What could have caused this?

ChrisZx7

New Member
May 15, 2012
794
4
0
Rochester, Ny
Gonna try n keep this as short n simple as possible.

Bought a Blaster off my buddy. Top end was rebuilt, bored .40 over. Brought it home, cleaned carb, changed oil, got it running. Ran sh*t out of it around yard for few weeks. Decided to go down rd. Went 1mile down road, took a right, went down next for like 1/4 mile. Bike died.

Brought it home, tore it apart. Top end blown, and noticed one of the shims on side of connecting rod to crank was gone. My buddy says there were pieces of it in bottom end, although i didnt see.

What would of caused that shim to blow apart and blow top end?

Stock engine bored .40 over
Oil injection still on it
I was at full throttle for 1/4 mile when it blew.
 
If you had it pinned all the way that might have done it, idk how the rest of the ride went up to that point but if it was running hot that could put the nail in the coffin.

Sounds like you might beat your ride, I never really keep it pinned i get there then back off a little.
 
The crank thrust washers can come out and bounce all around everywhere for a number of reasons.

2 stroke engines aren't exactly designed for WOT operation for extended periods of time unless they are specially prepared for that sort of duty (and some are!). Generally they're designed to operate under transient loads where they have the chance to cool off somewhat between periods of WOT. If you are going to regularly operate it at WOT, you absolutely have to make sure that EVERYTHING is in perfect order.

You need to make sure you have a perfectly leak free engine, all of the bearings have to be in great shape, you need to use only the best lubricants, all of the engine tolerances have to be PERFECTLY spot on, and you have to be jetted perfectly. Not kinda close, but perfect.
 
I did notice the engine was extremely hot. Hmm. So what am i looking to spend to get this thing rebuilt top & bottom? I cant get myself to put too much money into such a little machine.
 
Well, that depends on how you go about it.

If you undertake the operation yourself and only go back with part that you absolutely need, I could see getting it done pretty reasonable.

Assuming all of the other parts are working and functional and you have at least one additional bore left.
 
I did notice the engine was extremely hot. Hmm. So what am i looking to spend to get this thing rebuilt top & bottom? I cant get myself to put too much money into such a little machine.

Depends on how you want to do it, probably in the area of 4-500 to do it right. If you shop the forums for a used top end and used crank it would be cheaper but used motor parts are what they are. And its probably a good idea to replace every one of those bottom end bearing if your going to put the money into those other parts, it will protect your investment long term.

I got a complete top end thats all new in the for sale section of the forum, and another member has a used setup with low hours for sale there as well. either one is cheaper then the feebay options.
 
Depends on how you want to do it, probably in the area of 4-500 to do it right. If you shop the forums for a used top end and used crank it would be cheaper but used motor parts are what they are. And its probably a good idea to replace every one of those bottom end bearing if your going to put the money into those other parts, it will protect your investment long term.

I got a complete top end thats all new in the for sale section of the forum, and another member has a used setup with low hours for sale there as well. either one is cheaper then the feebay options.

X2 on everything except ALL of the bottom end bearings.... I don't change out transmission bearings unless there was something wrong with the transmission (or reason to suspect they're bad). The transmission bearings are run under full lubrication (transmission fluid being slung all over them) and not at nearly the rpm that the crank bearings are (primary gear reduction is like 3.7:1). Plus they're REALLY expensive to buy from the dealer...
 
Depends on how you want to do it, probably in the area of 4-500 to do it right. If you shop the forums for a used top end and used crank it would be cheaper but used motor parts are what they are. And its probably a good idea to replace every one of those bottom end bearing if your going to put the money into those other parts, it will protect your investment long term.

I got a complete top end thats all new in the for sale section of the forum, and another member has a used setup with low hours for sale there as well. either one is cheaper then the feebay options.

Ya, no way im spending 4-500 for a 200cc machine thats 20yrs old that cannot get good power pulled from it without dumping mad money. Ill just replace shim and throw a new piston in it. It blows again, ill scrap it.


lmao little machine....

It is when your used to riding a 130hp street bike.
 
Ya, no way im spending 4-500 for a 200cc machine thats 20yrs old that cannot get good power pulled from it without dumping mad money. Ill just replace shim and throw a new piston in it. It blows again, ill scrap it.

Part it out now. Unless you go through and do it right it WILL blow again.
 
Ya, no way im spending 4-500 for a 200cc machine thats 20yrs old that cannot get good power pulled from it without dumping mad money. Ill just replace shim and throw a new piston in it. It blows again, ill scrap it.

You should do some reading on that motor it doesnt take much money to make a ton of power just somebody who knows what they are doing with that cylinder.
 
You should do some reading on that motor it doesnt take much money to make a ton of power just somebody who knows what they are doing with that cylinder.

Ya, i read porting n polishing it gives some power. Idk, im just stuck. Im fighting myself bad to put money into this thing. I got the frame freshly painted sitting on work bench waiting...
 
From visiting Ken's web address, i cant not send it to him. I guess my engine is getting boxed up and sent to him. Money isn't an issue, just dealing with myself putting money into a 20yr old bike.
 
Ya, no way im spending 4-500

Money isn't an issue

????? I understand what you're getting at, it's not the dollar figure but the fact you don't necessarily want to put that into it.

Email sent to Ken, hopefully engine will be shipped out to him by end of week.

That's not the $4-500 method itstyler was discussing. He will get it straightened out but expect the figure to be higher than that.
 
I should clarify, it's not Ken I'm talking about being pricey, it's all "shops" (myself included).

In order to make it worth while to work on it costs a certain amount of money. Little things start adding up REALLY fast (bearings, gaskets, seals, misc small parts) and before you know it just a "simple" repair is a relatively large bill.

The method itstyler described that will be relatively inexpensive is a DIY parts searching method. I feel you'd learn more doing it that method and either come to respect (or despise :o) the "little machine" more.

For those who don't have the tools or the time there are folks out there that, for the money, will rebuild/build engines. It's just not going to be the least expensive option!
 
You can't just replace the thrust washer X(. Crank would need rebuilt. Was there damage to piston/cylinder? Way cheaper if you DIY. I:I These things are about as complicated as a rock. If you decide on a used crank, unless it's someone upstanding on here, you need to know what the side clearance of the rod is, and what the other tolerances are. Unless you're boogering :o it to off it, it will cost $$ to do it right.

Only special tool you need is a flywheel puller. DIY section has methods of case splitting/assembly without special tools. Been there/ done that.:D
 
Why would the crank need to be rebuilt? The thrust washer needs to be replaced, crank still spins around nice.

How does the crank come apart and be put back together? I think i read that it needs to be pressed back in with a good press, and needs to be balanced?