Engine locks up on bottom dead center

Schrockie · Oct 17, 2015

I bought the Stinger 60/80cc bike kit. Seized the the piston from running to lean. Replaced piston and jug and had it running then it just stopped while it was idling. Checked all the possible chain binding and clutch problems and all was good there. Found out the crank was locking up at Bottom Dead Center.
Removed clutch bevel wheel assembly and was able to break loose the crank and turn it freely but as soon as I tried to start it, it would immediately lock up again. Did this twice with same results. So something is causing the crank to bind and lock up. Before I do a complete tear down, any advice on what maybe causing this so I can have some spare parts on hand?

I have a Flying Horse engine kit arriving today but still want to repair other engine to keep as a spare or do another build. Any help is appreciated.

Bikeguy Joe · Oct 17, 2015

Debris in the case?
Bent crank? That's unlikely...
Bearings? It prob wouldn't lock in the same place though.

Keep us posted when you tear it down.

crassius · Oct 17, 2015

yeah, best to tear down & look

2door · Oct 17, 2015

My guess is something from the previous damage has found its way into the lower end. It must be a big piece to bind up a running engine though. I agree that a tear down is probably required.

Did you hear any strange noises before it seized up? Rattling, knocking, anything odd?

Tom

Schrockie · Oct 17, 2015

New engine just arrived so I was removing the old one, took off the flywheel/clutch wheel and tried to break free crank and I could feel grinding through the channel locks. Took a 1/2 to full turn for it to feel free and not binding on anything.

On the old jug and piston I did notice that one of the piston pin retaining clips was broke and had two gouges on the cylinder wall about 1/16 deep?

I'm going to get the new engine installed and running before I tear down old. Might be able to get to it tomorrow.

Thanks for the replies.

Troy

Bikeguy Joe · Oct 17, 2015

That would do it.

bairdco · Oct 17, 2015

Piston mighta been the wrong size.

Schrockie · Oct 18, 2015

Piston is the right size.

Agreen · Oct 18, 2015

The piston may fit in the cylinder, but can still be the wrong size. If the wrist pin is too high, that means when it goes to BDC that the skirt will hang lower and can contact the crank.

crassius · Oct 18, 2015

I'd guess that the missing pin is in one of the mains.

Schrockie · Oct 18, 2015

Thought of that and compared to old piston, perfect match. Plus I had it running for a good 15-20 mins before it just stopped.

2door · Oct 18, 2015

Schrockie said:
Thought of that and compared to old piston, perfect match. Plus I had it running for a good 15-20 mins before it just stopped.

That's why I didn't believe you had a piston problem. If the piston was hitting it would have hit every revolution, not just after a few minutes of running. If it was hitting at TDC then it could have been a clearance issue with the cylinder head when the piston got hot. But you seemed sure it was at BDC so that rules out piston to head issues.

Let us know what you find when you tear it down. It might help diagnose a problem that others would benefit from knowing about.

Tom

Schrockie · Oct 23, 2015

I've got the new Flying Horse motor installed but have a question. When watching videos installing new piston, jug and head that if the spark plug hole is off center of the head it should be on the exhaust side? Can anyone confirm or deny this?

I'm going to tear down the old motor Friday morning and see what I can find wrong in the crank case.

Greg58 · Oct 23, 2015

It will work either way, I have mine angled at the exhaust because it seems to run better. If you have clearance issues it can be reversed.

Schrockie · Oct 23, 2015

Tore it down, found the piece if wrist pin clip, circled in pic, didn't seem to be chewed up like it was getting caught in anything, but nothing else significant. This is my first time messing with a crank so I not sure what other kind of problems I maybe looking for?

Both of the main bearings seemed in good shape and functional as with the crank connector bearing. Anything else I should be looking for would be a great help. There wasn't any free standing oil in case but everything seemed well coated. On thing I did notice, is that inside the magneto cover there was oil in there also, is this a bad seal or something?

Troy

2door · Oct 23, 2015

Oil in the magneto area is generally a result of a bad shaft seal. Of course that wouldn't explain your original problem. And you're certain there is no obvious problem with the main bearings? Especially the one on the magneto, left side. A bad seal can be the result of a bad bearing which will allow the crankshaft to move off center.

Tom

crassius · Oct 23, 2015

hard to see in that pic, but a dark coil isn't from oil & I see no trail coming down from seal seat - new seals are cheap tho

Schrockie · Oct 23, 2015

There is no play in either bearing and both spin very well. The bearing on the clutch side can be partially removed off shaft, but magneto side won't budge. Do I need a bearing puller or something to remove these, is there some way to check them that I'm missing?

Pic shows clutch side bearing almost removed. Here's a better pic of magneto.

YesImLDS · Oct 23, 2015

My dax engine was just like that and ran just fine. The bearing will actually end up in the place holder ever from that position. I just put it back together because I couldn't get it off. Might try a flat head screw driver on each side and pry it up.

2door · Oct 23, 2015

The dark magneto coil doesn't concern me and there is no evidence of oil in the magneto area so I don't see a seal problem. But, since you've got it down this far I'd suggest replacing both seals while you have it apart. Cheap insurance, for sure.

I deleted that duplicate post for you.

Tom

Engine locks up on bottom dead center

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