#8 nose bearing

kent olsen · kent olsen's Garage

Just curious, Waynes book doesn't list the #8 nose bearing as a must replace component. However it looks like that is a common place for oil leaks.

I'm coming to that point in my 3.0L rebuild. Our host sells it for about $230. It didn't come with the main bearing set I purchased?????

Mine has a little wear on one portion, is that caused by the weight of the crank? Although this engine had a turned main bearing and I don't know how long it ran like that, could that have caused the wear spot on the #8 bearing?

Kent Olsen

cgarr · cgarr's Garage

Your rods get oiled from oil being fed from both ends of the crank and if you have a bad nose bearing you can loose a lot of oil to the rods, I would replace it as part of the rebuild.

Flat6pac · 08-21-2009, 12:52 PM

How can you have a bad nose brg because its immerced under pressure and oil 100% of the time.

matt demaria · 08-21-2009, 05:24 PM

Your rods get fed by the nose bearing only. Any extra clearance here robs the rods of oil. As crank spins, it wobbles and beats out the bearing on the inside and beats the nose bearing into the case. Eventually all the main bearings loose their actual centerline. This is one of the reasons for line boring.

Eagledriver · 08-21-2009, 06:27 PM

The wear spot is usually from the tension on the fan belt. It pulls the crankshaft up and wears the top of the bearing. You have to decide how much it has worn and if it needs replacing. I've never replaced one in the 3 rebuilds I've done and the 2 others I've assisted on.

-Andy

Walt Fricke · 08-22-2009, 08:20 PM

This bearing is usually not replaced. It just doesn't see the wear the others do. That's why main bearing sets don't include it.

If you have a case line bored (without cutting the joining surface so you can rebore to standard), you really want to be sure that the #8 is not also bored, as oversized ones are hard to come by. I have trouble imagining a case pounding out at this bearing's location. Hard to see a crank bent enough to do that living long enough to do so. If it did, I'd wonder about using the case at all.

Ditto with having a crank ground - leave #8 alone.

Look for the cost/availability of a 1st under/1st over #8.

Sure, if it doesn't spec out, it needs replacing. But measure carefully if you are worried about this.

External leaks here are not due to bearing wear, at least not on my engines. They are due to a bad seal or bad seal installation, or not using the newer style slightly fatter OD O ring on older engines.

I also put some of my case sealant around the entire outermost part (to car rear of the O ring) of the bearing before buttoning up the case. Having a little of this squeeze out into that side of the O ring groove causes no problems.

Walt Fricke

kent olsen · kent olsen's Garage

Thanks all.

There certainly is a wealth of information on this site. I'll talk to Mike at J&B tomorrow. Anything that is in the flow of oil seems pretty important but if it specs out and that wear spot is normal I'll just clean it up and install it with the new O rings.