Too many hours on crank?


12 replies to this topic
  • Jake92

Posted October 01, 2007 - 07:36 AM

#1

Got a few questions.
Ive got 90 hours on motor. Time for new crank? 250B motocross and hare scramble.

got some oil coming out vent. Could this be due to needing a new piston?
I know after 90 hours and not cracking the motor I deserve a lashing but I was proving a point to my Honda buddies.

  • Jake92

Posted October 01, 2007 - 07:37 AM

#2

Oh ya. Whats the best way to tell a worn crank?

  • grayracer513

Posted October 01, 2007 - 07:57 AM

#3

I know after 90 hours and not cracking the motor I deserve a lashing ...

Why?

Oh ya. Whats the best way to tell a worn crank?

See page 2-7 or 4-91 in your manual.

Unfortunately, there is basically no means of predicting when a ball bearing will suffer certain kinds of fatigue failures.

  • SUnruh

Posted October 01, 2007 - 08:02 AM

#4

jake,
change the cam chain, put in new valve springs and seals, new piston and rings and run it another 90 hours.
then you can really show them red boys a thing or 2. :confused:

  • Ga426owner

Posted October 01, 2007 - 12:52 PM

#5

90 hrs....geez it is just getting broken in......:confused:
new top end, valve check/adjust and cam chain and a adj camchain tensioner and it will be good another 200hrs:thumbsup:

Welcome to Yamaha

  • Jake92

Posted October 01, 2007 - 12:57 PM

#6

You guys like the adjustable cam chain tensioners on the yamis even? I put a manual one on my Honda
Grayracer, I thought 90 hours without rings was excessive but maybe not. Clutch finally puked this weekend so Ive got a dirt digger on the way!! As always the information from this site is priceless.:confused:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Ga426owner

Posted October 01, 2007 - 01:09 PM

#7

You guys like the adjustable cam chain tensioners on the yamis even? I put a manual one on my Honda
Grayracer, I thought 90 hours without rings was excessive but maybe not. Clutch finally puked this weekend so Ive got a dirt digger on the way!! As always the information from this site is priceless.:confused:


There just is not enough evidence to support that adj CCT are not good on yamis....me personally...it is all I ever use and not one failure.
At the least do rings....but you may as well do the entire topend if you are going to do it. You probably will be surprised how little wear there is there....especially coming from a honda

  • grayracer513

Posted October 01, 2007 - 01:17 PM

#8

A leak down test will tell you what the rings are really like.

As to the cam chain tensioner (for which I have only now learned there is an acronym), there is no evidence that I know of that suggests the stock Yamaha auto tensioner is less than perfect. IMO, it's a brilliant piece of design work, and a great example of how simplicity can be the most effective solution.

  • BBrown626

Posted October 03, 2007 - 06:29 AM

#9

I have seen a few posts here where folks are changing their timing chain. I have my engine in pieces for a tranny repair. The timing chain looks great. What is the problem with the chains? Why are people replacing them?

Thanks,

Brent

  • grayracer513

Posted October 03, 2007 - 07:30 AM

#10

Like any chain, they wear at the points where the parts move, which in a chain is at the pins, and the holes they run in. The wear makes the chain longer between pins (pitch) and that accelerates the wear on the sprockets the chain runs on, in addition to weakening the chain itself.

Since the crank sprocket is cut directly on the left axle, encouraging it to wear is hardly prudent, especially considering the very low cost of a new chain. To put it simply, it's cheap insurance.

  • Ga426owner

Posted October 03, 2007 - 09:58 AM

#11

I have seen a few posts here where folks are changing their timing chain. I have my engine in pieces for a tranny repair. The timing chain looks great. What is the problem with the chains? Why are people replacing them?

Thanks,

Brent


The chain stretches and must be replaced. It is cheap around 15-25bucks. I suggest replacing the CCT as all the adjustment can go with lots of hrs...and it is cheap too. Both of these are necessary insurance to get another 90hrs out of it w/o breakage

  • essex426

Posted October 05, 2007 - 12:08 PM

#12

It is cheap around 15-25bucks

Is it really that cheap in the US,i bought a cam chain for my 426 last year over here (england) and it cost my £55, think that is over $100.Seems you get parts a lot cheaper over there.

  • jeffboyd47m

Posted October 06, 2007 - 04:31 AM

#13

I have a 06 450 that has well over 200 hours of countless MX and desert races on it, I have even done the 24hrs of Glen Helen on this bike. I have never had to adjust the valves, but I did put a Wiseco piston (stock compression) in it at about the 100 hour mark. This bike still starts easy and runs great. I have always changed the oil every 5-6 hours (I run Maxima synthetic) and have never sucked any dirt through the filter.
Gray makes a lot of sense with the cam chain replacement though.
I would not worry about your crank as long as you have not sucked dirt and kept good oil in the bike.





Related Content

Forums
Photo

Is it worth it? (Cam and High compression piston) by macgi77


Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies
Forums
Photo

YZ450F 03 Sparks driving me crazy by SirAttard


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies
Forums
Photo

James Stewart back on a YZ450F by YamaLink


Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies
Forums
Photo

Megabomb Fitment by 288yz450


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
Forums
Photo

Michigan Motocross Tires by 288yz450


Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.