Engine Trouble Another 'it died won't start' query!

[Urban Fatbiker]

I'll get around to it. There will be plenty of room on the remote steer for my front channel speakers. Screen goes in center.
Put remote on end of handgrip?

Nothing like being able to park, put feet down, and take a nap watching some vids.

 

[Urban Fatbiker]

I got the engine off and gave it a good inspection.

Diagnosis is, double dumbass on me.

Crankshaft was fine. Piston and cylinder were scoured to bits.
And embedded in the cylinder wall? Looks like the piece of g-clip that got broke off at 140 miles. Never found it assumed it got lost in flushing the crankcase.

Guess it didn’t.
Start fresh with the new one, it’s better build second gen magneto 8mm mounts, use what I learned.
It’ll be going real soon, till then I’ll be fatbiking. It’ll be ok.

 

[Urban Fatbiker]

I was OK. Fatbiked til the weather turned.

Today, I started Buzzbike with the new engine, a second-time modified jackshaft bracket, new design chain tensioner arms of steel for chainring side. No slotted holes or shims on the rear mount. Fitted an 18-tooth 410 width sprocket in place of the 415 width 21 tooth.

Better lower engine mount too.

I reassembled methodically, got the engine sprocket rough aligned, disconnected. Got the chainring side aligned and locked in. Then removed clutch plate, reassembled drive side, tested feel and fit by hand and visually, re-shimmed, tested, and again till I found the sweet spot.

If it ain't nylocked, it is threadlocked or double-set. Nothing's breaking loose. That part was good in my post-mortem and now its better.

I'll have to take pics tomorrow in the woods. Damn it ran sweet today from the first crank. Climbed out my drive at mid-throttle. No bog no sputter, damn smooth. I hear whir from the drivetrain instead of rattle. Makes me smile.

Dammit there's no piece of broken g-clip screwing this one I hope.

 

[cdeuce1988]

Engine: 48cc w/ bofeng carb, expansion pipe, bbr s1 ignition module & coil.
Drive: shift kut jackshaft low gearing.

Failure: while rounding up our turkeys, I ran it crossways over a plowed field, several ruts, and it died, now will not re-start.

Tests and checks:

Fire- measured over 12V from magneto, a significant pulse from plug wire to ground.
Have not done visual check with plug NGK BP6HS.

Magneto- checked mount. 1 screw loose. May have been a factor, maybe not. Removed mag, key is OK not sheared. Ground is good, continuity 327 ohms.

Fuel- checked carb float bowl (full) disassembled checked level ok, jet clear no debris.

Compression at spark plug feels normal.

Intake suction? I can't feel any, and it seems its pushing air OUT???

I'm lost unless ya tell me a cracked piston or crankcase might do that.

I'll let this stew a bit b4 I take it off. I do have another ready.
Hope my post a bit better than the 'won't start what's wrong' query, I've lived the other side of that question too long to forget to plug it in.

One of your ignition wires probably pulled loose from inside your cdi box or from the magneto coil. Or, and I've had this happen before. You're spark plug wire could have pulled that lil screw loose that it screws onto from inside the cdi box. Order a new cdi box and magneto and spark plug. They sell those 3 as a set all over Amazon and eBay for like 12 or 13 bucks.

 

[cdeuce1988]

I got the engine off and gave it a good inspection.

Diagnosis is, double dumbass on me.

Crankshaft was fine. Piston and cylinder were scoured to bits.
And embedded in the cylinder wall? Looks like the piece of g-clip that got broke off at 140 miles. Never found it assumed it got lost in flushing the crankcase.

Guess it didn’t.
Start fresh with the new one, it’s better build second gen magneto 8mm mounts, use what I learned.
It’ll be going real soon, till then I’ll be fatbiking. It’ll be ok.

Oh yeah your lucky it didn't screw things up to bad. I had one get stuck so bad that I had to hit the piston with a hammer with a wooden block in between the crank case and under the cylinder just to knock it loose and out of the cylinder.

 

[Urban Fatbiker]

Oh yeah your lucky it didn't screw things up to bad. I had one get stuck so bad that I had to hit the piston with a hammer with a wooden block in between the crank case and under the cylinder just to knock it loose and out of the cylinder.

I still went with a new build I had. That one got hammered by bad timing and jammed pistons and a whole lot of learning.

Felt nice to break in a new one on a solid setup. I swear it kicks the crap out of the other one.

 

[GW's Motorized]

Engine: 48cc w/ bofeng carb, expansion pipe, bbr s1 ignition module & coil.
Drive: shift kut jackshaft low gearing.

Failure: while rounding up our turkeys, I ran it crossways over a plowed field, several ruts, and it died, now will not re-start.

Tests and checks:

Fire- measured over 12V from magneto, a significant pulse from plug wire to ground.
Have not done visual check with plug NGK BP6HS.

Magneto- checked mount. 1 screw loose. May have been a factor, maybe not. Removed mag, key is OK not sheared. Ground is good, continuity 327 ohms.

Fuel- checked carb float bowl (full) disassembled checked level ok, jet clear no debris.

Compression at spark plug feels normal.

Intake suction? I can't feel any, and it seems its pushing air OUT???

I'm lost unless ya tell me a cracked piston or crankcase might do that.

I'll let this stew a bit b4 I take it off. I do have another ready.
Hope my post a bit better than the 'won't start what's wrong' query, I've lived the other side of that question too long to forget to plug it in.

Your bike has a sort of double expansion chamber thing going on. Does that do anything or is it just for the flex pipe and muffler?

 

[Urban Fatbiker]

Your bike has a sort of double expansion chamber thing going on. Does that do anything or is it just for the flex pipe and muffler?

I orginally took off a torquer-up pipe and put on the banana, then added small muffler on end.

Then I thought.
Ya know what happens when you think.
Ya FAAFO

I chopped the torquer pipe and stuck it in the banana. Sounds like a scooter, has good power, climbed my hill better than an open pipe or my small muffler, so I welded it and called it done.