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View Full Version : why some 2 stroke engines fail and others go on for 1,000's of hours



andy dixon
21-11-10, 19:24 PM
some 582 cranks fail at 300 hours and others go on for 1,000 hours......even when fitted to the same aircraft with the same prop and flown from the same airfield.

For 25 years I've been building and re-building motorcycle engines for racing and speed,I first got involved in the racing engines whilst working for the world record breaking Padgetts of Batley,in their workshops as an engineer, so when 20 years down the line i purchased a quantum 582,i could not understand why some cranks fell to bits and others lasted 1,000 hours and more !

It would all seem to be the balance between cylinder head temp' and exhaust gas temp'.
It would seem that if you trim your prop angle to keep them both in harmony with each other (that's E.G.T. & C.H.T.) ,then the cranks last longer.
Having re-built probably 50 or 60 of these engines over the last 10 years (even before i started flying with one) and having half a dozen blown up ones sat on the shelf to look at and ponder over,i came across this talk on the Internet.

this 90 minute talk could be a bit "deep" for some readers,but others may just get the 'jist' of it !
it is by Brian Carpenter of Rainbow Aviation,a guy who is considered to be the world's best on Rotax 503 and 582 engines in light sport aviation

http://www.eaavideo.org/video.aspx?v=626943072001


not wanting to blow my own trumpet, but here are a some photos of a fire damaged engine i was sent for re-build,and the other photo is of the engine after a complete re-ferb.....every engine i do gets the "pretty look"
(all the original parts were used,just a new gasket kit and oil seals,vapour blasted every single part,even painted the head blue,i put the engine on the customer's 'school aircraft', and it is still doing well)

32543255325632573258

andy dixon
21-11-10, 19:44 PM
and this was a customer's 447 engine & gear box that had been stood in a garden shed since 1988.
i had a budget of 250 quid for a full strip to the last nut & bolt and re-build
.........

andy dixon
21-11-10, 20:29 PM
don't know why you shouldn't get them,my p.c. is a real dinasor,plus i'm a bit thick with computers and mine gets it o.k.
shure someone on hear will be able to help you russ.

GregH
21-11-10, 20:45 PM
That 447 looks fantastic, great job on both Andy!

martin rice
21-11-10, 21:05 PM
Crusty ? have you got your kiddie screening (security thingy) set to high?

Nickjaxe
21-11-10, 22:08 PM
Andy the way I read that video was that the pistons are the things that suffer not the cranks.....my guess why cranks fail...neglect....lack of use whilst using fully synthetic oil which is not supposed to be very good at corrosion prevention if the motor is not used on a more or less daily basis.....moisture in fuel again corroding the bearings ect. perhaps over revving due to flat a prop,

Have a look at this video about preserving your crank again by Brian Carpenter, http://www.eaavideo.org/video.aspx?v=680849310001



Nick.

andy dixon
21-11-10, 23:05 PM
oils are always an issue.....

mineral sticks the rings up,because it sticks to everything and won't let go......good if you don't use your engine much
fully synthetic is designed NOT to stick to stuff......so not much good at long term rust evasion
semi synthetic.....obviously half way between the two....

which oil should you use.........which came first,the chicken or the egg ? not a clue !

and yes pistons seem to be more of a problem than piston rings


for winter stick a cork up the exhaust and a plastic bag around the air filter,then as the air pressure changes it does not suck damp air in and out of the engine. ( but the bag can inflate to adjust the pressure)

in winter always stop your engine by pulling on the choke.....that way you get plenty of fuel/oil mix in the engine,the fuel evaporates and leaves the oil behind......

Mike Sands
21-11-10, 23:11 PM
Andy - funnily enough I was just thinking about getting my engine mirror polished. It's a 582 blue-head with 400 hours. I guess you have to have it completely stripped so that you can work on all the separate casings?
When I used to post on forums many years ago, I used to defend the 582 engines when everyone was switching to 4 stroke. My main point was that in all the failures you heard about it was rarely the engine itself that gave up the ghost, and much more likely that carbs had dropped off, or exhausts, or all the water had gone (3 times on mine). These kind of issues were just as likely to happen to 4 strokes .... and apparently have been happening with a vengeance on the 912S.
I check my 582 with a compression tester, and a cyclone wear-tool, every 10 hours, and at the same time inspect the piston crowns through the plug holes. I would be happy to run it for another 200 hours without stripping it, but the problem is I need to sell it and whoever buys it will want the confidence of having had it stripped and checked. Do you do this for a living? It would be a bit easier for me rather than take it over to Ecclestone as I think you are based in York aren't you?
Mike

Bob T
21-11-10, 23:12 PM
Wise words Andy. In a 2 stroke I would use semi, but in a 4 stroke I will always use full synthetic as I know it withstands much higher temperature without breaking down.

