Advanced Tech Info

Bearing and oiling system general notes:
- IN GENERAL, too loose (large) clearances are better than too small.
- Large clearances will reduce oil pressure.
- Clearance increase at the main bearings will have more of an effect on oil pressure than increases at the rod bearings (whether due to wear or setup).
- Larger oil capacity allows oil to remain cooler, and therefore maintain higher hot oil pressure. It also aids in engine cooling.
- The Fram HP series racing oil filters are low restriction and heavy duty. They have much higher oil volume capacity to prevent the oil filter bypass from opening up. It does not filter quite as small particles, but filtering all the oil is better than filtering part of it if some gets bypassed.
- I measured a 3psi oil pressure increase by switching from an AC Delco PF-24 filter to a Fram HP-4.
- With priority main oiling system engines such as Oldsmobile V-8's, Camshaft oil restrictor kits will reduce excess oil to the camshaft bearings, increasing oil volume to the crankshaft mains and rods.
- Camshaft oil restrictor kits will not cause damage the cam bearings.
- Install camshaft oil restrictors at mains #2, 3, and 4.
- Oil restricted pushrods will reduce excess oil to the valve train.
- Installing a high volume oil pump increases oil flow over stock to the cam and valve train, which stock already receive more oil than needed.
- Oldsmobile Toronado 6 qt. oil pans are 8-1/8" deep to the flat bottom, and 8-1/2" deep to the bottom of the drain plug. Milodon/Moroso 7 qt. pans are 8-1/4" deep to the flat bottom (drain plug is on the side).
- Shim the oil pump bypass spring .25" by adding a spacer behind the cotter pin on the Melling P/N M22-FHV or Milodon high volume oil pump. Shimming the oil pump bypass spring will provide additional pressure, but will NOT significantly increase low oil pressure due to excessive clearances.
- The Milodon #18865 high volume pump costs almost twice that of the Melling, but seems to be a higher quality pump. The Milodon's gears are the same size as the Melling's, but the internal clearances are held tighter (gear side and end clearance) and the quality of machine work looks better.
- On a 455 Oldsmobile with the bearing clearances correct, 50 psi oil pressure will keep the bearings lubricated up to 6,500 RPM.
- Have the crankshaft cross drilled. Olds big blocks are already cross drilled on the #1, 2, and 4 mains.
- Use Clevite 77 or ACL rod and fully grooved main bearings. The best main bearings for maximum oil flow to the rod bearings are modified Clevite or ACL bearings from M & J Proformance - these bearings hav the oil feed holes enlarged on a Bridgeport milling machine for increased oil flow. The bearings also have some other finishing preparation that make them well worth the money.
- You can also enlarge the oil holes yourself if you are daring by enlarging the oil feed holes in the main bearing upper shells to 1/4" and elongating the holes. Some need to be elongated in on direction, some in the other. Drill out the hole one drill bit size at a time, and carefully de-burr the bearing after drilling with a very small Dremel Moto-Tool grinding bit or by hand with a rat tail file. Dremel tools or other tools may build up heat in the bearing and create non-visible damage, so be careful and go slow. My personal opinion is that purchasing the modified main bearings is well worth the minimal extra expense.
- Install the drilled upper main bearing shells in the block and mark any block material blocking the enlarged oil feed hole. Remove the bearings and clearance the block in these areas by grinding a chamfer on the block feed passage.
- .0001" taper from the front of one crankshaft rod journal to the rear of the adjacent journal seems to be the maximum for good machine work. Rod journal sizes should not vary more than +/-.0001".

- ARP rod bolts are a must - clamping force is an issue at the connecting rods, and ARP fasteners provide much more clamping force than stock fasteners.
- When connecting rod bearings loose their crush (fit loose in the rod big end at disassembly), it is an indication of high heat at that connecting rod.
- Excessive heat at the connecting rod big ends will heat up the rod housing and expand it. The housing can shrink to a size smaller than it started at after it cools.
- Main bearing caps can walk under high loads, especially at high RPM they move front to back and twist.
- Cap walking transfers metal from block to cap, and vice versa.
- Stock engine internal reciprocating/rotating parts are heavier than equivalent racing/lightweight parts and produce more load on the engine than lighter parts at any given RPM.
- ARP main bearing studs provide more clamping force than ARP main bolts, and also eliminate wear on the block threads. They distort the main bores differently than bolts, so the main bearing housings should be checked for a line hone after stud install.
- 4 bolt steel caps are better than 2 bolt caps because they further help to eliminate cap walk and bearing deflection.

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- IDEAL PISTON TO WALL CLEARANCES:
* TRW-L2323F Forged pistons: .005-.006"
* Keith Black KB-132 hypereutectic pistons: .0030-.0045"

* NOTE: These clearances are much greater than the piston manufacturer's minimum recommendations, but are vital to prevent cylinder wall and piston scuffing.
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- IDEAL BEARING CLEARANCES:
** FOR HIGH PERFORMANCE STREET/STRIP 350-455 ENGINES:
.0018-.0025 main #1-4 (.0022" ideal)
.0023-.0040 main #5
.0018-.0028 rods
FOR STOCK REBUILDS / MILD PERFORMANCE SMALL BLOCKS:
.0010-.0022 main #1-4
.0015-.0025 main#5
.0010-.0025 rods

** NOTE: There is a debate from top engine builders as to what the ideal Oldsmobile bearing clearances are. The above specifications are what have repeatedly worked for myself and a couple other engine builders I know. Noone I know of has had success with less than .0015" clearance on mains #1-4 & the rods, or over .0040" main and rod bearing clearance.
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* This page updated 07/06/03*