krede Posted March 24, 2009 Report Share Posted March 24, 2009 I am trying to determine whether I need to re-drill the bores on my project engine. From the look of them there are no scratches dips etc. so I figure the only thing left to check it if the bores are worn "oval" or not. Now.. I have a cylinder bore dial gauge for this (first time I try it out) but I have no idea hos much difference is acceptable ?? Quote Link to comment Share on other sites More sharing options...
Pugsley Posted March 25, 2009 Report Share Posted March 25, 2009 I am trying to determine whether I need to re-drill the bores on my project engine. From the look of them there are no scratches dips etc. so I figure the only thing left to check it if the bores are worn "oval" or not. Now.. I have a cylinder bore dial gauge for this (first time I try it out) but I have no idea hos much difference is acceptable ?? I don't know the specs on the N9t , but a general rule of thumb is .004"-.005" for most engines. Quote Link to comment Share on other sites More sharing options...
Bean Posted March 26, 2009 Report Share Posted March 26, 2009 Looking at the FSM they don't give any variance measurement for the bore. On the exhaust side of the block it looks like there should some "cylinder bore class" markings near the cylinders. (A, B, C, D) Depending on what std bore class it has determines the measurement. All it says for the measurement is that it needs to be measured 40mm from the headgasket plane. For the standard bore: A - 91.692 to 91.699 B - 91.700 to 91.707 C - 91.708 to 91.714 D - 91.715 to 91.722 So it looks like if you ever got used pistons to repair an engine - you'd need to match them from another engine that had the same cylinder bore class. If your numbers are higher - they give over bore specs for 0.10+ and 0.30+ I'll post those numbers up if you need them. BTW - there's also ranges for the piston measurement if you need those as well. Wish I had a scanner hooked up - I'd just scan the pages for you. Rabin Quote Link to comment Share on other sites More sharing options...
krede Posted March 26, 2009 Author Report Share Posted March 26, 2009 Thanks for the replies guys. Rabin: Dont bother with the scanner.. I have a workshop manual myself .. But to be honest... measuring 1/1000 of a millimetre with any degree of accuracy is well beyond my capability with the tools and knowledge I have. My bore gauge has a range of 0.01 mm..as do all the dial gauges I've come across so that will have to do. I plan to measure the bores at the bottom where they should be completely unworn and use this as the "zero" value. then compare these readings to the ones from higher up the bore (yes my manual says 4 cm from the top too), so that is why I am mostly interested in the maximum allowable deviation from then "cross" measurements Quote Link to comment Share on other sites More sharing options...
Pugsley Posted March 29, 2009 Report Share Posted March 29, 2009 Thanks for the replies guys. Rabin: Dont bother with the scanner.. I have a workshop manual myself .. But to be honest... measuring 1/1000 of a millimetre with any degree of accuracy is well beyond my capability with the tools and knowledge I have. My bore gauge has a range of 0.01 mm..as do all the dial gauges I've come across so that will have to do. I plan to measure the bores at the bottom where they should be completely unworn and use this as the "zero" value. then compare these readings to the ones from higher up the bore (yes my manual says 4 cm from the top too), so that is why I am mostly interested in the maximum allowable deviation from then "cross" measurements Remember 1 MM = .03937 " inch if your tools are not metric Quote Link to comment Share on other sites More sharing options...
krede Posted March 29, 2009 Author Report Share Posted March 29, 2009 Remember 1 MM = .03937 " inch smile.gif if your tools are not metric Indeed Quote Link to comment Share on other sites More sharing options...
krede Posted April 4, 2009 Author Report Share Posted April 4, 2009 Right... just took my dial gauge to the cylinderbores. I found that the greatest deviation measuring "across" the same cylinder is 0,04mm just below the "charred" ring at the top of the cylinders. The difference from top to bottom measurements doesn't amount to more than 0,002mm To me these deviations don't justify the expense of re boring and fitting new pistons... But if anybody has a different opinion.. please speak up before I put the engine back together Quote Link to comment Share on other sites More sharing options...
V-M Posted April 4, 2009 Report Share Posted April 4, 2009 New rings is enough, and light honing needed to get ring fitting. V-M Quote Link to comment Share on other sites More sharing options...
krede Posted April 4, 2009 Author Report Share Posted April 4, 2009 Thanks VM.. I'll see if I can get it honed tomorrow... Then I will start hunting for piston rings on monday Quote Link to comment Share on other sites More sharing options...
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