story that oil was in short supply over a period of time. In other words. It wasn't like an oil cooler line ruptured. Rods 1,and 2 were locked up. Rods 3, and 4 spun in their rods. Rod bearings 5, 6, 7, and 8 are lightly grooved. But 8 was in the best condition of them all. Mains are all groove. Pistons, and cylinder walls have scratches.

Some may be interested in this. I need to figure out what went wrong. As this info might be of value to someone else some day. As the cause isn't real clear at this point. The oil level was on full. Glenn used Mobil one. The engine had about 8,000 miles on a rebuild. HV oil pump was installed. The work done appears well done by someone that does a lot of work on GMC's. Engine was balanced, APR rod bolts installed cost just under $200. Vary good quality bearings, pistons, and double roller timing chain. Heads have hardened seats with all new valves, and springs. The bearings tell a story that oil was in short supply over a period of time. In other words. It wasn't like an oil cooler line ruptured. Rods 1,and 2 were locked up. Rods 3, and 4 spun in their rods. Rod bearings 5, 6, 7, and 8 are lightly grooved. But 8 was in the best condition of them all. Mains are all groove. Pistons, and cylinder walls have scratches. Block is bored .060 over. Heads are in great shape. At thi
s point the crankshaft pistons, and block are now all junk. May come down that the heads, cam assembly, and water pump maybe the only parts that can be used again. Have an extra complete 455. Need to disassemble that engine to make a good short block.Bob Dunahugh




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There has been some controversy over oil starvation due to oil not draining back from the heads quick enough and letting the pan oil level getting down enough that the pump gets air. Joe Mondello was a fan of oil restictors to limit the amount of oil that gets up there. Restricted push rods, lifter bore orifice restrictors and cam bearing oil restrictors were used. Some went as far a external returns from the heads like John Helsinga posted http://www.gmcmhphotos.com/photos/discussions-2/p52098-cylinder-head-external-oil-drain-modification.html It could be the oil pick up clearance to the pan is too great. The Toronado pan we use is deeper than a rear wheel drive and takes a longer pickup. Possibly the oil drain from the heads is obstructed by the head gasket or the oil passage in the head is not quite right. There is supposed to be a baffle that mounts on the rear main, also different than rear drive. John Helsinga's pic again http://www.gmcmhphotos.com/photos/engine-failure/p50887-engine-bearing-failure.html Most of this stuff is on engines with HV pumps that turn a higher RPM than a GMC does but something happened to it.

Jim, I'm in the middle of having a 455 ci engine rebuilt that had been installed in a GMC motorhome The engine had approximately 40,000 miles before it was replaced with an EFI engine. At this point in time I was planning on having a high volume / high pressure pump installed. Is this the preferred oil pump for use in the GMC motorhome engines? When the engine was dismantled, there were no wingage trays in the oil pan. I was not planning on reinstalling windage trays. Should the windage trays be included in the engine rebuild?

. At this point in time I was planning on having a high volume / high pressure pump installed. Is this the preferred oil pump for use in the GMC motorhome engines?

Jim. Great thought's. The three baffles were in place. Had to just go out and check. It's the see. But didn't look as I disassembled it. The oil pickup hung down at about a 15 degree angle. So I think it was at least close to the bottom. And the oil pickup is a press in type. Reasonable press fit with some sealant. I always tack weld that type. The pickup screen was clean. As to drain back from the heads. The drains had been opened up. Someone did a good smooth job on the drains. These 455's in our GMC's run in the 3000 RPM range. At that RPM's. The stock drains are more then large enough. As for the HV oil pump delivering too much oil up in the valve covers. Thus needing to have the oil flow restricted to above the heads. That just isn't a good idea in our application. That oil is used to lubricate, and cool the valve train. And cooling the exhaust valve, and spring is vary important for us. If we ran our 403's, and 455's in the 6,000 RPM range. Restricting the oil is a g
ood idea in some of those applications. And as for the HV oil pump delivering too much extra oil to the top of the heads. Thus starving the oil pump of oil. That just will not happen in our case. Less just say that the oil pump relief valves in both the stock, and HV pump are both set at 45 PSI. Both the stock, and HV pumps will deliver the exact same amount of oil to the bearings. And valve train. That extra oil that the HV pump produces will just be dumped back into the bottom of the oil pan. I had a 1 ton truck that had bearing clearance issues. There was so much oil in suspension above 60 MPH that the oil pump would starve for oil. Back to the 455. Tonight I cleaned the HV oil pump. I did notice that the driven end of the the shaft that went into the pump had more weir on it then I expected. Next step is to take the complete oil pump assembly apart. The HV pump didn't cause this issue. But it's relief valve, and spring. many have had something to do with the amount of
oil delivered. The answer is there some were. Thanks for the thought's. Bob Dunahugh





Bob Dunahugh




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