Illus 34 Measuring Piston

standard piston or piston of the same oversize to which the cylinder was last refinished should be fitted to reduce clearance and effect reasonably quiet operation.

See "Emergency Piston and Ring Service," Page 87. If, in completely overhauling engine and putting it in like-new condition for a long period of further service, cylinders show more than .002" wear, they should be refinished to the next oversize step and fitted with new pistons.

When refinishing cylinders oversize, first add to standard cylinder bore size the oversize step apparently required to clean up bore; this gives the exact sizes to which cylinder should be refinished; example: 3.3125" (standard bore) plus .020" (oversize) equals 3.3325" (size to which cylinder should be refinished.) Check carefully with accurate micrometers to be sure of refinishing to this size. If this is accurately done, oversize pistons furnished in various oversize steps will fit with normal clearance.

Pistons are regularly supplied in the following oversizes: .005", .010", .020", .030", .040", .050", .060" and .070". Oversize pistons have their oversize stamped on head; for example: 10, 20, etc.

Cylinders can be refinished oversize either with a hone only, or with a boring bar followed by a finishing hone. In general practice only cylinders not scored and not badly worn are refinished entirely with a hone. Cylinders badly worn or deeply scored are first rebored to nearly the required oversize and then are finish-honed to exact size. When cylinders must be rebored to beyond .070" oversize to clean up, their oversize limit has been exceeded and the cylinders must be replaced with new ones.

Valve Guides (O.H.V. Engine)

Clean valve guides with Harley-Davidson special reamer, Part No. 11894-47, and check for wear and valve stem clearance. Standard valve stem-valve guide clearance is .004" to .006". Clearance should not be allowed to exceed .008" before renewing guide or, possibly, both valve and guide.

Valve guides are a press fit in cylinder heads. Therefore, when necessary to remove, press or drive them out of heads. Be careful not to damage valve spring covers when removing and replacing valve guides. Spring covers are held in place by valve guides, and when guides are removed, covers are free. Intake and exhaust valve guides are not interchangeable—top of intake valve guide is beveled; top of exhaust valve guide is flat.

New valve guides are reamed to correct size. However, when guides are pressed into cylinder heads, they may close up slightly; also the ends may be burred. Therefore, after new guides are in place, they should be sized and cleaned up with Harley-Davidson special reamer, Part No. 11894-47.

It is of prime importance that valve guides fit tightly in cylinder heads. If they don't, valves may not seat properly, spring covers will be loose and oil leakage between spring covers and cylinder heads will result. If original guide or new standard guide is not a tight press fit, an oversize guide must be installed. Oversize guides can be obtained .001" and .002" oversize.

After installing valve guides, valve seats must be refaced to true them with guides. See "Valve Seats," Page 47, and "Reassembling Cylinder Heads (O.H.V. Engine)," Page 52.

Valve Guides (Side Valve Engine)

Clean valve guides with Harley-Davidson special reamer, Part No. 11894-30, and check for wear and valve stem clearance. Standard valve stem-valve guide clearance is .003" to .0055". Clearance should not be allowed to exceed .008" before renewing guide or, possibly, both valve and guide.

Valve guides are a press fit in cylinders. Therefore, when necessary to remove, press or drive them out of cylinders (see Illus. 36). Intake and exhaust valve guides are interchangeable.

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