I recently bought an 04 Predator 50 that I knew needed a top end and some clutch work. Put a new top end on it, and replaced the missing clutch parts. It started right up, (but had some type of knock), but would run for about 10 minutes, then shut down until it cooled down. It will not restart until it cools down, then fires right back up.

The knock sounded like it was in the bottom end, but what's strange is (1) it comes and goes, (2) seems to make less noise as rpm increases, and (3) totally goes away after engine warms up (5-6 minutes). I've pulled the clutch and starter gear off and inspected them. The only thing I see that slightly looks bad might be the needle bearings behind the starter gear.

I replaced the stator because numerous people told me these bikes were famous for ruining stators, and because it didn't pass test specs when I checked it. Figured it had to be bad. I set the flywheel gap at .028.

It still shuts off after about 10 minutes. It idles fine (except for the noise) for about 5-6 minutes, then acts like it has a "miss" for a couple minutes, then dies.

I'm at a loss here. I know just enough to get me in trouble with these little engines, but I'm fairly mechanical. I was thinking a con rod bearing was bad, but why would it sometimes knock (and sometimes not), seem to dissipate with increased rpm, then vanish all together when the engine warms up ? Then I wondered if the needle bearings on the starter gear would make the noise if they were locking up ? Either way, I'm looking for suggestions !!!

I also need suggestions n why this thing only runs about 10 minutes. Will a bad rectifier, cdi, or coil do this on these engines ? This doesn't make sense to me.

Compression is 130 both cold and hot.

I'm in desperate need of help before I throw this thing in the river !!!!

 

ok, couple of questions before i give my thoughts. does the quad just die or does it start bogging down like it is losing fuel?

quick thoughts:
if bogging down, could be the float/needle valve stuck and not meeting fuel demand OR the fuel tank ain't vented and pulling a vacuum thus reaching equilibrium with the carb and fuel is no longer flowing.
if it is just dying, i've seen a regulator get hot and kill a quad. then once that cooled, it'd fire back up until it overheated.

food for thought.

 

The carb is new also. It starts to sound like a 4 cylinder with a miss, then it eventually dies. Once it starts to sputter, giving it gas does nothing for it. It still just dies. I did put my hand on the regulator tonight and it was VERY HOT. Would've definetly burned my hand if I left it on there. Kind made me wonder why it didn't melt the plastic body.

 

if you can keep your hand on it for a little while, it's running about 120°F. if you can't hardly touch it, it's way hotter than that and i believe that would point to a malfunctioning regulator. please check with the experts like others and OPT. they'll be able to help you out more than i can. i've just been somewhat familiar with those symptoms and those were my 2 fixes in my situations.

 

Actually, I may have mis-spoke. I was feeling the "resistor", not the rectifier. What does the resistor do on these little engines ?

 

The ceramic resistor block will get hot even on a brand new one. The "knock" you mentioned is what concerns me. May or may not be a bottom end going out,rod bearing,crank bearings,but sure sounds like it since it runs just for a few minutes and stops until it cools off.Could be starting to seize a rod bearing? Have had a bunch like this when only a top end was replaced and the bottom end wasn't addressed.Plus it can damage a new piston and bore job that you've already done.

 

Broke it down today, and I have to give myself cudos for some rather ingenious use and adaptation of a couple of gear pullers to separate the crankcase and pull the crank. None of the local dealers had the correct tool.

Anyway, the crank bearings are shot. I am truly surprised the crank spun at all. I'm not taking anymore chances with this thing, so I'm just going to replace the crank and con rod while I'm here. My questions are:

1- How on earth do I get the new bearings on the new crank, then into the crankcase ? I played hell getting them out of the case, and didn't even try to get them off the crank. Are they pressed onto the crank ?

2- Do the oil seals come out from the inside or outside of the crankcase ? Do I need to have the new seals pressed in or can I do it with a socket and hammer ?

3- What do I use as a gasket between the crankcase halves ?

 

You can find parts for these little ones at several different places. Eton,Polaris are basically the same except for body parts.Plus Ebay. The crank bearings can be heated and slipped on,OR just slip them on and use a dull punch on the bearing race only to seat a new bearing.Seals just pop out and in.Polaris 50 Crankshaft Assembly 13000 113 000 | eBay
50CC 2-STROKE PARTS
Use either Yamabond or Three bond 1194 for case sealant.

 

That looks like my crank, but that's not the part number I have listed for it.

Anyway, when you say race, are you talking about the inner or outer solid surface ? I would assume the inner ? Also, wouldn't heat distort the bearings? I have a small, propane plumbers torch.

BTW: You the man !!!! Thanks

 

Several other places on small engine parts on the internet along with Ebay and the one I've listed.Just call em up and see what will interchange. The race is the inner part. Won't hurt the bearings to heat them up to slip on the crank OR what I usually do is put the crank bearings in the freezer,heat the engine case up around the bearing area with your torch,take the bearings out of the fridge and they should just drop in(may take a little pecking to seat in the case). You can use wood blocks to have the engine up higher and a dead blow hammer or a wood block and hammer to seat one side of the crank in the case. The other case half can then be tapped on(sealant around the case edges)When it's thoroughly cooled down you can replace the seals. Then the bottom end is done!