Honda CBR 1000RR Forums banner
1 - 3 of 3 Posts

·
Tech Moderator
Joined
·
182 Posts
Yeah and have piston-tops ceramic coated.

No reason for that piston & cylinder scuffing. Only thing I can think of is lack of oil or really bad oil. Clogged oil filtre? Maybe send oil sample to lab for UOA?

I would test oil-pressure with mechanical gauge to ensure oil-pump and pressure-valve works properly.
 

·
Tech Moderator
Joined
·
182 Posts
those valve seats look worn way too wide..
 

·
Tech Moderator
Joined
·
182 Posts
You cannot just lap the valves because the seats are worn.


When seats wear and increase in width, that lowers contact pressure due to extra surface-area. Same spring-force is spread out across larger area and pressure is reduced. Imagine pressure-cooker lid that's not latched down, but just sitting on top. Valves aren't pressing down hard enough to seal. That's why on those exhaust seats, you see carbon all over the middle of seat.

Proper seat-width is minimum end of tolerance-range when valve-job is done. This generates highest pressure when valve is closed for best sealing. As seats wear wider and wider, sealing ability decreases as spring-force is spread out to wider area. Looks like your exhaust seat is well beyond wear-limits at 2.0-2.5mm. This results in sealing pressure of only 25-30% of new valve-seats. Lapping seats only pre-wears them out wider and decreases sealing-pressure even more.

Also ONLY use OLD VALVES for slight lapping of newly rebuilt seats cut by proper Sunnen VGS-20 cutting bit. You can't use your valves to remove those pockmarks on exhaust seats, won't be flat across and you'll destroy valves. They have hard-coating and cannot be re-surfaced if worn. If you use valves to repair worn seats with excessive lapping (more than 5-10s), your valves are destroyed and cannot be re-used.

I've been through this hundreds of times. You're gonna end up tearing this engine apart in less pthan month it you don't get worn seats cut back to 0.9mm lower-end of spec.

Machine-shop equipment has evolved tremendously in past couple decades. No longer need grinding stones to do each angle of seat. Single cutter-bit can do all 3-angles simultaneously. I always install beryllium-copper valve-seats since they conduct heat much, much faster than steel and saves your valves, especially in boosted applications. And for same effort, I can get perfectly smooth variable radius seats for much, much better flow. Way, way better than 5 or 7-angle "competition" cuts.

 
1 - 3 of 3 Posts
Top