Allen Nugent wrote:
> Scott,
>
> I have indeed (on a Dolimite Sprint head). Here is my method, and
>experience...
>
> I supported the head on 2 wood blocks, positioned so that I could slip the
> valves of one chamber into place. I put grease on the valve seats, so the
> liquid wouldn't leak. (There is no need to fit the springs and collets to
> secure the valves.
I'll add this much--I don't work that quickly, and kerosene or other
such solvents can gradually work through the grease, so I use the 5 lb.
checking springs used during valve timing to hold the valves in place
and put a slight additional pressure on the seats. I would also remind
Scott that the head should be milled true, and the valves and seats
should be ground and the valves lapped in _before_ cc'ing.
> I placed a plexiglas/perspex plate over top of the combustion chamber, again
> sealed with grease. (Don't use so much grease that it squeezes into the
> chamber, affecting your data.) The plexi plate had a hole in the centre, for
> adding the liquid; I had beveled the bottom of the hole, to facilitate
> removal of air bubbles; I subtracted the volume of the bevel from all
> measurements.
>
> I placed a laboratory burette into a retort stand, positioned it over the
> hole in the plexi plate, and carefully drained a precise volume of liquid
> into the chamber.
Since you're in biomed, you probably take burette use for granted, but
it's not for some others. <smile>
A few rules of thumb should be mentioned. Glass burettes are more
expensive, but have less dimensional change from ambient temperature
change than plastic. Plastic ones are more durable for everyday shop
use, but are usually no good when used with organic solvents. Try to get
one with a good valve. Teflon with o-rings to seal the valve to burette.
If the estimated chamber size is 30 cc, don't get a 25 ml burette to
save money--it'll drive you crazy trying to recalculate. Get a 50 ml. If
you want to cc within 0.2 cc, buy one scaled to 0.1 ml. Trying to
estimate the center point of the meniscus (the little arc that the
surface of the fluid makes inside the burette) is difficult enough, and
more so when the graduation of the burette is as large or larger than
your proposed inside limit of variance. Always measure from the center
of the meniscus.
Last, on burette use, no matter how careful you are filling the burette,
a fair amount splashes onto the inside wall of the burette. Don't
immediately try to take a reading--just wait a couple of minutes for all
the fluid to drain down, and always overfill the burette, put a
container between the burette tip and the cover plate, and bit by bit,
drain the burette until it's just at the "0" mark. Makes measurements a
good deal easier and insures that the valve is fully wetted, so
inaccuracy isn't introduced when first opening the valve.
> I chose kerosene as the measuring liquid, because, being blue, it was easy
> to see. I also thought it would have a lower surface tension than water, so
> that bubbles would be less troublesome; I was wrong.
I use automatic transmission fluid--the red is equally easy to see, and
the ATF already has a significant amount of detergent in it which acts
as a wetting agent.
> At one point, while trying to manouevre some bubbles out through the hole, I
> replaced the head on the wood blocks incorrectly, so that one valve was
> pushed open, dislodging the plexi plate in turn, and spilling precisely 34.5
> ml of kerosene down the front of my coveralls.
Light valve springs do help minimize little accidents...! <g>
A few last provisos, Scott, which others may have mentioned. First,
cc'ing the chambers won't make gobs of horsepower. It's sort of a
finishing touch to a complete blueprint job. The object is make each
cylinder behave equally to the others. Therefore, the block face has to
be true, the head has to be true, the connecting rod center-to-center
lengths have to be matched, and the piston pin center to crown heights
have to be matched, and the crank throws must be indexed. Otherwise,
there's no guarantee that the piston crown heights will be equal when
installed. If they are different, it won't matter whether or not the
chambers have been cc'ed, since the effective chamber volume at TDC will
still be different. If you can't go to the time and expense of all of
the above, then you should first assemble the block, measure the crown
top to block face height at each cylinder, calculate the volume there,
and compensate as you cc each chamber.
Finally, last, but not least--one has to match the smallest chambers to
the largest, so don't get wild with the grinder. Moreover, always
install _old_ valves in the chamber before grinding--they will help
protect new seats. (!)
Cheers.
--
My other Triumph runs, but....
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