Rave valve trimming

[Mekanix]

How would you do it with a .5mm overbore engine.

Replacing my raves on my ring snagged engine (in another thread)

Found out it was my lack of port chamfering....

Anyways.


How could I trim a rave valve 0.25mm and be happy with it?

I'm thinking of taking a dummy piston and sticking some sand paper to the skirt and scraping the rave on that a few times.

But how Can I measure that I've gotten 0.25mm off of it ?

Maybe install the valve and measure + retry ?

No experience in this department and don't want to rebuild this thing again for snagging a rave !

My original raves had nearly 4mm clearance in the center!!


Thanks

 

[griz400]

1/2 of what you over bore is ideal ... the way i do it is i use a scribe, and a feeler gauge the thickness i want to take off, scribe line, clamp in a vise lightly, take a half moon rat tail file, and it comes off real easy, -- raves are sorta soft metal , then use sand paper or emery cloth to sand/polish edge

 

[Mekanix]

Cool, what about the radius? As in the tips of the rave are going to be pretty close since the circle they follow is going to be bigger.

 

[smc0922]

The radius doesn't matter entirely. Make it as nice as you can but I just trace the edge in with a scribe and hit the grinding wheel. It's not exactly a precision part in regards to fitment against the piston.

 

[Mekanix]

Good to know.

Thanks.

I'm just over analyzing everything since my port chamfering failure resulted in a top end rebuild.

 

[smc0922]

Did you have the machine shop do the chamfer the second time around or do it yourself? And how long did it run for unchamfered? Just curious for my own knowledge.

 

[smc0922]

And there is a minimum spec for rave clearance, just be sure you are over it. It's around .015 I believe but don't quote me.

 

[Mekanix]

Machine shop wouldn't do the chamfering so I did it. Not knowing how much to do all I did was take the edge off.
Ran for 72 hours. Actually was still runming and didnt know there was a problem.
This time I'm im aware of how much to do and what to look for.



I remember seeing that somewhere in the manual.
Im only concerned when there is buildup on the raves or that the housings wear and the rave rocks to the side allowing the tip to get too close.