OS FS81-a Alpha destruction

[Geoff S]

Posted by i12fly on 25/12/2016 22:35:00:

Geoff beware, Derby bearings used to be very helpful and low cost but the last time I went the cost had risen dramatically and one I wanted they said wasn't made anymore, which was untrue so I bought online. I must say it was 2 years ago so they may have improved. I think the really helpful chap left.

It's nearer 5 years ago since I bought any bearings from them so my experience isn't recent. I know buying bearings always seemed a mystery to me. I used to buy them for my motorcycles and was usually offered them at up to a (supposed) 75% discount! I got a full set of 4 wheel bearings once for the (alleged) price of just one. Probably different now.

I buy a lot of stuff from Ian at Modelfixings (he's local, too) but never bearings. However, I would have no qualms about his service in anything he supplies so I guess his bearings will be good.

Geoff

[Keith Evans 3]

I've bought a number of bearings from Modelfixings .Very reasonable , and quick delivery as well .

Keith

[Tim Flyer]

 

Hi guys I had a good look at the engine and the con rod wasn't that bad and the inside of the crank case although scored certainly isn't a write off. I managed to get the bearings incredibly fast from Simply bearings mail order (36hrs!!), as i want to try to fly this weekend . I got them last time from model fixings too(they are excellent)but the ones needed weren't listed this time and i didn't want to wait with the Christmas period holidays..

I used some fine wet and dry and tidied up inside the crank case and con rod, plus cleaned out the oil holes in it. Aluminium had managed to wedge inside them! The soft aluminium tidied up well and the back plate is ok. I did the rebuild this evening with cleaning and a good re lube. Test Run on Saturday! If it Explodes I'm going straight to Laser... I already have an 80 on order for my Wot 4

The WORST bit was dropping the tiny little prop driver metal wedge on my shed floor. Finally managed to locate it about 40min later with a magnetic rod. It had found its way under the edge of a box!


 

 

Edited By Timothy Harris 1 on 29/12/2016 22:00:54

[cymaz]

Timothy, sounds like you need a magnetic tray for next Christmas

[onetenor]

Just a shallow roasting tn ( cut one down if needs be ) and speaker magnet or two sitting in it There are some really big ones available Trays and magnets LOL

[Hamish]

In addition to the magnetic tray, for "live" bits i.e. valve springs, I put tray in a large clear plastic bag to contain these items that what to whiz off.

At moment renovating an OS40 FS and really impressed by service from Simplybearings

[Tim Flyer]

Unfortunately it fell while trying to insert it during an " I must be careful moment". I have a few magnetic parts trays full of old bike bits😳 What I need is a clear out . When it fell it bounced on the hard Lino floor rather than hitting the soft mat. I think another mat would be good . I can't wait to test the engine on Saturday.

[Peter Miller]

As I have said in the past. Simply Bearings is amazing as they are shipping bedarings over the Christmas break when everyone else is shut down.

[Tim Flyer]

Yes cheers Peter good advice again. I ordered them Tuesday night and they were dispatched first thing Wednesday and with me Thursday. Despite the holidays 😊

[Broken Prop]

Hi Timothy

Sorry to read about the demise of your OS81. As a matter of interest, were you running the engine inverted in the airframe?

[Martin Harris - Moderator]

 

Posted by Timothy Harris 1 on 29/12/2016 21:57:47:

 

Hi guys I had a good look at the engine and the con rod wasn't that bad and the inside of the crank case although scored certainly isn't a write off. I managed to get the bearings incredibly fast from Simply bearings mail order (36hrs!!), as i want to try to fly this weekend . I got them last time from model fixings too(they are excellent)but the ones needed weren't listed this time and i didn't want to wait with the Christmas period holidays..

I used some fine wet and dry and tidied up inside the crank case and con rod, plus cleaned out the oil holes in it. Aluminium had managed to wedge inside them! The soft aluminium tidied up well and the back plate is ok. I did the rebuild this evening with cleaning and a good re lube. Test Run on Saturday! If it Explodes I'm going straight to Laser... I already have an 80 on order for my Wot 4

The WORST bit was dropping the tiny little prop driver metal wedge on my shed floor. Finally managed to locate it about 40min later with a magnetic rod. It had found its way under the edge of a box!

