Why engine bearings can fail in the Olds 455, and 403 as we use them.

[Bob Dunahugh]

I've never said that HV pumps are bad. Just use them in the applications that require their use. If you have a healthy engine with the bearing clearance in the .0003 inch range that GM recommends. After all. Their the ones that designed the 403, and 455. And they did a real good job. Time has proved that. The 455 that I'm working on now . Seems to have been well done. I've heard that some people put in HV pump as a preventative measure for the wear that will occur later. If done correctly at rebuild time. Most of us won't live long enough to see that day. As your bearing should never touch the crank. And the HV pump didn't save this 455. It's simple. Enough oil wasn't getting to the crankshaft bearings. And I will figure out what happened. The evidence, and story is there. We all make changes to our GMC's to improve what ever, as we see it. It's how we enjoy these things. It's a hobby for many. I get the change in the final drive ratio's, fuel injection, air bags, and that list goes on, and on for ever. And we have great vendors that enjoy our money too. ( GRIN ) The thing is that GM put in our engines the pump that they thought would do the job they wanted done. In the case of my GMC. That stock pump as done the job it was designed for. For 38 years. And a 154,000 miles. I just see no mistake to fix there. I'm not saying that anyone is wrong. The reasons that I seem to hear are ones that seem to come from opinions. I would just like to see some data that the designers at GM overlooked something. The dialog has been great. But it usually is here. Thanks to all. And you never guessed that I love talking power plants. There's always something out there new to learn about.

 

[Bob Dunahugh]

Rob. Did this answer your questions?

 

[robert mueller]

Bob,

Yes and no, I need to think about this a bit and reformulate my statement / questions re piston speeds.

Regards,
Rob M.
The Pedantic Mechanic

 

[richard michelhaugh]

There seems to be some misconceptions about engine bearings and oil pressure.

Our oil pumps are positive displacement pumps. They pump basically the same volume of oil per rev.
The pressure is generated by resistance to this flow. Bearing clearance and oil viscosity basically determine the resistance.
So given the same pump and oil viscosity, the oil pressure is proportional to the bearing clearance.
If you have larger bearing clearance, you can achieve the same oil pressure by using a higher volume pump.

Another misconception is that oil pressure determines the oil film thickness that our bearing journals are riding on.
This is not true. The film thickness is determined by viscosity, bearing width and rotational speed. Oil pressure is an indicator to whether the is
enough flow to dissipate heat and replace the oil that is leaking out of the bearing space. Notice the oil gallery holes are not on the same side as
the primary load bearing side of the bearing.

Lugging an engine increases the load on the bearings while at the same time reducing the film thickness by the slower rotational speed. This is the
recipe for high bearing wear and failure.

This is a simple description. There are many factors that play into this. Many of these factors change with engine speed and load, oil temp, etc, etc,
etc.

Trust me, Mother GM's engineers have spent a bunch of brain power and many years to determine bearing clearances, pump volumes and oil specs, etc. Go
by the GM specs unless you analyze your proposed changes taking into account these many factors and variables.

Rick M.

--
1974 26' Canyonlands
aka "The General"
Clinton, TN

 

[kerry pinkerton]

> As noted in an earlier email Dick Paterson uses Melling High Volume oil pumps,...

Dick also recommends the hardened steel shaft that drives the oil pump. Stock shafts can fail under the increased load of the HV pump. Have you
checked the shaft?

--
Kerry Pinkerton

North Alabama

77 Eleganza II, 403CI, Manny Brakes, 1 ton, tranny, lots of aluminum goodies.

77 Kingsley by Buskirk. Rear twins/dry bath, EFI Caddy.

Also a 76 Eleganza to be re-bodied as an Art Deco car hauler

 

[robert mueller]

Kerry,

The 455 I have in Humble was built by Dick so I would assume it has the hardened steel shaft. When I reassemble it I'll make sure it
is, thanks!

Regards,
Rob M.
The Pedantic Mechanic