503 Help

[barandbrew]

I have a 503 with single carb and points ignition. The log says 295 hrs .

 

Can anyone advise me how to test condition of motor and what service should be done. The motor starts and runs faultlessly.

 

JOHN

 

 

[Yenn]

If it starts and runs faultlessly it is probably OK.

 

If you take off the exhaust and intake manifolds you will be able to see part of the cylinder and piston. If the cylinder looks smooth and the piston is clean with good rings, all should be well.

 

I had a cough and misfire with mine years ago, so did that inspection and the bore was visibly scored, so I pulled it all apart and found the bores perfect, also rings. The lighting I used to inspect made the bores look scored. I now believe my problem was carby ice.

 

When the motor is failing I would expect higher rpm required to maintain the same airspeed, also a change in CHT and EGT temps. If these all seem OK why not go a little longer although to hone the bores and replace the rings is not all that expensive and will give peace of mind.

 

 

[barandbrew]

Thanks Ian

 

Is there any way of telling the bearings are ok without stripping the motor

 

John

 

 

[prwood]

Yes, there is a bir-end bearing tester which is quite cheap & screws into the spark plug holes. Not quite sure how it works but I think it measures TDC & if it is within certain parameters then the bearings are ok.

 

Regards Pete

 

 

[prwood]

Sorry that was BIG-END. Fingers going faster than the brain as usual!!

 

 

[barandbrew]

Thanks Pete

 

any idea where I can purchase one

 

Regards

 

John

 

 

[prwood]

Hi John,

 

Not sure who would carry one here. Try Wal at Bert Flood Imports Vic 03-9735 5655 or even California Power Supplies in the States.

 

Good luck..Pete

 

 

[Guest micgrace]

Hi

 

Another gadget somewhat useful is a leakdown test. Easy to make at home. Simply braze on a airline connector to a sparkplug with the ceramic part knocked out.

 

Then simply connect airline (a few lb psi, otherwise send piston to BDC real fast!) to modified spark plug and listen. Air will then leak past rings, crankshaft seals , 2 stroke (should be none) etc

 

Said device is useful for diagnosing some strange problems esp rings & vavle problems, although 2 stroke crankshaft seals must be perfect as well and can give some strange and hard to detact problems ie difficulty starting or tuning.

 

Micgrace

 

 

[barandbrew]

Thanks Micgrace

 

I feel a little more confident with the above info to have a look myself now

 

Regards

 

John

 

 

[Thruster87]

The Heads and Barrels should come off every 150hrs and the needle roller bearings /piston pins/circlips replaced as this is a high wear/high temperature area.Also the breaker points /jet needle and needle jet replaced . Cheers

 

 

[Ultralights]

im in the middle of the 150 hrly on my engine, how do you decarbonise the engine as reccomended?

 

 

[Guest Teenie2]

You can buy a workshop manual from Bert Flood.There is also a web site called something like " airwolf " (do a search) they have info on how to work on 2 strokes + I think you can buy videos that show you what to do and what not to.I think its a Canadian site.If you cannot find the site Ill get it for you.

 

Teenie

 

 

[Yenn]

John.

 

I don't know of a test for main bearings but if they are poor there will probably be leaking from the crankcase, giving poor running and also telltale oil leaks.

 

I do know of 503 motors which have done over 500 hours with no bearing problems. I have a catalogue from I think California Power Systems, which gives a great deal of info on Rotax. It is at the airstrip so I will look it out before monday and see if there is any relevant info which I can forward to you.

 

 

[barandbrew]

Thanks everyone

 

There is no doubt RAA pilots are very friendly people and willing to help those with more limited knowledge and this forum is a great source of information Thanks again

 

John

 

 

[Yenn]

John.

 

I now have the CPS book in front of me and there is a great deal of info in it, unfortunately it does not show up on their web site which is http://www.800-airwolf.com. The info on piston maintenance is good and they also give info on pressure testing, stating that a leak down test is of little use for 2 strokes. They recommend using a normal screw in compression tester but you must get 300rpm min. and a minimum of 80psi and a max differential between cylinders of 10%. As you are probably well on the way to completion now, this may be of little help, but it would be good for peace of mind to get hold of a copy of the catalogue.

 

 

[barandbrew]

Thanks again Ian

 

I will get a copy it will be good refrence for the future

 

Kind Regards

 

John

 

 

[Guest micgrace]

leak down test

 

John.The info on piston maintenance is good and they also give info on pressure testing, stating that a leak down test is of little use for 2 strokes. They recommend using a normal screw in compression tester but you must get 300rpm min. and a minimum of 80psi and a max differential between cylinders of 10%.

I don't quite agree with a leak down test not being of much use in a 2 stroke. If one has piston at TDC all ports are closed. However, air will find it's way past the rings into the c/case how much gives a solid indication of leakage. Remember the rings also work in reverse in a 2 stroke, see details why below.

 

Since it also goes into the c/case it also provides an indication of the health of the c/shaft seals which in a 2 stroke are critical for correct engine running

 

When the piston descends, it will somewhat compress the mixture in the c/case (say, 2:1) which helps to get it to the intake port to help "push" out the exhaust gas (main reason 2 strokes gobble fuel)

 

Since the easiest path for the mix to escape is the c/shaft seals it will go that way. However, this isn't immediately obvious hence the need for some sort of crude test. This is unique to 2 strokes, this escape of mixture problem.

