KX500 engine rebuild

[Marco810]

I'm in the processes of rebuilding my kx5 engine and thought make a build thread. My plans with this engine are, porting, 250 ignition, 41mm pwk (pump gas), and what ever else i can think of on a stock stroke x bore. The bike its going on is a conversion bike so im thinking about a CPI "Dune pipe" unless i can find a better topend cr pipe.

Jug before i sent it off. some chips in the plating. was the first time i had this engine apart, so go figures its been neglected



Gathering of parts. still need to send my crank off for rebuild

[cnrcpla]

Why are you putting a 250 ignition in it? What would that do for a 500? I no little about big bores, so sorry if that's a stupid question 

[Recovered]

the 250 ignition is 10 years newer.  probably smaller, less rotational mass too. 

[cnrcpla]

Oh ok. That makes sense. With the lighter weight that monster is going to hit like a beast... Videos? 

[Marco810]

Oh ok. That makes sense. With the lighter weight that monster is going to hit like a beast... Videos? 

Ive been wanting to get a Gopro for some time now..

Another thing with the 250 ignition is a more aggressive ignition curve. Thinking about a Lectron, anyone have experience with them?

[Recovered]

i dont think you can go wrong walking into target and buying the gopro for 299.

[cnrcpla]

Insert Quote
i dont think you can go wrong walking into target and buying the gopro for 299.

I have seen them for that price everywhere. And every time I walk by them I cant help but wonder what else I could buy for that price that would actually benefit me or my bike  SO instead I made a free mounting piece for my helmet or bars that holds any camera. (I just have to test it out)

[Marco810]

I thought about taping my phone to my visor before, but it didnt seem like the best idea. I like the water proof aspect of gopro

[cnrcpla]

Just put a plastic bag around your phone   

[Recovered]

You guys are ridiculous.

[SachsGS]

Are you building a drag racer?

I didn't know Lectron was still in business.They were a popular conversion for piston port/non reed bikes back in the 70's and worked quite well.

[dogger315]

porting, 250 ignition, 41mm pwk (pump gas), and what ever else i can think of

I recently built a CR500 engine specifically for MX so our two goals are miles apart, but some
of the mods I made would be beneficial for a dune bike.  For the top end, I had Eric Gorr do the
port and head work.  He recommended a Wiseco piston because it is more durable than the
cast OE.  I sent that piston and crank assembly to Crank Works for balancing at 6-8000 rpm
which is the meat of the powerband for a 500.  I also had all of the rotational internals REMed.
This process greatly reduces friction and heat and improves clutch action and shifting.  I also
installed a VForce 3 reed and a 2000 CR250 ignition with a Vortex IC.  IMO, all of these changes
would also be beneficial to a big power, top end engine. 

Here's a couple of pictures of my engine.  I look forward to following your build and to see what
you ultimately come up with.

With the lighter weight that monster is going to hit like a beast

Actually, the bulk of the weight (crankshaft), is still there.  The smaller rotor helps with the gyro
effect and makes the bike feel lighter and more manageable in the air and in corners.  The biggest
gain is going from an analog to a digital ignition and the ability to program the mapping.  You can
really increase the hit (if you're a sadist), or virtually eliminate it.

dogger

[Marco810]

Are you building a drag racer?

I didn't know Lectron was still in business.They were a popular conversion for piston port/non reed bikes back in the 70's and worked quite well.

Drag/play bike. I may just stick with the PWK, from what ive researched Lectron is more of a wide open only carb

porting, 250 ignition, 41mm pwk (pump gas), and what ever else i can think of

I recently built a CR500 engine specifically for MX so our two goals are miles apart, but some
of the mods I made would be beneficial for a dune bike.  For the top end, I had Eric Gorr do the
port and head work.  He recommended a Wiseco piston because it is more durable than the
cast OE.  I sent that piston and crank assembly to Crank Works for balancing at 6-8000 rpm
which is the meat of the powerband for a 500.  I also had all of the rotational internals REMed.
This process greatly reduces friction and heat and improves clutch action and shifting.  I also
installed a VForce 3 reed and a 2000 CR250 ignition with a Vortex IC.  IMO, all of these changes
would also be beneficial to a big power, top end engine. 

Here's a couple of pictures of my engine.  I look forward to following your build and to see what
you ultimately come up with.

With the lighter weight that monster is going to hit like a beast

Actually, the bulk of the weight (crankshaft), is still there.  The smaller rotor helps with the gyro
effect and makes the bike feel lighter and more manageable in the air and in corners.  The biggest
gain is going from an analog to a digital ignition and the ability to program the mapping.  You can
really increase the hit (if you're a sadist), or virtually eliminate it.

dogger

Looks great Dogger. Not sure if CR's benefit from piston windowing but it would be worth looking into. People claim a easy +2hp for the KX with a piston window.

Was trying to decide on weather or not ill get it balanced, did it make a significant difference?

[dogger315]

Thanks Marco.  The crank balancing was done for 6-8000 rpm which is the "meat" of the
powerband.  It brought the vibration level down to 250 levels - very nice for a long trail
ride or moto practice, no more tingly hands.

The piston window is a good mod for the KX port configuaration but not so much for the
CR's.  Here are a couple of pictures of my cylinder to see the difference between the two. 
The big thing on the CR is to relieve the exhaust port bridge and add some oiling holes to
the front of the piston.

I think the 41mm PWK will be more than enough for your application.  I started with a 39.5
(the KX OE) and switched down to a 38 for better low to mid and throttle response for MX.

dogger

[Twostrokepower!!!]

That is hands down the sexiest motor ive ever seen...