<VV> De-flashing

Larry Forman Larry at Forman.net
Sun Oct 30 21:12:30 EST 2005

At 07:51 PM 10/30/2005 -0600, Stephen Upham wrote:
>I have my own archive of vv posts that I think are interesting or 
>contained advise that seemed likely that I would use some day.  Tonight I 
>began to try to de-flash my heads.  I picked up on this method and was 
>lucky enough to have my mentor to lend me his bit.
>The advise is from a regular vv contributor and is as follows on p. 67:
>I like to use some power tools to do this (de-flashing).  I use an (sic) 
>1/8-inch by 6 inch "jobbers drill bit" to do that. . . . The 1/8 inch long 
>drill bit works best, since it not only assures the air flow width is at 
>least 1/8 inch; it also tends to remove some of the interfering side walls 
>of the cylinder fins that is caused by the castings not being precisely 
>aligned for maximum air flow.
>Well, when I started, I noticed that the 1/8" bit was snug to say the 
>least.  When it drilled out the first bit of flashing, I noticed that it 
>was also taking away some of the fin wall and creating upper and lower 
>groves in the fins.  It also appeared to get dangerously close 
>(eyeballing) to wearing away the top of what appears to me to be the 
>chamber for the fuel/air mixture (where luck would have me to start).
>I was a bit ashen at this point and stopped to await further guidance even 
>though the previous advise says not to worry about this and in fact using 
>this size bit makes the heads closer to factory specs.  BTW my bit is 12" long.
>Stephen Upham

I agree with the instructions.  I use a six-inch jobber's drill bit for 
most of the head deflashing.  I use the longer one for use near the carb 
mounting pads.  I also use a round tile cutting hack saw blade with one end 
broken off and either mount that in the drill bit or in a set of vice grips 
for making some of the area a little wider.

The reason I like the jobber's bit is for the stated reason in that it 
assures a 1/8-inch clearance.  It removes flashing as well as chamfers the 
fin wall that is often offset and tends to close up the opening beyond what 
was originally designed.  It does tend to make some round gouges but at 
least it is a lot better then before.  I have done many of these and never 
broke through any internal walls.  Others have followed the instructions 
and had equal success.

Be careful that the bit does not bind in there.  I have had them break in a 
fin.  If possible remove, but if it wants to stay, you still have more air 
flow than before.  Sharpen the remaining end and use again.

I think the 140's have slightly smaller openings versus the 110's.  The 
area where you want to remove the most of the flashing is around the 
openings below the spark plugs.  I sincerely doubt you are in any danger of 
drilling into a combustion chamber.

I would recommend you continue carefully and admire your work after an hour 
or so on each head.  You DO want to be careful and not drill any internal 
passages.  Just take your time.  You will be fine.  If there is any doubt, 
observe from below.  Place a white paper on the ground with good lighting 
on it so you can see from above.  If you like, drop the lower shrouds and 
exhaust for more vision.

-- Larry 

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