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Join Date: Aug 2007
Location: North of Boston
Posts: 163
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Question for engine builders -out of round tolerances
Hi all,
Search didn't really help much -- but I am assessing an 86 block for a DIY rebuild. I know I could simply bring the block to the machinist -- and I will before the actual rebuild -- but I would like to learn how to use measurement tools. So -- I have a theoretical question related to out of round measurement of cylinder bores. Forgive me if the question is dumb -- but I can't figure it out. When measuring the bore -- how do you actually determine the out of round spec? Is it as simple as taking a measurement in line with the crank and then 90 off of that? Then compare the 2 numbers? Or do you take many readings and average the readings? The reason I ask is that I have taken 4 measurements at each level (top, below ridge, middle and bottom) 1 in line with crank, 1 at 45deg to crank, 1 at 90deg and and 135deg to crank. Some of the readings show readings over the .020mm limits -- others are within the .010mm to .020mm spec. The average of all the measurements are within spec on 2 cylinders and slightly over spec with the other 2. (I am not sure if the average tells you anything or not -- not a math guy) I guess the question is this -- how out of round to too out of round? Can 1 point that is out of spec render the whole cylinder out of spec? Has anyone redone a motor with out of round slightly over spec? Thanks for any insight! -Dan C.
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86 944 NA 2.5 |
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04-01-2009, 07:36 AM
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Location: North of Boston
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Crickets ...
nobody? I am surprised a bit.
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86 944 NA 2.5 |
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04-02-2009, 07:30 AM
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Join Date: Jun 2006
Location: O.C. CA
Posts: 4,587
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almost all slanted engines wear "out of round" - if any dimension is out of spec, you need to correct it to have full compression and avoid further uneven and/or premature wear
sometimes on a slightly out of spec bore you can slap in new rings and run for a while, but it will never run "right" and will not last long |
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04-02-2009, 07:42 AM
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Location: North of Boston
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Thanks for the info
Anyone ever run with specs .001mm-.003mm over on taper or out of round specs?
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86 944 NA 2.5 |
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04-03-2009, 03:00 PM
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Join Date: Jul 2000
Posts: 5,732
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I would say that most run .001mm to .003mm out of round or tapered. With dial bore guages, you might catch the .003 but not .001.
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drew1 wife has 924 turbo |
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04-05-2009, 04:58 AM
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