gear from the crankshaft and the big clutch gear.

- Ok, how do I know this? Well sadly, the little drive gear now has a wobble due to there being a little bend in the shaft that its attached to.

- It doesn't wobble out of mesh and still has a good mesh at the furthest point of where its bent to now.

- Engine still starts and I put a new piston and rings in that I had spare. Also a new small end needle bearing, clips and g.pin.

Everything is checked over and secure now so should I just ride and enjoy the engine still? There is no leaks of oil on any seals and the bearings and housings are all good with smooth action and no slop. Im not happy about it but I am making the most of what I have without creating more issues and not missing out on riding when I want to. I am sure engines people have on here have run in a worse condition with success so let me know.

Lessons learned - Threadlock that screw and check before a ride. Done now.
Thank you.

-Storm-
 


Will'smotobikes19

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Apr 9, 2018
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1,419
About the gear wobbling that's quite common on motors even without a screw getting between. If you push the clutch arm in and spin the gears all of them have some oscillation. It's just from being poorly made. Sometimes the small gear isn't even fully seated from factory. Too many problems for me to mess with those things anymore but glad to help people.
 

Spare_Parts

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Nov 29, 2017
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1,167
Will is correct.

You should have left the piston and rings alone unless they had damage. The new rings may not seat depending on how much the first set wore in.
 

Firestorm

New Member
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Mar 27, 2019
Messages
14
Thanks for the replies guys.
So it would seem my idea of changing the piston out and top bearing was a bad idea? My reasoning for this is that as the screw passed through the gears there would have been a spike in torque on any drive connected to the piston so replacing with what I had would have given me less of a headache once started. My theory anyway.
Only put well under ten miles on the new piston and rings so I have switched back to the original before it makes itself comfy in the bore.
She starts first pop and revs out with no load with no major concern of vibration due to the newly bent shaft but my top end while driving and power has gone. Could this be the bend? even if it revs out under no load? Also what was an easy drive up my local hills has now turned into a big struggle for her.
There is wetness at the gasket at the bottom of the jug but its not leaking so am i right in thinking that the gasket isnt good and compression may very well be an issue here or its drawing in excess air? Idle is sweet but I assume that under load, this engine needs no leaks in any gasket? correct?
I want my power back and cannot be throwing any more money into this any time soon, so, ideas for a diy gasket that is known to work?
Using only houshold items too if anyone has any ideas? Some type of cardboard?
I need to ride it tonight somewhere but cant be bothered with crappy performance so will give anything a go.
Thanks folks

-Storm-
 

CrazyDan

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Jul 9, 2016
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1,661
You can make one with a sheet of copper, but not likely you have that. A cereal box may work, but not sure if it be perfect.
 

gary55

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Nov 27, 2012
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3,025
On the wobbly gear. Sometimes you can take a socket the same sixe as the gear and use it with a hammer to tap the gear fully onto the tapered shaft taking the wobble out of it them re tighten the screw. I have also seen the gears not porperly sized to the shaft allowing them to slip to far onto the shaft for the screw to properly tighten them. This will also cause a wobble and the screw to loosen in the first place. Something to look at. The odds of the output shaft bending in that short of a distance is highly unlikely. If it's running good I would just order another copper gasket because the sheet will probably cost just as much.
 
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JerboaJohn

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Jul 29, 2018
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900
your top end power will come back. it's reseating rings now that have to become friends again since 10 miles new rings undid what the first 80 miles from original rings wore in. give it couple tankfuls,, don't wind it out for a bit.
plus you pulled the jug 2x, it could be .5mm different position and you wouldn't know it except different sound from the rings
 

JerboaJohn

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Jul 29, 2018
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900
see how many cereal boxes = thickness of the original gasket. hafta cut that many gaskets. they are less than $1 tho, like 4.50 for 5 of em
 

gary55

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Nov 27, 2012
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3,025
Reading through what your experiencing now (like I should have done in the first place) the good revs but no power under load definitly sounds like a head seal issue. Since I don't know if your using a torque wrench for the head I will just throw this in. Over torquing can sometimes warp the head. Something else to look at. Might be fine but if not then just a new gasket won't cure your prob. Only applies to stock heads. Aftermarket heads don't have this problem. You can see a warp by eyeballing the head from corner to corner or use a strait edge. See the light showing through the gap in the middle where the heads has warped.
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Firestorm

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Mar 27, 2019
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14
Hi everyone and thank you for your words of support through this difficult time 👍
Last night I nearly lost my sh*t after putting her back together.
At TDC the piston was hitting the head; or so it seemed.... So I decided I would never look at the bike again and settled down for the night.
After a great ride today on my carrera (pedal only) I had time to ponder my options with this engine. I got back, ate and read these posts and took the cover off the bike to once again try and get it all good. I had a feeling the gasket was getting hit and not the head and to my surprise I was right :)
I trimmed down the centre hole with a sharp craft knife and got rid of the squashed parts and ended up with a tidy looking gasket to use.
Fitted it, torque head and then slowly roll forward to wait for the hit again....Nope...it worked and gave me lovely compression too.
So with new piston and rings and jug it fired on the third pop and I have started break in again. No leaks and no bull.
Off the bat it has its power coming back it seems but it will take time to seat the rings.
As for the bent shaft I described, well, its definitely bent on the little stub of shaft that comes out of the bearing and not the cog. I can feel a little extra vibration but not enough to concern me.
Its spins off centre due to the slight bend but not enough to create a mesh disconnect situation.
I have a theory that due to it not being perfectly central and true that it will not rev out as quickly due to the new inertial forces enacting upon that particular motion.
These engines rock but can bite at the worst moment. This place is the antidote.
Hope these posts help with this crazy issue as I couldnt find anything on running these with the issue I encountered hence the thread.
Thank you all very much. I will certainly be getting a brand new engine in a few weeks and will keep this one as a spare and learning curve.
I am going to baby that new motor so hard after all this! In the meantime, at least I can enjoy some riding.

Storm
 
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