2008 KX250F Cam (scuffing)

[Rich Rohrich]

Spam?

NAH, just dementia. ;)

 

[IndyMX]

I think you need to use Amsoil.

Yeah, you're right.. I do have way too much money laying around here doing nothing.

 

[IndyMX]

Well, I finally got all the parts I needed, and a little time, and the bike is back together and running fine.

The noise is gone, and it seems to run about like it did prior to the bearing going.

I do need to adjust the carb, it's popping and what not pretty bad.

Pilot too rich or too lean?? Anyone care to comment?

 

[Rich Rohrich]

Popping when, at what throttle opening, at what air temp?

 

[IndyMX]

60 degrees here now, and it's popping when you roll off the throttle..

A lot more than I remember it doing before.

 

[Rich Rohrich]

Assuming the pilot jet isn't partially blocked, and the exhaust isn't sucking cool air in at the head sealing surface, it's worth starting with richening the low speed fuel screw. Once it gets warmer you can probably lean it back out some.

 

[juniordragster123]

The lobe doesnt look all that bad. I'd remove the cam and get it polished and check into why it happened.

 

[IndyMX]

The lobe doesnt look all that bad. I'd remove the cam and get it polished and check into why it happened.

Thanks, but if you actually read the thread, you'd see that we're way past that point now.

But thanks for playing along though.

Assuming the pilot jet isn't partially blocked, and the exhaust isn't sucking cool air in at the head sealing surface, it's worth starting with richening the low speed fuel screw. Once it gets warmer you can probably lean it back out some.

Nope, the pilot is brand new, I changed from a 42 to a 45 while I had the carb torn down. And I made sure it was clean before putting it in.

I'll give the fuel screw a bit of a turn tomorrow.

 

[juniordragster123]

Lol sorry I didnt notice this was a 6 page thread before I posted. After I commented I red threw the entire thread.

 

[IndyMX]

Found out something interesting.

When the bike went back together, and started the first time, it jumped time. Really nice timing chain adjuster design.. NOT..

So.. from then on, I've had nothing but trouble with the bike.

Since I screwed up my leg, my brother took it to a friend of ours to see if he could figure out the problem.

They basically went thru everything I had done to it, and found nothing wrong. The guy doing the work remembered having a similar problem on a KX250F a while back.

His problem was that the gear on the intake cam shaft had slipped. He checked ours, and sure enough, it had moved.

He reset it, and tig welded it in place, runs like a cut cat.

 

[magneto]

What all did you finally end up replacing in the rebuild?

 

[IndyMX]

What all did you finally end up replacing in the rebuild?

Let's see...

I changed the oil pump, the crank bearings, piston, rings, wrist pin, circlips, all gaskets, intake valves & spark plug.

Plus I reshimmed the valves..

Also added an hour meter.

Not such a bad deal really.

 

[Rich Rohrich]

Indy - If the cam gear slipped you should look closely at the cam chain tensioner as a reason why. If the cam chain "whips" the sudden load/unload/load sequence could be the reason for the gear movement.

 

[IndyMX]

Indy - If the cam gear slipped you should look closely at the cam chain tensioner as a reason why. If the cam chain "whips" the sudden load/unload/load sequence could be the reason for the gear movement.

I agree 100%..

I'm thinking about having a machinist friend of mine convert it into a manual adjust tensioner. I know he can do it on a CRF tensioner, so hopefully he can do this one also.

 

[2strokerfun]

His problem was that the gear on the intake cam shaft had slipped. He checked ours, and sure enough, it had moved.
He reset it, and tig welded it in place, runs like a cut cat.

Indy: Just curious here. Are those gears pressed on the camshafts?? Looked up parts fiche and appears gear/shaft appear to be sold as one unit.
question 2: How the heck would an average person would even be able to recognize a slipped gear on the shaft? Is there a mark?

 

[whenfoxforks-ruled]

The slipped gear thing, it will be very hard to start, if not impossible. If it slips too far, the valves will hit the piston$$$$.

 

[IndyMX]

Indy: Just curious here. Are those gears pressed on the camshafts?? Looked up parts fiche and appears gear/shaft appear to be sold as one unit.
question 2: How the heck would an average person would even be able to recognize a slipped gear on the shaft? Is there a mark?

Yes, it's just an interference fit. I imagine the shaft is slightly tapered and it's held on by friction. Sort of a lousy design if you ask me.

The average person probably wouldn't ever figure this one out.

You'd need a degree wheel and knowledge in their use. I have neither.

I guess the best way to recognize something like this is by having an intimate understanding about your bike.

I did notice the last time that I had the valve cover off that the intake cam lobes didn't look like they were in the right position, but I just assumed I was out of my mind, considering that the timing marks on the gear were in the right spot. They weren't off by much, but it was noticeable.

That should have stopped me and caused me to investigate why the lobes weren't where they should have been. Next time I'll know.

 

[2strokerfun]

Good Stuff! Thanks

 

[whenfoxforks-ruled]

Even on the Honda's, using or buying something to check with a degree wheel is priceless! Just like pulling the trigger on your judgment calls?

 

[IndyMX]

Even on the Honda's, using or buying something to check with a degree wheel is priceless! Just like pulling the trigger on your judgment calls?

Yeah, another tool I have to buy.. freakin fantastic..

 

[Rich Rohrich]

Hot Cams has a really nice kit for degreeing cams. The excellent piston stops alone are worth the price of admission.

http://www.hotcamsinc.com/index.cfm?fuseaction=cProducts.view&productid=531


Here's a great article on Cam Degreeing and Lobe Centers by Doug (Mr. Bonneville) Meyer

http://www.muzzys.com/articles/lobe_centers.html