I have a inside micrometer in .001 graduations. I have a telescopic gauge and a 3-4 inch micrometer in .0001 graduations.

I measure a new stock LS6 block and I get 3.897 with the micrometer. I use a telescopic gauge and measure that with the micrometer and I get 3.8971. I guess I am measuring correctly.

If that is true then would a stock LS6 that has not been honed (I don't see the cross hatch pattern just a nice circular pattern) measure at 3.897? I thought the advertised size on the LS6 block was 3.900.

 

GM calls for a 3.8976-3.8983 (99.000-99.018mm) bore in the service manual.

At what point in the cylinder are you measuring? The bores will be slightly out-of-round without a torque plate installed.

The telescopic gauges are good for measuring most things, but a high-quality dial-bore gauge would be preferred for an accurate measurement of the cylinder bores.(Sunnen,etc.)

Jason

 

I am measuring about .5-1 inch below the deck. I am trying to decide what bore gauge to get so I can be more accurate. I am leaning towards a peacock brand in .0001 graduations. I know there are better out there but I won't be building engines that frequently.

So, it sounds like I am close in my measurement and the values I have are within spec and there is to be some variation in the bore size from the factory? I read from you message I might be under in my measurement but that could be due to my lack of skill at taking these measurements.

I am just trying to make sure I have what I think I have for a block so I can order pistons (casting number is correct). The size for the LS6 after market pistons is suppose to be 3.903 to 3.905 and I want to make sure I was OK to order in those sizes.

 

measure the bore at 0 and 90 and top middle and bottom of the bore.
then compare your #'s
you SHOULD be within a .0005 of the true measurement if you dont mike all the time.
are you measuring over the id mike w/ your o.d. mike, thats the way to do it.
dont trust the numbers form the id mike alone, they will be off!!
i mike stuff all the time to the .0001 of an inch.
miking over the i.d. mike is the preferred method over the telescoping gauge.
bore gauges rule if you have alot of parts that are the same size, cyl block for example. just check each measurement three times and see if they are within +-.0002"
i would definately invest in a bore gauge!

 

most miking errors from what i've seen training guys usually indicate a number smaller than the actual measurement

 

I used the telescoping gauge and the internal mike and I verified my findings with the outer mike. This is my first time miking so I could be off for sure. I did get a set of standards from 1 to 5 for sanity checks. I think my mikes are correctly zeroed out. I will try again when I get a bore gauge.

Regarding training: any place on the block or any part that would be good to mike to perfect the skill? Where the measurement is pretty well known - block is new.