Engine Oil with Zinc

[Joe K]

Hi Everyone,

I saw an earlier topic about oil (synthetic) and several of you like the non-synthetic Kendall oil.  I was wondering if anyone has an opinion on using engine oil that contains zinc.  I heard several years (decades) ago they removed zinc from oil because it ruined catalytic converters.  But that zinc really helped engines, especially flat cam engines.  Since many of us have the 1969/1970 bikes I thought it would be a good idea to use this type of oil.  Lucas Oil sells a 10-30, 10-40 & 20-50 Hot Rod & Classic brand with Zinc and other additives for older designed engines.  Please let my know your thoughts.

Thank you,
Joe K.

[Sam]

Oh boy. Everyone has an opinion on engine oil! I'll give you mine.

Never synthetic in these engines. The clutch/seals/gaskets weren't designed for it. The oil should be changed every 3k miles (plus or minus), so the long lasting benefit of synthetic oil is moot on these bikes.

As far as zinc, I do have some experience with that too. I've rebuilt a bunch of cb750 engines now and, after talking with a lot of people who have built far more vintage engines than me, I am convinced that breaking the engine in with an oil that has zinc is probably a good idea. It adds a layer of lubrication as the engine "seats itself" into healthy operation. BUT, oil with added zinc can be corrosive if left in the engine too long.

So, I use it for the first 600 miles of breaking in an engine. I never stay at the same RPM for more than a few seconds and I slowly work myself up to higher rpms as I get past 300 miles. At 600 miles, I drain the oil and use Honda GN4 oil.

Its worked for me!

[Joe K]

Thank you, Sam for your opinion and explanation.  I value it coming from someone with your experience.

Joe K.

[madjack4]

Hi i agree synthetic oil does not do the clutch any good but i disagree with gaskets and oil seals how can synthetic oil affect oil seals and gaskets i have 13 bikes of all makes 10 of them 60s and 70s inc my sandcast im in the motor trade so i have 10/30 semi synthetic car oil in 45gallon drums ive used it in all my old bikes for the last 20 years and im not a polisher i use all my bikes all year round no problems with seals or gaskets leaking the only problem i had a few years ago was clutch slip on my cbx 1000 but i am shure it was just old age i replaced it and carried on using same oil no more problems lets face it we are dealing with very old tech on our bikes (sandcasts) u could run them on chip fat and they would be ok most owners of sandcasts never ride them anyway so it definitely wont matter what oil they use

Regards