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pwmac(at)sisna.com
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 Posted: Sat Sep 16, 2006 6:05 am Post subject: Rotax 9XX: TCP, Dip stick, Hydraulic Lock |
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Hi Eric,
Lots of subjects. Long discussion.
Syn oil:
The purpose of TCP (a fuel additive, not an oil additive) is to keep
the lead deposits from clinging to the valve stems. When this happens
the friction becomes greater than the spring force and the valve
hangs open causing the valve to burn and requiring a top overhaul to
correct. The TCP also helps prevent deposits in the piston rings.
Thus it is very desirable if using leaded fuel. I suppose there might
be some benefit in reducing sludge in the sump but I have never read
of that benefit. The stuff is commonly used in the lyc/cont engines
for the purpose stated. The kind of oil used in the engine is not
relevant to the above discussion
I forget what the oil additive is that Lyc specified for my C172 but
it was not TCP. Sorry. Maybe someone can fill in that detail. I must
say that all the engine issues I had with my Lyc had to do with the
valve sticking other than that Lyc said that for them to warrantee
the engine I had to reduce the oil change intervals and use the oil
additive. They just replaced the jugs to correct the sticking valves
and did not require me to use TCP.
Comments:
IMO, to be safe change the oil at short intervals and use semi syn.
But, is there a real benefit over a high quality petro oil? These
days the petro oil used in cars does not prevent the 200k mile engine
life. If one is using syn to protect against high temps it would be
more logical to get a proper oil cooler. If one likes the easier
starting benefit on syn then use petro with a lower viscosity and/or
a stronger RG battery. If one is using syn to get lower friction I
believe the benefit is very small. If one is using syn to extend the
oil change interval then the user is mistaken as the change interval
actually needs to be shorter.
The arguments for syn/semi syn are very weak when using leaded fuel.
Rotax does not REQUIRE syn with unleaded fuel. It is just one of the
options. Rotax strongly recommends using the motorcycle oil that has
the gear lube. This is applicable with petro, Syn, & semi syn. Not
many oils available in the US have been tested. To bad for us.
I wonder if the latest oil formulation has reduced the sludge
formation. There have been many recalls of autos due to sludge
formation caused by the use of petro oils in engines with high oil
temps. I noticed that Rotax now Requires the use of service grade
"SG" or higher
Dip Stick:
Another change that evolved from the US EPA wherein the oil
chemistry reduced the anti-foam additive because it was contaminating
the cat converters. However, this oil resulted in an improvement in
fuel economy due to additives that reduced friction. This change
applies to all oils including Syn. Rotax has identified some oils
that did not change as they were motorcycle specific and you will
find them on the approved list. Rotax raised the oil level in the dry
sump tank to account for the additional aeration due to foam and they
wanted to avoid any compromise in the lube system. Make me wonder how
such a small change could make a difference? There are oils available
that should not require the new dipstick due to old formulation, but
how long will they be available? Rotax published a new list this week.
Hydraulic lock:
This is caused by non-optimal location of the dry sump tank and the
use of very low viscosity oil. The higher the tank is then gravity
overcomes the ability of the oil pump and other system flow
resistance prevent leakage/drainback into the sump. This is
exacerbated by using very thin oil, especially after a hot shutdown
when using an oil like like 5Wxx (or full syn?). On older engines
wear in the pump creates less resistance to oil draining. I suppose
that one could increase the resistance in the oil line from tank to
pump to lessen this issue. Or add a flapper check valve for the
increased resistance. Beware, any change from the Rotax design
requires testing of oil flow rate and pressure at the pump inlet to
avoid engine failure.
BTW this is a generic issue with all dry sump engines but seems to be
more of an issue with the Rotax. Just be sure to check the oil level
before every flight. And if it is lower than it was when you parked
the plane after a flight then take corrective action. The auto racers
do not have this issue very often due to their use of very high
viscosity oil like SAE 50 and their use of scavenge oil pumps with
high back flow resistance instead of using crankcase pressure like Rotax does.
A 10Wxx or 20Wxx oil would be a recommendation of an action to take
to prevent drain back.
Comments anyone? Please cross post to both lists using the "reply to
All" button.
I hope this helps, Paul
==============================
At 03:49 AM 9/16/2006, you wrote:
[quote]How about this angle to the thread?
We know that Rotax states that the 912 motor requires synthetic
(with no 100 LL) or semi synthetic (for when 100 LL) is being used,
for reason of lubing the reduction drive.
But how about if you purchase the TCP lead scavenger fuel additive
from John at Sport Plane LLC / Kitfox. ( side note: John, why don't
you have your S.P.llc catalogue on your Kitfox site ?)
The way I am thinking of this is; If I use the TCP to remove the
lead, then there is no issue with the oil I use and we could use
full synthetic.
Any thoughts on this?
Another question. (New topic, KITFOX 912 OIL TANK DIP STICK)
For us who have the 912 with the oil tank behind and above the motor.
Why are we using the new replacement dip stick?
I know that there was a Rotax service memo about this.
This will only load the system more than full and you get a dirty
belly or you get hydraulic lock after the plane sits for a while and
gravity drained the oil to the lowest places.
This happened to me. It is a good thing that I always hand prop a
couple of times with power off. I would hate to think of what would
happen if I used the starter! Could have bent something.
Has anyone had the hydraulic lock problem?
Eric, Atlanta.
Mark,
All I know about this subject is from the Rotax bulletin on preferred oils
and the Rotax seminars.
Synthetics are recommended by them for unleaded fuels only. When using
occasional leaded fuels they recommend a synthetic blend or full mineral if
using 100 LL.
If you would like to read their bulletin on this, follow the links below to
the numbered bulletin. When I change oil, I wipe down the oil tank with a
papertowl and without fail, if I have been using 100LL as in a long cross
country, I get a pasty residue from the tank. It is light gray colored.
With the exception of the gear additive recommended by Rotax because the
engine oil also lubricates the gear box, I am comfortable with their general
recommendations for all four stroke engine types.
It would be good of course to have other data from other engine types to
eliminate the need to extrapolate.
http://www.rotax-owner.com/
SERVICE DOCUMENT RETRIEVAL SYSTEM
SI-18-1997 (2004)
SI-912-016 (2006)
Lowell
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