Ironhead CCing my combustion chambers

[billeuze]

There's really only one way to know for sure your compression ratio and that is to CC your heads. As far as I know there are 2 ways to do it:

1. measure the combustion chambers of the fully assembled engine.
2. Measure the Head volume and cylinder dome displacement and do the math

I'll be doing it both ways. Partly to make a double check for myself and I want to keep a record of Head volume and piston dome displacement for the future when it comes time to order new pistons. I know that already the pistons i have are not made anymore so I can't just order more the same by part number.

This my new engine under constuction. I'll be milling the heads to increase compression but I have to know exactly what its at now so I know how much to take off. So here goes. Note these heads don't look like iron heads, that's because they are shovel heads, but the procedure is the same and they are sitting on ironhead cases.

Tools needed: dail guage and burette. A burette is like a 3 foot long test tube with a valve at the bottom and measurement lines all along the side. 100ml is the perfect size because you only have to fill it once, 50ml works but you have to refil it which makes more room for error. Plenty of pictures of my setup as we go along here:

Before starting into this, I took the cylinders off, and packed the spaces between the rings with axle grease then put the cylinders back on. This'll stop any fluid getting past the rings.

First, find Top Dead Center. My heads are off to start with so that makes it a bit easier:
(EDIT: I mean find top of bore. TDC is a technical term for an exact point on the crank rotation. I didn't find that point. simply a point close to it where the pistin still at the top of the bore)


Hmm, look at that, the red mark on the left side of the timing hole window is the finger nail polish I put on the factory TDC mark. Seems to be off a bit - good to know.


Now I've got to lock the crank in place so I don't lose TDC. You can gently, carefully screw a bolt into the timing hole until it snugs up against the flywheel. Instead I put a little piece of polyetheline tubing in the timing hole then put the plug back in on top of it pushing the tubing into the flywheel. This puts plenty of friction against the wheels to stop it rotating and I don't have to worry about going too tight as the tubing just flexes and bends.


So, now I bolt the heads on. You are suposed to use a compressed head gasket but I am doing this without head gaskets. I already know the compression ratio is too low so by omiting the gasket now, I'll be closer to what the end result will be after I mill the heads and add a head gasket. I just put a bit of grease on the gasket surface to prevent leaks. Then I prop up the engine till the front head is level:


Then tip it over until the front spark plug is sticking straight up in the air. Brace engine, remove spark plug, hang burette over spark plug hole:


easiest is to fill the burette first to above the mark, then bleed some off the bottom till the level on top is right on the 0 line, then clampt it above the hole you want to fill.


Your supposed to use denatured alcohol to measure. But that is really hard to find here in Canada, especially on a Sunday night. So I just used antifreeze. It doesn't really matter much as long its not water which can get things rusty. Well it can matter if you get something trickling down into the bottom end that shouldn't be there. That's why alcohol is good because it just evaporates. But for me it doesn't matter, the bottom end is together just for mockup, its coming apart again. If using a clear liquid like alcohol, add food coloring to make it easier to see. Actually I'd guess any alcoohol would do: isopropyl (rubbing alcohol) should be OK, Probably my memory of having to use denatured and not isopropyl is more to do with flushing brake lines than CCing. But if you can get denatured, you'll be safe as that's whats generally recomended.

shutup Bill and post anoter picture:


Fill her up the the third spark plug thread is what I read on another forum. That took a total of 87 CC. Oh yeh, it looks higher on the photo but that's becasue the photos doesn't show the muniscus. you take the reading from the bottom of the muniscus. Same with the 0 level full tube shown earlier, it really is at 0, just doesn't show in the photo:


repeat prcocedure on the rear head and I get 88.4 CC:


strange thing with my rear head at top dead center sits .007" lower than the front piston. This is with respect to the top of the fire ring. That 7 thou adds up to 1 cc which probably accounts for most of the 1.4 CC difference between the 2 cylinders.

I'll just save those numbers for later. Now on to the second method of measuring combustion chamber volume

[billeuze]

For the other method of measuring combustion Chamber volume. I started with the piston in the bore (still with the the rings all greased up) but lowererd down so the piston top is below the cylinder top so you can submerge the whole piston dome in measured alcohol (or anifreeze or whatever). I had the piston down 1" from the top of the cylinder. Then grease up the top of the fire ring to prevent leaks and place a piece of plexiglas on top. You need a hole in the plexiglas big enough to put he spout of your burette and this hole should be at the high end of the plexiglase surface. I made a bit of an incline here but found its not enough - have to tilt it more so that a spirit level bubble is completely over to one edge.




So, You'll see here I couldn'd get all the bubbles out. Also This used more than 100 ml and I drained it past the 100ml mark which just got me all confused on how to add enough to compensate for how far below 100 I went, then how to add just a bit more and subtract what more I drain. because its not all subtraction. since the scale is upside down, it is perfect for reading how much you used in one shot. But when adding a bit more and draining a bit more you have to be careful because what it my normal way of thing is subtracting is really adding on this upside down scale.


So this was a bomb and I started over. my dome hight is only .71" so I don't have to go down a full incch and I can enter .835 into a spreadsheet just as easily as 1.000 so there is really no need for nice round number 1 - especially when it brings me over the 100ml mark. 0.8 gets the top of the dome under water and .035 is the height of the piston deck below TDC, total is .835. This time around it worked a lot better and i ended up using 82.6 CC. Well actually 82.8 but I spilled some drops so I'll call it 82.6.


