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SERVICING 191+8 OVERHEAD VALVE ENGINES FOR B:ST OIL CONTROL AMD OIL MILEAGE

Anything above 250 miles per quart of oil is considered normal oil mileage In any case where oil mileage may be reported considerably below 25O miles per quart don't jump to the conclusion that piston rings or cylinder bores or booh are in bad order, ana tnat the reported heavy oil consumption must b& due to exressiv» oil passing rings into the combustion chambers and out with the exhaust. There are otnsr reasons for abnormal oil consumption.

sing through ons? or both combustion chantsrs, and an engine top h- .!•«)» Co determine why. If thfcre is (k> evidence of heavy excessive oil is pns end job will have tc sing through ons? or both combustion chantsrs, and an engine top h- .!•«)» Co determine why. If thfcre is (k> evidence of heavy excessive oil is pns end job will have tc exhaust smoke or plug fouling, but nevertheless you confirm the report of oil mileage considerably below normal, it nay b:- due to one or more of the"conditions described in thD following three paragraphs, in which case engine probably will not need to be opened ur for internal inspection.

Mayoe front chain oiler is adjusted to feed an excessive amount of oil, and possibly motorcycle has also boon equipped with a rear chain oiler as supplied by various accessory producers. A combination like this, sot for excessively heavy fe-ed, can account for as much e.s 50$ of the oil used..

Possibly oil pump check valve ball is uot seating perfectly, and oil is being lost to the outside through breather when motorcycle is standing for any length of time,

Possibly considerable oil is being wasted due to a leak somewhere about engine as a result of a sandhole in one of the castings, a broken or damaged gasket or push-rod cover seal, or loosened fittings.

Where investigation proves that low oil mileage is due to an excessive amount of oil passing through combustion chambers and out with the exhaust, proceed as follows with an upper and job.

1. When removing cylinder heads, carefully inspect head gaskets around the holes that match the oil passages that feed oil to the overhead fittings, and drain back the discharged oil. If you find a break or furrow between one of those holes and the inside diameter of gasket, this alone is enough to account for excessive oil consumption,, plug fouling, and heavy'exhaust smoke. Unless gaskets are in perfect condition and form .a perfect seal around these holes, the combustion chamber of the cylinder involved will be flooded with oil. Also examine cylinder head joint face around these holes. If the joint face between one of these holes and combustion chamber has been nicked or deeply scratched, the result will ta the same as with gasket damaged as described above.

Also examine cylinder base gaskets as cylinders are removed. Observe whether or not gaskets are in good order around the hole punched for oil passage up the right side of cylinders. A break in base ga«ket from this hole inward is likely to result in the oiling system running lower than normal pressure, and an ovar supply of oil in crankcaae.

2. Remove eylinder head covers and stake a close inspection of rooker arms. 0b6«Yd particularly that welch plugs (one in eaeh end of arm) axe securely in place. If an arm is found with a welch plug out, be sure to find the plug, as It may be lodged somewhere in the oil return channel down the left side of head and cylinder. Unless found and removed, it will probably eventually shift Into a position where it completely blocks the return channel. In this case the cylinder head will be flooded with oil, and the Job of removing cylinder will have ^o be done over again in order to remove the obstruction. Vhere a weloh p^ug has eome out of place, it can be reinstalled by soldering or braaing, A welch plug that appears to be even slightly loose should be treated in the s&me manner^ as a &issing or badly leaking welch plug will drop overhead oil pressure 60 low, especially when oil is hot, that pushrod hydraulic units will become noisy. >o7t number? covering rocker arm welch plugs are: Large plug 109-UgA, Small plug 109-Ug. (Latest rocker arms which went into new assembly near the end of the l^^S season have no welch plugs. Only one end of the arm requires pluggi.'-g, and a solid, drive fit plug is installed. Only rocker arms of this construction are now supplied on parts order.)

Also inspect rocker arms for loosened or broken pushrod ball socket. A ball socket in bad order may also bleed av;sy enough oil so that pushrod hydraulic unit6 do not get the oil required for normal aui*itness of operation. (The pushrod ball socket has been so changed o.vi strengthened that thero will probably be little if any breakage in the future. This item is still net supplied on parts order, even though it is listed in th« part«- catalog, Th-irs will o? further word at a later d^ts in regard to thopssilulity of dealer servicing of arms with broken or damaged ball socket,)

