enginehistory.org

[rwahlgren]

7-6 At time of assembly, coat cylinder pistons, crankshaft main and masterod journals, masterod bearings, main bearings, tappets, and tappet roller pins with STP (Chemical compounds division of Studebaker Packard Corp)

And there is more in the photo of the page of the 4360 overhaul manual.
(Here is where the link should be ?)

Link to History of STP.
https://en.wikipedia.org/wiki/STP_(motor_oil_company)

So far everything I have found on STP says it has zinc or ZDDP in it.
And this below.
I've known this for years.
https://www.finishing.com/277/02.shtml

????

[dpennings]

didn't know it was based on German WW2 tecnology. Ironically the German couterpart to STP is Liqui Moly which uses MoS to improve lubrication, as much as I know, this was used in American flight engines to enhance the operation time after a loss of oil.

[kmccutcheon]

STP is often recommended as a component of build-up oil. However, its use as an oil additive is discouraged. It not only attacks silver, but also promotes the formation of cylinder deposits that can form hot spots and lead to preignition.
_________________
Kimble D. McCutcheon

[dpennings]

ZDDP was once a common additive in engine oils for cars. Many older engines suffer from modern ZDDP free oil (e.g. the Chevrolet Small Block engines), but youre right, it has disadvantages. For modern car engines it is unsuitable because it lowers the effectivity of the catalyst and will block soot trapps.

It can make sence to increase the amount of ZDDP in race engines, so STP was useful in this applications.

[rwahlgren]

All reply's above yes all well known info. But using it like the manual says and putting it on those silver bearings is the question.

[kmccutcheon]

[rwahlgren]

The Lead alloy overlay is on top of the silver on the bearings, so maybe okay. Later in the photo of the manual it says to mix it at a certain percentage with SAE 50 engine oil to lube everything else.
I don't think STP is an FAA approved lube for aircraft engines, so ?
Putting it in the cylinders, on pistons, on engine build up, its difficult to make a thin film with it? I don't think the starter would turn the engine?
SAE 40 would be a better choice.


Good news if true.
https://www.youtube.com/watch?v=P7bSnBnpg5g

[kmccutcheon]

[dpennings]

it might have nothing to do with the addetives, but with the viscosity. STP seams to be a very thick and sticking fluid (as seen in the Link), so it will help to prevent corrosion on the cylinder surfaces if the engine is stored after beeing rebuilt for a longer period of time.

According to my knowledge, ZDDP acts in areas with an high contact pressure (cam to cam follower) and not on cylinder liners. the ZDDP will form al layer of Zink on the contact surfaces, but therefor some operation time will be needed.

[rwahlgren]

[dpennings]

did the 4360 really have silver plated bearings?

According to the links above, the ZDDP content in older STP is very low (8 ppm) which is lower than the limit of 10 ppm (written in your link) for the EMD engines with silver plated bearing.

Maybe, at that time, the negative effect of ZDDP on silver just wasn't known as this bearing technology and ZDDP was quite new at the time.

Of course, STP might have had a much higher content of ZDDP in the 40th, since it must have had an effect, otherwise it wouldn't have been possible to convince commercial customers of it. For private car owners, the phycological effect is more important and 8 ppm is close to a placebo effect.

[rwahlgren]