James, did you ever think of filling the pits at a weld shop?
Also, as I recall, newer race heads prepared by Weld's CNC machines are
delivered and usually run with rough machine marks still in the combustion
chambers.
It's my recollection that the smoothing wasn't worth the extra expense
according to the company.
Matt
(62 Skylark in the garage thinking of a heart transplant to a willing MGB)
on 12/17/03 10:49 PM, James J. at m1garand@speakeasy.net wrote:
> All,
> The problem with uneven surfaces in a combustion chamber is that you
> don't get uniform heating of the surface, and the peaks often become
> hot-spots which cause pre-ignition and dieseling. It also promotes
> carbon build-up too, so it is more than cosmetic. This is pitted enough
> around the stock valve seats that it has undercut the edges a bit.
> Also, does anyone know what that little keystone shaped protuberence
> behind the spark-plug hole is? I think it has to do with flame-front
> propagation. Regardless, it's pretty eaten up too.
> Since I wrote the original post, I went at the chamber with an
> abrasive wheel on a high-speed drill. This is a black sponge-like
> material that is impregnated with abrasive. It took out the small pits,
> but the deep ones (and there's alot of them!!) remained. I was doing
> some basic porting too, with a carbide tool designed for aluminum. If
> you use the tip, it barely removes any material. I used that and got
> out most of the big pits in the open areas and then hit the surface
> again with the drill abrasive. To the naked eye, the chamber doesn't
> look any different than the rest, but it still looked like a bunch of
> aluminum chips went flying earlier. Unfortunately, I can't get to the
> areas where the valves are closest to the edge of the CC, and also
> around the (formerly) sharp edges of the keystone thingy.
> I'll have to cc the CCs (measure the volume of the combustion chambers)
> to see how much damage I did.
>
> As far as finding a single head, I was hoping that somewhere out there,
> somebody had experienced similar problems, bought another pair of heads,
> and kept the single good one from the original pair out in the barn, and
> would be willing to sell it to Sgt. Pepper's Lonely Heads Club Block.
> But I can see what the shop says about this one in the meantime.
>
> Thanks for all the inputs,
> James J.
>
> David Kernberger wrote:
>
>> James et al.
>>
>> A single Buick 300 head is probably going to be hard to find. Do
>> you really think you need it? Others may want to add their comments to
>> mine, but I think the damage you describe is more cosmetic than functional,
>> unless something is broken or cracked. What do others think about this?
>> I'll bet that a basic smoothup of any really high spots with a small hand
>> grinder would be perfectly OK. Not enough to remove much metal, so CR will
>> not be affected much. Nobody's going to see inside the engine after it is
>> assembled, so the only real question is if it will cause problems in
>> operation. That's my 2 cents worth.
>>
>> Regards,
>> David Kernberger
>>
>> -------------------------------------------------------
>>
>>
>>
>>> All,
>>> Anyone have a single, aluminum Buick 300 head they want to get rid of? I
>>> was cleaning all the carbon off of my heads and then bead blasting them, and
>>> one combustion chamber is so heavily pitted, that I don't think I can use it
>>> It really looks like the dark side of the moon. I guess that the whole
>>> chamber could be ground (polished) down to virgin aluminum, but I'd then
>>> have to do it to all CCs, plus the corresponding loss of compression.
>>> Thanks,
>>> James Jewell
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