akschu

akschu

Well Known Member
Patron
Hey Guys,

I'm sitting here thinking about lycoming camshafts and how to protect them and have a few thoughts I want to run by the group.

I know that lycoming camshafts work fine if you fly all of the time (don't let them get dry) and my engine builder says to not idle the engine too long which makes sense since the engine oils the cam much better at higher RPM, and because it's common knowledge that cam wear is higher at lower rpms which is why you always run a very high idle when breaking in a cam.

Those things said, some people say that the fix is to use the firewall forward cam mod where they drill holes in the camshaft allowing for forced oiling. I don't see how that would fix the dry start problem, but it would help with running your engine at idle, but then again simply not letting it idle right after engine start isn't that hard to do either.

Now, if I install a pre-oiler then my camshaft would never start dry which I think may work, but the cost is high ($700 for the cam mod, and $500-$1500 for the preoiler depending on if it's certified or not.)

Even if the camshaft is lubed before start, that won't help if I let it sit long enough to rust (which I try not to do, but would be kidding myself if I thought I was going to fly every week without fail) unless I went out to the airport once a week, flipped the pre-oil switch, gave it 2 minutes to lube the engine, then left.

Another option is camshaft coatings. I'm not aware of any certified process for this, but given that the cup cars use this process and turn at 9500rpm, I think this might be a good solution. It would prevent metal on metal contact and also protect the cam against rust. Seems like that combined with at least monthly flying and limited idling would make a cam go for a long time.

Anyone have any thoughts on this? I just want to make sure that my engine goes TBO if at all possible.

Thanks,
schu
 
Good points, Schu..

...but years ago in SCCA, we made pre-oilers from small, used fire extinguishers, mounted upside down. We teed into the oil pressure line and opened a valve on the extinguisher after the engine started. It put around a quart of oil under pressure in there as long as it was running. The main purpose was if we lost oil pressure momentarily from either heavy cornering or braking, the pressurized pre-oiler would push the oil into the system until the oil pump stopped cavitating.

Before shutdown, we'd close the valve on the upside down pre-oiler in the cockpit, trapping the oil under pressure and as we turn the starter the next time, open the valve and bingo, pre-oil. Some guys also added a tire valve so that if the pressure disappeared, they could re-pressurise.

My late boss had terrible wear problems with the cams and lobes of the Merlin in his P-51 and an engine guy recommended adding 10% STP at oil changes to give the oil more stickum since he only flew it once every coupla months and the long distance the oil had to travel before reaching the cams meant a lot of premature galling. Believe it or not, the cam problems essentially went away because the coat of oil/STP was still there. I use 10% in my 0-360 for that reason.

Regards,
 
Two diffeent issues

And which one is more important is up for debate..

1) Galling as you describe..Not sure if the accumulator I installed helps or not..i just like seeing the oil pressure come up before I start..I also have a block heater that I keep plugged in (1ooW no thermostat) that hopefully keeps the oil nice and runny. I also don't like seeing the oil presure drop as I go inverted..so this way I have an uninterrupted supply.

2) Camshaft rust..When fuel burns it makes water vapour..Some of the combustion gasses end up in the crankcase. i think it is likely the crankcase is full of saturated air at about 180F..Now air at that temperature can absorb a LOT of water..Much more water than it can when it cools to ambient temp..So as the engine cools the water vapour condenses on the upper part of the crankase, then drips down onto the cam..if the cam is not continually coated in oil..its rusts.

One way to prevent this is to build an engine dehumudifier from a fish tank air pump and a column of silica gel.. afew posts on how to build on VAF.

I got much more success with building a long narrow column (5 feet of 1.5 pvc pipe with end caps) than a short fat one like coke bottle.

So now I have an accumulater, dehumidifier and a block heater..I should never have to fly it eber again to keep it pristine inside..:)

Frank
 
Non-approved oil additives & RUST

STP, to the best of my knowledge, is a viscosity enhancer (VI) which is really just more of the same as what is already in your automotive 5w-30, for example. Yes, it may work. It also is not designed for the conditions found in our airplane engines.

Since we are talking about auto/truck products, take a look at Lucas oil stabilizer. I have never used it. I am only mentioning it because you are concerned about keeping oil on the cam and their in-store demo machine is impressive. They sell it a lot to truckers around here.

You could also use Tufoil. This product will provide benefits far beyond what STP or Lucas can. I don't know if they are compatible and would not use them together. I use this product even though the mfr. is not in favor of it (he flies a Bonanza) because it is not ashless. I run LOP a lot and have no problem with cylinder deposits from it. This product takes a different direction than viscosity.

Some folks use Av-Blend or Microlon. While both of these are "approved" for aircraft engines, I have grave doubts about their efficacy and would not use them. Microlon is just Slick-50 renamed, as far as I know. Av-Blend is also a renamed auto product. Both have had issues with the FTC over their claims.

Also take a look at CamGuard, an approved product for our engines. It was designed for the problem you want to solve. It's probably a very good product.

Lastly, I totally endorse the suggestion to use a dehydrator, store-bought or home-built. IMHO it is totally stupid to rely on oil alone when you can easily remove the water vapor that cannot be prevented.
 
I had my camshaft, bearings, pistons skirts and oil pump coated with the same stuff NASCAR and NHRA use. It reportedly reduces friction and holds oil. Have talked to others who had a 540 and P&W coated and were quite happy. Will be putting the engine together this weekend, so no long term data for you. But I can tell you it has at on a shelf in a hanger for about a year with not a spec of rust on it.
 
Last edited:
In the early 70's, it was Embry Riddle's practice to add a container of STP at each oil & filter change (50 hr intervals). I know as I was an A&P working for Commander Aviation in Ormond Beach who did half the C-172 fleet and C-310s (DAB did the other half of their fleet). We routinely made it to our insurance co. approved TBO of 2500 hrs. with absolutely no issues. I also got to see the innards of these time-expired O-320's as a student assistant to their A&P school (I was in academics working towards a degree). While we could have re-used the followers, we replaced with new. The cam's went back in as received. Note that most importantly, engines in ERAUs fleet are run regularly and even in that climate, never sat long enough for moisture to do damage. Will I use it in my TMX-IO360 when it arrives? Probably not - I'd prefer other means that keep the innards dry.
 
Another Option

Mattituck installs 4 spray nozzles high in the case halves to spray the cam lobes, so this is an option to drilling your cam. The nozzles spray in a conical pattern and make a fine mist or fog of oil spray. This is part of their TMX experimental engine package, but they did these mods for a reasonable fee on my previously certified IO-360. They also add an oil feed to the thrust surface at the front of the case, and put small grooves in the top of the case above the cam journals to eliminate oil leaks from the hydraulic effect of oil coming off the camshaft and being forced into the silk thread between the engine case halves. This has historically been a problematic area for oil leaks.

Yes, you still have the dry startup problem, but if using a preoiler and dehydrator, one should be able to preserve a cam (and other internals)indefinitely without running the engine regularly.
 
You must log in or register to reply here.