POWERHEAD
90-826883R2 JUNE 1998 Page 4-25
STANDARD CYLINDER BORE DIAMETER
20/25/20 JET BORE TYPE STANDARD BORE DIAMETER
ALL MODELS S/N OG202749
AND BELOW
The cylinder bores are chrome
and cannot be rebored or effi-
ciently honed. Check each cylin-
der bore for an out-of -round
“egged shaped” cylinder. A maxi-
mum of 0.003 in. (0.076 mm) is
allowable.
2.562 in. (65.01 mm)
ALL MODELS S/N OG202750
AND ABOVE
The cylinder block is Mercosil
and the cylinders can be rebored
to 0.030 in. (0.762 mm) over-
sized. Check each cylinder bore
for an out-of-round “egged
shaped” cylinder. A maximum of
0.003 in. (0.076 mm) is allow-
able.
2.562 in. (65.01 mm)
HONING PROCEDURE
a. When cylinders are to be honed, follow the hone manufacturer’s recommenda-
tions for use of the hone and cleaning and lubrication during honing.
b. For best results, a continuous flow of honing oil should be pumped into the work
area. If pumping oil is not practical, use an oil can. Apply oil generously and fre-
quently on both stones and work area.
CAUTION
Whenhoningcylinder block,remove honefrequently andcheck conditionof cyl-
inder walls. DO NOT hone any more than absolutely necessary, as hone can re-
move cylinder wall material rapidly.
c. Start strokingat smallest diameter. Maintain firm stone pressure againstcylinder
wall to assure fast stock removal and accurate results.
d. Localize stroking in the smallest diameter until drill speed is constant throughout
length of bore. Expand stones, as necessary, to compensate for stock removal
andstonewear.Strokeatarateof30completecyclesperminutetoproducebest
cross-hatch pattern. Use honing oil generously.
e. Thoroughly clean cylinder bores with hot water and detergent. Scrub well with a
stiffbristlebrushandrinsethoroughlywithhotwater.Agoodcleaningisessential.
Ifanyoftheabrasivematerialisallowedtoremaininthecylinderbore,itwillcause
rapid wear of new piston rings and cylinder bore in addition to bearings. After
cleaning, bores should be swabbed several times with engine oil and a clean
cloth, then wiped with a clean, dry cloth. Cylinders should not be cleaned with
keroseneorgasoline.Cleanremainderofcylinderblocktoremoveexcessmateri-
al spread during honing operation.
3. Hone all cylinder walls just enough to de-glaze walls.
4. Measure cylinder bore diameter (with a snap gauge micrometer) at top, middle and
bottom of each cylinder. Check for tapered, out-of-round(egg-shaped) and oversize
bore.
IMPORTANT: Ports must be deburred after honing.
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