 

 

Edited By Timothy Harris 1 on 29/12/2016 22:00:54

Good on you, Timothy. I've been biting my typing finger over the last few days as I wanted to suggest smoothing out any sharp edges on the con rod and giving it a try! I would certainly have considered trying it myself but didn't want to risk suggesting something that could end in tears (e.g. a rod through the crankcase!)

DA friend had a Saito 50 which internally digested its rear bearing Surprisingly, a replacement gear pair for the camshaft (the teeth balked at trying to chew bearing parts) was a reasonable cost but the little piece missing from the piston skirt and scuffed con rod would have made a repair uneconomical. I suggested a little stress relief of the damaged components with careful filing/polishing and with about £8 or thereabouts worth of bearings from a commercial supplier, rebuilt the engine for him. This was 7 or 8 years ago and (touch wood) it's still performing perfectly on a regular basis.

Good luck!

Edited By Martin Harris on 30/12/2016 12:49:00

[kc]

This might be the time to ask if plain bearings would be better in engines for sports flying ( i.e not compettion models with engine size limits) Is it really necessary to have ball bearings in these medium size 4 strokes or is it just a way to ensure the engines wear out and need replacing?

Plain bearings work well and last (nearly) forever in the smaller size two strokes -for example the Enya 30SS and 40SS which have plenty of power too. So why not in 4 strokes too?

[Tim Flyer]

Thank you Martin for the encouragement. It does seem the aluminium is quite soft on the conrod and crankcase so hopefully not brittle. It was easier than i had expected with a small bit of wet and dry paper to smooth over the marks an looks like I will still have plenty of thickness. If the crank an cam interface had broken which I had suspected before strip down I think the story would have been different. The engine was side mounted in an Acrowot. I did also use after run oil. However as mentioned by others this engine doesn't have a crank breather so not much oil gets into the crank case via the head. The only thing I did not do was remove the valves and springs for a clean. I didn't have any of the small spring retaining clips and didn't want to risk reusing the old ones, given that the valve coking isn't too bad. I might try using 2 stroke oil as after run oil instead as I was still a bit surprised that there is carbon on the valve. My use of this engine is quite relaxed and I won't be thrashing it as it is going back into the Acrowot if tomorrow's test is successful 😊

[Tim Flyer]

A Happy update. Managed to get back early tonight and did the test run. The engine started swiftly and ran beautifully with very little vibration. Dare I say as good as new😉. I'm a very happy chap now. Thanks all for the encouragement. Next time I will be much quicker to change the bearings. One solution to this engines lack of crank breather problem would be to tap the back plate and put in a pipe so I could get the after run oil in . However I don't think I will bother 😊. I'm just going to enjoy flying it and watch it carefully.

[Subalib]

Hi Timothy I tapped my OS 81 Alpha in the middle of the back plate for the sole purpose of injecting after run oil.

[Martin Harris - Moderator]

Posted by kc on 30/12/2016 13:01:48:

This might be the time to ask if plain bearings would be better in engines for sports flying ( i.e not compettion models with engine size limits) Is it really necessary to have ball bearings in these medium size 4 strokes or is it just a way to ensure the engines wear out and need replacing?

Plain bearings work well and last (nearly) forever in the smaller size two strokes -for example the Enya 30SS and 40SS which have plenty of power too. So why not in 4 strokes too?

Perhaps we might get an informed comment from Jon if he sees this but I suspect that lubrication may be a major factor. In a 2 stroke, fuel is drawn past the bearings in copious amounts whereas the 4 stroke relies on blow by and airflow carrying small amounts around the engine.

Hopefully, Subalib's modification won't affect the designed flow of oil laden air through the camshaft area which is a design feature of many model 4 strokes. I'd use a stopper at the end of a piece of fuel pipe to block it when the engine was in use.

Edited By Martin Harris on 31/12/2016 10:41:04

[Jon H]

I don't think I have ever seen a model 4 stroke with a bushed crankshaft and I can think of a few reasons why.

First, on a two stroke the engine fires every time the crank rotates and so the load on the crank remains far more constant than on a 4 stroke where you only get it to fire every other time the crank rotates. While I am sure a bush would survive this irregular pounding in the short term I doubt it would appreciate it long term.

