Vintage Dirt Bike Q & A

Rode the IT 465 for the first time yesterday... Well the first time beyond going up and down the street. This bike is a beast. So much power. My buddies on their bikes were halfway across the pit going all out and I could start from a dead stop and pass them before reaching the other side!

The bike vibrates pretty bad, much worse than my CR250 Elsinore. When it gets up into the powerband it literally hurts your hands on the bars. Feels like every joint in my hands have arthritis. After riding hard for a bit I could hardly move my fingers to brake and clutch. Is this how these bikes are supposed to run? What could be causing it? Performed nicely, just rough on you.

Other than the vibration the bike ride really smooth. It doesn't bounce around so much I assume due to the nice suspension technology and huge monoshock rear. The bikes weight also seems to help in smoothing it out. The downside is that you really have to throw your weight around to make the bike respond. It takes a lot out of you. In general I feel much more beat up than after riding my Elsinore, and my hands are sore.

Anyhow, the day didn't end that well. The engine seized up after two hard passes across the pit. After those two passes I was cruising along riding behind my buddy on an XR200 to let the 465 cool off. Well apparently it was a bad idea because it seized up after a minute or so of light trail riding. Turns out the idle throttle set screw came out. My theory is that the extra air pulled in through that hole caused a lean condition not bad enough to be very noticeable but enough to heat up the engine too much. Other theory is that the 465 is just too big a motor for the cooling it has.

Any thoughts on the vibration or seizing up? Hopefully it didn't do too much damage but I suppose I'll find out soon enough when I pull it apart.

These engines do vibrate....certainly more than a 250. Your description of sore hands and beat about sounds excessive for a properly set up 465.

They are also amoungst the toughest and reliable motors and have adequate cooling under severe race conditions.

Your engine has issues that need sorting if it siezed under the conditions you described.

Check for loose mounting bolts....most probably severly flogged out mounting holes if it has been run with loose bolts.

Crankshaft / rod may be dead.

What actually siezed....piston, crank or gearbox?

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'84 Honda CR500
'84 CR125
'85 KX125
'83 IT490
'82 Maico 490
'80 YZ465
'75 Husky CR360 GP Mikkola
'75 CR250
'72 DT2MX
'91 XR200

Worn main bearnings cause all manner of vibration like you mention. They also lead to tons of air leaking past the main seals. That leads to lean seizure.

Still, check your motor mount bolts. If any of them are loose/missing she will shake you like mad.