Hole in Piston - Kasea AC 90cc

[jrns281]

Just want to thank in advance for the wealth of knowlege I have been able to review sincerely appreciate the advice.

Well sons mini-racer (Kasea 90 AC) blew a hole piston and in need of top end/ possible bottom end rebuild (I assume). We only use it at the dunes and not for racing. The cases are fine and it is an "Air Cooled". He was riding and the bike just stopped. and when I wen tot kickstart it, the kickstart locked. So I open the case and was able to free it. So when I spin the crank it only spins until it locks up then I can turn it in the opposite direction until once I again it locks up. Its almost like something is jamming the crank. I plan on removing the cylinder and hopefully see exactly what is wroing.

My ? is should plan on doing both the bottom and top end? Is there a way I can avoid the bottom end? We dont race just dune ride?

Thank and will post tommorow once I find out what could be the problem.

[LT80]

Can't plan on anything till you get into it and see.

[greenmachine70]

If you're not racing then save some money and check this guy out. Bought cranks, pistons and cylinders form him back in our air cooled days and they were ALL quality parts. Took 2 weeks to get here but they always did.
You can buy whole top and bottom end for about $200 and get a big bore and stuffer crank as well. Won a local championship on these parts and a 2nd at Dade City when we had a class of 100's with 26 riders. They do work well.
As for the hole in the piston...did you advance the timing? If so turn it back to stock or get more pistons
http://stores.ebay.com/Autotech355-P..._fsub=13810429

[jrns281]

Removed Cylinder Jug and piston, now the crank turns freely as it would not before removal. I did not force it as I did not want to damage anything. There were some piston metal dust around the crank. Since we do not race, is there a way to clean or wash away those particles? Any recommendations would be greatly apprecaited by my son.

Thank you

[LT80]

I've washed them out before with no problems.
A guy in another forum just purchaced a complete new top end for 75 bucks shipped off of ebay.
Hetrick (among others) can supply the same thing for approx 200 or so.
Me, I'd bite for the 200 option. I really have to question the quality of the $75. kit. Just don't make sence to me.

Now like the one gentelman eluded to (timing statement), it seems that your piston detonated. Detination can be caused by the timing being adjusted improperly or from old or low octane fuel basically doing the same.

[jrns281]

Once I removed the jug, I was trying to see if on the connecting rod it would saysthe mm size so I know what to purchase. the.crankahaft is not stock, and says "Rocket" on the side. Is there anyway to confirm tje stroke length so I know which kit to buy? I also agree on purchasing a more major brand.kit.

Thank you

[greenmachine70]

Since ALL Kasea, drr, apex are made in Taiwan why would you question the parts made in Taiwan. These parts are as good as any out there. Ran these stuffer cranks for 2 seasons in 2 of my own motors and one of a friends. Never a problem with any of these parts. Very good quality. I would not hesitate to buy these again. No one could ever see any difference in the parts or quality, just 1/3 the price.
If you're just doing top end here you go....
http://www.ebay.com/itm/Top-end-8-po...31085954796%26
And here is the crankshaft too..
http://www.ebay.com/itm/Performance-...item35ceec6e8e

Look in this guys ads he gives good measurements so you can verify everything. If you're a budget guy this is for you. If you want to have help from the big builders then you spend the extra money and buy the stuff from them for 3x price

[jrns281]

It seems like a very good deal and will check him out as to what is available for my sons 90.

My only other question is it looks like it has an aftermarket crankshaft. Without splitting the cases, is there a reasonable way to determine the length so I know what top end kit will fit?

Thank you again guys, my knowledge of these motors continues to grow with every thread.

[nastynotchback1]

You can buy the top end and put it together.Then check your squish and adjust as needed with shims or gaskets.

[ontargetracing]

You can measure the stroke with a dial indicator and measure the wrist pin size with a caliper. You can google how to do these measurements. If is a stock 90 cylinder it should be a 42mm crank with a 12mm wrist pin.