akouzmit

On May 2013 I have purchased new OS GF40 from Tower Hobbies.
Prior that 4-stroke engine I had good experience with SAITO-14C/17/21/30 and 36.
These Saito engines are marvel pieces of equipment I love so much as they run so well.
I have expected similar experience from well reputation OS brand when they came with the first 4-stroke gas engine . . . and I wasn't disappointed at all . . . until about 6 hours engine in service (excluding one hour for brake-in period).
I have used the highest quality oil mix of 1 to 20 and flown my 2.4 m plane over 20 times until I noticed lost of power.
On closer inspection I have found that exhaust rocker axle is wear out ~40% of its diameter and rocker was loose quite a bit.

http://www3.sympatico.ca/akouzmit/Sa...le_wear_40.jpg

http://vimeo.com/77313341

http://vimeo.com/72599357

I have replace rocker axle once and flown another 10 times and this time I was waiting for lost of power and I noticed it earlier in about 10 flights with new exhaust side rocker and rocker axle.
close inspection shown the same wear on exhaust side rocker axle.
i have replaced it 3-rd time, pre-lubricated axle with special high temperature molybdenum based lubricant and ... Winter came with very cold and windy conditions... Leaving me to wait for spring time....

I have contacted OS support a few times sending them photos and video as evidence of the problem, but the answer didn't satisfy my expectation.


I'd like to ask all other GF40 owners if they noticed anything similar to what I described.

I have to say that engine was used at 100% throttle from 20% to 30% of the time.
The issue is looks to me as a luck of the lubrication at heavily loaded exhaust rocker which is also overheated during engine running at full throttle.
I have to say here that engine is mounted on the plane w/o cowl, thus cooling is just perfect.

This is my "TEST" plane I am using to brake-in new gas engines before they go to more expensive planes:

http://vimeo.com/72161738

As you can see it is fully exposed to air flow, thus cooling is not a problem in my case.

Please, post here your experience with OS GF40 4-stoke gas engine.

Thank you,
Andrei. Humber Valley RC Club.
Toronto, Canada.

youngguy

My Feedback: (7)

Thanks for sharing your experience. I was considering purchasing one for a scale model I have. I guess I will wait and see how this is resolved.

akouzmit

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I would advice you to go with SAITO FG-40 as a superior replacement.
I have Saito FG-36 one and extremely happy with engine.
Saito FG-40 is in the same size and weight as 36, but 4cc more powerful.
Saito used 36 one as a base and then widen cylinder and piston in order to get 40cc.
I have many Saito engines and I can tell you they are very reliable marvel pieces of equipment.
OS just entered that 4-stroke GAS market last spring and look like they didn't test fist 4-stroke gasser well enough.
Saito 40cc is a bit heavier compare to 40cc OS, but this is the only disadvantage.

Mikola

what was the answer from Tower ? did you contact OS japan ? did you get a new engine or free repair ?

akouzmit

Yes, the replacement or fix was offered, but:
1-to replace one badly design engine by the same badly design engine .... I do not see any reason to get the same issue in 4-5 hours with replacement engine;
2-I have great experience with mechanical stuff and I can fix (and I did it) myself.
3-after seeing this issue 2 times I believe it is design flaw and I expected OS to admit it and make some changes.
4-I love this engine except this one issue. When it go with replaced rocker axle it is running so lovely and so reliably that I don't want to give up yet;
5-I have a few great ideas to implement in order to fix issue my way and see this coming season if issue is gone.

The engine is very good in any other aspects and I really like it.
After total of over a10 hours it is starting and running super smooth idling at unbelievable 1140 RPM.
If I can resolve engine issue it will be one of my lovely engines to put on German engineers designed 2.4 m plane.
Until then assigned plane is still sitting in the box. :-).

Once again I'd like to hear some feedback from other GF40 owners.

AK.

kerwin50

Take the new engine. Never work on a new engine as that may void the warranty.

Mikola

silly reasoning... if you don't get a new one you will never know if it's just an issue of your engine...
anyway you are the only one posting this problem on gas engine forums. good luck

Mike.

akouzmit

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There are not so many GF40 sold since May 2013.
On this forum no one GF40 owner replied yet.
On the other forum, where I started thread at the end of last season I just got 3 replies from GF40 owners and it is in over 6 months by now, statistically speaking it is a bit premature to say that this issue is only with my engine.
Also those 3 GF40 owners reported that they mostly used engine with 50-70% throttle, but in my case I have been using engine about 30% of the time at 100% throttle. I believe it make big difference in temperature around exhaust rocker and where oil is evaporating .... reducing lubrication. At the end of last flight I opened rocker cover right away before engine cooled down and I did it intentionally to check lubrication.
I found that rocker on fuel intake side is very well lubricated, but at the same time the rocker at exhaust site is absolutely dry!
One non-surgical thing I'd like to try is to put larger prop in order to reduce RPM at full throttle ... more-less saving overall system thrust. I have noticed thar RPM grow with the same prop by about 500 rpm since braking in period due to moving parts loosening more and more in these 10 hours in operation. At this time it is on the upper boundary of the recommended rpm, thus in the air it is ~500 even more.
High rpm may be a contributor to the issue although I am using Saito engines in the same manner for a long time w/o any issue with lubrication.

