Re: {Chrysler 300} Re: Motor Oil Zinc

Mr.Douglas: I have no intention to provide you with "a lot of grief". However, you may be talking apples and oranges. I agree your 1947 DeSoto engine can probably run fine without ZDDP additives in the oil, but it uses very low valve spring pressures and modest revs. My guess is the springs would test at about 100-140 lbs open pressures and I doubt the engine sees over 4,000 rpm. By the 1960s, revs were approaching 6,000 for American high performance engines and open spring pressures were close to 300 lbs. At this point, ZDDP becomes a necessary additive to oil to prevent lifter and camshaft failures, especially on break-in. Today, American camshaft designers are using open spring pressures approaching 600-700 lbs in racing usage (though usually with roller lifters), and flat tappet cams are normally approaching 400-500 lbs for American V-8's. With these lifter loads, ZDDP is crucial to prevent lifter and camshaft failure. Oil refiners have, over the years, determined lower levels of ZDDP (catalytic converters hate zinc) will normally still protect the valvetrain on older engines especially if the engine already has a number of miles on it and all the parts and pieces are well acquainted. Most oil refiners will recommend ZDDP levels above 1,200 for ideal protection in V-8 pushrod motors. However, ZDDP levels can get too high (too much of a good thing) and levels above 2,500-2800 are not the best for long term usage.

Dyke Ridgley

Ridgley Racing

5500 Walmsley Rd

Decatur, IL 62521

217-865-2300 p

217-865-2309 f

On Fri, Jun 23, 2023 at 2:34 PM Kurt Brueske <kurt.brueske@xxxxxxxxx> wrote:

I don't know if it constitutes "hard science" but I had an Uncle (RIP) with a PhD in Metallurgy who spent time in Cripple Creek CO in the 50s/60s mining molybdenum which is used as a dry lubricant. Uncle Jim was also a "car guy" and he told me zinc had “polar” properties meaning that it has a natural attraction to iron/metals in engines and other machines. Conversation was a long time ago but I suspect this material (and properties), suspended in oil, would promote adhesion of oil to metal surfaces, reducing friction and oxidation of internal engine components if left sitting for long periods of time (I'm definitely guilty). He recommended it.

KB

On Friday, June 23, 2023 at 9:26:23 AM UTC-5 James Douglas wrote:

I am sure I will get a lot of grief but…

I use straight 30 or 40 without any zinc. The ZINC thing is in my opinion is much ado about nothing. Years ago, I talked with someone who does the testing of engine oils for a very large organization. Their job is to evaluate the oil companies’ oil for conformance to their published specifications. They have a room of engines that are the most blueprinted and checked engines in the world. They must be to detect what oil does or does not due to them. They are also all non-hydraulic cam engines.

They have found no wear differences with or without zinc in the engines. Period.

They have found that a number of camshafts in the 1990's, when a LOT of cam production moved out of the USA, had issues with Rockwell Hardness on the lobes. In fact, I know of several engine builders that now send out camshafts and lifters for Rockwell testing. Guess what? Several of them fail even recently.

I suspect that proper hardness treating of cams and lifters drives much of the speculation about Zinc. I could not find one single "hard science" document on the subject. A lot of opinion, but nothing definitive where two exactly the same engines in all respects were run with and without zinc and the wear differences were measured and documented..

My 1947 Desoto Suburban engine I built 20 years ago, has about 75K miles on it. I run it in the Hills of San Francisco and the Interstate to my place out of town at 70 MPH. The car is about 5000 pounds. I looked at the cam a while back with the side covers off and a bore scope. The cam was NOS when it went in. It looks fine with no evidence of advanced wear. I never used any zinc.

James.

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