Putting the big bore on the 250

I ordered the DR-Z250 300 kit for my new-to-me Drizzlet from Thumper Racing (they said they had a core, and would just send me the kit ready-to-go; I'd get a core refund once I sent my cylinder in). I did notice some oddities about it - the machining cost was twice what they said on the site, and the kit said 340, and oh, the cylinder looked like it was not off of a DR-Z250. A little investigation, and yes, they sent me a kit for a DR250.

I'm working out the exchange/partial refund right now, but the one thing that was clear was that they don't have a core over there. So I pulled the cylinder off of my Drizzlet last night; we're going to MotoGP on the big bikes over the 4th holiday, so that should give plenty of time for turnaround before I'll be riding that bike again.

A few things that came up while taking the cylinder off...

One is that the jetting had always felt off - it felt quite lean, and struggled under load. I decided to just get the big bore, instead of working out the jetting with the stock bore and then doing it all over again. Well, the plug was pretty white, and the exhaust valves showed signs of leanness - and the head bolts were frighteningly stuck. I had to use the impact followed by a breaker bar with a cheater atop (and a coordination of arm strength with my hubby), and we were sure the bolt head was going to break off just before the bolt broke loose on two of them. But they all came out, and all went in the trash. The smell that came up when they came out was strange, like very burnt oil; I think the thing has been running too hot, and that somehow stuck the bolts more than they should have.

I did note that, while the weld slag in the header was not present, and the airbox has been cut, and the Yosh is quite free-flowing, the butter-soft screws on the float bowl look unmolested. If all of those mods were done without a rejet, no wonder it was too lean!

Any damage from lean-ness should be nicely fixed by a new piston and new machine job on the cylinder, though, so that's fortuitous. And I've put in a Thumpertalk store order including new float bowl screws and new head bolts/washers. :worthy:

I did ride in a parade this weekend, which gave me a chance to try out the Vapor I installed and the EBC SM rotor. I still need to install the tach sensor (again, on my list of Might As Well Do While I'm Doing The Big Bore), but the speedo is pretty necessary for me on the street.

I'm trying to decide between an SM wheelset and just putting dualsport tires on the stock rims. Street just tears up the knobbies. :lol:

Thats sucks about recieving the wrong kit :worthy: Also seems a bit rude that they aren't offering to cover postage since they made the mistake and sent you the wrong kit.... I'd almost just get the refund and buy the kustomkraft kit instead... just to show thumper racing that their customer service is poor, and dont deserve your business.

as for the barrel, if they aren't sending you an exchange one like the DR kit had the cost should drop dramatically as they should supply the new sleeve, and it is then up to you to get a machine shop to press the new sleeve in and hone it to match the new piston.

Incidentally since you are returning the old kit, maybe you should send your barrel with it so that they can do the machining for you, then its just a matter of bolting it all together.

I also found when doing mine that the head bolts were extremely tight... I was also very worried I'd snap them. but they came appart fine. I actually reused the bolts with no ill effect yet.

When you say evidence of lean damage to the valves, are they still in good enough condition to reuse? or are you thinking of replacing them? Things like valves and valve seals may be worth replacing at this stage if you see wear. Mine were fine, but I had to replace my cam chain, it was right at the end of the Adjuster.

Anyway Good luck with it. Hope you are happy with the result :lol:

The exhaust valves have white, ashy deposits, but they looked fine when I cleaned them up. And yes, I sent the jug in when I returned the kit - they said they'd do one-day turnaround on the machine work, and refund me the difference (the DR250 machining costs twice what the DR-Z machining does), shipping, and core charge. I'll wait to say they've made it right until they actually have, of course. :banana: I wanted to go with them because they're semi-local and I hoped the timing would be better that way - but the best-laid plans of mice and women, etc.

I did find a new 46-tooth AFAM aluminum sprocket at the local Cycle Gear on closeout for $20, and picked it up. I'll probably swap it out with the 47-tooth my hubby has on his DR-Z400S, since 46 might be a little tall; I just think with the big bore I can gear it a little taller than it is right now (49t) once I have the big bore, and make it more dualsport-y. :worthy: It had a 51t on it when I bought it, and although it was fun in the dirt, it just topped out way too soon on the street.

a 46 will be be fine. I have 14:45 and it feels good for everything...except speed, so I am thinking of going to a 43 or seeing if a 15 will fit the front.

Any luck with your BB kit yet?

They messed up the bore and had to order a new cylinder... they said I'll have it by Monday (official explanation, direct quote: "The boring machine sometimes has a mind of its own."). :worthy:

But from a quick search, a lot of people have had positive experiences with them, so go figure.

There was a fire in the shop next door to us the day we put her cylinder on the boring machine and I know Roadstergal is upset but the fire was beyond our control and yes we did make a mistake sending her the wrong kit.

I couldn't even get in to access the computers so I could call everyone and update them on what happened. It took a couple days for cleanup to take place before we could start work again. Her cylinder was on the boring machine when the fire happened. My tech came back in after the fire and started cutting right where he left off. We went to install the sleeve and the cylinder failed quality control.

I found out later after, I talked to her husband about the over cut cylinder, the depth gauge was dropped during the fire mayhem and was what caused the over cut. My machinist knows to reset the gauge but the part time office help didn't and didn't tell it us was dropped until after the fact. When you are cutting to .0005" it doesn't take much to throw the machine off. It can be something as simple as a piece of lint or a metal sliver that interferes with the depth gauge, or someone can drop the depth gauge. We do our best to keep this from happening and I wish I could say it never happens but it does happen rarely. We've had 2 out of 1093 cylinders we've done in the last year. Unfortunately Roadstergal's was #2. All I can do at this point is replace the cylinder and beg for forgiveness.

Roadstergal's cylinder measured .003" Interference and quality control requires a min .0045" interference fit on our sleeves. If the bar over cuts even .001" We will not use the cylinder and risk the sleeve moving once the motor gets to operating temp.

That's sucks about receiving the wrong kit :worthy: Also seems a bit rude that they aren't offering to cover postage since they made the mistake and sent you the wrong kit.... I'd almost just get the refund and buy the kustomkraft kit instead... just to show thumper racing that their customer service is poor, and don't deserve your business.

Why would you say something like this? Were you involved in our conversation I'm not trying to be rude here but how could you possibly know how we handled this? Our plan was to get her kit out the same day we received her core. Unfortunately due to outside circumstances we couldn't honor that promise. We did refund the shipping back to the shop and core charge straight away once we got back into the shop.

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