3. The next st?p is checking cylinder heads for pu3s:*.ble oil leak from the top of head into tao intake port. There is considerable oil discharged from overhead fittings onto fop of head, and if there is a lssk; through the head into the intake port, due possibly to a loose valve guide or a sand hole, some of this oil will be sucked thro-ugh into inlet port and combustion chamber. Enough will be sucked through to cause plug fouling, heavy exhaust smoke, and to drop oil mileage way below normal. In other words, t'.^e result will be the same as if rings and cylinder boras wero in baa order. • This check should be made by applying air pressure to intake port and at the same time applying gasoline or solvent to top of head around valve guide and the surrounding area above inlet port. If there is a leak around valve guide or elsewhere it will be indicated by bubbles. Even the slightest leak found must be corrected. If thore should be a leak around inlet valve guide, due simply to guide fitting loosely in head, it probably can be serviced satisfactorily with an oversize guide. Oversize valve guides are listed in parts catalog. If, however, it is found that guide hole in head is out of round, there is no satisfactory repair, When a new oversize guide is installed to replace one found with a lerk by i^, repeat the air test after new guide is installed, even though it does seem to drive in with a normally tight fit. If hole in head is out of round, guide may drive in tight, but still have a leak by it. A sand hole through head into intake port can usually be repaired with low temperature welding material.

A 6et_ of fittings with which a dealer can make a auick air pressure check for inlet port leakage is in the making, but not yet available. As soon as these fittings are available, you will be advised through a supplementary bulletin. In the meantime you can devise a temporary means of making this check. All you need is a plug or cork of a size to fit cylinder head inlet nipple. The plug must have a small pipe installed through it, so that air pressure can be applied. With inlet valve assembled and plug pushed tight into inlet nipple, apply air pressure and at the same time apply gasoline c: solvent to the top of head around valve guide.

The exhaust valve guide should also be tight in head. However, if there happens to be a minor leak by it, thore would bo little if any effect on oil comsumption.

U. Next check cylinder bores and pistons for size and general condition. If it is found that cylinder bores are not enlarged enough, due to wear, to require refinishing oversize, make another extremely close inspection of the bore of each cylinder, to be sure that tho ring path is smooth and polished as it should be,with only minor up and down scratches where the piston thrust faces take bearing against cylinder bore. If the ring path in one or both cylinders has a dull, lapped appearance, tnis indicates that there are probably a multitude of fine scratches the length of ring path, all around the bore, as a result of ring scuffing. If this condition exists, bore should be refinished oversize. Simply re-ringing a scratfched bore, even though the new ring set includes the most effective type of oil ring, is not likely to effect a satisfactory oil seal. Bear in mind that there is a difference between scored cylinder bores aid scratched bores. Scoring, which results from high speed or overheated operation, is damage that can't be overlooked and leaves no choice about refinishing. Bore scratching to the extent of excessive oil passing, even with new rings, is not so readily observed. Take no chances on cylinder bore condition. Unless the bore is unquestionably smooth and shiny, except for minor streaks or scratches where piston takes bearing against cylinder bore, refinish.

5. The new piston ring combination to be used on each piston is two No 265-compression rings for the 6l O.K.7. or two 265-41 compression rings for the 74 O.H.V. A new type vented oil ring is to be used, Part No. 22374-1*9 for the 6l 0 H V or Part No. 22364-1+9 for later I9I+8 74 C.H.V. Since the new type oil ring is 3/16" wide it cannot be used on the earlier 1948 - fk O.H.V. piston, because that piston had an oil ring groove only 1/8" wide, later 1948 - 7^ O.H.V. pistons have oil ring groove 3/16" wide. This change went into production with engine i'o. 4SiX 10184. All parts order pistons now furnished for tho 1948 74 0. H. V. of course, have the wider oil ring groove.

_ When servicing an early 1948 - 7U O.H.V. equipped with pistons with 1/8" oil ring groove, which are still in condition for further use, use vented oil rine 266-UlA, which is 1/8» wide.

All of the piston ring numbers shown above cover standard size rings. In the future when pistons or rings are ordered, according to information in Parts Department letter of July 12, covering pistons and rings for 1948 O.H.V. models, instead 01 furnishing four rings, all alike, -Der piston, the new combination of two compression rings and one 3/16" wide vented oil ring per piston will be furnished.

For sometime the 3/32" wide compression rings furnished for 1948 overhead engines (also apply to earlier than 1948 74 O.H.V.) have been bevel backed rings.

i/^dn™f..rlne haS th0 iQner edge bev3l0d. This side of ring is or should be marked TOP . This type of ring must be installed in piston with the beveled edge upward, whether or not that side is marked "TOP". If installed with beveled edge downward, this type of ring becomes an oil pumper.

6. The next step ia to convert the oil pump as follows:

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