Valve train rumors Cr450

Joined
Jul 7, 2000
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#1
I had heard through the grape vine that the 450 uses both bucket over shim and rocker arm design. This would place the cam over the intake valves [bucket and shim] with rocker arms opening the exhaust. More compact and less weight than twin cam set up. Anyone care to confirm or dispell the rumor. Anything to add? I hope they put them on a fast boat from Japan.:D
 
Joined
Jan 27, 2000
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#2
MXN4FUN. This is true. In fact, the exhaust rocker is a roller design. Check out the post from mtngoat, CRF450 link. Click on engineering.
I think i just saw a picture of my next motorcycle.
 

holeshot

Crazy Russian
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#3
?

The exhaust valves seem to have only one adjustment screw -what am I missing here? If I ever buy one of these, I think I'll get Ol'89r to adjust the intakes for me. ;)

 
Joined
Apr 11, 2001
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#4
Single OHC

Interesting. But this certainly is not new technology. My '86 Alfa Romeo GTV6 uses a similar design. The single cam (well, single cam per V side) sits over the exhaust valves and operates them directly via shims and lifters. The intake valves are operated remotely very similarly to what is shown in the new Honda engine. The only difference is that the Honda uses a roller and the Alfa engine uses short push rods that ride on the cam lobes.
It was a very innovate engine design at the time, but Alfa subsequently modified the engine to a DOHC configuration. Later they went to a DOHC 4 valve system.
At first glance it would sure seem that the elimination of one cam would reduce weight. (And I certainly like the roller better then the push rods of my GTV6.) But it would be at the expense of more friction. The single cam system introduces many new contact points: the roller, the rocker pivots, and the rocker bearings. The DOHC configuration was developed SPECIFICALLY to reduce the number of friction points. Weight is not the only enemy.
To me, this engine looks like it is exaclty half way between the 4-valve SOHC XR engines of today and a DOHC engine. Ok, maybe not quite half way since there are only 4 valves instead of 5.

Dave M.
 
Joined
Feb 2, 2001
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#5
The Exhaust valves appear to use shims for the adjustment. Look closely at the valve train photo and you will see the shims sitting in the valve retainer. That lone adjuster is for the decompression system.

KLX