XR600 valve clearance question???

[TEETBOYSDAD]

I replaced my camshaft and rocker levers, redid the top end, set the valves acording to spec .004 (int) .005 (exh) ran the bike about 100 miles, engine was running fine but I thought I would reset the valves and to no real surprise the settings were a little loose about .008-.010 I figure new parts breaking in,so I reset them to spec .004 and .005 and took the bike for a ride and had a noticeable power loss slower acceleration. So I reset them again and increased the clearance back to .008 and .009 took the bike for a ride again and power is back much quicker acceleration. Has anyone had any experience in this? or have any ideas?. There are no performance mods done to this bkie except for Super trap exhaust, I'm not sure what the stacking is in the silencer I bought the bike with it on.

[Beyond The Pale]

That sounds strange. I'm not sure about after a rebuild, but in my experience with cars and bikes, the clearance decreases as the parts wear. The valves and valve seats slowly wear and this reduces clearance. Increasing clearance is due to rocker arm or cam wear.

Did you check the clearance when it was totally cold. I only check valve clearance after the bike has cooled for hours. Doing it first thing in the morning is best. Since the aluminum head casting expands more than steel, the valve clearance increases with temperature.

[TEETBOYSDAD]

I'll see once in the next 100 miles what the clearance is. I'm under the assumption that installing a new camshaft and rockers with a light coating of assembly grease probably acounts for the seating or wearing in of the rocker assembly. what seems odd to me is that the extra clearance makes it run better.

[Beyond The Pale]

My understanding is that valve timing is a compromise. The valve timing requirements are different at low and high revs. With extra clearance the timing changes. Particularly, the intake closes sooner. This helps to make a little more torque at low rpms. You lose a little at high revs though. Maybe that is what you experienced.

[beezerjoe]

Depending on which cam is installed sometimes the manufactures will specify certain clearances for a particular cam in order to achieve what is to be considered by them proper timing and lift to get optimum performance out of thier cam.

[kellismechanic]

That sounds strange. I'm not sure about after a rebuild, but in my experience with cars and bikes, the clearance decreases as the parts wear. The valves and valve seats slowly wear and this reduces clearance. Increasing clearance is due to rocker arm or cam wear.

Did you check the clearance when it was totally cold. I only check valve clearance after the bike has cooled for hours. Doing it first thing in the morning is best. Since the aluminum head casting expands more than steel, the valve clearance increases with temperature.

As parts wear, the clearance INCREASES:prof: , as the wear, things get looser, but this still sounds strange. Oh, and if the valve seats wear, you have a big problem, they just don't wear, they will burn or crack, but not just wear out.

[Beyond The Pale]

As parts wear, the clearance INCREASES:prof: , as the wear, things get looser, but this still sounds strange. Oh, and if the valve seats wear, you have a big problem, they just don't wear, they will burn or crack, but not just wear out.

I guess that has just been my experience. I have never had cam/rocker arm wear. So I have never seen the clearances increasing. I have had a lot of valve and valve seat wear. Yes, that included replacing a few of the valves and valve seats on my 600. As far as I can tell cam and rocker arm wear are symptoms of poor lubrication and I call that abnormal wear. I call normal wear the slow recession of the valve/valve seats. For me it is a very slow processs. I would say around .001 per 3000 to 5000 miles. When my seat fried it jumped massively. On the last ride before the head rebuild, I had to adjust the clearance during the ride, because it went to zero and the engine would no longer run.

I did have the clearances increase once. That happened when my XR500 cam decided to eat the bearing surface on the head. It was the end of that bike.

[HawkGT]

As parts wear, the clearance INCREASES:prof: , as the wear, things get looser, but this still sounds strange. Oh, and if the valve seats wear, you have a big problem, they just don't wear, they will burn or crack, but not just wear out.

I'm with cleonard.

The parts that always seem to wear the most for me over time are the valve sealing surfaces--the valve seats and valve faces--especially on intake valves. As these places wear the valve lash clearances DECREASE, not increase. If the valve starts seating deeper into the valve seat the clearance between the top of the valve stem and the rocker will go down.

[creeky]

I've had the same experience as cleonard and HawkGT.

[Kawabuggy]

+3 on the DECREASING clearances due to valve seat wear