Max
21-11-10, 23:15 PM
Andy those engines look the nuts! Do you think Charlie Fox should have a rebuild, shes only done 64 hours but then again has been sat for 5 years....

Max

andy dixon
21-11-10, 23:46 PM
MIKE SANDS......QUOTE.....Andy - funnily enough I was just thinking about getting my engine mirror polished. It's a 582 blue-head with 400 hours. I guess you have to have it completely stripped so that you can work on all the separate casings?

SENT YOU A p.m. MIKE

Kestutis
22-11-10, 08:42 AM
Everybody say full synthetic collects moisture. But everyone in our club use full synthetic for many years and they are not daily fliers and no rust was found during engine strip ever ...

We use Castrol, Total and Shell ...

P.S. I put NGK BR8IX (iridium plugs) into my inverted 447 - nice and easy start first pull every time and it added about 100 rpm too :)

Bob T
22-11-10, 10:23 AM
The old spark plug thing has been doing the rounds for years on the motorbike forums, but I don't believe that you will get anything more than a new standard spark plug.

Mike Sands
22-11-10, 10:39 AM
I've always used the full-choke-to-stop method (summer and winter), with silkolene comp 2 plus (semi synthetic). When I inspect the pistons the crud is always within the 0.5mm limit. But here's the thing .... I used to strip the top end down every 50 hours as per the original recommendations, and there was never much carbon build-up. BUT always the ring (or rings, I can't remember) were stuck in their grooves. I can guarantee you that if I stripped the engine now the rings would be stuck and no way would I be able to get the oil ooze thing that is supposed to be the check. But the compression is great. At first I believed that the rings were stuck when the engine was cold but as soon as it fired up they 'melted' and freed up, but there are two problems with that theory. The compression when cold would be very poor leading to poor starting (which it doesn't), and since I started checking compression with the engine cold and it's still good, it must be simply the movement of the pistons that is freeing the rings in their grooves.
Mike

andy dixon
22-11-10, 11:03 AM
326632673268

people could not understand why rotax recommend you strip and inspect the crank on a 'blue top' at 300 - 350 hours.
i took the top off the engine in front of the customer,the customer said don't bother stripping the rest of it because it looks fine.but you could not see the crack from looking down the "hole" but i could just feel a clicking on my fingernail as the crank went round.

anyhow there was a bit of a damp patch on the p.t.o. end of the oil seal so it got stripped whilst the customer watched (he wanted to gain some knowledge)

these pics are what we found,the engine was probably 3 or 4 hours from disaster !
(and this was only last year,not 20 years ago when materials were poor quality) engine was made in November 2006
poor guy had to pick his jaw up off the floor !

please download the pics and blow them up to a good size.......

Bill Scott
22-11-10, 14:12 PM
Just a thought on shutting down the 503..... As it doesn't have a choke, I simply bring it back to idle and then cut the mags. That seems a bit gentler than just cutting it when it's running at higher speeds.
Andy, Does that seem sensible ? I'm thinking about the gearbox mainly.

Sam
22-11-10, 16:26 PM
Andy, looks good to me, but I have no idea what I'm looking for !!!

How many hours did this engine have ?? Your worrying me as I have a blue top with 295hrs which has just had another 100hr service (not 300hr service) plus crank/bearing clearance test.

I guess the clearance test isnt going to reveal all possible problems !

Where abouts are you and how much do you charge for a rebuild ?

Nickjaxe
22-11-10, 17:38 PM
Mike its as far as I know its the lower ring that normally sticks and the top one takes care of all the compression....I did read somewhere that they will run fine with just the top ring...but the lower one helps keep the piston centred and stop slap....right or wrong I dont know,

I know last time I de-coked my 503 at 50 hrs on new pistons...the lower rings where sticking in there groves the top where free....and had also heard that the lower rings free up when the piston is hot,

So as an experiment I heated the piston with an electric hot air gun....sure enough the ring was soon free in its grove with not a lot of heat.

Nick.

andy dixon
22-11-10, 20:12 PM
SAM.... i will send you a P.M. also

on the 3rd pic there is a crack in the crank lobe about 12mm long,it's cracked right through but is almost invisible from the inside but is so obvious from the outside (you can't see the outside 'till you do an engine strip)

the crank had done 350 hours over 27 months,the guy purchased the engine brand new and had never been in bits until i took it to bits.


