Detuning YZ450f for easier maintenance


9 replies to this topic
  • jereb

Posted October 18, 2013 - 03:31 PM

#1

I want to detune a yz450f street-legal supermoto. It is mostly A-B riding, I'd say 30% highway miles, with some twisty roads once in a while. Very tame riding.

 

The maintenance schedule is really strict on this race bike. Given the tame riding, does that automatically reduce the maintenance schedule, and by how much?

 

I don't need anymore than 35hp or 40hp max - it's already a very light bike. Is it possible to get a low compression piston (ie. 10:1 or 9:1) to reduce it by this much? Or what are some options I have for detuning?

 

Stock it is recommended to have oil change every 5 hours, valve check/adjustment every 20, and piston/rings every 40.

 

I have a goal of increasing this by 7x between riding style and engine detuning (it'll give me roughly oil change every 1000 miles, valves 4000 miles, piston/rings 8000 miles).

 

I like having a commuter that weighs just 240 pounds, so going the easy way and buying a street bike is just not what I'm going to do.

 

Does anyone have any insight as to how I could achieve my maintenance schedule goal?

 

Jeremy



  • grayracer513

Posted October 18, 2013 - 04:47 PM

#2

Buy a real street bike.

 

Reducing the horsepower output will not change your maintenance intervals unless you constantly operate at 90% capacity.  The  main issue with street ridden YZ450's is gearing and the shared oil supply. 

 

It's a simple matter of revolutions per mile.  The stock gearing produces 7100 RPM at 60 MPH.  Even with a 14/45, that's still 6100 at the same speed.  That's "mileage" on the piston and crank that a real street bike doesn't get. 

 

If you use a good enough top tier motorcycle specific blend, like Amsoil MCF or Mobil1 Racing 4T, you can probably run the oil change interval out to around ten hours.  Having the oil tested at a lab such as Blackstone will tell you if you can go farther.



  • jereb

Posted October 18, 2013 - 09:22 PM

#3

Thank you for your reply.

 

What is meant by constantly operating at 90% capacity?

 

I only need a fraction of the power so I'll run a 13/28 to reduce the mileage. Is this relative, ie. half the revolutions = half the maintenance?



  • grayracer513

Posted October 19, 2013 - 08:20 AM

#4

What that means is that if you have two identical engines, one with the capacity to produce 30% more power than the other, the additional capacity is not a significant liability unless it's used.  Both engines would last the same amount of time running at a 20 HP output level in spite of the fact that one can produce 40 and the other 55.  It's the same strain either way until the demand for power above 40 hp is placed on the more powerful engine.

 

If you want higher gearing, you are going to have to use something larger than a 13 at the front (15 is the largest possible with the aluminum frames), and the smallest 5/8" pitch sprocket you could have custom made to fit the rear hub is a 35 (smallest commercially available is about a 44).  A 45 pretty much constantly rubs on the swing arm.  With gearing like that, low gear becomes impractically tall, and the clutch will suffer in stop and go traffic.

 

If you're absolutely dedicated to the project, you could swap in the transmission from a compatible model WR450.

 

The bike isn't a low maintenance street bike, and there isn't much you can do about it.



  • jereb

Posted October 19, 2013 - 03:55 PM

#5

Thanks for explaining that.

 

I was thinking about going with a wide-ratio transmission. I'm sure the project will come together. Thank you for your help.



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  • NitrousR1

Posted October 20, 2013 - 07:24 AM

#6

The wr wide ratio gearing will definitely help. 5th gear is a lot taller and great for supermoto. For piston life don't go by yamaha's suggested 40 hours, for a pro mx'er that's perfect. For anyone else I'd suggest 100 hours, or if your really revving the bike out on the highway then 80 hours.

  • Garett0439

Posted October 20, 2013 - 08:48 PM

#7

I have have gone 150+ hours on my 250f piston so far, riding the crud out of it and living on the rev limiter. I just put a timing chain in it which it didnt need, I dont plan on a piston until mabe 300 hours or until it starts to smoke. My brother went 500+ hours desert racing his 426, without anything done to the engine, until the rod bearing seized. My dad probably has 300+ on his 06 450, his is still running great too we havent done a thing to it. Delo 400 oil change every 8 hours
Yamahas are bulletproof.

  • NitrousR1

Posted October 21, 2013 - 07:51 AM

#8

I have gone that far on pistons as well but is it worth risking a $2000 rebuild over a $150 piston? Same goes for timing chains- $20 is cheap insurance for a interference engine. If you replace the wear items on a schedule you will not have the pricey 4 stroke rebuilds that you hear all about.
I have a supermoto 450 as well and it is very rough on the engine. Requires rebuilds more often because of the constant high rpm you turn on the highway. Mine has wr gears which significantly helps lower the cruising rpm and therefore rebuild intervals. At 80 hours my supermoto piston is ready to be replaced and at 100 my mx bike is ready for a piston.

  • MidlifeCrisisGuy

Posted October 21, 2013 - 05:35 PM

#9

A WR450 would be a better choice. If you want light weight, I lopped 22 pounds off mine. Its 238 lbs dry.

  • YoTRacer158

Posted October 22, 2013 - 08:18 AM

#10

If you're looking for less power and better street ability why not just get a WR250R?





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