Thumper Racing out of Marshall, TX seems like a good choice for an engine upgrade. If you have used them, I would appreciate comments about their work.

Re-bore of an existing top end is$140;
A complete parts kit is $497;
Sending the engine in for a turn key upgrade is $652;
A motorcycle drop off adds +$150.

$802 for a turn key upgrade looks very promising. A slip on muffler would cost ~$250 for ~2HP. A full system would cost ~$400 and add ~3HP.

Would the stock exhaust work with this engine upgrade? If so, it seems like doing the engine work first is the most cost effective route for horsepower. Would a re-jetted 340cc engine with a stock exhaust run ~24HP?

Now for a dumb question - Do I need to buy a 300cc cylinder case/jug or, will my factory unit work with the milling and relining?

THANKS!

 

You will have to ask ThumperRacing if they are willing to sleeve and overbore your 249cc stock cylinder. Sleeving and boring the stock cyliner CAN be done. There is a former forum member named Marty who had a machinist named Bill Blue due the work.

If you want to try to get a used 292cc cylinder off of Ebay, you could have the machinework done without any down time for your bike until you actually install the jug.

For another option, theres is www.kustom-kraft.com They don't believe in sleeving, but they will bore the 292cc jugto 331cc and re-nikasil it along with providing you with ahigh quality, forged JE piston, rings and clips for about$400.00 (if you provide the jug).IfKustom-kraftprovides the jug, the price goes up to over $700.00. The heat transfer characteristics of this proceedure is much better than sleeving...it translates to longer engine top end life, but to each his own. I will take reliability over 9 extra cc's and the added weight any day. There is a reason they don't sleeve them in the factory anymore.

 

I had mine done at thumper. I trnsported the whole bike. Theywillneed a 292 to start with.The 249 cannot be bored to this diameter. They provided a 292 from ebay, and bored it. They also provide a wiseco piston, proprietary, new jetting, tuning, testing, andother work. Whatever the tech details, they resolved them and it works perfectly.
For more info,I did a write up on this forum, "experience with 340 kit" a few days ago.
Frank

 

Dean,

Sleeving is used in lots of engines so, why would sleeving a four-stroke motorcycle engine be too difficult? Why did it stop? Was it due to expense and machine time in mass production or was there a true techincal problem?

I'm a little confused right now because I have received contradictory information but, it seems the KLX-250S cylinder is the same as the KLX-300 model other then the bore size difference. I know the older Asian spec KLX-250 (R's?) had a difference in the crankcase to cylinder area which would require a modification. It seems like Kawasaki streamlined production by making the engines more "common" for parts in mass production.

Best Regards,
Sid

 

Nikasil electro-plating conducts heat to the cooling jacket more efficiently. Also, I don't like the idea of dissimilar metals expanding and contracting at different rates. The 331cc kit from Kustom-Kraft will also"completely transform" your bike, but if you just have to have the extra 9cc's andantiquated steelsleevingprocess, so be it. There is virtually no difference in price between the Thumper Racing kit and that offered by Kustom Kraft.

Contrary to what the other poster stated, the 249cc cylinder CAN be over-bored to 331cc's.It will need sleeving though. Bill Blue has successfully done at least two of them. If there is a subtancial price break, I can see the logic of going with a sleeve. If you turn-in the your stock 249cc pistonto Bill, you will save big bucks over buying a complete kit.

There actually IS a difference between the 292 and 249cc cylinders. You can see the difference by measuring the inner and out diameter of the cylinder wall. The 292cc cylinder is thicker, so there is more material to work with. That's why most machine shops prefer to work with the 292.

1997 is the magical year when the production process was streamlined. Both engines(300R and250S) now share the samediameter ofcase opening. Ifyou have the 250R, which was built from 94 to 96,you need to have the case machined to enlarge the opening.250S owners will have no such worries.

 

I'm not looking to stir the pot or start a flame war between Kustom Kraft or Thumper Racing fans. It just seemed to me that re-using the 249cc cylinder would save ~$300 and sleeving is a proven technology used in many applications that I think are more demanding then mine.

If the sleeving is strong enough and good enough, we are talking about ~50% ($300/$650 plus shipping) the price of the uprade if I ship the engine off to Thumper Racing. Is more modern technology worth ~50% more? Maybe I will get lucky and find a KLX-300 cylinder on Ebay .....

In either case, a 300cc cylinder is probably best. Either Kustom Kraft or Thumper Racing would make me really happy.

 

Hello all,
Just got back from a week in Colorado. Trying to catch up onwhats going on. As for the difference between the 250 & the earlier 300 cylinderthey are the same except for the bore. I have boreda couple of the 300 cylinders to 330 & (5) 250 to 330. The outside dia. of the 330sleeve is thesame dia. as the outside dia. as the stock 250 cylinder outside dia.
I talked with thumper racing beforeI left they say the cases does not need bored out to fit the 340 kit. You can make a 250 cylinder into a 300, 330 or a 340.
I just made my wifes 250 & mine into 300 real happy with the way they run.

 

Bill,

What kind of sleeves do you use?

The Kustom Kraft website says theirs are a "slippery slick moly 2000" alloy sleeve. They warranty sleeves for (5) years, but only warranty nikasil coatings for (1) year. So, it would seem to me that sleeving is less of an "antiquated" method, and more of a "proven" method of cylinder repair or enlargement.

 

Bill, thanks for responding. I made the statement about the outer diameter based upon some measurements that one of our forum members made awhile back, but since you are the machinist I'll have to go with what you are saying. It makes sense that they would streamline the jugs as well.

Maybe the reason a lot of places say they can't bore the 249cc to 330 is because they are thinking of the old KLX250R (94-97) cylinder which must have had a smaller outer-diameter because its case needs machining to accept a KLX300 cylinder. This is only models built prior to 1998 though. There are warnings to that effect on large bore kits made locally in Japan. Since most people in this forum own a 250S, that shouldn't be a problem. I do remember some poor guy on one of theBritish forums thatordered a 300R cylinder forhis 96 250R and found thathis case neededmachining. What bummer that must have been.

 

Both are proven. Nikasil coatings aren't exactly a new process, but rather one that has been perfected over decades. I just wrote to Kustom-kraft to ask why their big bore kits offered for the KLX300 and 250 are nikasil rather than sleeved and am waiting for an answer. I also asked them about the waranty.

Here is my best guesson why they don't put sleeves in the KLX large bore kits.

You have to remove more metal from the cylinderin order for it to accept a steel sleeve. If you look atMarty's 250Scylinder that was sleeved and bored by Bill, he had tobore into the water jacketto make a bigenough hole for the sleeve.This can creatthin spots that might lead tofracturing of the alluminum which surrounds the sleeve. We'll wait and see what their answer is.

As for the waranty question, I don't think it has anything todo withlongevity or which process is more 'proven.' My guess is that it's because it costs 4 times as much to repair a Nikasil coating ANDNikasil is heavily usedinrace bikes, which take a thorough thrashing all of the time.

I will also add that Nikasil has less friction and superior long-term wear characteristics.