Oil for Classic Car

[RDY4WAR]

Depends on the rebuilder. While the clearance spec range for main and rod bearings for most production engines hasn't changed much in the last 60 years (or longer) there was a tendency by a lot of shops to go a bit looser during a rebuild. Often this was also accompanied by an HV or HV/HP oil pump. It wasn't until recently that things started to shift the other way with a focus on keeping clearances tighter and with lower tolerance for deviation. @RDY4WAR can probably expound on that a bit, given his building experience.

My grandfather had a built (~425HP) Ford Y-block (312) in a marine application that was a former vintage race engine. It was freshened before install in our application (1931 Chris-Craft Cadet) and was not built loose (rotating assembly was also balanced and blueprinted). When I started looking after it, I ran M1 5W-30 in it. It spec'd a 30 grade and had good oil pressure on a 10W-30 (VWB or GTX, which is what my grandfather stocked at the cottage) or a 5W-30 despite being a 50's vintage engine.

All the old mills I remember (30's, 40's, 50's) spec'd an SAE 20, 30 or 40 depending on ambient, with, IIRC, the option for a 20W-20 if temps near freezing were anticipated (it has been many years).


Lots of OHV engines still in production including the FCA/Stellantis HEMI and the staple of GM's fleet, the LSx series engines. The new Ford 7.3L engine is also pushrod. Many examples spec an xW-20.

Most, if not all, of the old pedestrian (non-HiPo) pushrod mills had very mild valvespring pressures and didn't rev very high. They typically ran out of steam at less than 5,000RPM and if you decided to explore beyond where they stopped making power, you'd be greeted by valve float.

The additive packages of oils in the 60's, 70's and 80's were not as advanced as they are today. And, despite the restriction imposed on phosphorous, ushered in with API SM, older oils were not necessarily higher in this AW additive, as some VOA's of vintage oils have shown.

The huge shift away from flat tappet to roller camshafts in OHV engines meant a rapidly shrinking market for FT cores and quality took a hit as a result. In many instances, lubricant choice was blamed for wiped lobes on mild aftermarket shafts when in actuality the problem was the metallurgy. Now, that's not to say that you could slap in a wild Lunati Voodoo stick with API SN GTX 5W-30 and you'd be "good to go", but for mild builds with moderate ramp rates and lobe profiles, the claim that you needed "20 billion PPM of zinc because the EPA neutered our oil" was really driven by poor quality cams, oils were an easy scapegoat.

All that said, my recommendation for older engines varies depending on how tightly they were built. An HDEO like @Astro14 noted, say a 5W-40, is typically a very safe choice if one was built a bit looser. For a stock clearance Ford Windsor, I'm a fan of Mobil 1 0W-40 (or Castrol Edge Euro 0W-40). The full-SAPS Euro additive package is far more robust than anything available on the shelf when the engine was new and there's no restriction on the AW chemistry. IMHO, some more details on the OP application are required here, as potentially either of those may be a solid option.

Agreed.

The main reason a lot of engine builders, particularly production shops, went loose on clearance was to speed up production. Wide clearances lets them get sloppy with crank journal machining and slap the engine together quickly without worrying about clearance issues. Tighter clearances require more time, effort, and money (that's the key one) to machine the journals precise and ensure the clearance is consistent not only all the way around the journal but also from one journal to the next. Production shops make more profit the more engines they send out per day. When time is money, "good enough" becomes the standard. Optimization goes out the window. It's not just bearing clearance. Crankshaft end play, crank balance, piston to wall clearance, ring gap, squish distance, valve seat angles, and many other specs are usually not optimized either. I rebuilt a 331ci SBF Blueprint crate engine and reused all of their same hard parts, kept the compression the same, just optimized it a bit better, and picked up +15 HP and TQ on average from 3000-6500 rpm. Same heads, cam, intake, carb, pistons, crank, rods, rockers, pushrods, lifters, etc... It also had more oil pressure with a 5W-30 than it did previously with a 10W-40.

This is why when someone asks me about crate engines, I always recommend they go speak to a local reputable engine builder to have an engine built for their needs. Not only will it be better for their use, but it'll be more optimized and more reliable. Plus, if there is an issue, the local builder is much more likely to work with you.

 

[FordFETruck]

What? Bearing clearances haven't changed in the last 60+ years for "normal" engines. Also, how many in-block cam engines are required to use a thicker grade oil than an overhead cam engine? With a TSB, Ford back spec'd 5w-20 (from 10w-30) oil for my 1965 designed 1993 4.9L flat tappet engine.

A lot of classic car engines are often built with wider than stock bearing clearances when they go through a rebuild process for various reasons especially if it's a performance minded engine. When I tore down my 159,000 mile original 352 it had really worn out crank and rod bearings, but they plasti gauged at .0015". The new 390 was built with .0024" rod clearance and .0026" main. Those clearances are at about the max clearance for stock in my Ford shop manual for those engines but that was the minimum the machine shop wanted them to be at considering I told them I wanted the clearances set for use with a Xw40 in mind.

 

[Chris142]

For those of you suggesting a 50 weight: why so thick?

Because they are assuming that the 287 taxi motor is now a race engine

 

[cheesepuffs2]

Because they are assuming that the 287 taxi motor is now a race engine

That's my takeaway too. People seem to have rose-tinted glasses in viewing any vintage V8 as being some beast of a lopey engine.

Newsflash: many of these engines were low-key, mild cam, boring mills that had very low power density and require nothing exotic. They simply need... oil.

 

[RAVL]

Fwiw, we would rebuild with stock bearing clearances and spec the oil based on the original manufacturer viscosity. We would run full synthetic in a high quality brand like Liqui Moly. But these were for motors from the 1980s and early 1990s, mostly Euro (BMW straight six, Volvo turbo four, MB staight six and 16v four). These were high quality builds and they would typically be very durable when installed in the car. We did not run high viscosity oil because the build was sloppy in some respect.

I have no issue with the folks with different views, as I said I was sharing my experience and understand different motors and different builds may indicate a different viscosity. Much interesting reading here/. Makes me want to build again . . . .