I was going by what I was told by multiple sources.

However, earlier today I was curious so I got out the calipers and took measurements off both the 249cc cylinder and the 292cc cylinder and from the best that I can tell, the 249cc cyl is an underbored 292cc cylinder. Therefore, one should be able to overbore the 249cc cylinder by the same amount as one can the 292cc.

I specifically asked this question to two shops that did overboring, both of which listed the KLX250 and KLX300 with big bore kits and both told me that you can't take the 249cc cylinder to 330cc, that you had to start with the 292cc cylinder to do that. But according to my measurements, that doesn't appear to be the case - maybe there is some bad information floating around out there with regard to this.

When I spoke to my shop a little bit ago about this, the owner indicated that he did not actually have a 249cc cylinder to take measurements from, but when I told him my measurements, he did agree that it appears that the 249 is an underbored 292. He's going to try and borrow a 249 and do his own measurements to confirm. I wouldn't mind to let him borrow mine but I don't want to pay the extra shipping weight - I'm shipping 2nd day and the price goes up a lot with extra weight.

Of course, it's too late for this to really help me ... I've already got my bike apart and my 292 packaged up and shipped. I'll still have my 249 of course, but this information might help someone else.

 

that is interesting nobrakes....

 

So, if it is true that we can make our KLX250S into a KLX292S for the cost of gaskets, piston, piston pin and rings?

H'mmm, I guess that is the next step in mods.

Do you think you might be able to get a quote from your machinist as to what boring the stock cylinder will cost?

 

I must admit that the bike was running really great before this, even before getting the pumper carb. But what can I say - I'm addicted to torque. The 300 upgrade really made a nice improvement and I'm looking forward to another one by going to 330cc. I don't know if the relationship between stroke volume and horsepower is linear, but if it is, going to 330 should be about double the improvement as going from 249cc to 292cc.

I doubt that is in my future. From what I understand about that, increasing the stroke requires a new crank? and piston rod? Stroker used to do this back in the day and I think it was pretty expensive, requires splitting the case, and you'd have to ship your whole engine which shipping alone would probably be as much as this big bore mod, let alone all the labor and parts.

Not sure I'd know what to look for here - do you have anything in particular I should look for? It looks pretty straightforward and clean to me.

What I did plan to do while I have it all apart and everything easily accessible is re-cap the bypass vents with more durable plugs since the Help brand plugs that I used have received numerous bad reports of cracking. As well as regrease some bearings such as steering and swingarm. Also, I plan to add your PCV valve to the end of my crank vent hose and then add another short extension to raise my crank case vent up a little higher so it is not so exposed. And some other tid-bits that should keep me busy for the time that my cylinder is being worked on.

I thought about maybe tweaking my carburetor settings while I have it out. After adding my 300cc cylinder I've noted a mild studder at the mid-range and an accaisional decel pop, though idle is perfect. I think this might just be an air mixture adjustment, but I'm running a #125 jet so I wonder if I should go a little higher to a #128 or even #132. I didn't really want to mess with the carb any more especially since I've got a pumper on order, but while its all out on the bench which is the hard part, and jets are cheap, why not.

 

I definitely think you can bore the 249 to 292 without any problems. But if you can go to 330, why not do that?

The place I'm getting mine done is http://www.Kustom-Kraft.com . He has done several KLX250S's taking them to 330cc using the 292cc cylinder. Maybe if one of you can ship him your 249cc cylinder, he can confirm whether or not for sure that you can take it higher an on up to 330. But if for some reason he can't, he should still be able to take to at least 292cc for you. Send him an e-mail, the owner's name is Marvin and his communication is very good. I have at least one good solid report about their work by a fellow over on ADVRider who was very happy and no problems to report.

