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STP in Aircraft Radial Engines?

 
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rwahlgren



Joined: 15 Aug 2003
Posts: 324

PostPosted: Sun Dec 20, 2020 17:33    Post subject: STP in Aircraft Radial Engines? Reply with quote

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

????


Last edited by rwahlgren on Mon Dec 21, 2020 12:32; edited 1 time in total
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dpennings



Joined: 10 Dec 2016
Posts: 48

PostPosted: Mon Dec 21, 2020 04:33    Post subject: Reply with quote

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.
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kmccutcheon



Joined: 13 Jul 2003
Posts: 298
Location: Huntsville, Alabama USA

PostPosted: Mon Dec 21, 2020 07:52    Post subject: Reply with quote

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.
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dpennings



Joined: 10 Dec 2016
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PostPosted: Mon Dec 21, 2020 09:49    Post subject: Reply with quote

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.
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rwahlgren



Joined: 15 Aug 2003
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PostPosted: Mon Dec 21, 2020 12:31    Post subject: Reply with quote

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.
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kmccutcheon



Joined: 13 Jul 2003
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Location: Huntsville, Alabama USA

PostPosted: Mon Dec 21, 2020 13:26    Post subject: Reply with quote

rwahlgren wrote:
But using it like the manual says and putting it on those silver bearings is the question.


The damage STP would do to silver would require some time. Using the small amount during a build, which would subsequently be washed away in the oil supply is not a problem.
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rwahlgren



Joined: 15 Aug 2003
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PostPosted: Mon Dec 21, 2020 17:56    Post subject: Reply with quote

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
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kmccutcheon



Joined: 13 Jul 2003
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Location: Huntsville, Alabama USA

PostPosted: Mon Dec 21, 2020 19:22    Post subject: Reply with quote

rwahlgren wrote:
I don't think STP is an FAA approved lube for aircraft engines, so ?


The manufacturer's overhaul instructions are FAA approved, so if the manufacturer recommends, it is legal. I've never used it full strength but mixed 50/50 with oil. Also, I would not put it in the cylinders as that would inhibit break in.
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dpennings



Joined: 10 Dec 2016
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PostPosted: Tue Dec 22, 2020 04:20    Post subject: Reply with quote

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.
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rwahlgren



Joined: 15 Aug 2003
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PostPosted: Tue Dec 22, 2020 12:59    Post subject: Reply with quote

dpennings wrote:
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.

If you coat silver parts with ZDDP and it stays on them for that longer period then, this pertains.
https://www.finishing.com/277/02.shtml and NOTICE the author says
ZDDP will cause engine failure. So yes it is all about the additives, and is why aviation piston engine oil DOES NOT HAVE ANY ZDDP IN IT.

I just found this, https://www.youtube.com/watch?v=mqiUFklL_XI
lab test results? Compare to this, https://www.youtube.com/watch?v=P7bSnBnpg5g
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dpennings



Joined: 10 Dec 2016
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PostPosted: Wed Dec 23, 2020 07:12    Post subject: Reply with quote

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.
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rwahlgren



Joined: 15 Aug 2003
Posts: 324

PostPosted: Wed Dec 23, 2020 12:50    Post subject: Reply with quote

dpennings wrote:
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.

I'm not sure what it has for bearings, I know they changed the bearing overlay at some point in commercial engines, not sure about the military ones.
The manual mentions about using silver plate to increase the thickness of some parts to improve fits. You may have something about them not knowing the affects back then. I did find out that overhaul shops do not do everything mentioned in the old 40's and 50's engine overhaul manuals. The one I talked to said they did use STP many years ago but not now.
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