Too many hours on crank?

[Jake92]

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]

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

[grayracer513]

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]

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.

[Ga426owner]

90 hrs....geez it is just getting broken in......

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]

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.

[Ga426owner]

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.

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]

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]

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]

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]

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]

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]

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.