KX500 BIG BORE KITS

[monster malibu]

Anybody know who makes big bore kits for the KX500? I'm not sure yet if I want one, but would like to know where to get one. My bike has alot of power, but more is always better.

[Hillclimb#42]

 There are all kinds of upgrades on here to get power where you need it, but I'm not sure about the big bore kit. You already have a reed spacer, pipe and silencer, and fresh piston? I suppose you can get a new sleeve and bore it to whatever size, but the Kaws have the Electrofuse coating, which I think is an advantage over other mfg's. Stock cylinders are strong and easy to get pistons for. Like I said already, there are options to get more ponies easier. I would refer you to my engine builder @ Thomas Racing Service for a big bore app. I am 100% sure that he can do it in the same turn around as any stock cylinder, but I would not be in a hurry until you get alot of feedback about the pros and cons of the mod. This will be an interesting thread to watch, because I'm sure there are alot of opinions about this topic.

[stewart]

i think you can make a lot of power very relieabley with stock bore and stroke

[maddoggy]

i'm not completely sure but i think a big bore kit would involve boring out the cyl. large and sleeving it to whatever the desired size. heres the problem. anyone whos worked on diesel engines alot knows about the problems associated with sleeves. they tend to wear holes in them from internal electrolisis(or harmonic induced cavitation). the wear occurs on the water side of the sleeve due to tiny bubble explosions that are vibration induced. knowing the revs on these k5s are high, in my opinoin, the sleeve wear on a 2 stroke would probably be worse than on a large low rev diesel. however, if a sleeve kit is chosen then change coolant at least 1 or 2 times per riding season. the sleeve wear is excellerated when running out of spec. coolant in the engine. my opinion only,  MADDOGGY

[BigGreenMachine]

Pretty sure Kustom Kraft does bigbore kits for the 500. They are a great company and have been into motor building for over 20 years now.

[demographic]

Don't know if you have sidecar motocross over there but over here they take KX 500 engines and get a bit silly with them.
One of the lads that used to come on here (Scarykxer) has had his bored out to something like 570 cc

Bored out and I think they use a 2mm oversize CR piston as well which is 91mm in diameter and change the conrods to CR ones that are aparentely stronger.
I am not sure if they also offset the crankpin to increase stroke.

They also use the Maico engines (you lot might know them as the ATK intimidator engine but its a Maico all the same) and they are re badged as Zabel engines.

Think they are something daft like 700cc, don't fancy licking one of those over with my left foot though.

[don46]

i'm not completely sure but i think a big bore kit would involve boring out the cyl. large and sleeving it to whatever the desired size. heres the problem. anyone whos worked on diesel engines alot knows about the problems associated with sleeves. they tend to wear holes in them from internal electrolisis(or harmonic induced cavitation). the wear occurs on the water side of the sleeve due to tiny bubble explosions that are vibration induced. knowing the revs on these k5s are high, in my opinoin, the sleeve wear on a 2 stroke would probably be worse than on a large low rev diesel. however, if a sleeve kit is chosen then change coolant at least 1 or 2 times per riding season. the sleeve wear is excellerated when running out of spec. coolant in the engine. my opinion only,  MADDOGGY

When the cylinder is bored it does not get into the water jacket, you shouldn't have to worry about electrolysis. Now you can use a new style cylinder, but if you desire to go more than 88mm you'll need to weld up the upper kips, or use an 86-88 cylinder. You don't have to install a cast iron sleeve, you can have it bored and re-plated. I have one that is 91mm, it works good, but, not sure if it's worth the work. I would have the Mods that Stewart has posted, I did a cylinder with the head, piston and 44mm carb mod, the thing hauls, it pulls a ton more gearing. Wiesco makes a 88mm piston, you could get your cylinder bored and re-plated to 88mm install the new piston and you'd be good to go.

There was a post asking if anyone had tried a PVL ignition with the Mods by
Stewart, I have and didn't like it at all. There is to much compression to spin the motor fast enough to fire, once running no problem, but getting running no way. The PVL works good on a lower compression motor. by my estimation my motor with the Stewart mods has 180ish psi of compression.

[Rotorised]

This is all great info guys, cheers. I have recently taken my cylinder off to port a big bore, but have found it is allready sleeved, so now im thinking a 540 kit. I would like to run the same mods as some of the members here but i dont think it is possible as in Australia we only really have access to 98 octane fuel and would be looking at detonation. Has anyone here got any engine mods for this kind of fuel?

[monster malibu]

Anybody ever dealt with KUSTOM CRAFT? They list a BBK for the KX500, it's a 540. I'm not sure about the BBK yet, but I'm still thinking about it. I like the idea of more power and speed.

[monster malibu]

I can't be the only one that's interested in the big bore kit for the KX500. Somebody's got to have one?

[stewart]

thers a lot of ways to make more  power 

[YUNGGUNNAZ]

if you are gonna do the big bore you'll have to get head chamber cut accordingly if you are set at 0 deck and use steel .010 gasket.also ports will have to be redone to compensate for the bore,including exhaust auxillary ports.not to mention powervalve mods to clear piston.LA Sleeve offers the kit also.hope this helps.

[monster malibu]

Hey guys, this is what's done to the bike so far- pump gas porting, Boyesen rad valve with Moose torque spacer, Pro Circuit platinum pipe, racing clutch (brand not sure) 13-47 sprockets. Instead of a big bore kit what else can I add?  I was also thinking of a carb over bore. Would I gain anything by switching the pipe out for a gnarly pipe?

[Arigato]

I can't be the only one that's interested in the big bore kit for the KX500. Somebody's got to have one?

I had one on my KX as well as a lot of porting, bored carb. etc.   It made so much power that it literally twisted the crank.  The crank was balanced and welded too.  Nowdays I stick with the stock bore and get my power from the porting and other mods.

[don46]

I have 2 K5's with 3 different motor's, one is a LA sleeve 540 (that is really only a 527) the other is a 560, and the 3rd motor is a stock 86x86 with the head cut and the piston modded. The 540 is on Nitrous so it's really hard to tell just how good it runs in stock trim. The 560 has tons of torque but doesn't rev very fast, and the stocker revs quick and has tons of overrev, it'll pull 15-48 gearing no problems (hillclimbing).

In my quest for power I've tried many combinations, and frankly the cheapest route was as good as any of the others, invest in a lectron.