BILL...........never known an A or B type gearbox fail of it's own accord,they are a fantastic gearbox.

as a rule 377/447/503 engines like to be above 2,000 rpm where they will run very smooth......532/582 like 3,000 rpm to run smooth.
if you have no choke to flood the engine,the only thing you could do would be to flick the mags off and instantly put on full throttle to pull through as much fuel as you could
so the trick to stopping abnormal engine/gearbox wear, all them little brackets snapping off your engine and cracks in alloy plates etc. is to try and keep the engine off tick-over..........
.......but the cost of the extra fuel used would probably be 20 or 50 times the cost of the maintenance costs

MAX......... 64 hours is nothing as for engine wear,but 5 years stood is something to consider,but in saying that you have had the engine running and it seems fine. only things to worry about with stood engines are oil seals and gaskets rotting,apart from the usual corroded aluminium

Max
22-11-10, 20:29 PM
Thanks Andy - as the engine will be off anyway how do you suggest I get it to look as good as the ones earlier in the thread? Just lots of elbow grease and polish?

Max

andy dixon
22-11-10, 22:17 PM
MAX.............. i strip the engine down to the last nut and bolt,
take all the bits for vapour blasting.....
the bits that are going to be painted go for 'alkaline' etching,then electrospraying and left in the low bake oven for 48 hours.(never had the paint flake off ever)
aircraft grade 8.8 stainless bolts and nuts etc, or new yellow triple anodized over zinc aircraft grade.
use the correct paint for the part your painting
all new genuine gaskets
and of course a lot of hours work the customer never sees.
it takes 2 days to strip and build an engine......it takes about 3 and a half days to do the same strip with the mint-up job.
the price difference is about 100 quid including all the extra parts........

it's more cost effective (for me) NOT to mint the engine but 99% of my customers want the minting job as it transforms the bike or trike it's going on.

Max
22-11-10, 22:23 PM
Thanks for that Andy - When Charlie Fox needs a rebuild I know where she'll be going ;)

Thanks

Frank Thorne
22-11-10, 23:30 PM
Do you electro spray the exhausts and if so who does it and what paint?

andy dixon
28-11-10, 14:08 PM
found this article that makes good reading.....if you click on the link you will get the pictures too
http://curedcomposites.netfirms.com/twostroke.html


Two stroke engine mystery solved



This article relates to the Rotax brand, although there are others in use, their numbers are small and I don’t have first hand experience with them.
As you probably know, two strokes have a bad rep. Most of it is well deserved and they do quit, however there is more to that story and it really doesn’t have to be that way.
Here are the reasons, first the generic, the two stroke engines require to be installed and operated (tuned) in a specific way which is different then your average GA four stroke, the difference is actually small but the consequence of not following the rules is far les forgiving with severe bad results .

Unfortunately, the manufacturer itself makes no attempt to educate the user how to run these engines properly, in the enclosed manual they tell you the max RPM,EGT, CHT range and that’s it, there is absolutely no mentioning how to select the correct prop for the speed range of the aircraft and how strongly the load on the engine affects its tuning (Rich/Lean) which happens to be one of the most common reasons for the engine seizures.
Now, that the word seizure is out , we have to know what it is and what causes it. Two main reasons cause the seizure.

1- high temperature difference between the cylinder and the piston which will result in insufficient clearance between the two and causing too high friction , melting the side of the piston and smudging it onto the cylinder wall,

2 - lack of lubrication, creating basically the same result .

What prevents the seizure under normal running condition,

1- we mix oil with gasoline or sometimes inject it (better way when done properly), to keep those parts lubricated.

2- keep the temperatures - specially that of the piston under control and this is the tricky part, the piston is cooled by the fresh cool air/fuel mixture entering the crankcase and by keeping the combustion (EGT) low enough by setting the mixture on richer - cooler burning side. Here you can see how leaning the mixture is a double edge sword , the combustion temperature (EGT) goes up and at the same time amount of oil for lubrication is reduced. This is why a seizure is most likely caused by the combination of the two factors rather then one or the other.
Here is the most important fact, the two strokes, not having the valves to control the fuel charge/exhaust discharge rely on so called tuning of the engine, which is a function of the exhaust system , piston porting, carburetor setting, and (Which is almost newer mentioned but equally important ) - the load on the engine, all these factors must be in harmony, and you can’t for example make up for too low engine load (which creates lean condition - high EGT) by increasing the jet sizes to make up for it and lower the EGT that way. Why you ask, because now your carburetor is out of tune from the "piston porting " and exhaust system design, two wrongs will not make one right, you may manage to keep the engine from seizing that way , but fuel consumption will be high, temperatures will read odd , peak power will be less and carbon will build up faster.

