Tom,
Don’t forget to be just as diligent in looking past the bearings and placing as much emphasis on how you install them in the engine.

Ron Sledge of King Bearing was a presenter at AETC this year and reiterated some overlooked fundamentals of bearing selection. Credit a part of this information to his presentation

The proper oil clearance is the minimum space required for the journal and bearing surfaces to slide adjacent to each other, without contact, on a hydrodynamic lubrication barrier, avoiding boundary or mixed lubrication scenarios. These clearances are determined by:
• Journal and bearing asperities (surface finish) min 4 Ra
• Oil viscosity
• Operating temperatures
• RPM and load
Tighter oil clearances;
• Reduce peak bearing loads
• More even distribution of unit loading over larger areas of the bearing surface
• Stronger oil film
• Oil viscosity and oil pressure can be reduced lowering frictional and parasitic pumping losses.

In other words, in most disciplines of motorsport engine builders are moving away from (including BBC marine engines) .003” + bearing clearances, 70 + PSI oil pressure, and high viscosity synthetic (or mineral based of any viscosity) oils. I had extended conversations with Lake Speed Jr. and other lubricant suppliers represented. They all concurred on these points.

Oil temperature;
Cooler is not better. The additive packages are designed to function properly at a predetermined operating temperature. You will not do your engine any favors running engine oil temps < 200º. It is also recommended to minimize the delta in/ delta out operating temp to the lowest manageable point. For those concerned about where to measure oil temps both those data points are critical. For example if you run a 240º pan temp, try to keep the post cooler inlet temp to around 210º. Keep in mind, the amount of thermal increase in your lubricant due to valve spring heat rejection is often underestimated.

Bob

Bob, thanks again for the info. To put this into simpleton terms so that I can understand it, I think you are telling me that marine engine builders are moving away from high volume / high pressure oiling systems (HV pumps) with larger clearances, and more in a direction of tighter clearances, lower pressures, and lower viscosity synthetic based oils. Previously, I was running a Melling Select 10778 pump with 20W50 mineral based oil. My oil temps were usually in the 180* range measured in the sump, and I never saw much higher than about 230* after a 4000+ RPM run. Wondering if I was just running too thick of an oil in my rig. I will need to consult with my engine builder to verify clearances, but he was most likely running the .0025 rod / .0030 main clearances that were the norm for BBC builds. Regarding oil temp, most of the thermostatic oil adapters that I have seen open around 180*, so it may be hard to maintain the 200*+ temps that you advise.

Can you clarify your statement on oil temp deltas? Is that delta managed by oil cooler size? In respect to valve spring heat rejection, are you saying that the oil temps in the valvetrain are significantly higher than those in the pan?

Sorry for all the follow-up questions, but I think this thread may prove helpful for others besides myself who are in the process of building a reliable performance marine engine. Thanks again!

I will start a separate thread with some detailed pictures of my main and rod bearings.

Good Info Bob. Theres been some talk lately about certain builders recommending NOT running oil thermostats, and running the oil cold on big power engines. I cant see the reasoning behind that. My buddy heard this, and now is removing his oil thermostats, because he ''heard'' its better to keep the oil ice cold. IDK, I suppose Mercury has it all wrong running oil stats on the 1075's and 1350's.

i keep the oil and engine temps at 120* in my donzi engine..12 running hard and usually a hard run @ 6200 rpm's and its still together..

I been smoking for 15 years, still alive but....

To follow up on what Bob said about oil temps, perhaps running gigantic coolers to keep oil temps below 210* is overkill, and maybe even harmful in some cases. I was running the stock Merc oil / ps cooler on mine. I realize most would say this is undersized for my application, but I never saw temps over 225* or so. I eliminated most of the restrictions in the lines and fittings by going to a thermostatic sandwich oil filter adapter and #10 AN lines to the cooler with long sweep 90* fittings. I was thinking about getting a larger dedicated oil cooler, but now I'm not so sure if this is even necessary. Would like to find a way to keep temps between 200* and 250*.

I know it has been discussed before ad nauseum, but what is the upper limit for oil temps for mineral oil - say 20W50 like I was running? Or should I switch to something thinner? What is the upper limit for the synthetics?

my oil temps always run 170 ish, I have no stats and run all stock TRS coolers and lines... I have been wanting to raise them temps hust over 200 thinking engines may perform a little better... I think they are too cold..

No doubt! Along with a LOT of other racers, builders, etc.. I also notice a lot of people get confused between pressure and flow, and think that 100psi oil pressure is a good thing.. Like it's the pressure that keeps the crank off the bearings..

I get 180* cruising. Running WOT for a few miles, creeps to 210*. Running Bellhousing coolers with Merc Racing oil stats. Both engines identical on temps, senders in the pan. Seems to work well. Oil lines are all -12 with full Flow 90's. PSI is about 75 running, 40-50 idling.

i have about 60 psi @ 6200,,,25-30 at idle.small oil cooler ..i also run full syn oil and filter..8qt oil pan..i only run about 2-3 miles at that rpm then i cruise at 5 k