Setting Compression

[cal 67]

I just finished measuring the deck height on all four of my cylinders. This is an 1835 with flat top pistons and an Engle W100.

#1:  .032 in.
#2:  .029 in.
#3:  .046 in.
#4:  .039 in.

I'm using a used AS 41 case and it seems that the case surfaces are different heights. This is the first time that this has happened to me. They've always been close. I used the same barrel and piston for all four measurements.

I've already closed up the case. Should I double-check all of my measurements and get the barrels cut or get shims made? What's better? Head shims or barrel?

Also I've just recently started measuring cc's by myself and I'm second guessing the Latest Rage brand unit that I have.  Does anyone else use the same one? I just want to make sure it's accurate.

Also with the W100 cam it seems that I can go no higher than 7.9 or 8:01 static compression to get my dynamic at 7.18 or 7.22 for 91 octane.  Is that really as high as I can go? My inlet valve closes @43*.

Thanks.

[Greg G]

Did you check the rod lengths to make sure they are all the same? They could be some of the reason for the different deck heights. May be try using the same rod, piston and cylinder to check all four decks.

[cal 67]

I didn't. One of the case surfaces looks lower than the rest. I just assumed it was the block.  How do rods measure differently? Does it happen if the small end bushing is reamed too far one way or the other or the actual rod? If the rods are different lengths, can I simply correct it with different shims? It's not going to be a high HP killer. Just something that can make decent power to 4,000.

For the next engine, what tools can I use to measure the rods?

[Busstom]

Keep this in mind:  both barrels on either side of the engine MUST be at the same height - you don't want the head skewed when you go to torque it, and expect it to seal.  

If your variation is on the case decks, you should be able to see it with the naked eye...get a straight metal rule, 12 inch long, and set it on edge across the spigots on the decks, and look for daylight (any kind of light) underneath the ruler.

Assume you shim them up to a zero deck, with the intent of running say .060 copper gaskets, then you'd have some awfully pricey (and thin) shims under those barrels. (edit: to clarify that confusing statement, shim to zero following barrel machining...of course, if you were machining them, you'd obviousy just take them down accordingly to nail them where you want 'em, assuming you found the error on the decks).

Sorry for the confusion.

[white66bug]

Your case was decked with respect to the case halves and not to the centerline of the crank.

[67Beetle2017]

I just finished measuring the deck height on all four of my cylinders. This is an 1835 with flat top pistons and an Engle W100.

#1:  .032 in.
#2:  .029 in.
#3:  .046 in.
#4:  .039 in.

I'm using a used AS 41 case and it seems that the case surfaces are different heights. This is the first time that this has happened to me. They've always been close. I used the same barrel and piston for all four measurements.

I've already closed up the case. Should I double-check all of my measurements and get the barrels cut or get shims made? What's better? Head shims or barrel?

Also I've just recently started measuring cc's by myself and I'm second guessing the Latest Rage brand unit that I have.  Does anyone else use the same one? I just want to make sure it's accurate.

Also with the W100 cam it seems that I can go no higher than 7.9 or 8:01 static compression to get my dynamic at 7.18 or 7.22 for 91 octane.  Is that really as high as I can go? My inlet valve closes @43*.

Thanks.

Since you used the same piston and rod, you will need to measure the crank (stroke) and the case deck to really see which is off.  Most likely the deck of the case is off a little.  You can have Rimco or (another experienced air cooled machine shop) deck the case.

[James2]

Have the case decked. I learned this the hard way also, one those things I do now on every case.. Just consider your doing a mock up now, and finish up to what other problems you may have, then tear it back down and get everything corrected.

[neil68]

I have used different shim stacks on the 1/2 cylinder side and the 3/4, but the stacks must be the same for both cylinders of each head (so that the cylinder head will sit level).  Since your 1/2 DH's are only 0.003" different, why not add a 0.010 to bring that head up to 0.039" and 0.042" which gets you closer to the 3/4 DH?

This would give you:  0.042", 0.039", 0.039" and 0.046".  Then try to mix and match your rods to see if they vary slightly in length and you might be able to get "very close" for all four cylinders.

As stated above, decking the case doesn't always work if the crank center line is slightly "off" in the case.

Good luck!

[Ohio Tom (DdK)]

A "re-sized" rod will measure shorter. I learned that recently.. Thanks to Don Pauter..