Info:

Engine: OS FS-70SII
Fuel: 15% Nitro 18% Castro
Prop: 13X6 MA
Fuel Tank Setup, - 2 line - (1) for exhaust vent to tank and (2) fuel supply to carb.


Symptoms:

1. Oil leaking through the exhaust valve port, through the plastic valve cover on the engine and ends up on the outside of the engine, creting a varnish on the ouside of the exhaust and smoke when I am flying - impressive but not desired effect!

2. Max RPM is obtainedat 3/4 throttle, no apparent RPM increase between 3/4 and full.

3. Max RPM at 8900


What I have done so far:


- Valve tappet clearences for both intake and exhaust were a little too big.. Closed the gap as per spec.

- Max RPM now 9900 (up from 8900)


My Thoughts:

Is this engine designed to have some blow-by through the exhaust port to lubricate it?

I am wondering if I have something in the head preventing the exhaust port from closing all the way (i.e. carbon varnish residue and the valve cannot close the valve all of the way...
Any help would be appreciated...

Geoffrey M.

.

My brother has this engine and it turns a 13x6 MA around 10200 using 10% nitro and 20% synthetic oil, so you're probably OK there.
If oil is coming out of the exhaust through the threads, using teflon tape or other thread sealant should stop it.
All of the oil in the fuel should be blown out the muffler. It is not supposed to burn. So, for a 10 ounce tank of fuel you should have 1.8 ounces of oil thrown into the air or on your plane.

This engine is a 4-stroke and the leak I am referring to appears to be coming through the exhaust port valve, not through the exhausut manifold itself (via a leaky thread/seal where tape would help).

I guess my questions is fundamental: Is oil supposed to be up in the Valve cover above the intake and exhaust vavles? I am guesing yes as lubrication is important for any engine, especially a 4-stroke that has valves. So I am guessing the source of oil comes from the cam shaft, up through the push rod casings and up into the head cover.. Unles of course there is blow-by is designed (through the exhaust valve into the valve cover) but after further inspection of the head when I took it apart, the valves look to have a tight seal on the top of the head

Does this make sense?

If so, then oil must have a method of escaping the valve cover and does so by dripping on the exhaust.... This is not a closed 4-stroke system where oil is sealed in and needs to be replaced and checked (like a car engine)

Am I way out in left field here?

Geoffrey M.

Oil does come up through the pushrod tubes to lubricate the rocker arms, springs, valve stems, etc. I think it also drains back through the pushrod tubes when the engine is not running. I cannot see any other passages on my engines that would allow it to drain. Since the engines have just a single ring, there is definitely blow-by that puts fuel into the bottom end. The blow-by is what lubricates the engine.

Firstly, unless OS has changed the engine mid production run, the rocker cover should be black and made of aluminium.

The engine comes from the factory with no seal or gasket on the rocker cover and they can leak in use. Many of us smear a little RTV sealant on the mating faces to seal this.

It is entirely possible - and in fact desirable - that oil is coming into the rocker box via the exhaust valve guide. My inverted Surpass .52 and .91's rocker boxes are usually full of oil when I've checked the tappets.

With a smear of sealant on the rocker cover and teflon or sealant on the exhaust threads, these engines are among the least messy glow engines available.

Oil will come through the exhaust port, that's how it lubricates the rocker arm and push rods and pollutes the silencer. As for the RPM, 13X6 isn't enough prop. You're having to run it too rich just to keep it running. I run a 14X4W on my 3d planes, a 14X6 on scale models and a 13X8 on sport models. Also, make sure you're using a quality 4 stroke plug. The fuel should be fine, I run 20 / 20 in mine, and I don't have excess oil leaking around the rocker cover. If you take the rocker cover off and the rocker arm is dry, you're running WAY too lean. Another thing to look for is the crankcase vent. If the line is crimped or the tubing is too small, it can send air back up through the pushrod tubes not allowing the oil from the head to go down the tubes.
Now I have a question. Did you buy this engine new? If so, did you do the break-in according to the manual?

Yes my rocker cover is aluminum (after a second look).....

I broke the engine in as per spec and it was purchased it new (although it sat in a box for 3 years without me opening it).... I was using a 13X6 prop as per the instructions on the kit (1/4 scale GP Cub - which I added on GP fiberglass floats). and from advice from others in this forum.... I was going to experiment with a 14X6 so perhaps that is the better way to go.

Sounds like everything else is normal with my engine, just some oils leaks through the rocker cover... I will apply some RTV sealant and I should be good to go...

I just wish the manual was a little more informative and explained how this 4-stroke was designed to lubricate itself....

Thanks everyone for your help!

Geoffrey M.

I've got a fairly new one that isn't that messy at all. Oil is supposed to blow by a certain amount to provide lubrication to the top end - that's the main source of lube for it by my understanding. I imagine some comes up from the push rod tubes but getting past the cam followers sounds like a trick to me.

I started mine out with a 13x6 APC and it ran fantastic at over 10k on 15% nitro. Over some break in time it just seemed like it was over revving with that prop so I put a 14x6 on it and it's just phenomenal. That's the same prop I run on my 91 4 strokes - this is a powerful engine and I'm contemplating buying another.