Zinc reduction in engine oil

[Guest ron]

There has been quite a bit of talk recently on the MG forums about problems caused by the reduction of zinc in oils for petrol driven cars, mainly causing excessive wear of cams and followers particularly at running in time. I've pasted a small extract from an American article which although tedious is worth reading;

 

'Around the time of the flat-tappet lifter shortage, motor oil was experiencing its own changes. Engines with flat-tappet cams have extremely high pressure loading at the contact point between the lifter crown and the cam lobe. According to Mark Ferner, team leader for Quaker State Motor Oil Research and Development, "Even stock passenger cars can see pressure in excess of 200,000 psi at the point of flat-tappet/cam lobe contact." To prevent excess wear, traditional motor oil included a generous dose of antiwear additives, primarily zinc dialkyl dithiophosphate (ZDDP). "The chemistry is such that the additive is a combination of zinc and phosphorous," says Rockett Racing Fuel's Tim Wusz. "Typically the phosphate amounts are about 75 percent of the zinc amounts. For example, if there was 0.100 percent zinc by weight in the motor oil, then the phosphate is about 0.075."

 

Ferner adds, "The zinc reacts with the cam lobe's iron surface. That creates a sacrificial chemical coating strong enough to keep parts separated to reduce the wear." Although great for keeping a flat tappet alive, as an engine ages and develops blow-by, some of the additives flow out the exhaust where they can degrade oxygen sensor and catalytic converter performance. Faced with ever more stringent emissions standards and the governmental mandate for extended emissions-control- system warranties, the OEMs got together with the motor oil makers and decided to reduce the amount of ZDDP in street-legal, gasoline-engine motor oils. After all, they weren't needed with modern roller lifters and overhead-cam followers. The reduction first started in the mid-'80s, and it has been a gradual process, but the latest API SM and GF-4 specs have reduced ZDDP content to such an extent that the new oils may not provide adequate protection for older, flat-tappet-equipped vehicles running nonstock, performance cams and valvetrains. And it will only get worse; projected future oil spec revisions will likely reduce ZDDP content even more.'

 

The last sentence is probably the most significant.

Ron

[Richard Crawley]

Is this likely to apply to the specialist oils designed for use in older classic engines e.g. Millers, Penright Duckhams etc?

[Guest ron]

Richard

Don't think it will apply to Penrite, I've never used them because of their price, but when the excuse is 'environmental' a lot of pressure is put on companies to do something. The zinc reduction hasn't happened in diesel lube oils yet by the way.

As a matter of interest Duckams 20/50, which used to be freely and cheaply available round here has vanished off the shelves, one of the shop owners told me he had stopped stocking it because they had hiked the price so much?

Ron

Edited October 23, 2006 by ron

[Guest harry dent]

Can all the TR specialist's come out of the closet and advise us on what is going on and what oil we should be using.I drive my TR5 quite hard and even more so on the track including Classic Le Mans(Brilliant!)Mallory Park and do not want to wear the engine out too quickly.I use Havoline racing oil so I will have to check the speck.I used to use Penrite,so I may have to go back to this.

Regards Harry.

[Guest ron]

Well I've laid the car up for the winter and done an oil and filter change, the only oil I could get was Halfords 20/50 for classics which looks and smells exactly the same as Duckhams 20/50 except it's nearly twice the price! can't find Duckhams anywhere.

Ron