SBC Rebuilding for Modern, Low-Weight Oil Usage?

[NewbVetteGuy]

Totally curious, what's required when doing a rebuild of an SBC to enable it to run a modern low weight oil?

Smaller crank bearing clearances (how small? Is there a table for a given oil weight?), napier scraper 2nd ring to help with any oil that gets past the oil ring, what other bearing clearances? Normal volume and pressure pumps fine?

Also curious whether lower weight oil will cause issues with the newer high rpm-capable retrofit hydraulic roller lifters...



Asking simply to understand.


Adam

[RevTheory]

I've been wondering the same thing, especially when Morel lifters say no more than 5w-??. I'm definitely keeping my eye on this thread.

[pdq67]

Look,

My old junk301 and later 406 was fine with standard oil.

WW's best and filter's too, for years

pdq67..

[travis]

Look,

My old junk301 and later 406 was fine with standard oil.

WW's best and filter's too, for years

pdq67..

There is significant power and mileage gains to be had with thinner oil.

[NewbVetteGuy]

Found this on an Engine Builder Mag article; anyone disagree or have additional input on other important clearances when changing oil viscocity?:

http://www.enginebuildermag.com/2015/12 ... -pressure/


Here are some recommended rod bearing oil clearances for various oil viscosities:

.0015 to .0018 for 5W-20 or 20W

.002 to .0024 for 5W-30 or 30W

.0025 to .0029 for 10W-40 or 40W

.0030 to .004 for 20W-50 or 50W

.0041 to .005 for 10W-60 or 60W

For main bearings:

.0015 to .002 for 5W-20 or 20W

.002 to .0025 for 5W-30 or 30W

.0026 to .003 for 10W-40 or 40W

.0031 to .0041 for 20W-50 or 50W

.0042 to .0052 for 10W-60 or 60W



I found someone quoting an old GM Factory Service manual, and the manual seemed to recommend different clearance ranges for the front, intermediate, and rear main seals (tighter at the front and wider at the rear); not sure how to translate the generic clearances above to main bearing-specific recommendations...

The other posted factory manual stated the main bearings clearance recommended ranges and tolerances as:
• Front main clearance from factory manual: 0.0008 - 0.0020
• Intermediate: 0.0011 - 0.0025
• Rear: 0.0017-0.0035

So, 0.0018 +/-0.0002 for the front, 0.0018 +/- 0.002 for the middle/intermediate and say 0.0020 +/-0.002 for the rear main bearings sounds like it would be appropriate for running 5w-20; no?



Adam

[engineguyBill]

First thing to check when contemplating low viscosity oil is the condition of the crankshaft. It must be absolutely straight and the main journal bores in the block must be straight as well. Then the engine can be assembled with recommended bearing clearances, typically the middle of the engine or bearing manufacturer recommendations. Light weight oil (5W20; 5W30; 10W20, etc) can be used very successfully.
High volume oil pump is OK for street use, but race engine will work better with standard volume pump.
Second ring is primarily an oil scraper, therefore the Napier design will be a more efficient scraper. The most important aspect of the cylinder wall condition is the fact that crosshatch and plateau honing operations must be done correctly.

[Truckedup]

I hear some engine guy taking about "enough bearing clearance and oil viscosity to from an adequate wedge in a high output engine" Meaning typical .003 clearances and 20/50 oil....Ii there truth to this?

[DaveMcLain]

I hear some engine guy taking about "enough bearing clearance and oil viscosity to from an adequate wedge in a high output engine" Meaning typical .003 clearances and 20/50 oil....Ii there truth to this?

No, I don't think there's much truth to any of that really... I believe that the hydrodynamic wedge effect is stronger with less not more clearance.

[user-17438]

In order to run tighter tolerance successfully, you need to have tighter tolerances everywhere.

Crankshaft run-out, main housing bore, rod housing bore, parts that don't bend.. Blah blah blah.. The length of the crankshaft has part to do with clearance you can run, the material, Engine output.

Solid engine mounts or rubber, front plate or front and mid plate.

Aluminum block Vs iron block

I have run 5w20 on an aluminum drag racing engine with. 003"main and .0027" rod. But this engine would be pushed to and from, leave at 70degree water temp. Tighter clearances would scrub the bearings even with thinner oil.

Most times its a trial and error job to get it right

[engineguyBill]

I hear some engine guy taking about "enough bearing clearance and oil viscosity to from an adequate wedge in a high output engine" Meaning typical .003 clearances and 20/50 oil....Ii there truth to this?

No, I don't think there's much truth to any of that really... I believe that the hydrodynamic wedge effect is stronger with less not more clearance.

This is correct. Hydrodynamic wedge will be formed between the bearing shell face and the crank pin, regardless of vertical oil clearance. The viscosity of the oil has no affect on the ability of the wedge formation, either. And yes, it is very possible/likely that the lesser amount of vertical oil clearance will result in a stronger hydrodynamic oil wedge.

[KnightEngines]

You need to run enough clearance to allow for flex/whip in the crank & ovaling in the rods under combustion load.
How much flex/ovaling you get is determined by the rigidity of the parts used, the output of the motor & the peak rpm the motor will see.
Add in machining tolerances (out of round, taper etc) & clearance has to account for worst case.

