Post by Admin on Feb 21, 2012 15:58:54 GMT -5
We will keep moving valuable tech tips to the top each day plus adding new ones each week. Valve settings approximately every 4 to 8 races is valve lash. Our first year of racing, we generally
kept the RPMs around 5800... valve lash seldom changed. In running closer to 6200
(not recommended), we find the valve lash opening up after 4 to 6 outings. Here is
what we do:
1. Remove both valve covers. Make sure you keep spare valve cover gaskets on hand.
2. Rotate the engine in the run direction until the exhaust valve rocker just tightens.
3. Measure the intake valve lash (the clearance between the rocker and valve stem).
The gap should be .012 inch nominal. DO NOT force the feeler gauge; it should just fit.
Break the lock nut loose on the rocker at the push rod end and use the Allen to set the gap.
You will need to hold the Allen screw stationary when re-tightening the lock nut to
100 inch pounds. Sometimes it takes a few trys since re-tightening the lock nut can
change the gap.
4. Once the intake is set; continue rotating the engine in the run direction until
the intake valve rocker just loosens.
5. Measure the exhaust valve lash. It should be .014 inch nominal. repeat the above
adjustment procedure to set the gap.
Note that generally, more lash = more torque at lower RPMs and less lash =
more RPMs with less torque. I don't vary from the .012 / .014 settings myself.
Re-check the lash settings on both cylinders before reinstalling the valve covers.
It helps to remove the spark plugs first to eliminate compression resistance.
Always check for bent push rods and rockers. I roll the pushrods
across a granite machinist surface to see if they're bent. Compare the rockers
to a good one and look for extreme wear (denting) at the valve stem end.
REPLACE THE SPRINGS ALSO. They loose compression strength quickly. Removing the
valve springs is tricky and we have a tool we made to compress the spring with
the rocker removed in order to remove the valve keepers. I'll elaborate in next
weeks installment of tech tips.ek.
kept the RPMs around 5800... valve lash seldom changed. In running closer to 6200
(not recommended), we find the valve lash opening up after 4 to 6 outings. Here is
what we do:
1. Remove both valve covers. Make sure you keep spare valve cover gaskets on hand.
2. Rotate the engine in the run direction until the exhaust valve rocker just tightens.
3. Measure the intake valve lash (the clearance between the rocker and valve stem).
The gap should be .012 inch nominal. DO NOT force the feeler gauge; it should just fit.
Break the lock nut loose on the rocker at the push rod end and use the Allen to set the gap.
You will need to hold the Allen screw stationary when re-tightening the lock nut to
100 inch pounds. Sometimes it takes a few trys since re-tightening the lock nut can
change the gap.
4. Once the intake is set; continue rotating the engine in the run direction until
the intake valve rocker just loosens.
5. Measure the exhaust valve lash. It should be .014 inch nominal. repeat the above
adjustment procedure to set the gap.
Note that generally, more lash = more torque at lower RPMs and less lash =
more RPMs with less torque. I don't vary from the .012 / .014 settings myself.
Re-check the lash settings on both cylinders before reinstalling the valve covers.
It helps to remove the spark plugs first to eliminate compression resistance.
Always check for bent push rods and rockers. I roll the pushrods
across a granite machinist surface to see if they're bent. Compare the rockers
to a good one and look for extreme wear (denting) at the valve stem end.
REPLACE THE SPRINGS ALSO. They loose compression strength quickly. Removing the
valve springs is tricky and we have a tool we made to compress the spring with
the rocker removed in order to remove the valve keepers. I'll elaborate in next
weeks installment of tech tips.ek.