Repair and replacement

Damaged Parts.

Abnormal damage such as burrs,nicks, scratches, scoring, or galling should be removed with a fine oil stone, crocus cloth, or any similiar abrasive substance. Following any repairs of this type, the part should be carefully cleaned in order to be certain that all abrasive has been removed and then checked with its

mating part to assure that the clearances are not ex-cessive. Flanged surfaces that are bent, warped, or nicked may be repaired by lapping to a true surface on a surface plate. Again the part should be cleaned to be certain that all abrasive has been removed. Defective threads can sometimes be repaired with a suitable die or tap. Small nicks can be removed satisfactorily with Swiss pattern files or small, edged stones, pipe tapped threads should not be tapped deeper in order to clean them up, because this practice will invariably result in an oversized tapped hole. If scratches or galling are removed from a bearing surface of a journal it should be buffed to a high finish. Generally it is impossible to repair cracks; however, welding operations may be performed in some parts of housings, providing the area is not a stressed section of the part. For example, almost any area of a rocker box may be welded, but no part of the cylinder head except the fins may be welded.

Painted Parts.

Parts requiring use of paint for protection or appearance should be painted in accordance with the following recommendations using material from the following list of approved material. Thinner –Toluene or equivalent (AMS3180 or equivalent Federal Spec. TTT- 548). Primer - Zinc chromate (AMS3110 or equivalent MIL-P-8585). Enamel - Phthalate resin type (AMS315C or equivalent MIL-E-7729).

NOTE

All machines bosses should be masked before painting. Do

not paint areas under hold down nuts where torque is required.

Aluminum and Steel Parts.

Parts shall be cleaned and degreased prior to painting. Apply one coat zinc chromate primer, thinned with approximately two parts toluene, and air dry. Apply one coat of enamel and bake at 250°F., to 300°F., for one-half hour. Enamel may be allowed to air dry but an inferior finish will result. Parts from which paint has not been removed may be repainted omitting the primer coat. 3-30. Magnesium Parts. Magnesium parts should be cleaned thoroughly with a dichromate treatment prior to painting. This treatment consists of cleaning all traces of oil and grease from the part by using a neutral, non-corrosive

degreasing medium followed by a rinse. After which the part is immersed for 45 minutes in a hot dichromate solution (3/4 lbs. of sodium dichromate to one gallon of water at 180°F. to 200°F., quantity as required). The part should then be washed thoroughly in cold running water, dipped in hot water and dried in an air blast. Immediately thereafter the part should be painted with a prime coat

and engine enamel in the same manner as prescribed for aluminum parts. 3-31. Shroud Tubes. Shroud tube should be thoroughly cleaned and dipped in zinc chromate primer thinned to spraying consistency. After the primer is dried the shroud tube should be painted on the outside with engine enamel. 3-32. All paint applied in the foregoing operations should preferably be sprayed; however, if it is necessary to use a brush, care should be exercised to avoid an accumulation of pockets of paint. 3-33. Replacement of Studs. Any studs which are bent,broken, damaged or loose, must be replaced. The method of removing studs depends on the type of stud and manner in which it is broken. The procedure for removing and

replacing studs is as follows:

a. If there is sufficient thread area available on stud, use a collet grip tool consisting of a tapered collet that threads onto stud and a housing that slips over the collet. Tighten bolt on top of the housing and draw collet into housing to lock puller on the stud with a tight

grip.

b. If the collet type tool cannot be used, drill a small hole into the stud. Employ a pilot bushing to guide drill into center of stud when stud is broken beneath the surface of the crankcase. Redrill the hole to enlarge it to accommodate the proper size extractor. Using the extractor, remove the stud.

c. After studs have been removed, check for size and condition of threads in stud holes to determine whether oversize studs must be used for replacement. Coat threads of studs with thread lubricant. Specification JAN-A-669, and drive stud to correct depth by using a suitable stud driver. 3-34. Corrosion Prevention. At the conclusion of all repair operations and subsequent inspection, coat all steel parts

with preservative oil.