I was also considering to do the work at Four Stroke Works, http://www.fourstrokeworks.com , where I ordered my carburetor, but he already has my money for the carb and I'm still waiting on that, so I figure I'll at least wait until I get my goods before sending more money his way. I really like Jerry's credentials who formerly was the Chief Technician of Stroker Inc - the KLX300 experts. He's currently retired and runs FSW out of his home. I think Jerry is just really busy and I just ran out of time on FSW and want to get this overbore started.

 

Hey guys, I might have been too hasty claiming the 249cc looks just like an underbored 292cc. I don't know how much of a difference it will make, but the thickness of the sleeve on the 249cc cyl is 7.1mm while the sleeve thickness on the 292cc is 6.0mm. The 249cc bore is 72 mm while that of the 292cc is 78 mm or 6mm difference. This would mean a 3mm of material needs to be removed from the 249cc sleeve which would leave only 4.1 mm remaining, while the 292cc sleeve still has 6.0 left at the same bore size.

Extending this to 330cc, the bore needs to be 82 mm which means 4 mm more than the stock 292cc cylinder which implies 2 mm of material removed from it which would leave 4mm remaining.

But this same amount would leave only 2.1 mm remaining on the 249cc cylinder.

So while a quick check of dimensions make it look like the 249cc cyl would work, I don't think it really will - not enough sleeve left after overboring. I think would would need to be done is that the 249cc cylinder would need to be bored out, re-sleeved, then bored again to the right size. I'm guessing that process is comparable in price if not more than simply buying a 292cc cylinder to start with.

Sorry for the false good news.

 

Dam Man, and I was getting all pumped too about just having my stock cylinder bored.


I got to agree with Marty here on this. I've thought about heads myself too. Cam's and headwork is some of the best things you can do to a motor, People do it all the time to their harleys to give them more HP and performance. The question would be " Doing Exactly What " to the little Klx head for more performance. Since I dont think there are aftermarket cams for our bike would there be any point in doing the heads. I dont have the answer to that or know exactly what could be done But the one thing I can suggest is to shave the head just a couple thousands of a inch which would bump the compression to say 11.5 to 1. Thats Got to be worth something and since Brian will be at 330cc he could benafit from headwork more then any of us. If it was me I would be talking to the machinist about that too. You never know...



LV

 

Well, I do think you could probably bore the stock cylinder to 292cc, even though you wouldn't want to take it all the way to 330cc. Of course, boring, plating, and honing is not free, but is probably cheaper than buying the stock 292cc cylinder new.

I can tell you that the 292cc upgrade was pretty significant and I considered it well worth the expense, but in all things, do your own research, YMMV. What is significant and worth it to me may not be so to you, yadda yadda.

I think after the 330cc I'm going to be done with the major engine mods unless someone comes up with something cheap and easy. Mostly what I want is low-end torque. Most of you have gotten that by altering the gearing ratios. I tried changing the gearing ratios and didn't like what it did to the cruising RPMs (too high for my liking). So I went about it by increasing the raw horsepower instead via larger bore size, but I retain the stock gearing which is more to my liking, especially for highway cruising. There is no replacement for displacement.

Now, if you guys with gearing at 14:49 also do a big bore - how will you keep the front end down? That's my question

 

Quote So while a quick check of dimensions make it look like the 249cc cyl would work, I don't think it really will - not enough sleeve left after overboring. I think would would need to be done is that the 249cc cylinder would need to be bored out, re-sleeved, then bored again to the right size. I'm guessing that process is comparable in price if not more than simply buying a 292cc cylinder to start with.

Or you could just buy a DRZ 400 LOL Just kidding.......sort of hehehe ain't I a stinker?

 

Not a stinker - I think that is a perfectly valid question. For me, a 37.2 inch seat height is pretty much a non-starter. Also, 5-speed tranny is a negative as is no electric leg. Is the DRZ street legal? I think it is off-road only so you'd have the expense of dual-sporting it that you don't have with the KLX250S.

So it's not quite a slam dunk - more like six in one, half-dozen in the other. Besides, if I bought the DRZ, I probably never would have signed up on this Kawi forum with all you fine folks.