Altering deck height for varying cc heads

[wprater]

Originally Posted by boosted79

When you say you might chamfer the edge, are you talking about the edge of the plug pocket or some place else? I'm not sure I'd do the edge between the chamber and the mating surface by hand.

I was considering the chamfering the mating surface to combustion chamber after doing some research. However, it sounds like you're not recommending it, and I don't think it essential at this point.. so maybe I'll postpone. Heading out of town again; off my project until Sat. now..

cheers!

[boosted79]

I'm recommending the chamfer on the mating surface not be cut by hand. I know I wouldn't trust myself to do it by hand, I'd cut them on my lathe but maybe other people have done it by hand successfully? KTL doesn't think the chamfer is necessary with the pistons so maybe just leave as is. I would do that before I took a die grinder to them but that's just me.

[KTL]

My point of reference is a buddy who built a 3.3L short stroke via 100mm JE pistons in LN Engineering Nickies cylinders & SC "large port" heads. His heads had no issues w/out a chamfer in the combustion chamber.

I'd either have them machined for the chamfer if you really want it, or work on the original spark plug relief area with your grinding bur bits.

[wprater]

KTL are you saying you think I think work on the original plug hole or the secondary one? I was going to work on the 2nd one a bit.

going to leave the mating surface alone.

[KTL]

I'd massage the original spark plug location since it's the place where there's a lot of variability & meat to grind on. Work on the side away from the valves.'

I'd be inclined to leave the new 2nd plug hole alone because it's already so clean & tidy.

[3literpwr]

Make sure you get an idea of how much material you need to remove by pouring out that amount from your burette. A CC or two is so little and those bits, are going to hog material like no tomorrow. Last thing you want to do is having to lower your CR because of a grinding mistake.

[wprater]

Originally Posted by 3literpwr

Make sure you get an idea of how much material you need to remove by pouring out that amount from your burette. A CC or two is so little and those bits, are going to hog material like no tomorrow. Last thing you want to do is having to lower your CR because of a grinding mistake.

great idea! I will get one of those tiny burettes at Hardwicks. Im will be using an air gun die grinder and it's got really nice flow control, so I can set it very low.

[kenikh]

Lots of good advice here. When trimming the plug hole, take your time, especially on the first one. Round the sharp edges to a nice 2-3 mm fillet, then remeasure the dome volume. Lather, rinse, repeat. For the rest, you'll get a feel and the process will be much quicker.

[wprater]

getting these heads CC'd was quite a learning experience. I tried two methods, one with a fill tool while assembled on case and rings greased. as well as a flat disc on top of the heads with a fill hole. I ended up getting consistent results with the latter method and went with that. I did two rounds of measurement to be certain I could replicate the measurements.

here are the new values I was able to measure with the heads on the bench:

	1	2	3	4	5	6

1st	89.4	89.4	89.1	89.3	89.6	89.1

2nd	89.5	89.4	89.0	89.3	89.6	89.1

these numbers vary by as much as 0.6cc, where the original numbers I had were off by up to 1.2cc. I want to get them all within 0.1cc.

I also measured my over the dome volume of the pistons in the cylinders, so I can calculate my CR when Im done with the grinding.

I'll be massaging 2,3,4,6 to try and get them up to 89.5/6 . hope to get this done today or tomorrow and will report back. thank you all again for all the input here!

[wprater]

This took a lot more material than I thought, so I re-measured at least 4 times. Tried two different bits, but Im happy with the results.

Got #3 from 89.0 to 89.5. Will finish the rest on Monday and get these heads on finally!!

[wprater]

Got all the heads equalized now. Quite a bit of work (trial and error) to get them all even. Im very happy with results and smoothed out those pockets too.

	1	2	3	4	5	6

1st	89.4	89.4	89.1	89.3	89.6	89.1

2nd	89.5	89.4	89.0	89.3	89.6	89.1

Final	89.7	89.6	89.6	89.6	89.6	89.7

I seem to have varying deck height from top/right/bottom/left (12, 3, 6, 9 o'clock) when using calipers to measure the deck height. This is while looking at the cylinder with the top facing at 12 o'clock.
Not sure how to fix this without machining those case spigots?

[boosted79]

Not sure what you mean by " top/right/bottom/left."

[kenikh]

12, 3, 6 and 9 o'clock on the piston.

[boosted79]

Oh, ok. You'll get some variance just because the piston has some rock in it due to wall clearance.

[kenikh]

That's what I told him. If you want dead nuts measures, you need to pin solder at the 4 clock stations and crank the heads to install torque. Then there's no rocking.

[wprater]

Yeah.. and I think it could also be slight wobble in my caliper, if I don't carefully set it down straight.