I get a perverse thrill out of finding weird problems in engines and trying to figure out WHY they happened. Eric calls my workbench Streamwood CSI :rotfl: The only thing more fun than finding and analyzing this stuff is trying to figure out how to photograph it so the story is told properly.
My old Olympus C-2500L did a really nice job with macro pics, but I wanted to really dial it up so I bought a real macro lens for my Nikon (Sigma macro 105mm F2.8).
So to christen it here's a cool picture of the wear on a 2004 CRF250F camshaft. Specifically it's closing ramp of the exhaust lobe. The CRF engines use a roller finger follower. What makes it interesting is the high rocker ratio they use. Passenger cars generally use a 1.5 rocker ratio, performance engines will go up as high as 1.7 ratios, and the CRF uses a WHOPPING 1.9 ratio. The result is really fast exhaust valve guide wear, and some pretty bizzare wear patterns on the rockers and exhaust lobes.
This one has a huge flat spot at the tail end of the closing ramp, not to mention some serious surface wear and evidence of the roller hopping off the surface right after the nose of the cam as the roller trys to follow the cam surface. This is probably from loft over the nose or general valve float.
First pictures with the new lens, using a handheld speedlight and a hunk of white cardboard as a reflector. They came out pretty good. :)
Here's the cam lobe pic at 1024 :
http://www.ericgorr.com/images/CRF250_exh_cam_closing_ramp_wear_1024.jpg
Here's the cam lobe pic full size no JPEG compression (BIG) :
http://www.ericgorr.com/images/CRF250_exh_cam_closing_ramp_wear.jpg
My old Olympus C-2500L did a really nice job with macro pics, but I wanted to really dial it up so I bought a real macro lens for my Nikon (Sigma macro 105mm F2.8).
So to christen it here's a cool picture of the wear on a 2004 CRF250F camshaft. Specifically it's closing ramp of the exhaust lobe. The CRF engines use a roller finger follower. What makes it interesting is the high rocker ratio they use. Passenger cars generally use a 1.5 rocker ratio, performance engines will go up as high as 1.7 ratios, and the CRF uses a WHOPPING 1.9 ratio. The result is really fast exhaust valve guide wear, and some pretty bizzare wear patterns on the rockers and exhaust lobes.
This one has a huge flat spot at the tail end of the closing ramp, not to mention some serious surface wear and evidence of the roller hopping off the surface right after the nose of the cam as the roller trys to follow the cam surface. This is probably from loft over the nose or general valve float.
First pictures with the new lens, using a handheld speedlight and a hunk of white cardboard as a reflector. They came out pretty good. :)
Here's the cam lobe pic at 1024 :
http://www.ericgorr.com/images/CRF250_exh_cam_closing_ramp_wear_1024.jpg
Here's the cam lobe pic full size no JPEG compression (BIG) :
http://www.ericgorr.com/images/CRF250_exh_cam_closing_ramp_wear.jpg
Attachments
Last edited:
