I've done it again...

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.

KevTrem

Well-Known Member
Messages
897
Location
Newcastle, UK
Evening all.

So, last Sunday we had a bash meet at a BMX track local to us. I snapped the Baja pull start on 3rd pull due to fouled plug and my temper, so that got put away and the truck was pulled out instead. Anyways lots and lots and lots of big jumps, plenty fun until exhaust got loud, snapped the flexi.
Anyways I've now welded that up but when I tried to start the truck it's sounded horrible, like metal rattling horrible.
I've had something similar before, turned out to be a loose coil and loose flywheel due to the easy start nut stripping.
So, pulled it apart, coil tight, flywheel tight, couldn't see anything, so ripped into the engine wondering if the clutch was loose etc. Pulled flywheel off and the key fell out, but in a funny way. This is what I've found, I don't know how I manage to feck things up like this. Anyways got 3 or 4 spare flywheels but they are stock, so gonna spend half hour on the lathe tomorrow and mod them for the easy start.
Wouldn't mind but I had a spare machined flywheel, fitted it to the Baja just yesterday FFS.
Anyways some pics of the damage, crank looks fine BTW.
Last image is 1 machined and 2 spares that need machining.


20210416_195104.jpg20210416_195057.jpg20210416_195116.jpg
 
Is that keyway damage from drivetrain reverse shock landing off jumps ? Im no driving expert but i believe its best to stay partially into the throttle when airborne so as to create a "soft" landing and not stress out your drivetrain ?
 
Is that keyway damage from drivetrain reverse shock landing off jumps ? Im no driving expert but i believe its best to stay partially into the throttle when airborne so as to create a "soft" landing and not stress out your drivetrain ?
More than likely, gonna go through the whole truck over the weekend, nothing else looks damaged only the flywheel and exhaust.
I'm also gonna leave the big jumps for E car's and use trucks for flowing jumps, field bashing and RC tracks.
 
It looks like your key worked loose somehow ?? you can see the galling and expansion around the key slot this most likely caused the crack as well , maybe an undersized key ??
 
I've had that particular flywheel come loose before, so chances are the taper fit wasn't right. Anyways got couple to machine this morning. If I remember I will get a pic of the crank later today before fitting new flywheel.
 
Last edited:
Post a pic of the crank keyway. I'm curious and need more clues...
Ordered a new crank, upon further inspection I think crank has had it, also ordered couple woodruff keys.
The keyway has tapered sides now where key has laid over.
I put one of the machined flywheels on, started it up and sounded great for about 3mins then started knocking/banging again. Shut it down, pulled it apart and found the flywheel had loosened off, also a build up of aluminium on the crank taper.
It's currently built up and in the truck, will tear it down fully when parts arrive mid week.
 
Engine rebuilds are fun👏🏻 enjoy
I'm a maintenance engineer by trade so do love spannering especially building engines, more used to working on production machines in a cleanroom, love the chance to get dirty lol.
I keep thinking about buying the high torque 30.5 OBR, think next engine breakdown will be decisive.
 
Well the 29cc 30 Degree's North engine has been rebuilt and is running. New crank, gasket set and a pair of woodruff keys delivered.
I don't have pics of the rebuild, but will get a pic of the old crank next time in the garage.
Thanks again for the help lads, much appreciated.
P.S. engine fired straight into life, 2nd pull after priming.
Also didn't realise how easy and uncomplicated these 2 strokes are to rebuild.
20210421_103115.jpg
 
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock    No Thanks