Opinions on Bearing Oil Clearances

[randy]

Been gathering parts for a winter teardown and was about to shop for plastigage so I looked up the clearances in the manual. Lo and behold, this is what I found:

78E manual:

Rod .0013 - .0021 in
Main .0009 - .0017 in

79F supplement:

Rod .0017 - .0025 in
Main .0014 - .0023 in

Now, I know the bearing sizes never changed, so either Yammy decided that the clearance could be a bit more generous or ....... or what?

Anyone notice this before? I don't recall ever seeing anything about this in the forum.

[DGXSER]

Strictly guessing, but if they truly developed the 78 to be the MOST powerful model. They may have determined that when they "detuned" in 79 they did not need as tight of clearances due to less forces.

[Ivan]

Oil clearance tends to be a whole bunch of voodoo.

Generally if you shoot for .001, you'll be ok. Now if you run a big block with a high volume oil pump and set the bypass valve too tight, you may want to open up those clearances or twist the drive off.

The higher clearance may not carry as much pressure at low engine speeds, but that is when there isn't a terrible high amount of force on it anyway.

[trbig]

All I can think of, is since '78 was the first run, first try... after speaking to mechanics and such during the year it was out, they came back with the 2nd set of numbers. The second set of numbers you see are the same clear on out to the XJ.


Tod

[crazy steve]

As a good bit of heat is carried away by the oil, maybe they figured getting more in there to remove more heat was good....

'78E original owner