TE250 to TE310

So what’s it take to make a TE250 into a TE310? There have been a couple of threads and it’s clearly more than changing the jug and popping in a bigger piston, but there aren’t a lot of details out there. That’s why I’m starting this thread as I begin the final phase of our project.

Let me start off by saying, it is far easier selling the 250 and buying a used 310 for most folks. However, for us it made sense. My son’s bike is in great shape with a number of mods. Plus, he doesn’t let go of his favorite toys! His only criticism—the 250 doesn’t have the hill climbing and open stretch power of his riding buddies’ bikes. Especially, at higher altitudes. Handling was never an issue.

With the occasional TE310 being parted out of the crate, our decision was sealed when we found a zero hour TE310 bottom end, cylinder, piston and rings. In the coming days, I’ll be posting what we’ve learned along with part numbers.

Wait- ...what?! you can buy zero-hour 310 parts from a bike in a crate. Wow, really?

How often and where do these kinda deals surface? If you stumble across another one, please LMK.

http://www.thumpertalk.com/topic/1021246-2010-te250-x-lite-big-bore-options/

I think my timing had a lot to do with it. I actually passed on the first one I came across and then found another bike a couple of weeks later. This was during KTM's acquisition, which probably had something to do with it. I just did a quick eBay search and while not cheap I found an engine, a case, and a bottom end, so parts are still out there. I'm guessing the bikes are gone at this point.

Before starting the project I heard that the 250 cases don't have enough room for the added stroke, which Ty confirmed. I never looked into if the 250 cases could be clearanced, since I already had a 310 bottom end so that could be an option. It would be interesting to hear if anyone has gone this route.

In hindsight a used, but rebuildable bottom end would have been fine since I ended up opting for the crank mod for increased reliability.

Thanks for posting that link. It's great starting point and the one of two post that originally got me thinking about this mod. Once up to my eye balls in the project, I found some additional things are required and that need attention. For example the case issue.

My son and I installed the 310 tonight. Next up...I need a bung welded to the Titanium exhaust, which is beyond my MIG welding skills. Just another reason to stick with stainless! I'm planning to add Autotune to the bike and I need an O2 sensor.

I converted my 2010 txc250 xlite to a 310. Needed a cylinder, piston, timing chain, timing chain guides, head bolts and crank. Had to bore the cases for the bigger cylinder to fit which usually has to be done with any brand bike when installing a big bore kit. I also bought the race ecu and 12 port injector for the 310. Had the power commander with autotune but I'm not a fan of more wiring. With the race ecu the bike runs perfect.

Good to know. It's nice to know those 250 cases can be used. I totally agree with your wiring comment. We just finished updating to the race ECU, which is actually labeled TXC310 2012, along with the 12 port injector. We only added the Power Commander V for now, but will be installing Autotune shortly. I'm not a big fan of the wiring. Specifically the tap connectors. The PCV has one and the Autotune even more. I didn't want to end up trying to track down multiple taps if she doesn't run well. I plan to add it once we're up and running. We originally ran the JD tuner when it was a 250 and it worked great, but wanted the benefits of Autotune.

One of the additions we made was the 310 drain back kit. I seem to recall that someone posted some schematics of the hose routing, which differs from the 250. I can't for my life find them by searching. Can someone send me a link?

Found it...thanks Tinken!

http://www.cafehusky.com/threads/2012-te310-drain-plug-oil-return-line.36559/page-2

Now here's my dilemma. On the 250 frame hose #7 goes to the fitting on the underside of the frame top tube closest to #10. Hose #6 (the one going to the airbox) connects to the right side where the #7 hose on the 310 connects. The 250 doesn't have a frame connection on the forward, left side of the frame. So here's my thinking, add a Y fitting to the hose coming out of underside of the top tube of the frame. That way I can connect hose #7 and hose #2 that goes to the drain back kit/sump. The hose going to the airbox can stay where it's at. Can anyone think of a better solution?

I don't have the drain back kit on my 250 to 310 conversion. I just vent it like a tc250. The hose from the frame goes down in front of the engine just about to the bottom of the engine. The problem I had with the hose going to the air boot was it acted like a vacuum by pulling oil from the engine at high speeds.

