Top End Rebuild - Stock or Bore? *Pics*

[Supergumby5000]

Hey all, I picked up an '02 blaster for $350 with a blown top end. I want to rebuild it for my 9 year old brother. It doesnt need to be made into some monster bike. I just want it to run and be reliable. My family lives in a village in alaska with little resources so I want to build a simple, reliable, easy to work on bike. I'll be deleting the oil injection system and rebuilding the top end. Other than that it wont get anything exciting.

The only modification I can see is FMF exhaust.

I am a 4-stroke guy and I've never rebuilt a top end before. The kickstarter was stuck when I got it. turns out it was because of metal chunks that broke off the piston. I flushed the bottom end out and now I need to rebuild the top end. Here is what the cylinder/piston looks like:












The piston is obviously toast. It looks like the previous owner tried to hammer on it when the kicker got jammed or something. There is some scoring in the cylinder that you can physically feel. It isnt awful or deep but it isnt smooth either.

The main question is can I just hone the cylinder and get a stock piston kit or will I need to bore because of the scoring on the cylinder? And if I need to bore what is the process? Do I have to send my cylinder somewhere to get bored out?

Any help would be appreciated. It looks like Vito's sells a complete top end big bore kit for a healthy chunk of change. If i can use a stock piston kit i'll rebuild it myself, but if i have to bore it might be cheaper for me to find a used top end on ebay or something.

Any opinions/guidance would be much appreciated.

 

[Larry's Shee]

Shipping is going be the killer for you. Definately get it bored. The best way is have it measured, get the piston, bore/hone to fit piston.
As to flushing the bottom end, you may or may not have gotten all the chunks out, best way is split the cases to flush the bearings. One piece the size of a grain of sand will roast a bearing.

BTW,

Welcome!!​

 

[Blaaster]

As Larry says, it is a must that the cases be split and the bearings fully flushed or preferably replaced.

Trust me the oil injection system is very reliable and unless you wish to run a certain oil at an obscure ratio, stick with the injection.

Any good machine shop should be able to bore and hone the cylinder, but they need piston in hand first.

Make sure that they chamfer the ports.

 

[Supergumby5000]

Let me clarify - My family is in Alaska. I just moved to California, so it is easy for me to get parts. I am building this bike and shipping it.

As far as splitting the cases, how much work does this actually involve? I am mechanically inclined but I havent torn into the bottom end of a 2-stroke before. Can I pull the case apart from the flywheel side of the case or do I need to disassemble the clutch side? It seems the flywheel side would be a significantly less amount of work,

 

[Awk08]

welcome to BF !

doing a bottom end for the first time can be overwhelming, but can be done.
watch these vids for tear down and reassembly, then decide if it's something you'd
feel comfortable tackling yourself.............

disassembly
http://www.blasterforum.com/threads/blaster-engine-disassembly-vid.42997/

reassembly
http://www.blasterforum.com/threads/kor-engine-assembly-vids-no-crank-puller-needed.51169/

 

[dirtysquared]

Let me clarify - My family is in Alaska. I just moved to California, so it is easy for me to get parts. I am building this bike and shipping it.

As far as splitting the cases, how much work does this actually involve? I am mechanically inclined but I havent torn into the bottom end of a 2-stroke before. Can I pull the case apart from the flywheel side of the case or do I need to disassemble the clutch side? It seems the flywheel side would be a significantly less amount of work,

Welcome! If you can get parts easily..... tear it down, get that cylinder measured, bored and honed to the next acceptable size piston. Doing a bottom end looks overwhelming, but if you take your time, pay attention to details, and ask questions on here, you'll get it done. I dissassemble the bottom end, label all parts and put them in ziplock bags (its $5 well spent), draw a diagram of where it goes and what it is....then re-assemble with the correct torque values, new washers, bearings, seals, etc..

These are good engines to break down and learn from. Watch the video's Awk sent ya and you'll be dying to do the job.

Good luck!

 

[Blaaster]

Hack and I are surely blessed and were born with photographic memories, has saved us many dollars in zip lock bags.

 

[Supergumby5000]

allllrrriiigghhhhttt I guess i'll dig into the bottom end to make sure there isnt any junk in there. I spent a good hour flushing it but I guess i better double check.

It looks like I can get a complete top end kit (including the cylinder) on ebay for between $200-$300. I think I will go that route rather than boring. This is for a 9 year old and it will be his first manual atv.

$350 for the atv, $250 rebuild kit, and he'll have a fresh blaster for $600. Cant complain about that.

 

[Blaaster]

As some reassurance for you, exploded pistons have a great habit of leaving microscopic particles of themselves in the bearings.

A particle no bigger than a small grain of sand lurking in a bearing can cause catastrophic damage costing many dollars.

 

[Larry's Shee]

Post a lincto the cyl you're looking at. IMO, it's still cheaper to get you'rs bored.

 

[Herpderplol]

Post a lincto the cyl you're looking at. IMO, it's still cheaper to get you'rs bored.

Opinion? It would be cheaper to get it bored. thats a fact haha