Boring out cylinders - 787cc

[g_campbell]

Can anyone help me determine what to do in regards to boring out the cylinders?

The questions I have is,
-Do i need to make carb adjustments?
-What do I do about the rave valves?
-What size bore over should I do?

There's a small amount of pitting in one of my cylinders.

 

[Mekanix]

Only bore the minimum required to clean it up.
No carb adjustments necessary.
Dwpending on the bore size you may need to clearance the raves to maintain a certain clearance.
Which is 0.5mm or 0.020" between the rave edge and cylinder wal.

 

[g_campbell]

Only bore the minimum required to clean it up.
No carb adjustments necessary.
Dwpending on the bore size you may need to clearance the raves to maintain a certain clearance.
Which is 0.5mm or 0.020" between the rave edge and cylinder wal.

What is involved in providing clearance for the rave valves? Filing them or just adjusting them?

 

[Mekanix]

Filing them a bit.

First get the piston kit and bore the cylinders. Install the rave.
Measure how far the entire lip of the rave is from the cyliner wall using a straight edge and a feeler gauge. Rock the rave back and forth just to make sure that if it shakes around that that the tips don't come any closer.

For mine i did trial and error. I put 800 grit sand paper around an old piston and used that as my sanding block.
I passed the rave up and down the side of the piston 2-3 times and checked for clearance. Repeat as many times as necessary to get the .5mm clearance.

Mine took very little when going from 81 89 to 82.5mm.

There was 0.5 clearance before i bored the cylinder to 82.5.
When i bored it that changed the clearance by half the difference.

So it made the cylinder 0.5mm larger in diameter but that means the rave was only 0.25mm closser.
That means there was still 0.25mm rave clearance after boring. I corrected that to get to 0.5mm again.
My valves would rock a bit so i took a bit more off the tips just so that the clearance was maintained in all scenarios.

 

[lucas_santos]

what could happen if you file the rave valve to much?

 

[Mekanix]

You would loose low end power.
My first set that came with my machine had almost 4 mm clearance in the center. So i got some new valves and clearanced them properly.

One way to give you an example would be to run it with the rave caps off. It just boggs on low end.