I do get some blow by oil residue on the bottom of the engine and frame but its not anything to worry about.

So are you saying you just disconnected the hose to the airbox and instead ran it down the front of the frame? Not having the drain back would make oil fills easier.

Yes. There is a post about this being done by someone else. I'll see if i can find it.

TE310 oil change

Thanks for the link. I actually ended up mirroring this set up, with a couple of exceptions. After removing the hose and plugging the fitting on the airbox with a vacuum line cap and a hose clamp, I added a short pre-curved piece of hose off the fitting under the tank. I used DAYCO hose (part # 71376). By cutting it in half (using the lesser radius) it provides a perfect bend, hugging the frame and angling toward the radiator. I went with this route instead of using the existing hose, since it was somewhat kinked close to the frame connection after rerouting. I then added 1/2" to 1/2" nylon hose splicer barb (WATTS PL-426) at the end of the new hose and then connected the existing bike's hose to the other end. That gives you plenty of length. Lastly, if fitted one of UNI's crankcase breathers (part # UP-124). Overall, it's slightly smaller than the K&N allowing it to fit slightly lower behind the skid plate. Plus, it has a neat little hole that allows it to be zip tied. I also found that this filter that's a push-in style for 5/8" line actually fits into the stock hose. While seriously snug, I liked the fact that it would be as restrictive than the 1/2" filter. I also found that there's very little clearance under the tank and that the hose clamp (closest to the frame) can come into contact if not carefully aligned. End ended up using double zip ties on each end of the barb connections. I'll have to double check all of this after spending time on the bike, along with how this all handles the heat and oil usage.

Below is the list of parts I used in the conversion. I’m by no means an expert, so feel free to add to this list. I’d also like to share my great experience with the folks at ZipTy Racing who handled the rebuild and head porting. The bike now easily keeps up with our RFSs and is a blast to ride. Jeff at Hall’s Cycle was also great in locating the remaining parts I needed.

I purchased a complete TE310 bottom end. Sounds like the 250 cases can also be used after boring, but you’ll still need a 310 crank, rod, and piston/rings along with a cylinder. Plus I went with the ZipTy’s crankshaft mod.

• Head bolts (3) — 8B00A6564
• Head bolt (1) — 8000A6564
• Timing chain (1) — 8A00A6933
• Chain guide/shoe (1) — 8000H3396
• Tensioner (1)—8000H3398
• Oil line (1)—8A00A7022
• Head gasket (1)
• Base gasket (1)

I also opted to upgrade to the racing injector kit, since I needed a 310 ecu (8000H7557). I also added a Power Commander V with AutoTune, along with an Akrapovic pipe.

Nice to haves:

• Exhaust gasket from head to pipe (1) — 8000H0015
• Crush washers for clutch fluid bleeder (2) — 80021480
• Silicone hose kit (eliminates thermostat)
• Spark plug
• ZipTy tank spacers
• TE310 rubber bellow connecting the throttle body to head (1)—I don’t have a part number, but there’s a H3265IT on its side. This provides a much better connection/angle with the higher cylinder head height.

Forgot one KEY part...a 310 cylinder.

Quite an effort...any $$$$$ total.

I never added everything up and it would be totally different if you bored your existing case. The rebuild cost would be the same between just rebuilding the 250 or bumping to a 310. All of the smaller parts listed above ranged from were less than $10 each. Some under a dollar. The couple exceptions are the timing chain at $46, cylinder head bolts at $13 each, and the ecu/12 port injector at $343. Those prices include our cafehusky discount. Crank, piston, cylinder are your big ticket items. Like I said earlier, it really makes sense to just buy a 310 from the get go. My situation was a bit different. In the end, the bike is awesome!

Hi guys,

I am looking to fit a 310 kit to my tc250 this coming week. I have ordered everything except an ecu... Is this necessary for the 50cc or so increase? Also is the injector different. Not looking for max power at this stage just want to make sure everything works ok. (ecu will come later other wise)

Many thanks,
Glen

Just as an anecdote we put an 300 Athena kit on my 08 TE 250. The numbers on the 3 fueling stops were 127, 116, 110 or something like that. I know the #1 was high 120's for sure. Kind of makes sense when trying to get 20% extra fuel delivery. George@Uptite did it.