First. Can the front timing cover fit influence oil pressure? Next. Can worn cam bearings infuence oil pressure? Can high valve spring tension wear cam bearings prematurely? The lower timing gear has 3 keyway positiions w/different shapes. What does each represent? This is all in reference to a 455 engine that "may" have been overhauled but looses oil pressure. Thanks. OJ
1) No, unless the cover is warped and not sealing correctly to the block, very unlikely, 2) High valve spring pressure does require more power to turn the cam and puts higher pressure on the front cam bearing and timing chain. 3) I would say the three key ways would be 0 (straight up), -4 (4* advanced), +4 (4* retarded) How does the engine lose oil pressure? Does it lose pressure totally, or after it warms up? Describe the problem in more detail please.
Cam bearings can drastically affect oil pressure if worn. TA makes better cam bearings that would be more suited to high spring pressures. Even stock replacement cam bearings made these days seem to be way better than the originals.
Ok here's the story. Got the short block that was supposed to have been overhauled recently. Cylinder ridges were cut and block was clean so I did the heads, shimmed the valve springs (recommended for the cam I used) and milled the all the surfaces true. Slipped in the cam, new rollar chain and Posten S curve intake. Fired it up and as the engine warmed up the oil pressure dropped like a stone. Re built the oil pump with high flow gears and high pressure spring. Got 70 lbs cold but same result. As it warmed up the pressure faded to zip. This week I tore the engine down thinking the mains were gone. I was surprised to find no copper. They looked to be in good shape as well as the rod bearings. Nothing spun and the cylinders were worn only slightly. After scratching my head for a moment I finally checked the cam bearings. Almost GONE! Supid stupid. Took all to Moffit Machine in Boise and they suggested that besides the cam bearings the timing cover may be warped. Never heard of that but live and learn. Getting back to the lower timing gear. For a mild build, where's the optimum position. 0-+4 or -4 degrees? Thanks for your replies. Sometimes I can't see the forest through the trees. OJ
OK, with the Buick V8's, you need to realize a few things. The oil pump is in the timing chain cover. It is also in the front of the engine. The cover is aluminum, the gears are steel. Aluminum expands more than steel at a given temperature. The gear pocket has critical dimensions, most importantly, the depth. End clearance is measured from the gear faces to the oil pump cover surface. The optimal end clearance is .002. When the gears are installed in the cover, the gear faces should actually be ABOVE the gasket surface, by about .002-.006. To get the end clearance correct, you use the correct thickness gasket. Say the gears protrude .004 above the gasket surface. Using a .006 gasket will give the preferred end clearance. If the pocket is worn, so that the gears do not protrude at all, it will not be possible to get the correct end clearance. What happens as the timing cover expands from heat, is that the clearances inside the pump grow, and oil bypasses the gears. This limits pump efficiency. It is also possible that the clearance between the gear teeth and side of the pocket to be excessive. In addition, it is common for engine rebuilders to completely disregard the main and rod bearing clearance specifications from Buick. Rebuilders will clearance it too loose, like a Chevy. Now you have oil pressure loss from front to rear of the block, bleeding out of the excessive clearances. Add to that the oil thinning from heat, and it is easy to see why oil pressure can be OK when cold, and then disappear when hot. Years ago, the fix was a High Pressure/High Volume pump kit. It consisted of longer gears and a spacer plate. The downside of those kits is that it increases the load on the front of the cam. That can wipe the front cam bearing, especially with thick cold oil, and the tendency for someone to rev the engine when it is cold. It can overstress the cam bearing, timing chain, and damage cam/distributor gears. Even a HP/HV pump kit won't work if the timing cover is worn, and the engine clearances are wrong. A stock oil pump, set up correctly with the correct internal clearances will supply plenty of oil pressure as long as the engine bearing clearances are also correct. Buick bearing clearances are tight for a reason. If the Timing Cover is worn, and out of spec, get a new one, and set the pump up right. Make sure the Main/Rod clearances were set correctly. As far as the crank gear key ways, there is no correct position. The multiple key ways are there for adjust ability. The cam has to be degreed in to make sure it matches the cam manufacturers specifications on the cam card. The requires a cam degree wheel, and the knowledge to use it. We have a thread on Cam degreeing. It is a sticky in this Forum.
Oil pump end clearance (page 36) http://www.buick-riviera.com/servicemanual/060-46-99.pdf Main/Rod Bearing clearances.(page 43) http://www.buick-riviera.com/servicemanual/060-46-99.pdf
http://www.taperformance.com/proddetail.asp?prod=TA_1531B http://www.taperformance.com/proddetail.asp?prod=TA_1704 http://www.taperformance.com/proddetail.asp?prod=TA_1558 http://www.taperformance.com/proddetail.asp?prod=TA_1502 http://www.taperformance.com/proddetail.asp?prod=TA_1510A
Larry,This is like doing a book report in high school. If you skip the details you're busted. I guess these engines are the same way. It works fine if you follow directions and don't skip the details. Thanks for all the info. Sometimes the long way is the short way. OJ