Any GF40 owner is reading my post ?

AK.

SkyPilot101

I Think ! Your problem may stem from an improperly heat treated rocker shaft, and not overheating / lack of lubrication. If such is the case, it is probably an isolate ocourance, and a new engine would not suffer the same wear problem. I would have jumped on the chance to turn in the troubled mill for a new one, but that's just me !

if I understand your problem correctly, the rocker shaft is experiencing heavy wear from the rocker boss, but the rocker is not ?

akouzmit

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Yes, the rocker itself is "doing well" :-), but axle rocker sitting on
Please, see photo in the original post.
I also was suspecting incorrectly treated axle, but OS support sent me 2 new and one of them, which I used as a replacement got the same wear as the first one in the same conditions. I also was informed by support guy that over hardened axle has higher probability to be snapped from the load and it is why axles in 4-stroke OS engines are less hardened than rockers.
I believe the issue is due to luck of the lubrication, which is happening at high rpm causing overheating on the rocker side.
As I mentioned before the fuel injection side rocker and rocker's axle are perfectly fine.
it is not axle hardening issue.
AK.

ozzieflyer

I've had mine running since September last year, run over 10 litres through the engine, running a 18x8 and this engine for me has shown no issues, just getting better and better.
No wear that I can see or measure.
Running Petromax synthetic oil at 32:1.
Just love this engine, I bought another one.

MKnutson

I've been running mine for about 9-10 months now without any problems.
You had this issue quite a while back originally, and I've been watching mine ever since for wear.
So far, no excessive wear, not even valve adjustment needed yet, and it runs very strong.
Under the valve cover everything is totally oiled, but I don't run it at full throttle for any real long amounts of time.
Maybe you need a larger engine for what you need to do so as not to need to run it at full throttle so much.

Mark.

captinjohn

Send it back & get a new engine. Period!

akouzmit

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Hi Mark, Yes, I think full throttle and high RPM are the contributors to the problem.
Before I experience problem for the first time I was running engine in relatively relax mode for the first 3-4 hours before I went to full throttle for the next hour or two running engine 20-30% of the time at full throttle.
After that I noticed loss of power.
After rocker axle and rocker replacements I have run engine at full throttle 20-30% of the time practically from the beginning just allow engine to run first 30 min in relaxed mode.
And this second time I have noticed wear much earlier.
I think by running engine not at full throttle we are masking hidden issue in engine design.

I have to tell you that I am using SAITO FG-36 and FG-21 at full throttle close to 40% of the time ( for FG-36 even close to 50% of the time) and I have never run into such problem as with OS GF40.

This is why I was quite sure to start using OS GF40 at full throttle until I run into wearing issue.

Well , I am happy at list 2 owners replied to me with positive feedback ... although we are using engine in a different modes.

I am waiting for the temperature to go above freezing point to start testing my engine with 2 modifications:
1- I put larger prop to reduce max RPM at full throttle;
2- I have pre-lubricated rocker and rocker axle with high temperature molybdenum base sticky oil.

I am planning to fly 3-4 hours below 80% throttle and inspect rocker axle.
If things are OK I am going to fly the next 2-3 hour at full throttle 20-30% of the time as before and inspect rocker axle again.
At that point depend on results I will make a decision what to do next.

Thank you for feedback,
AK

BlackPhantomDragon

What size prop were you using and what size prop were you planning to go to?

ozzieflyer

I'm running an 18x8 as the local OS distributor has advised to let the 4 stroke petrol spin up, not to load it down.

Certainly early days, when I first got the engine, I had a bigger prop and it didn't sound or run as nice as it does now.

In the model I am flying, probably 70% of the time its been running at full throttle. Have checked under the rocker, nice and oily and so far none of the wear issues.

BlackPhantomDragon

Hey thanks Ozzieflyer
I am thinking of buying one for the Phoenix LA-9 I bought.
I have the OS33Gt in a Spacewalker ii and just waiting for a good weather day to maiden it.
Question about tightening the propnut with a spinner. The 33 seems to have a bit of problem in that as tight as I do the nut up the prop still moves and hits the spinner. Tried sandpaper between prop back plate and back plate and hub but still moves. Had any problem with the 40?

