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Stroke Measurement
https://slantsix.org/forum/viewtopic.php?t=54009		 Page 1 of 2
Author:  63dartdude [ Thu Dec 05, 2013 1:08 pm ]
Post subject:  Stroke Measurement
Okay, when I asked about the compression ratio, I was insisting on 4.250 as the stroke, and was told I was probably measuring wrong, and it should be 4.125. So I bought a digital caliper. And look at my cylinder 6 photos.


Image

Image

What am I doing wrong? The number 1 cylinder where I previously said 4.250 came in on the digital caliper 4.279. Cyl 2 was 4.288.
Author:  Fopar [ Thu Dec 05, 2013 1:20 pm ]
Post subject: 
Measure at TDC then measure at BDC, subtract TDC from BDC that will give you the stroke.

Richard
Author:  63dartdude [ Thu Dec 05, 2013 1:26 pm ]
Post subject: 
Thanks Richard. 4.318 minus the .233 equals 4.085. Can I assume I just have one of these measurements wrong, and it is 4.125?
Author:  Fopar [ Thu Dec 05, 2013 2:51 pm ]
Post subject: 
Sounds reasonable. You might recheck.

Richaes
Author:  63dartdude [ Thu Dec 05, 2013 3:10 pm ]
Post subject: 
Thanks. And I will find a buddy to help me. Turning the crank, and holding that device could be part of my problem in accurate measurements. But you got me straight on the stroke math anyway.
Author:  CNC-Dude [ Thu Dec 05, 2013 3:24 pm ]
Post subject: 
You will get a more accurate reading in the center of the cylinder between the bores or at the front and rear. The piston rocks where you are checking it and can give you some inaccuracies.
Author:  63dartdude [ Thu Dec 05, 2013 3:56 pm ]
Post subject: 
Sounds good. So basically find a ruler or something like that, and place it over the cylinder. Then use the caliper off of that. Then measure the depth of the ruler, and subtract that. That sounds pretty easy to try out. Thanks.
Author:  Mike'68Dart [ Thu Dec 05, 2013 4:23 pm ]
Post subject: 
225 slants do not come all the way to the top of the cylinder bore, you need to measure, as you are doing, and get figures with the piston at TDC and also at BDC. The difference between those readings will give you the true stroke.

The different measurements you got from #1 and #6 could have been carbon build up or acceptable tolerance at initial machining of the block, crank centerline vs top of block.

My block has about .002 deviation from #1 to #6.

Mike
Author:  63dartdude [ Thu Dec 05, 2013 4:32 pm ]
Post subject: 
You called it - carbon build up. I will be replacing the pistons, since they will be removed for the block milling. Which I hope to do next month. I know that will impact my compression ratio. But after I put in the pistons, I will measure again, and adjust it with the head milling.
Author:  CNC-Dude [ Thu Dec 05, 2013 11:16 pm ]
Post subject: 
Quote:
Sounds good. So basically find a ruler or something like that, and place it over the cylinder. Then use the caliper off of that. Then measure the depth of the ruler, and subtract that. That sounds pretty easy to try out. Thanks.
No, just move your calipers 90° to the left or right from where you show in the pics and measure using the deck as the stop like you are there.
Author:  63dartdude [ Fri Dec 06, 2013 1:04 pm ]
Post subject: 
I started doing the measuring but thought it looked too deep. I looked at the piston, and in the center there is a hole that it was going into. So I changed over to the other side, and got more like what I thought it would be .


Image

Which side should I do it on?
Author:  robertob [ Fri Dec 06, 2013 2:31 pm ]
Post subject: 
If you do it at the front and back there is less piston rock (in-line with the pin).
Author:  emsvitil [ Fri Dec 06, 2013 3:23 pm ]
Post subject: 
Quote:
If you do it at the front and back there is less piston rock (in-line with the pin).
If you have piston rock front to back you've got problems.............
Author:  robertob [ Sat Dec 07, 2013 12:11 pm ]
Post subject: 
Quote:
Quote:
If you do it at the front and back there is less piston rock (in-line with the pin).
If you have piston rock front to back you've got problems.............
Not necessarily - a few hundred thousand miles of running and there is enough clearance at the big end and in the piston pin bores that it can add up to .005-.010 of rock in the "wrong" direction.
Author:  CNC-Dude [ Sat Dec 07, 2013 9:20 pm ]
Post subject: 
Quote:
Quote:
Quote:
If you do it at the front and back there is less piston rock (in-line with the pin).
If you have piston rock front to back you've got problems.............
Not necessarily - a few hundred thousand miles of running and there is enough clearance at the big end and in the piston pin bores that it can add up to .005-.010 of rock in the "wrong" direction.
I think the problem he's indicating is that your junks worn out if you have front to back piston rock.....you don't see that as a problem?
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