None of this has much to do with oil viscosity, clearances need to be what they need to be, excessive clearance can be band-aided with extra viscosity in the oil, but not by much.

The main thing to look at with running thinner oils is the pumps ability to push enough of it through the bearings - you'll generally use a little more oil pressure & turn the oil in the bearings over faster.
This had advantages in that the oil spends less time under load & local oil temps in the bearings will be lower - so you have a larger safety margin before you coke the oil & have a bad day.

I think the misinformation commonly spouted about running tighter clearances with thinner oil comes from OEM companies running tighter clearance in newer engines & thinner oil - that's not because the thinner oil works with tighter clearances, it's because OEM machining & parts rigidity has improved a lot over the years (allowing tighter clearances) & thinner oil has milage benefits.

[GARY C]

thinner oil has milage benefits.

You can document this fact in direct line with EPA standards put on the OEM. Brian with BnD automotive sent me that data several years back, if I can dig it up I will post it

[NewbVetteGuy]

I think the misinformation commonly spouted about running tighter clearances with thinner oil comes from OEM companies running tighter clearance in newer engines & thinner oil - that's not because the thinner oil works with tighter clearances, it's because OEM machining & parts rigidity has improved a lot over the years (allowing tighter clearances) & thinner oil has mileage benefits.

Thanks for all the feedback and context.

Here's me fully showing my cards: my single family-owned 79 Corvette L82 4 bolt mains with 13k original miles. I want to modernize the car for its 40th anniversary. This includes a great many things to me that I won't even begin to go into, but where the drive train is concerned, my goals are: dramatically improved power (ea estimates 440hp, 470ft lbs vs my stock 225hp and 270 ft lbs), improved fuel efficiency (?sequential multi port injection, 4L60e overdrive and low stall lockup TC, increased CR and DCR, headers, & friction reduction at every turn I'm hoping will at least double the 11.1 mpg), and longevity (100+k miles before another rebuild) using modern parts.

I'm laser-focused on my goals and I already have my engine's top-end planned and purchased (Profiler 195s, Mike Jones roller cam (227 intake duration), high rpm-capable retrofit hydraulic roller lifters, and comp ultra pro magnum 1.6 RRs, & FIRST fuel injection long-runner intake to support multiport injection-very torque and MPG focused build that EA calls 440hp in a 350 CU IN flavor) and my 4L60e trans swap completed; now I'm looking to the bottom-end which involves a premium 383 stroker kit, and a high-quality rebuild. 6" rods with lighter weight, forged 4032 shorter skirt pistons with appropriate modern designed skirt profiles and anti-skuff coatings, the thinnest, highest quality ring package that I can get, and a high quality plateaued finish to support them, now I'm looking to see what's required to get the fuel economy and torque benefits of being able to use low viscosity oil- if I'm spending the money to have a machine shop rebuild the bottom-end and buying a new stroker kit, I want my MPG, too!

I might be a bit nutty pursuing such an "odd" set of goals and starting from near zero knowledge doing it, but I'm happy to spend ridiculous time and effort pursuing it slowly and learning one thing at a time, so any general guidance made practical and real is greatly appreciated.

If the OEM Parts and Rigidity has improved allowing tighter clearances, I'd like to know what parts and clearances are important and what they look like. I'll be setting the rev limiter to 6,300 rpm; my HP peak should be 6,000 according to Jones.


I'm also curious if the oil wedge rises and wanes due to the pressure fluctuations in a geared oil pump; maybe exacerbating the challenge of having less clearance between parts with tighter clearances like this? -If so would going with something like the Melling Shark Tooth Helical Asymmetrical pump help to keep a more consistent oil wedge between parts?



Adam

[NewbVetteGuy]

thinner oil has milage benefits.

You can document this fact in direct line with EPA standards put on the OEM. Brian with BnD automotive sent me that data several years back, if I can dig it up I will post it

Mileage benefits and power benefits. Those are exactly what I'm after and the reason for asking my original question of what is required to properly support low-weight oil usage in an SBC.


Per my long previous post, I'm looking to modernize my old GEN1 SBC L82 to get as many benefits as possible from modern parts and know-how; I'd like an SBC rebuilt to look as much as possible like an LS motor while still being an SBC. Yes, I understand this is a way more expensive way to get there, yes I understand I'm putting way more money than I'll ever get out of the car if I ever sell it, and yes I understand that there's nothing remotely resembling an LS motor intake for an SBC motor (that probably saddens me the most); but it's my build and I want as LS-like of a gen1 SBC as possible, down to trigger wheel ignition, although I haven't talked myself into coil packs, yet...

Now what do I need to do to get these benefits and be able to run thin, low viscosity oil in my SBC safely?


Adam

[engineguyBill]

Adam,
There is no correlation between oil pressure and the formation of hydrodynamic oil wedge between the bearing shell and the crank pin.

The oil only needs to have enough pressure to insure that the oil is delivered into the eccentric area of the bearing, adjacent to the parting line. Crankshaft rotation will enable this oil to form the necessary wedge. Due to the fact that a liquid cannot be compressed, the oil wedge function is quire successful in keeping the bearing shell and the crankshaft pin from having physical contact with each other.