MTK

Curious, do you use a double nut on the 33? Is the prop wood, plastic or carbon? How much vibration is being generated? If your set-up is a little out of balance and the engine is hard mounted, vibes will loosen most everything.

I have several 33's and I use double nut on one of them because I had one available. It's not been touched in 100's of flights. On the other hand, all my engines are soft mounted so they probably don't really count. Soft mounting pretty much eliminates loose props if things are fairly well balanced

ozzieflyer

Never had a problem with either the 33 or the 40.
Just make it good and tight, well balanced, and I always use the double nut.
I have used both apc and wood props, not issues.

Maybe check the balance again on the prop.
Phoenix LA-9, now I'm jealous, I love the look of the plane, and the 40 will sand awesome, and really make it go.

akouzmit

New report on OS GF40 (March 31, 2014):
Very nice day (+10C, relatively calm conditions)
It is like a gift after long and cold winter J
Setup changes:
1) New rocker axle and new exhaust rocker as well (3-rd one since the original one).
2) Prop changed from APC 18x8W to Xoar 19x8;
3) Exhaust rocker axle pre-lubricated with high temperature moly-paste (molybdenum based lubricant);
4) Max RPM on the ground went down from ~8300 to ~7400 (prop change);
5) 20:1 Evolution oil mix as before (no change);

Trials:
Flown 2.4m plane 4 times by 28+min each time.
10% of the time at low-to-middle throttle and 90% time at 85% throttle;

Results:
Inspected exhaust rocker axle after 2 flights (after ~56min) =>No wearing at all, but exhaust rocker looks a bit dry compare to fuel intake rocker.
I have added a bit more moly-paste on exhaust rocker axle.
Flown two more times for about the same 56min.
Inspected exhaust rocker axle again after 1hour 52min in total (after 4 flights) => No wearing!
I also noticed that PCV valve spitting much less oil than before(last year).

My conclusion so far:
I think the main thing, which help to illuminate extensive wear on exhaust rocker axle ... is reduced max RPM.
With new prop it is about 7300-7400 RPM on the ground.
With old APC prop it was ~8300 RPM on the ground.
Taking in consideration that in the air max RPM is about 10% higher . . . I was on the top RPM boundary for this engine with APC prop.
Another thing, which support this is PCV valve, which is built based on ~2mm metal ball and spring.
At very high RPM that metal ball has some inertia and is not fully closing valve, which allow some amount of oil to escape. This is reducing the amount of oil going to the top of the engine for rockers lubrication.
I think lowering RPM is a key factor, which helped to illuminate excessive wear on the exhaust rocker axle.
Moly-paste may also helped a bit, but I can’t say for sure.

Another factor, which can play a big difference is engine orientation.
My engine is mounted piston UP, thus rocker lubrication is a bit lean.
I think most of the pilots are mounting this engine with piston pointing down, which definitely help with rockers lubrication.

This is everything for now.
Ahead of us spring and summer, thus more reports will follow J.

MikeAndersonCA

28 minute flights? Really? What are you flying?

akouzmit

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Yes, I am flying ~14 pounds 2.4m (90") plane for aerial photography. It has 900cc tank an can fly over 1 hour at 65% throttle. Once it is on the ground there is about 20% fuel is still left in the tank.
4-stroke gas engines are very economical on fuel consumption especially after over 10 hours in operation.
it is very common for me to fly this particular plane for 30-35 min 4-times in one day, which is ~2 hours in the air for ~ 3.5 hours at the field.
This plane can take 3.2kg camera on board with camera mount, but flight time then about 35min to be safe.
Andrei.

kipuetz

anybody know the specified valve clearance for OS GF40.?
Regards, Karl.

CustomPC

What are the specs on the Evolution oil you are using?

The first batches of evolution oil were actually Mobil 1 which is good stuff. More recent batches of evolution oil are totally different. Its blue in color and i suspect is morgans coolpower.

Nearly all 2-stroke oils are designed for just that, 2-strokes. They are not designed to lubricate valve trains and they tend to evaporate or varnish up on the exhaust valves because gas burns hotter than glow.

Try the Stihl HP Ultra, for 2 reasons.
Stihl make 4-stroke pre-mix engines similar to our model engines and the ultra is the oil that they specify in those engines.
It has the highest flashpoint of any 2-stroke oil i have found. Its not going to evaporate or varnish as quickly as other oils.

There are hundreds of anecdotal reports from happy Stihl ultra users getting good results.

Lastly 20:1 is not necessary in the OS. It had needle bearings on the conrod so 32:1 is fine. Saitos need 20:1 due to their bushed conrods.

kipuetz

Matt,
what do you mean by soft mounting you engine, can you please explain?
Regards,Karl.