I received Ed Kollin's permission to re-post this here. It is the clearest and most thorough explanation of the subject I have ever read. The rest of this post is Ed's,

Camguard has been used for over 3 million engine hours spanning 17 years. Camguard contains no friction reducing additives precisely because of the Continental starter adapter. It is friction neutral. It does not affect the friction coefficient of the oil it is used with. The anti-wear additives in Camguard protect the 2 components in the adapter that wear. See below. The adapter has oil flowing through it.

There are different kinds of phosphorus anti-wear additives that provide wildly different friction coefficients. The phosphate ester in the Aeroshell 15W-50 and W100Plus is a very good friction modifier in piston engines. It decomposes readily to form low friction phosphate anti-wear films. However, one reason it decomposes easily is because it hydrolyzes (breaks down in the presence of heat, moisture and metal) to an oil soluble phosphoric acid derivative. Not particularly desirable.

The phosphorus compound in auto oils (ZDDP) forms a high friction anti-wear film that negatively affects fuel economy.

The small amount (110ppm) of phosphorus compounds is Camguard are friction neutral, intentionally, as are the other ingredients, because of the Continental starter adapters.

And for clarity, it is NOT the synthetic base stock components that affect the friction coefficient, but the additives. You can have the same slippage with 15W-50 (semi-synthetic) and W100Plus (non-synthetic).

Old Style Adapters

The older style adapter contains a heavy spring with a gear at one end while the other end is captured in a housing sleeve. There is a shaft that runs through this spring and it has a gear at one end that connects to and turns with the engine. When the starter is engaged, it turns the gear which winds the spring down (because the other end is captured by the sleeve) until it tightens on the shaft. At this point, the captured shaft begins to turn with the spring and cranks the engine.

When the engine starts, and the key is released, the spring unwinds (as springs do) until it is fully relaxed and it no longer touches the now spinning shaft. For the spring to unwind and release the shaft the starter must turn backwards freely when the power is removed. If it does not, it sets up a high wear situation of the shaft and the spring surfaces where they contact each other.

Think of a Chinese finger trap where one of your fingers was a spinning shaft and you are pulling them so the trap tightens. This is what happens when if you use a starter that does not release. This is the case with the Iskra starter or a lightweight starter that has been cranked too long and has overheated (affecting the bearings and making it hard to turn). The ONLY starter I recommend is the “Heavy” Delco starter. You can simply test your starter motor. If you can turn the nubby shaft both ways with your fingers, you are fine.

If there is wear of the shaft and spring (because the starter does not release) then the spring needs to wind down further to grab the shaft. At some point the spring is wound so tightly and the outer diameter is reduced sufficiently that the other end of the spring (the sleeve captured end) cannot hold and you get slippage.

This housing sleeve is the interface that is susceptible to slippage due to friction modifiers. And ONLY a worn (marginal) spring/shaft can be affected by low friction lubricants. An in spec adapter CANNOT BE MADE TO SLIP, I have tried!

New Style Adapters

The latest incarnation of adapter does away with the sleeve and uses a much thinner, lighter and more flexible spring. A small amount of friction is all that is required to wind the spring onto the shaft. These adapters do not react much to the frictional characteristics of the oil/additives. However, they do have MUCH more fragile springs. Used with lightweight composite prop and a mistimed engine can spell disaster for the adapter. If the engine kicks backwards the adapter spring breaks where it bolts to the gear forcing the need for replacement.


Ed

Edward Kollin
Technical Director
Aircraft Specialties Lubricants

Awesome! Thanks.

More information from my mechanic via Niagara.

Don't know if you have an early or a late adapter? Easy way to tell, pull the prop forward aways, then backwards. If it's as smooth going backwards as forwards you've got an early adapter (the spring is not in contact with the shaft). If it feels a little tight, and you hear or feel a "ratcheting" - you got the late adapter (the spring is still in contact with the shaft).

Pretty clear to me which adapter I want on my plane. And mine is the old style. Old school is the best school. In this case anyways.

When did the new-style starter adapter come into use? From the above description, mine sounds lke a new style-- 1993 factory reman engine, adapter's never been replaced.

My take on this one is that I prefer the new style. Don't mind hand propping and if it does break, can hand prop it till get time or somewhere to fix. Mine breaking was most likely a result of bad mags, operator error etc. When I sent mags off for overhaul one of the cams was shot and everything was pretty much wore out on both. So yeah I'll take the clean breaking spring over the one that can bind and your screwed if your out in the boonies, which is where I usually am. Anything that runs the risk of putting metal in my motor is no Bueno IMO. I think both styles suck and it's too bad Continental doesn't have a setup like Lycoming. They could have atleast not put it on the very back of the motor in the hardest to reach spot possible [emoji28]