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Engine Bearings

By holding the dimensional tolerances of the bearings, seats, and crankshaft to close limits such as .0005 the interchangeable type of bearing permits replacement of upper or lower bearing half without any hand fitting whatever.
The methods of manufacture utilized in building the inter-changeable type bearing to the fine degree of accuracy demanded are controlled by patents in some cases. Two large bearing manufacturers, the Federal Mogul Corp. and Bohn Metal Co. supply several car and engine manufacturers, while a few of the ear manufacturers, such as Marmon and Oldsmobile, build this type of bearing for their own use in their own plants.
Fig. 10D. A typical crankshaft main bearing
Oil grooves in bearings have received considerable study in recent years, and the choice of the majority of the manufacturers has been concentrated on a few well-worked-out designs which have replaced the many fantastic and almost useless designs of former years. Oil grooves are omitted on most pressure systems.
Two types of oil grooves which are widely used are shown in Fig. 11.
Fig. 11. Two easily produced and efficient types of oil grooves in the bearing halves. The shimless connecting-rod bearing is always made for pressure lubrication and is usually grooveless.
Efforts to secure permanent anchorage of the bearing halves in the cap and crankcase have led to the adoption of cast-in or integral bearings in many cases. Approximately 96 per cent by numbers, of American passenger car engines use lower connecting-rod bearings of the cast in babbitt type.
Another method, commonly used to prevent rotation of the bearings, utilizes shims that are wide enough to exert a pressure on the bearing half, when the cap is drawn down.
Locking screws which secure the bearing to its seat are also widely used either without the retaining type of shim or in conjunction with it.
The S. A. E. standard babbitt metals and certain proprietary combinations are widely used for the connecting rod and main bearing lining, and when in doubt as to the most suitable metal, the maintenance operator will make no mistake in specifying S. A. E. metal.
Bearing Fitting Methods
There are six general methods of bearing fitting used among the American car and engine manufacturers, as follows:
1. Bore or fly cut, and line ream only, on the main bearings.
Bore, broach' and line ream only on the connecting-rod bearings.
I Broach is a method of bringing to size either a square or circular orifice by means of a cutting tool of the non-rotating type; for example, most all connecting-rod lower ends are finished by broaching at the factory and broaches also are used on piston-pin bushings. Some of the concerns who make broaching machines or broaches are J. N. LaPointe Co., New London Conn., The Cutter-Wood Supply Co., Boston, Mass., Sheldon Machine Co., Chicago, Ill., Connecticut Broach and Mch. Co., New London, Conn.
The hand scraper is used only to touch up the ends or fillets of the rod and crankshaft bearings.
Connecting-rod bearings are given a burnishing operation to impart final finish.
This method has more adherents among manufacturers than any of the other five methods conunonly used. It is used by five of the large engine companies, including such firms as Buda, Continental, Falls, Waukesha, and Wisconsin. Of the 16 car manufacturers, whose bearings are fitted in this manner, 4 are in the over $4,000 class.
2. Bore or fly cut and line ream, followed by hand scraping for surface finish on the main bearings.
Bore or broach, ream, and finish surface by hand scraping on connecting rods.
Three of the firms which manufacture their own engines and use this method are in the over $4,000 class.
One engine manufacturer is included in the list of 13 adherents to this method.
3. Bore, or fly cut, followed by hand scraping, no line reamer being used on the main bearings.
Bore or broach followed by hand scraping only, on the connecting rod bearings.
Two car manufacturers and one engine manufacturer are listed as using this method.
4. Main and crankshaft bearing holes with caps installed are rough bored, then semi-finished bored, leaving about .008 for finishing cut, which is done with single point tool having a diamond insert.
Bearing shells are installed in finished holes (no liners or shims being used) in cap and case.
Caps are bolted down, and are finished cut by same process using single point diamond insert tool.
The same method is followed with the connecting rods except that the rod holes or bearing seats are ground to a specified diameter instead of being bored; the joint faces of rod and cap are then lapped to form the joint.
The bearing halves are inserted and finished in a fixture with a single-point diamond insert tool.
Two car manufacturers, both in the over $3,000 class, use this method. Very similar to method No. 5. Bearings may be replaced in the field without hand fitting.
5. A method which combines some of the features of the four methods mentioned, except that the hand scraper is not used on the bearings themselves, al-though the bearing seats are sometimes hand scraped.
The first operations consist in preparing the seats or holes in the case and lower end of connecting rods.
It is necessary that the case and rod holes be accurately finished, and for that reason several different methods are being used at present.
The holes or seats for bearings are either bored, line reamed, fly cut, or ground.
Some firms line-ream and hand scrape the case holes; another firm grinds these holes, and a third manufacturer uses the single-point diamond insert tool.
The bearings are made by a special method and are held to very close tolerances, especially the inside and outside diameters.
After the case holes have been finish-machined, the bearings are installed and the crankshaft is bolted down permanently.
The bearing halves that permit this method of bearing fitting are of what is known as the inter-changeable type. It is said that replacement of this type of bearing in service work is accomplished

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Carburetor Manuals: Engine Bearings