I have a friend with '55 Chevy with warmed over engine ( not for racing ) with flat tappet cam and lifters that were ruined with synthetic oil. He was told the new synthetic oil was intended for new engines with closer engine clearances than older motors.
It may have something to do with the lack of zinc. In one of the past Hudson Club newsletters one fellow recommended using Zinc Additive such as Edelbrock , Lucas, Rislone ,etc. even with the non-synthetic oil . Most of these are stocked by Auto Zone, PEP Boys, Walmart and others. Older oil used to have the ZDDP ( zinc) . Suggest you read Internet - Why Classic Car needs Zinc Oil additive. The additive is cheap insurance if it prevents engine wear .
Good luck

What happened to the 55 engine? I use conventional oil and add ZDDP additive for break in, then I use synthetics in all my vehicles, just stick to the recommended viscosity.
Here is a note from an Amsoil tech
LEN GROOM
Technical product manager
Amsoil

A. In most cases, classic engines that have been using conventional oil for several years should stay with conventional oil. The seals get accustomed to the lubricant, and big changes (like switching from conventional to synthetic) can cause them to leak. For rarely driven cars, the risk is not worth the reward, so just stick with conventional oil. Now, if the engine is getting rebuilt, then you can go with synthetic (and then stay with synthetic) after the breaking-in process.
More info-
https://www.amsoil.com/newsstand/classic-and-vintage/articles/reduced-zddp-and-wear-protection/
and- From the Bob is the oil guy site-
https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1049812

Gentlemen, thanks very much! Interesting reading ahead for me . . .

John,

I've been told that 15W-40 is a good oil to use. It is marketed as being for diesels, and contains some additives that are not good for catalytic converters, but apparently are good for old engines. My 232 Pacemaker engine is working well, having used this oil for the last 20,000 miles. Before that, I used 10W-40 oil, for another 30,000 miles. These miles were almost all highway miles on long-distance trips (the car has overdrive), almost all during weather that was neither too hot nor too cold. I also use this oil in my 1935 Hudson splasher, but it doesn't get very much exercise.

Per

The jury is still out on the suitability of synthetic i9ol for splash lubricated engines, and I have not come across anyone who is willing to be the guinea pig. It is probably a question for the oil company boffins to answer. No one doubts the ability of synthetic to protect better, but what of it's ability to fling around and drain easily into main bearing gutters?

Gentlemen, Thanks very much for your input!

Gents, I'm relatively new to this club and forum, but I've participated in several other forums for Mercedes, Fords, and others for many years. Synthetic oil is one of those topics that elicits strong opinions, whether informed or not!

I've been using synthetics for 40 years now. I've used several brands, but primarily Mobil 1. I'm an engineer too, and have had several technical discussions with tribologists at motor oil companies (Mobil-Exxon, Amsoil, Joe Gibbs Driven), and car companies (Ford). I've also wiped a cam several times due to lubrication failure (in a Porsche 914 track car I used to run). Based on my reading and those discussions, let me pass this on to you, if you are not already familiar with it.

The generally recognized most demanding lubrication requirement in a piston engine is the cam-follower contact. This interface has the highest contact pressure in the engine, because the nose of the cam pushes hard on the flat surface (actually very slightly convex) of the lifter, and against the opposing force of the valve spring and the weight of the lifter and valve train. This force is concentrated in a very small oval area on the nose of the cam and the face of the lifter in a wiping/scuffing motion. The ZDDP actually transforms into a solid lubricant under those extreme pressures. Furthermore, those forces increase dramatically with increased RPMs. This is why motor oils have ZDDP in them, and improvements in the content and quality of the zinc/phosphorus additives were required to support the development of muscle car engines of the 1960's.

Fast forward to the catalyst era: The main downside to ZDDP is that the zinc will coat and neutralize the catalytic converter over time, based on how much oil the engine uses. Manufacturers realized that they could not continue to build engines that required high levels of ZDDP and warrant the emissions system for 100K miles or more, as the EPA continued to mandate longer periods of emissions system performance. By 2000 or so, new engine designs were using roller lifters or followers to reduce the peak force and eliminate the wiping action on the cam/follower interface in order to use oils with lower amounts of ZDDP and lower viscosities (to help improve fuel consumption). Likewise, modern oil specifications have greatly reduced amounts of ZDDP and different specs for testing the cam follower wear. In this case, newer API oil specs are NOT better for old cars.

So what does this mean for us Olde Car Guys? Several things:

(1) try to find oils that have high levels of zinc. Several oil manufacturers produce these, including Joe Gibbs Racing, under their Driven brand. Amsoil does too. Mobil 1 and other major brands do not. In general, "racing" oils have higher zinc, but I haven't kept up with who has what for a long time. Oils specifically formulated for Diesel engines also have higher zinc, but again, I'm not sure how much in which brands. However, here's a hint: If the fine print on the back of the bottle says something like "not for use in catalyst equipped cars" then you can be almost certain it's because that oil has high zinc and phosphorus, which is good for our purposes. Check out the bottles of Ford Motorcraft Powerstroke Diesel Oil at your local McParts store. The front label specifically says "Over 1000ppm of phosphorus" and the back warns not to use in catalyst cars. That's the jackpot. Another hint: if the label says it meets the older diesel specifications, CF and lower, then it will have more zinc.