So now (if you’re still reading this) if so many of these seizures are caused by too low engine load why does it happen so often. Here are the typical reasons.

1. The pilot is descending in a shallow descent at a relatively high airspeed and throttle partially open (about half way or so). This is very dangerous setting, the mixture will lean out significantly but it does not necessarily shows up as too high EGT because the engine is not really producing much power and remember its not necessarily over the limit EGT but rather the difference between the piston and cylinder temperature . All three bad conditions are met here , combustion (piston) temperature is high, cylinder temperature is low (not much power produced) and low amount of oil entering the engine. Even an engine that is otherwise well tuned can seize this way.
I recommend to do your descending at only slightly above or at idle rpm at slow airspeed somewhere between best glide and best sink.

2. Static rpm too high caused by pitch on the prop set too low. Many people seem to think that if the book for their 503 engine states max hp develops at 6500 , that’s what they should set it for (down on the ground), some even believe the more rpm, the more power they get and use the max rpm number .These numbers are way too high are very likely to cause very lean mixture conditions in flight, because when the aircraft is in motion the prop unloads and the rpm will soar , then in cruise mode with the throttle retarded to keep the rpm in check very lean running condition is created, this should be indicated by high EGT but often people don’t pay enough attention to these warning signs , and/or don‘t realize how dangerous this really is until its too late.

The static rpm should be set well below the max hp rpm and the optimum depends largely on the speed range of the aircraft, generally the higher the cruise/top speed the lower the static rpm is set even if that means lower then max hp rpm in climb mode. Only on very high drag aircraft with very narrow speed range you can set the static rpm higher so it gets close to max hp in the climb mode as you will not unload the engine on such an aircraft even when you level off to cruise.

3. Another potentially bad combination is using very large (diameter / blade area) prop for a given engine, in which case the pitch must lowered considerable to bring the engine up to the acceptable RPM. In this case, even when the static rpm is rather low, the engine load will start dropping very rapidly as soon as the aircraft start gaining the speed . Only very slow aircraft can use such a combination successfully , perhaps a special purpose one like a hang glider tow plane or a powered parachute.

Unfortunately I see just such bad a combination on the new Ison’s airplane. They are using 62 inch powerfin prop, 2.5 gear ratio, on only 22 hp (???) , that’s a very large prop for that engine, In my guess the pitch will have to be no more then about 23-24 inches . If I’m correct, with this combination at 6000 rpm the prop blades will be at zero angle of attack and zero thrust as soon as the airplane reaches airspeed of about 55 mph.


4. During past 15 or so years with the ultralight movement on the rise, many conventional aircraft designers, some of them well known and capable, realized the great potential of these small size, light weight , low power two strokes have to be used for a new kind of very small, light and fast aircraft, I mean low power by their standards as anything under 100 hp is low power to them, a number of them were build but unfortunately quickly found out about the pitfalls of those little two strokes and usually the hard way. Many experienced engine failures early in flight testing , many aircraft were destroyed , the little two strokes were labeled unreliable and unsuitable for "real" airplanes and projects abandoned, creating a good part of the bad reputation. It is my believe that this low success was mainly for the lack of knowledge of how to use these engines properly, they had no experience with them and tried to use them in a very difficult application, not knowing the difference from the old four strokes .

There is however at least one great success story . The Mike Arnold’s AR-5 powered by rotax 582 holds the word speed record in the up to 660 lb category - 212 mph (or something like that). To hear from Mike himself click here

Another very good page written on the same subject in different words is here

Legal disclaimer: This article is only a one man’s opinion and may contradict with experience and advice of others .

Bill Scott
28-11-10, 21:16 PM
Andy, I have a 503 in the Mighty Rans and pre-mix my fuel. So, I'm always running at 50:1, would you agree that is perhaps a bonus in terms of protecting the engine from some of the problems described above?

andy dixon
28-11-10, 22:52 PM
yes i think it is, i took off the oil pump system and went over to pre-mix in the fuel,probably use twice as much oil and need to de-coke more often but it is a price worth paying in my book.....also i now taxi at slightly higher revs to stop the engine from rattling and shaking about

Bill Scott
28-11-10, 23:03 PM
Ah yes, de-coke at 50hr intervals........... Or, maybe a dash of Redex in the pots to clear it out perhaps? ;)

Nickjaxe
03-12-10, 20:25 PM
KESTUTIS, you say all your mates use fully synthetic.....what's the climate like in the country where you live....is it warm and dry or damp and cold like the UK.

Nick.