deck height

[1967JMG]

Quick question,
According to the Specs Section on Classic Inlines, the deck height for the 200 is .019 in.
On all calculations for compression ratio, I have been using this data.
But i just saw today on the Falcon 6 Performance handbook site it saying that the deck height is .025 in.
So which is correct? or did it vary by years? Those small numbers sure do make quite the difference when making those C/R adjustments....

 

[Eric Rose]

There are different heights for different years from what I have seen. Some of the later low compression motors have the deck heights of .025 or so.

 

[1967JMG]

the falcon website says the deck height for a stock 67 200 was .025. IIFC, the 67 had 9.2:1 compression though.
Very intersting.... Just another one of those things I wont be %100 sure of till i really tear into the sucker. Then more adjustments!

 

[CZLN6]

Howdy Back JMG and All:

The spec dimension of .019" may be a techical specification. The .025" we use is based on actual measurements of many 200 blocks. It is not unusual for the technical specifications and the actual measurements to be different. The .019" may have been the way the engineers designed it, but .025" is the way it got built. I'm not sure were Mike got the .019" he used in his specifications post, but the only way for you to be accurate is to remove the head and measure the deck height on your engine. Chances are pretty good it will not be .019" or .025". You have to understand that quality control on these lopo engines was not very good, and there is no telling what has happened to these engines during the past 42 years. If Mike found and posted SAE specifications, and you were blueprinting a "Stock" race engine, then that would be a key dimension.

Another interesting note is that '64 200's advertized a CR of 8.7:1, '65, '66 & '67 200's were @ 9.2:1, and '68 - '70's were 8.8:1. In all the 200's we've been able to inspect there is no discernable differences, that would effect CR, in those years; same pistons, head gasket, deck height and chamber size. Of course, advertizing hype is different from the real world too.

So, what you read is a good place to start, but it is no substitute for doing your own measuring. And, in my opinion, .006" will not make a noticeable difference unless you are at an "On-the-edge" level of CR.

That's my two cents, for what it's worth.

Adios, David

 

[JackFish]

What is the best way to measure this? I have a dial indicator and magnetic base.

 

[CZLN6]

Howdy Back:

Jackfish- Yup, that may be the "best"/most accurate, but we've done it with a straight edge and feeler guage too. Just make sure the top of the piston and the block deck are cleaned up first. In taking accurate measurements, the old adage, "Good tools make for good work" holds true.

Adios, David

 

[JackFish]

Um I was really asking how to do it?
0 it on the deck? Then slide sideways...?
Should the dial indicator be centered half-way on the "land" of the piston? They're dished.
Can you tell by looking at a pic what dish size these pistons might have?

http://www.stationwagonforums.com/forums/gallery/files/4/0/9/pistons_original.jpg

 

[CZLN6]

Howdy:

Sorry Jack- Yes, it matters where, on the piston top, you measure. I measure directly over the piston pin location of both sides of the piston. If you measure on the piston edges perpendicular to the lay of the pin, or side to side, piston rock, on an old engine can give you mis-reading. I typically start measuring just inside the notch marking the front location of the pistons. It is important to measure and record everything on disassembly and on pre-assembly, before machining, with new parts. New parts will vary from the old. Oversize replacement pistons typically have less pin height, to compensate for machining. New bearings and tighter pin fit will alter piston height too. You will need to know that amount to be able to do accurate machining.

Q- "0 it on the deck? Then slide sideways...?"

A- Yes, that will work, but do it several time and practice the procedure to get the most accurate readings.

Q- "Should the dial indicator be centered half-way on the "land" of the piston? They're dished."

A- Yes, but this is not critical. Take a reading is several places on the top/non-dished part of the piston. Make sure it is clean.

Q- "Can you tell by looking at a pic what dish size these pistons might have?"

A- Yes, between the big dish, 13cc "Calif Emmissions" low compression and the standard 6.5cc, OEM and replacement pistons. The top landing on the OEM/replacement pistons is about 11/16" wide, well over a half an inch. The C/E pistons landing is about 3/8" wide.

I'm glad you ask for clarification. I hope that's what you needed.

Adios, David

 

[JackFish]

Did some measuring today. I got no more than .023 max and .019 min with measurements taken a few times at spots on the front and back of the piston tops, mid point on the outer ring.

So based on the other specs my comp ratio appears to be on track at about 9:1, give or take a point or two.

 

[mugsy]

When I measured the deck on my engine, I did justas described: "zero" the pointer on the deck then rotate the stand/dial indicator and measure to the outer land portion of the piston. I went one step further and back rotated the stand/dial indicator back and re-"zero"-ed it. When I swung the DI back it was usually off a thousand or two. If I rezeroing it was off by 0.005 or more I threw that measurement away and redid it until I got a lower number.

I also measured 4 positions on the piston: Noon- 3 o'clock- 6 o'clock and 9 o'clock (with Noon being front of the piston towards the water pump) I surprised at the rock that was measured. I was going for a zero deck and needed this info so the pistons stayed away head. Anyway, I forgot what the "rock" measured, but it definetly is there.