Figrue 8-4. Borescope instrument

Figure 8-6. Borescope instrument in position

for cylinder bore inspection.

(6) Connect borescope control transformer

( f i g . 8-4) in 110 volt electrical circuit and insert

b o r e s c o p e into cylinder (fig. 8-6), Visually adjust

light intensity and mirror angle until a sharp

clean image of the cylinder bore is apparent.

I n s p e c t i o n of the cylinder bore should be made

a t three levels, lower, middle, and upper position

o f the cylinder to assure maximum coverage of

the cylinder wall surface. Polish marks the

length of the piston pin travel may be evident on

the cylinder side walls on a line parallel with the

cylinders. These lines normally are not serious

and are caused by the movement of the piston

pin allowing the pin end plugs to come in contact

w i t h the cylinder walls. Other wear lines, surface

scratches, and wear patches that are not con-

t i n u o u s the full length of the cylinder bore are

usually not significant.

(7) A normal shiny area will often appear at

midbore and usually on the anti-thrust side of the

bore (below exhaust valve on left bank and

below intake valve on right bank). This shiny

area will not extend the full length of ring travel

a n d should not be confused with scuffing of the

cylinder wall.

( 8 ) Cylinder bores that show evidence of

in. or more scuff marks, must be replaced. Re-

hone cylinders and thoroughly inspect (para 6-

31 and 6-32), dimensionally check and clean

thoroughly before reinstalling cylinders on

Figure 8-5. Checking piston position

engine. R e p l a c e m e n t c y l i n d e r s w i l l r e q u i r e

with brass rod.

8-9