|
Date: Tue, 10 Feb 98 09:19:00 PST From: Slootweg Paul To: mini-list@autox.team.net Subject: TECH: Cyl. head chamber volume measurement |
|
Last night I was trying to figure out how much to remove off a cylinder
head to achieve a certain cc. The head is a 12G295 (29 cc chambers)
intended to go onto an 850 engine (24 cc chambers) - i.e. I need to lose
approx. 5cc.
Firt of all I tried by filling a chamber with the required volume and measuring the difference between the head and liquid level. Using log graph paper (has more divisions/mm) I measured the distance at approx. 1.7 mm. But I didn't feel comfortable with the measurement - was the head level? had I dealt with the meniscus? etc. So I came up with an idea. Although the walls of the chamber slope slightly inwards, over very small increments it can be considered straight. In which case all I needed was the area of the chamber from which I could then calculate the necessary depth. To get the area I proceeded as folows: cut a square of (ordinary) graph paper - a bit bigger than the chamber and place this with the grid uppermost accross the chamber. Then place on top of this a sheet of carbon copy paper (carbon side down onto graph paper) and on top of this another sheet of plain paper. Then holding this lot in place, gently trace the outline of the chamber with the back of a wooden spoon. When do this properly you get a nice thin outline. Trace this over with a pencil and then count the squares inside. Add it all up and there you are - you have the area! Now it is simply a matter of dividing the required volume by the area to get the depth needed - in my case this worked out at 1.66mm - which also mean my original measurement must have been quite close. (BTW I found the area of the chamber to be 30.05 cm2) I think the nicest part of this method is that it avoids the silly pratting about with water/alcohol/whatever and I am convinced that for the kind of changes we're looking at it's likely to be more accurate. Paul |