Oversized bore/piston options for 400

Can anyone give me the down and dirty on oversize pistons for a 99 400? I dont want to buy a cylinder, but I could do a sleeve. What are the options for a over-bore only (with plating?) or a sleeved cylinder? Big bore kit sounds nice, but Im thinking hotcams and a simple refreshing of the top with just a bigger piston If I can. I have a feeling this has been done to death allready so will go search, but the options cannot be many as Tacoma Motorsport couldnt find a single oversized piston for my bike...



I can attest to the quality of the Lukes Racing Kit. Have one on my 01 and have been very happy with it. Also highly recommend the hot cams. The combination of the two together is amazing.

mmmmm, 2 hot cams, mild porting job, 420CC, YZ timing, powernow, uncorked pipe, full custom moto-pro suspension (already did that), I think I'm gonna like it!


Darn straight you will. That's just about what I've got...HotCams, 13.5:1 Wiseco piston, Eric Gorr Porting, Lukes Raqcing 444 Big bore kit, YZF Pipe, Power NOW, JD Jet Kit, ESP suspension...all that and a CA plate, too. Life is most certainly good.

So my WR400 has a whats it... nicsil coating from the factory? If I had had a steel sleeve inserted and could not get the thing recoated in the nicsil coating, is a plain chrome coating acceptable? Isnt that classic motor machine technique? What rings would you guys recomend with a chrome bore lining?



as far as i know, the sleeve and coating process is far more involved than what we may assume.

I have researched getting my 400 barrell bored and recoated, (electrosil/nicosil) and have had some mixed feedback over recoating.

apparently the nicosil coating aids in the heat dispersment function of the barrell and i would only recommend using the nico/electrosil method due to the high temps our bikes run at.

the only other alternative is a 426 barrell from yamaha, approx $550 AUS.

hope this helps.

good luck

With an iron sleeve, you don't need any plating. Bikes ran iron bores for years without any real problems, and LA Sleeve swears by them. They bore out your cylinder a lot oversize and press in an iron sleeve. I'm not sure if they bore it out to the water jackets like you do on a V-8 or not...you might call them and ask them. The advantage, at least the way I see it, to a sleeve is that it's reworkable by joe average machine shop if you stick it. You also don't have to worry about the nicasil or other plating peeling or chipping if it wasn't properly applied. The disadvantage is that you have different metals in the mix with different heat transfer and thermal expansion characteristics. As far as going overbore and replating your stock cylinder, the nicasil plating vendor that both Eric Gore and Lukes Racing (along with RPMs and I don't know who else) use is US Chrome. They replate many, many OEM and hi perf cylinders for both consumers and race teams. They know their stuff and they rarely have problems. Advantages are that you get better heat transfer to the water jackets, and the coating is more durable than a bare cast iron liner. Plus, most hi perf pistons (JE, WiseCo etc) are designed to use Nicasil plated cylinders. I would definitely talk to them before running their product in a cast iron liner. The only disadvantage to the Nicasil plated approach is that if you do stick it, you have to have it stripped, the damage welded up and machined, then replated. Of course, a big bore kit eliminates the need for that...

I've used big bore kits from both Gorr and Lukes on my bikes, and have had no trouble with them. When adding up the cost of new piston, rings, pin, gaskets, and the machine work necessary to fix a buggered up cylinder, either by sleeving or welding up and re-grinding, the Big Bore kit wins by about a Benjamin...with, at least from my experience, no decrease in reliability. The only advice I would give (besides do it)is to order an extra set of gaskets and rings when you buy the kit. That way, you will have them available when it's time to re-ring, and not have to remember who's stuff you used and what the part numbers are to order from the TT store; and to make sure they are legal for the class you are racing (if you're a racer).

One more thing about running the 444 kit with the hot cams...the hot cams tend to rev a little bit quicker (ok...a lot quicker) than the stocker. The big bore kit revs a little bit slower due to the added weight of the piston, so the powerband is somewhat of a middle ground between the WR and YZ, just with a whole lot more of it.

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