it died

[hungff77]

I was riding my BWs (Zuma) and at about 65kph (~40mph) It died. Electric start has no respones, and kickstart is lock. I guess the piston is gone and the ring too. Hopefully the crankshaft and the connecting rod is safe. You can check my garage for my set-up. It is not even any fast setup, the top speed that I ever obtain is like 82kmph, (~51mph). I even upjet to 84 main, and the plug is dark-brown... ;no

I am most likely going to switch back to stock cylinder with the next exhaust. I think i will match the cylinder head i am using right now and match it to the stock cylinder and remove the head gasket. I still have no time to take it apart yet.

Just a question, will a sized piston cause the kickstart locked too? I just hope the crank is ok (keeping my finger cross...)

I will let you guys up-to-date.

Frankie

[pinkymingeo]

Yes, it'll lock the kickstart.

[speedy_scooter]

Did it make any strange noises first or did it start to bog and then die? It does sound as though your piston is done with.

[hungff77]

Yep, it start to bog, then make some bewah sound, and then I feel like it is loosing power/compression/topspeed. I also think the piston is done. Oh yeah, and this last for like a hundred km before it died.

[hungff77]

Finally took it apart today and it is the piston, it is broken...Shatter a few pieces. It is the top, crankcase end, where this is two holes on top, that is where it is broken. I find a few metal pieces in the cylinder. The rest may fall inside the exhaust. Guess I will went back to stock cylinder, stock head.

Frankie

oh, and the crankshaft/connecting rod were safe. wheww....

[zuma ned]

have you flushed the crank case for metal peices...????

[florida derbi rocket]

hey, If you would..post some pics of the piston..with the holes ...we learn from these incidents. Thnx John

[hungff77]

have you flushed the crank case for metal peices...????

1. Have not yet, as I think some metal pieces fall in the exhaust.
2. Also, how to flushed?
3. I will post some pic, as long as I can get the circlips out and take the piston off. as tips that i can take the circlips off easily?

Frankie

[speedy_scooter]

Just grab the clips with a set of needle nose pliers.

[hungff77]

Yes, I have been doing it, but it still take some time/skills/practice to take it out easily. I am just think if there is any trick that make it even easier. Like turning at which direction at any degree, or just pull it out hard...

[zuma ned]

heres the metheod.

1.grab one of the little bits that kick up with the pliers.
2. now slowly twist the pliers while pulling back. if ou grabbed the left side kick-up, twist anti-clockwise. if you grabbed the right side kick-up, twist clockwise. while twsiting slowly pull backwards and they should just come out.
3. now throw the little circlips as far as you can so that they dont get used again.

[zuma ned]

oh, also.

flushing out the crank case means getting in the washing it all out with fuel or keroseen or someother cleaning solvent...NOT WATER. then blow and dry it all with compressed air gun.

[speedy_scooter]

I would say get a heavy duty carb cleaner or that Marvel Mystery Oil and flush out the case with that. And you dont have to compressed air it out you can always just drain it of any drips and then let it air dry for a day or two then go back and stick the new motor on and all.

[florida derbi rocket]

3. now throw the little circlips as far as you can so that they dont get used again.This is good advice..people can argue all the time about re-using gaskets and Cir-clips...but why be one of the stories..install new ones..

[speedy_scooter]

Yea especially since they are like $5 tops for a new set of clips.

[zuma ned]

yep, seen too many ruined engines from the "well its too late to get some new ones from the shop, so ill just use there ones again". re-used gaskets and circlips are some of the largest causes of new engine failure.

[hungff77]

Here is the pic of my broken piston.
First of all, when I check my piston, it burns clean, it is not lean.
The top part, as you see, the end is just broke off, both top and bottom.
My piston basically like being chop off. i find metal peices in the cylinder, crankcase (still need to flush it, have detached the crankcase w/ rear wheel from the frame), and inside the exhaust. I guess some peices have already fly out of the exhaust...

The cause? Has no idea. the wrist pin bearing is still in one pieces. all the pin is still in it. The only cause I find could be a Divine revelation that I should go back to 50cc.

Also, the crank/connecting rod seems find.

Frankie

[pinkymingeo]

Looks to me like it seized. Your revelation should be that it's not smart to buy junk iron cylinders.

[hungff77]

Well, here is the thing, I try to install my stock piston in, when I put everything in, the piston will Not do a complete turn, a locking appear. Then I look at it thourgh the reed valve hole, what happen is I see the piston skirt is touching the cranksaft bearing and it won't go anymore. The symtoms is like the connecting rod is too short. So I try it without the
wrist pin bearing, and it works fine, the piston can go for a complete stroke.

Since the whole thing is stock, what I am thinking (and guessing) is the bearing in the connecting rod is gone. (I kind of think it melted, as I took further inspection, it is like some metal been melt and coming out of the connecting rod/crankshaft part, where the bearing is)

So I think/guess what happen to my whole situation is the bearing in the connecting rod/crankshaft is damaged, causing the connecting change it's position and too much free play. And it end up like it shrink 1mm. Then when it pull the piston down stroke (toward the crank), it's new position casue the piston skirt to hit the crankshaft (also the piston expand when it is heated), result in locking and broke the piston skirt.

Since my BWs has only 3000km on it, I doubt it is the pump malfuction. I think it is more the stock carb is just way too small for a 70cc and a pipe combo, where it rev pretty high.

So I guess I need a new bearing, but since then, I think I should just get a new crank. Geee...how can I get the three gozillian tight screw off? You know the three screw at the starter fan...

Frankie

[speedy_scooter]

Got a question for ya, when you take the crank and push up and down on it, straight upand down, does it have play? If so then the rod bearing is toast. As for getting those three screws off i'd try a long handled screwdriver and see if that gives you enough leverage. If not try using an airgun with a screwdriver bit and see if that brings it off.

[pinkymingeo]

Just drill them. Only takes a few minutes.

[hungff77]

Got a question for ya, when you take the crank and push up and down on it, straight upand down, does it have play? If so then the rod bearing is toast. As for getting those three screws off i'd try a long handled screwdriver and see if that gives you enough leverage. If not try using an airgun with a screwdriver bit and see if that brings it off.

yep, it does have fair play. I think it is the rod bearing causing all the problem. It is like should I replace the bearing only or get a new crank...decision, decision...

either way, i am still thinking about go back to stock cylinder, to save more gas. But first, it is to fix the crankshaft first. Still, the conclusion is the stock carb is not set for high rpm.

[zuma ned]

only get a new crank if nessecary. inspect it thouroulgy for breaks, cracks, stress marks or any other abnormalites. if your lucky you may just get away with some new crank bearings.

[pinkymingeo]

The rod bearing is bad. Not many shops are equipped to replace them, and the cost would be prohibitive. Just replace the crank.

[just me]

I agree with pinky if the rod bearing is bad it is better to just buy a new crank. Not many shops will want to mess with such a small crank. Would be cheaper to buy a new crank.

[speedy_scooter]

Yay, now you can get a full blown stroker kit.:D