How to measure your cylinder bore (pics)

JPMartin86

New Member
Apr 14, 2009
173
6
0
Worcester
What you'll need:
Cylinder
Bore Gauge
Digital Micrometer
Pen
Paper
Calculator

CIMG5157.jpg


You'll use the bore gauge to find the width of the cylinder as shown in the picture. Make sure the bore gauge is level then tighten the lock.

CIMG5159.jpg



You will measure 3 spots; Top being (x), Middle being (y), & Bottom being (z) of the cylinder. Each spot will be measured in 3 different angles. Each color represents a different angle
Red being (1), Blue being (2), Yellow being (3).

crisscross.jpg


After you have tightened the bore gauge use the digital micrometer to measure the bore gauge. Its good practice to zero out the micrometer before measuring. Make sure to write down each measurement.

CIMG5160.jpg


For example my measurements are:

X1 - 66.39mm
X2 - 66.45mm
X3 - 66.46mm

Y1 - 66.38mm
Y2 - 66.48mm
Y3 - 66.43mm

Z1 - 66.47mm
Z2 - 66.42mm
Z3 - 66.46mm


The reason you have measured the bore in 3 spots at 3 different angles is (a) to get the average bore size and (b) to find the cylinder taper. The math to find your average bore size of each "spot" is:

X1+X2+X3= 199.3 ÷ 3 (the # of times you measured the "spot") = 66.43mm

66.43mm will be my average for the (x) measurements.

You can then do the math of each "spot" average to get an overall bore size.

(x average) + (y average) + (z average) = 199.31 ÷ 3 = 66.44mm



The Blasters stock bore is 66mm. As you can see my cylinder is worn out pretty good, and i will need to have it bored out to 66.5mm. Here is a chart to figure out what your next bore size will be and what piston/rings to purchase.

66.0mm - .000 bored over
66.5mm - .020 bored over
67.0mm - .040 bored over
67.5mm - .060 bored over


I am not a professional engine builder or a master mechanic so if there is any wrong information here please let me know and i will correct it immediately.
 
Last edited by a moderator:
only one problem with the post thats not a micrometer that a digital vernier caliper..

a micrometer looks like a C-clamp and are much better for what your doing..IMO
B1p2.gif


other then that good job!!
 
I would like to rebore my engine to a wiseco over .060. how do you rebore it ? do you have to polish it after or ?

You probably cant do it yourself. You would need a cylinder boring machine like this one.

Rte_750_Cylinder_Boring_And_Surface_Milling_Machine.jpg


After its bored you do not polish it, you will need to hone the cylinder to a "cross hatch" as seen in this pic.

0508_Crosshatch_sunnen.jpg
 
Im putting a .020 over kit in my blaster and machine shop asked me what piston or rings clearan es are are pls help

Give the shop the piston, and if they are any good they will know what tolerances to bore to.

If they do not know, take it to a shop that knows what they are doing.