(2) Knowing that the forces on the cam/follower increase greatly with increasing RPM, keep your RPM in check. The load on the engine makes almost no difference to the cam follower contact pressure, only RPM; so you can mash the pedal to the floor all you want, just stay well below redline.

(3) DO NOT add zinc additives to your oil! All the knowledgeable people I spoke to warned against this "fix." It turns out that there are several dozen different formulations of ZDDP, and choosing the right one(s) to blend depends on the oil base stock and other additives in the oil (detergents and additives to neutralize acid buildup, for example). Furthermore, some of the aftermarket "oil treatments" actually have the reverse effect, and cause the additive packages that the oil manufacturers have carefully balanced, to precipitate out! Don't do it. Quality oils are cheap enough, so just choose the best oil to begin with.

(4). If you don't already do regular oil analysis, start now. The FAA requires regular oil analysis on commercial aircraft for good reasons. You get advance warning if your engine is starting to deteriorate, in time to do something to prevent it, or at least to schedule a rebuild instead of getting a rude surprise. I do this on my old cars, my Ford GT supercar, and my motorcycles. It's cheap--about $25 with Blackstone Labs. Do it at every oil change or once a year. I use it to decide when to change my oil, instead of just changing it every XXX miles or months. I will state this emphatically: Oil analysis allows me to extend the change intervals so that I save money by not changing the oil before it needs to be changed, greater than the cost and inconvenience of doing the oil analysis!

As for the question about whether to use synthetic oil in 212 oil splasher engines, I would look at it differently and instead look for oil with high levels of ZDDP, whether synthetic or dead dinosaurs. The cam/follower is more demanding of the oil than the piston/wall. If you have that covered, the rest will be okay too.

Peter,

Thank you for the detailed information. Are you aware of any other contact surfaces that could give trouble? The gear on the oil pump of the step-down 6 engines (a high pressure pump in contrast with the splashers) has been mentioned as a possible problem location.
Anyhow, this seems like less of a problem for cars that have roller followers (such as my '28 Packard).

Per

Thank you for your reply, but it does not cover exactly the answers as to how a synthetic oil will act in a splash fed engine. Hudson are probably peculiar in that there are different requirements. 1. for the cam followers, particularly from '34 -47, 6 cyl, and '34 -52 8's which have solid 4 inch radius cam followers, which are wiped by the cams and very susceptible to extreme wear and hollowing out of the follower surface, and cam noses. Here, a high-zinc oil will be necessary. 2, for the connecting rods, and these are probably the best lubricated parts of the engine, as they directly scoop up the oil from the troughs, and this is forced through the bearing by the internal grooves and out the sides, with the excess being flung up towards the camshaft and main-bearing feed gutters. 3, the main bearings, which are gravity fed through quite a small hole in the block and into the bearing surfaces, whence it is circulated internally through the machined grooves in the bearing surface. The points of concern are A. how does a synthetic oil perform at high speed in flowing back as the con -rod scoop comes around each time. If the oil is too thick, or sticky, then it will literally form a groove and perhaps starve the bearing. B. How freely does a synthetic oil flow by gravity along the feed gutters and into the main bearing feed holes? Again, if the oil is sticky, it may cling to the sides of the gutter and not flow freely. This the unanswered question, as I see it. I have seen extreme wear in both the cams and lifters of these engines, obviously caused by inadequate lubrication. It is not a problem with the Step-down and Jet motors, as the lifters revolve each time they are activated, as they are slightly offset from the centre line of the cam. My two-bob's worth!
Geoff

Geoff, the viscosity of the oil is what's important for the flow and splashing of the oil. Doesn't matter whether it's synthetic or dino. Choose the correct hot viscosity number (the higher of the two numbers). If you choose something like 5W-30, you will get more splash lubrication when the engine is cold, than a straight 30-weight oil when cold. The way you are using the term "sticky" implies the oil will not flow as well as dino oil, which is definitely not the case. The viscosity tests directly measure the flow of the oil, so a 30 weight synthetic oil flows at the same rate as a 30 weight non-synthetic oil.

Yes, synthetic oils supposedly stick to surfaces (forming a very thin film) longer than dino oils, but I'm not sure that is still true. I don't know of any testing of that hypothesis in recent years, whereas the formulations of non-synthetic oils have advanced dramatically since those old claims were made.

Per, the toughest lubrication point in most engines is the cam/follower interface. I say "most" to allow for the possibility that some engines might have other trouble spots. The brass distributor drive gear seems to commonly wear in Hudson 6 engines. Maybe higher ZDDP would help this spot too, or maybe not. Maybe it's due to a hard steel gear running against a softer brass one, and the Hudson engineers just accepted that wear as the price of not causing wear to the cam gear, which is harder to replace. If I had to choose one over the other, I'd make the same choice. However, the great majority of modern engines with distributor drive gears don't seem to have this problem, so obviously there are ways to design it to last.