 

A bit of thinking will suggest the escape of mixture via c/shaft seals and insufficent c/case compression will severly dilute the incoming charge to the engine combustion chamber.

 

If you ever wondered why a 2 stroke will give the "false" impression of running the best it ever did before blowing, this is why. The mix is now closer to stocheiometric = more power. (may have been difficult to start) Just turn the fuel off to see what happens!!

 

As for a compression test. It's a must for all engines, but for 2 strokes it gets complicated. A theoretical compression ratio of 9.5:1 will NOT give a corresponding reading of, say, 180 psi but will be more equivalent to a C/R of 6.5:1 of say, 90 - 100psi. (80 psi bottom limit) Look up the repair information to be sure, this is just a generality.

 

As for rotax, I haven't seen one fail (seal) but you never know. It is relatively common on land bound engines. ie m/bike and l/mowers and they fail.

 

Micgrace

 

 

[vk3auu]

Bearing tester

 

Thanks IanIs there any way of telling the bearings are ok without stripping the motor

John

The bearing tester mentioned is basically a dial gauge which sits in a fitting which screws into a plug hole. There is also a small pump which can suck the piston up and down when it is placed at top dead centre without the crankshaft moving. The dial gauge then measures the total play in the little and big end bearings.

 

 

[Guest Teenie2]

Its called a Cyclone bearing tester.

 

 

[Knighty]

Unfortunately with the cyclone bearing tester it will only let you know when the bearings have excessive wear and by this time the engine is about to go bang anyway. Once the case hardening on the bearings start to fall away it only takes an hour of hard work for the rapid deterioration to take effect. I have seen a Rotax motor tested fine without any sign of abnormal wear and manage to throw a bigend in another 5 or so hours and seize. This was not due to lack of maintenance or faulty fuel/oil quality or ratio! Please keep in mind, bearings and case hardening are funny things that normally work one minute and fall apart the next without warning and especially if they are under extreme load as per a 2 stroke on takeoff & cruise.

 

My 2 bobs worth.

 

Knighty

 

 

[Yenn]

For what it is worth, a friend of mine with a Supercat with 503 Rotax, landed on an island beach along with several others. When it came time to leave it wouldn't start, so we took the cowls off and looked at it, nothing obviously wrong. Gave it a bit of a prime and after replacing the cowls it started and ran beautifully, sounded sweet. He went back to his own island airstrip about a couple of miles. When i next saw him he had the cylinder head to show me. It looked as if someone had taken to the inside with a jackhammer. The little end bearing had disintegrated and gone through the bottom end, some needle bearings had gone through the port and done the damage and this happened while he was travelling home, it still sounded OK when he shut down he said.

 

I don't know if any bearing test would have picked up the problem before it happened but we certainly couldn't hear it.

 

 

[Knighty]

Yep, when they want to go bang the engines do it on their own time without warning, nasty little blighters aren't they?

 

Knighty

 

 

[ZULU1]

503 motors

 

I have seen those units do a 1,000hrs with mineral oil and still tough. I know that Ratex advise otherwise but those cranks are real good. I wouldnt touch it until 500-600hrs (except decoke). The 503 is derived from the snowmobile design. BUT its still a two stroke. My last 582 blew at 190hrs and again at 370 hrs, hence the last two stroke I will own !!

 

Just steer away from synthetics as I have seen a few pop using those oils and keep to unleaded as much as possible. I have even seen water absorbed as premix over night with synthetics as we drained water from the fuel next morning.

 

I quite like the 503 though..

 

Cheers Paul

 

 

[eastmeg2]

There's a good article in the July 07 Soaring Australia - HGFA Mag, about oils for 2 stroke Rotax engines. it does mention that the Synthetics will attract water and not to use synthetics if the engine will go for any length of time more than a few weeks without being run.

 

Apparently the absorbed water creates rust pits on the crank and before you know it your 503 or 582 goes POP. So it seems that onyl way to go is with the mineral based oils.

 

Rgds,

 

Glen

 

 

[ZULU1]

Synthetics

 

Thats quite interesting and is exactly our observations. Although I am not qualified to comment in a technical aspect the cranks were pitted and the bearings in both my incidents had in fact exploded. The engine was using a Fuchs semi-synthetic oil, with a mix of Mozambiquan (87 or whatever rubbish) and 100LL avgas to get the octane up to something respectable. The ambient was 40 plus and humidity between 80-90% most of the time. I was using the 582 auto lube and still added some oil to the fuel.

 

Strange phenomena was that the engine kept running hotter and hotter, egts remained perfect. Fuel consumption went up to 22 ltrs per hour and that was it at 190 hrs!!

 

The SA forum has a lot to say all the time regarding oils, chainsaw and otherwise and this depends pretty much where you live. In Jhb. it is not as humid as the coastal regions, they get away with it. At a starting point of 6,000ft they need all the power they can find and tend to use synthetics (which apparently improves power). I would from expensive experience not risk it.

 

Whilst on the subject, the SA forum has found a fuel filter that is too fine, this is a small glass type. Very smart looking toy..It has been responsible for several (expensive) engine outs. Rather stick to the standard M Benz diesel filter which give good service in harsh conditions much the same as experienced in the bush of your part of the world.

 

After changing to 4 stroke power, i run the motor as hot as possible within limits, the HKS states max 120 degrees and uses Synthetics, this evaporates off moisture (at least I hope so). No worries in 260 hrs which for me so far is a record !!

 

Safe Flying

 

Paul