Dirt bikes

Screw whip. I'm working on the Bubba Scrub. I'm starting by just picking up both feet and placing them on the pegs while stopped and falling over.

 

Baby steps

 

I notice most of the guys in SX start jumps sitting and then as soon as they leave the lip they are standing until they land. I need to stop trying to ride it like a bmx bike, probably why I stand over most jumps. Need to find a good table and start working at it.

 

If you've ever ridden a very competitive SX course you'll see how close the jumps are to the turns. They all seat bounce because all of the very huge jumps are RIGHT out of a corner. It gives you way more pop and traction to project out and over the double/triple. Usually, if you're at speed, stand, if you're still accelerating, seat bounce..

 

That's a seat bounce. I know "how" to do it, I just "can't." My excuse is that I'm an enduro guy, until you are being passed by the AA guys in the woods and on the track.

 

Thanks for the explanation, still infinitely more to learn about all of this and work at.

 

Thats me on a SX track too. I am reasonably fast thru the trees but I get on a SX track my brain knows what I need to do but my wrist says "Nope"

 

I've spent a lot of time at MX/SX tracks with pro riders - I know how it works in theory and practice but actually doing it is a HUGE difference. lol. I know that reving the bike brings the front end up, or hitting the rear brake lowers the front end. Simple. But actually doing that when I'm in the air? no chance. I'm just along for the ride when my wheels leave the ground. I enjoy doing little jumps like water bars when riding on trails, but when it comes to hitting a track and actually hitting a "real" jump- homey is rollin' that like a mofo.

the best advice I got when I got my 4 stroke and started riding on jumps was to stay on the gas up the face of the jump. If you roll off before you leave the jump the front drops quickly. and usually in a bad way. Not saying you have to be full throttle over the jump but don't cut the gas on the face.

 

And I'm slow through the trees, so it's a double whammy for me. Sometimes literally.

 

if the snow tracks have their purpose liquefied:

https://www.facebook.com/video.php?v=782473778570871

 

That's sick.

 

Yep, until you crash and it sinks to the bottom of the lake.

 

... and hydro-lock it.

 

Day 2 of dirt-biking: stock cam chain tensioner failed, which apparently is a pretty important part, at least according to my particular engine who decided to let me know with a clackity clack clack. Well...needed a new piston anyways. I'll be adding an APE tensioner as well and fixing the grooved clutch basket while I have the engine apart.

I was quite surprised to see how cheaply made the auto-tensioner on the CRF450 is after pulling it out. I guess they wanted to keep things light, but man, it's a pretty important part. Sigh, it's probably my fault somehow anyways.

 

Bummer, never was a fan of the Honda dirtbikes. If it wasn't the cam chain tensioner it was the valves receding into the head on them. Well at least you now get a lesson in top end service on a 4 stroke dirtbike.

FWIW my Yamaha has been bullet proof and I'm at 35 hours on it. My Suzuki's were always hard to kill as well. Put 150 hours on a RMZ450 in the woods and the top end looked great except for some ring wear. Piston looked great but I replaced it anyway. That bike had one valve adj and that was at first 8 hours they never moved afterward. I checked my Yamaha valves at 30 hours and they were spot on the money. I buttoned it back up and put in a new spark plug and we rolling.

 

i don't know what year your crf450r is Kman0066 .. but if the cct actually failed, you may have a massive massive rebuild expense on your hands. may wanna get into it before spending any money on parts just yet. hate being the bearer of bad news, but it's usually catastrophic when that actually occurs. it's really rare, but it does happen

ps: i had 1200 hours (yes, twelve hundred) on my 2004 crf450r. original cases. replaced cranks, pistons a number of times, head and cylinder 2 or 3 times.. lots and lots of intake valves. but she was a good bike. Have 0ver 770 on my 08 on the meter. had manual tensioners on em both.

 

Wait, dirt bikes have valves? Oh, right. I forgot about those...

 

It's an '07. Valve clearance was (and still is) spot-on. The spring inside the tensioner was in pieces and it was no longer tensioning at all (fully withdrawn). I've got the motor town down and I don't see any damage other than the tensioner. I did shut the motor off after it made the noise (it didn't die on it's own). The timing chain has kinks in it, so it's going in the trash as well. The hour meter has 68 hours on the bike, but I don't know for sure how much it really has, so I'm going to refresh a lot more stuff while I'm in there. Getting new: clutch basket, pistong/rings/pin, timing chain, and a manual tensioner to go in.

Trying to evaluate the crank and rod now. The pin fits well on the top end with no play and the crank spins nice. There is a small amount of play in the rod bottom end but looks like there is supposed to be a little. Just found the service limit (0.6mm), so going to check that tonight.

I think I may have been lucky and the sound was just the timing chain slapping around. I don't see any evidence that the valves were actually hitting the piston.

 

any up-down play in the rod, the rod bearing is toast. yes, there is a spec for side play. The tell-tale sign is when you start seeing metalic flakes in your oil filter (MAIN REASON TO NOT use re-usable oil filters)..

if you plan to keep the bike a while, get a billet clutch basket. you will need to grind the large drive gear off your oem basket, and use RED locktight on the small screws that hold it on the new billet basket. OEM baskets will last about 50 hours before notching badly.

and yea, if your cct failed, and you don't have more damage, you need to play the lottery.

 

Unless you are pretty sure it only has 68 hours, I remember cranks being pretty cheap. If you are going to ride much, just put in another and now you will know you are at. I've lost a crank on a CRF250R, because of a dropped valve, and the entire motor was junk.