I did have a stubborn air bubble hanging between the piston top and the plexiglas. ihad to tilt the engine quite abit and tap onthe plexi quite hard to dislodge it - that's where the spilled drops came from that you can see onthe glass:


Those head bolts yu see on my plexiglass probably aren't necessary, They are not bolted down, just placed there so the glass dowsn't slide - but the grease holds it pretty tighjt and it doesn't slide anyway.

Next, on to measuring the head volume. Same kind of deal:


It takes a while to fill but once it hits the top you have to be quck on the petcock to stop it and take it slow to the end. Here we are with a bubble left at the top end to fill:


and full. 165 CC. yeh no way around it its more than one burette full

[billeuze]

Now for the calculations. The first method is easy:
my bore is 3-7/16 or 3.4375. divide by 2, square it and multiply by PI which means my bore is 9.28 square inches. Multiply that by the stroke of 4.5" to get 41.76 cubic inches. Divide that by 0.0610237438368 to get CC which comes to 684.37. Add to that the measured combustion chamber volume of 87 CC for a total of 771.37 CC when the pistion is at BDC. Take the TDC measured chanber volume of 87 and divide it by the calculated BDC volume of 771.37 = 8.87:1 Compression ratio

The second method has about 10 x the mathematics of the first method. If everything is done right we should get the same chamber volume. I didn't. I'm out by 3 CC (0.3 in the compression ratio). I don't know why yet. next weekend I'll do the rear head by this method and plug the rear numbers into my spreadsheet, Then If need be I'll redo everything - it has to match in the end.

I'm not going to write out 10x the above math in longhand so I'll just post a screenshot of my spreadsheet. The calcs for the first measuring method part are on top. The second method below. All calculations are in column C. Of course only the results show in column C so I've copied the formulae to column F for your reference. I hope I didn't screw up with it but until method A equals method B, Something is wrong somewhere.

[Hopper]

Wow, that's getting technical. Nice job.

[zipdog]

Originally Posted by billeuze

Now for the calculations. The first method is easy:
my bore is 4-7/16 or 4.4375...

Not to nit-pick, but I think that's 3-7/16". The result is correct, and it's correct in the spreadsheet. I first looked at that and thought "only 83 cu. in. with a 4-7/16 bore? What gives?" A 139 cu. in. shovester would be the mother of all sporties!

[rivethog]

....TDC mark. Seems to be off a bit -

I don't see a degree wheel in any of your pics. How did you determine where TDC is?

I'm out by 3 CC (0.3 in the compression ratio). I don't know why yet.

It doesn't look like the right hand sparkplug is the same reach as the left hand one. Optical illusion?

[hcrashster]

Dial Indicator falling off it's high point. As you no doubt know.

One thing I've noticed over the years is that the factory markings can be off. Sometimes......way off.
Factory screw up or a PO? Doesn't matter, it just is.

[rivethog]

Originally Posted by hcrashster

Dial Indicator falling off it's high point.

That's not an accurate way to find TDC. If you use only a dial indicator, the point where the indicator falls off it's high point will be different depending on which direction you rotate the engine due to piston dwell. You need to split the difference between those 2 points to accurately find TDC. You need a degree wheel to do that.

It is a common error to miss T.D.C. by a few degrees due to the piston dwell at top center.

http://www.iskycams.com/degreeing.html


Page 2.
http://www.cranecams.com/uploads/instructions/803.pdf

[hcrashster]

Originally Posted by rivethog

That's not an accurate way to find TDC. If you use only a dial indicator, the point where the indicator falls off it's high point will be different depending on which direction you rotate the engine. You need to split the difference between those 2 points to accurately find TDC. You need a degree wheel to do that.

With the heads on and using a piston stop, yeah, that is the way. The only way.

With the piston available for measurement of travel, a dial indicator will give you the most accurate measurement.
You could do a forward and reverse course of travel and split the difference. But what are the gains? A few .0001 will tell you bearing clearance and perhaps wear but I think the main point is to determine your flywheel markings. [To me anyhow].

All in all, I admire the pursuit of precision. Always admirable in engine building, but in total, a waste of time for anything but a full on race motor.

[rivethog]

Originally Posted by hcrashster

With the heads on and using a piston stop, yeah, that is the way. The only way.

With the piston available for measurement of travel, a dial indicator will give you the most accurate measurement.
You could do a forward and reverse course of travel and split the difference. But what are the gains? A few .0001 will tell you bearing clearance and perhaps wear but I think the main point is to determine your flywheel markings. [To me anyhow].

All in all, I admire the pursuit of precision. Always admirable in engine building, but in total, a waste of time for anything but a full on race motor.

Heads on or heads off, you've still got piston dwell. Every cam manufacturer recommends using a degree wheel to determine TDC, heads on, or heads off. The only difference is that with the heads off you have to use a dial indicator to position the piston in the exact same position BEFORE TDC and AFTER TDC (mimicing a positive stop), then split the difference. The longer the stroke and longer the rod, the more piston dwell you're going to have. How many degrees does the timing hole in a Sporty crankase cover? If your TDC measurement is off by 3 degs, then the timing mark will appear to be off by 3 degs also.

Even with the heads off, the positive stop method is more accurate, and recommended by most cam manufacturers.

On my 4-5/8" stroke BT with stock length rods, there was about 6degs of piston dwell (no movement of the dial indicator at "TDC").