10k rev limit

Message

banzairx7 · #11 Post by **banzairx7** » Mon Jan 17, 2005 1:51 pm

QUOTE

Originally posted by cannondale27
For anyone with any doubts about these statements read Dirt Rider the last two issues have had in depth articles on valvetrains and everything they said can be found elsewhere.The new 250 4st motors the replacement interval is cut in half 20 hrs.They run at 13,500 rpm vs the 11,500 rpm of most of the 450's.Valvetrains are the same so 2000 rpm extra doubles the wear.Now go the other direction and 10,000 rpm should just about get you double the time.Not worth the power loss for me though.

I have doubts, major ones at that. Yamaha and Honda make some of the most powerful sport street bikes around. These motors rev as high if not higher than any atv engine. Figuring an average of 60mph on a street bike when you hit 3,000 miles that would be 50hrs of engine time. Those engines go MUCH longer than that before the valves need to be touched.

cannondale27 · #12 Post by **cannondale27** » Mon Jan 17, 2005 1:53 pm

A big killer of valvetrains is downshifting or landing off a jump on the limiter and clutch out.Your rev limiter cant stop the increased rpms on the motor from the tires turning the motor over.

haydug · #13 Post by **haydug** » Mon Jan 17, 2005 1:56 pm

QUOTE

Originally posted by banzairx7
I have doubts, major ones at that. Yamaha and Honda make some of the most powerful sport street bikes around. These motors rev as high if not higher than any atv engine. Figuring an average of 60mph on a street bike when you hit 3,000 miles that would be 50hrs of engine time. Those engines go MUCH longer than that before the valves need to be touched.

Scott: he is referring to the YZ 450's, CRF 450's and also the 250's. Yes, they do reccomend that time frame, and if you read anything from Pro-ciruit, they are crying now about the cost of racing the 4-strokes. 3-times as expensive!! But, they do their scheduled maintenence! I have a 2003 crf 250 sitting here now waiting on a head from Honda. I have another waiting on stainless valves. There is a total of 4 of these bikes that ride around here, and 2 are in my shop waiting on parts. Sound familier??

cannondale27 · #14 Post by **cannondale27** » Mon Jan 17, 2005 1:56 pm

The four cylinder bikes valvetrains are under way less stress than our motors are.Dont forget only two of the piston on a four cylinder are up at one time.You can cut the valvetrain speeds by1/2 on a four cylinder versus a one cylinder.

banzairx7 · #15 Post by **banzairx7** » Mon Jan 17, 2005 2:17 pm

The amount of cylinders doesn't matter. Valvetrain speed will be half of the engine speed on any otto cycle four stroke engine. The 4 bangers are just getting more power strokes per revolution.

cannondale27 · #16 Post by **cannondale27** » Mon Jan 17, 2005 2:26 pm

Yes you are right.But talk to some of the stuntriders riding streetbikes.Also why do the valvetrains on streetbikes often take a dive after a light crash.RPM must not be the only factor in why the valvetrains do last longer in a streetbike.

Derno24 · #17 Post by **Derno24** » Mon Jan 17, 2005 2:36 pm

QUOTE

Originally posted by cannondale27
A big killer of valvetrains is downshifting or landing off a jump on the limiter and clutch out.Your rev limiter cant stop the increased rpms on the motor from the tires turning the motor over.

I'll agree with the first statement, but if you are banging the rev limiter in the air you need to work on your shifting not correct the valvetrain.

This is what I was talking about though guys our rev limiter isn't the issue here and most of you agree with me. It seems more to me a heat related issue than a lack of quality parts.

I have heard the same thing as Doug that they took quads and dirtbikes alike and stuck them on the dyno and just tortured the snot out of them so I don't buy the rev limit idea.

JeffQuadShop · #18 Post by **JeffQuadShop** » Mon Jan 17, 2005 3:30 pm

Just to clairfy what Doug said, I run my quad engines stock with the Blaze map, I have not lowered the rev limiter. I do change my synthetic oils and filters every race (I think any of the new breed of high performance 4 strokes need these same maintenance schedules).
I do however feel that the custom maps with the higher rev limiters do accelerate engine wear.

theJeStEr1340 · #19 Post by **theJeStEr1340** » Mon Jan 17, 2005 3:36 pm

Wow, compairing a quad that is jumped and abused in the woods to a street bike is the worst. Like someone said, landing a jump or downshifting into a corner is **** on a motor, you don't see too many street bikers down shifting into a corner, usually they are easy and let the RPM's drop enough. It is 2 completely different things. Yes, they are motors, but we abuse motors worse than they do. Anyone know how often Street bike Racers (closed course) replace their valve train? It would be a good thing to look into.

cdrookie · #20 Post by **cdrookie** » Mon Jan 17, 2005 4:29 pm

a sudden downshift of a gear or two to pull the front end of a street bike up has to be just as hard on the valve train as downshifting into a corner.