How to measure your cylinder bore (pics)

[JPMartin86]

What you'll need:
Cylinder
Bore Gauge
Digital Micrometer
Pen
Paper
Calculator

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.

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).

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.

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.

 

[blasterboy069]

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 ?

 

[Cochise]

Very helpful post!

 

[NOVIS]

very helpful. i remember doing this in auto clas lol. +1

 

[samolia]

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

other then that good job!!

 

[JPMartin86]

Thank you for the correction.

 

[JPMartin86]

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.

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

 

[mpiller]

Where did you get the bore gauge?

 

[yamahablaster19]

Very helpful post thanks

 

[jus_me]

nice post.. have some green..

 

[barttskyus]

Is just what I need,Thank you very much!Available to download 2004-2013 yamaha yfz450 service repair manual
__________________

service repair pdf manual Download​

 

[AssWild]

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

 

[mustangdave]

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

I was actually wondering the same, im sure i could just look it up but if someone more experienced would help... that would be much appreciated

 

[Blaaster]

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.