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2. A pretensioned drive is not detrimental to both chain and
shaft bearings. However, excessive slack is also harmful due to
chain whip and possible tooth disengagement.
3. Worn sprockets should be replaced, if possible, or
reversed so that the chain is not hooked by work teeth.
4. The general maintenance lubrication procedures
mentioned in regard to roller chains are applicable to silent chains.
5. V-belts are not driven by the action of the sheave grooves
upon the sides of the belt.
6. V-belts should never be run on or forced over sheaves.
7. Used belts which are still serviceable should not be
matched to make full sets.
8. Provision should be made for applying tensions either by
adjusting the center distance or by the use of idlers.
9. Wide and narrow grooves resulting from poor machining
or uneven wear in service will not result in "differential driving"
and reduced belt life.
10. Gears are used most where compactness of design, quiet
operation and large speed variations and ratios are required.
11. The herringbone gear is actually a double helical gear cut
together so that the end thrust obtained with a helical gear will be
cancelled out.

Exercise 4. Fill in the gaps
1. Two typical applications of roller chain are seen in Fig. 8-5
where a double strand of 2-in. pitch chain is used as a ____________
drive within a selective transmission and a single strand of motorcycle-
size chain is used to drive a __________ pump.
2. Some designs now introduce the lubricant into the
__________ through the shaft and thence out the root diameter of
the sprocket into the chain.
3. Actual lubrication is extremely important to good
__________ and the recommendations of the manufacturer should
be followed as closely as possible.

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