Ted68 wrote:The only instance where the clearance may increase would be a gear set. No?
On a crankshaft the bearing clearance is set by the builder. In the valve train there is either the predetermined lash setting or constant contact in a hydraulic system.
How does this compare in practice to dry film lubricants?
In theory gears could also be cut to maintain the same tooth clearance.
It depends on the accuracy of the machinery, which is fine of course at the top level but difficult for ordinary machine shops.
I am unsure also on the availability of shell bearings of the required over sizes in the limited quantities. Very costly and not a big enough improvement in most applications. Of course at the top end a good machine shop could machine accurately enough to bring the journal size to accept available sizes.
In my experience dry film lubricants are only of use for assembly and light load use. For a big V8,the main problem I remember is the large volume in the oil system of the engine that results in semi dry bearings unless proper attention is given to high volume supply at start up as well as during running at high power output. To many bits wizzing round in a big eight to gain much from slightly more efficient bearings. Of course it does depend on the level of modification and tune the engine is up to. Years ago I used to use Vandevell shells in lead indium and close up the clearence by half a thou so as to hold oil better. The reverse on big piston couple of thou extra on the fit with teflon buttons on the skirts and as few rings as possible and non on the skirts. Had some demon perfect circle rings at one time. O ringed head fit of course, upping compression or supercharging takes the power way up on those agricultural yank motors and a high nitro mix plays havoc with those rubbish standard head gaskets.