Another issue would be that even with the best will in the world a bush will have some play in it, certainly more than a ball bearing will, and this would be less than ideal if you are trying to mesh gears on that shaft while its flopping about. Laser, saito and Enya all use bushes on their camshafts, but they see load only in one direction where as a crank has loads in more than one direction so are not going to stay true.

Lubrication could be a factor, but I am sure there are ways around that.

The biggest issues in the beginning was probably cost vs power vs expected service life. Given that 4 stroke engines are more expensive than 2 strokes to make the extra cost of the bearings is more easily lost in the final price, they also have higher bearing loads than two strokes. Also remember than most early model engines were two stroke diesels and ran for only 1-2 minutes at a time in free flight models. They did not have the extended run times RC control allows and so were not required or expected to run for many hours. While its true many of these engines are still in good condition after over half a century of use, I doubt that many of them have the same number of hours on them as a well used ball raced engine from the last 25 years. While many r/c plain bearing two stroke engines have been produced they are a rarity these days and with the move away from cross flow porting, the introduction of ABC style engines and ever increasing power output from say 1985 to today, plain bearings on overhanging cranks have been left behind.

As for the backplate mod I cant see any harm in it. Many Saito engines have their breathers in the backplate, although personally I think that having it under the cam chest would be a better bet.

[Martin Harris - Moderator]

I read about the breather/lubrication relationship while researching the seemingly strange addition of an air pump with no apparent function on a Saito twin with a common crankpin. The reason was due to the crankcase volume remaining unchanged due to the opposed piston movement there was no forced airflow through the engine and the Saito reference specifically mentioned the breather as an integral part of their cam/follower lubrication system on the singles. Since then, I've been wary of making changes to any 4 stroke's breathing arrangements!

[Jon H]

I am less than convinced by that airpump idea. sure there wont be any pulsing of air but all those parts flying about will create air flow. also the rings will scrape oil off the cylinder walls and this oil will be thrown into a mist by the rotating crank etc. so I don't totally buy into that notion

[Tim Flyer]

I think Subalib's idea for the breather is good and as saiid it can easily have a stopper on if when the engine is in use. As the rocker cover is exposed on my Acrowot I decided that  i can add after run oil via the rocker cover for the moment as it runs down the rods into the crankcase. I think I will do the tap though at some stage . Thanks again Jon for your great advice😊. I had Three near 20minute flights on Saturday and it runs as good as new😊😊

 

Edited By Timothy Harris 1 on 01/01/2017 21:57:41

[Martin Harris - Moderator]

Posted by Jon Harper - Laser Engines on 01/01/2017 18:31:23:

I am less than convinced by that airpump idea. sure there wont be any pulsing of air but all those parts flying about will create air flow. also the rings will scrape oil off the cylinder walls and this oil will be thrown into a mist by the rotating crank etc. so I don't totally buy into that notion

Saito did though - and went to a lot of trouble to provide the pump...but as my next engine is due to be be a Laser I must have total confidence in your opinion and Lasers' own lubrication!

[Engine Doctor]

Posted by Timothy Harris 1 on 01/01/2017 21:55:31:

 As the rocker cover is exposed on my Acrowot I decided that  i can add after run oil via the rocker cover for the moment as it runs down the rods into the crankcase. I think I will do the tap though at some stage .😊

 

Hi Timothy. Applying after run oil into the rocker cover won't help with oiling the bottom of the engine as it won't get past the cam followers. The crankcase is a far better place to fit a vent to apply oil if needed . If the crankcase has no suitably thick part then the backplate will be fine. Many foursrtokes use the backplate for the breather nipple. Some later models fit the breather near the cam box to encourage oil to circulate onto the cam gear and then draw the waste oil into the inlet manifold to be burnt. Oiling the valve gear now and then is required but it only needs a light oiling . The best way to keep the bearings in good order is to run your engine dry when it's hot at the end of a days flying to get rid of any methanol in the crankcase. Oh and listen for any odd noises .

[Jon H]

Posted by Martin Harris on 01/01/2017 23:01:53:

Posted by Jon Harper - Laser Engines on 01/01/2017 18:31:23:

I am less than convinced by that airpump idea. sure there wont be any pulsing of air but all those parts flying about will create air flow. also the rings will scrape oil off the cylinder walls and this oil will be thrown into a mist by the rotating crank etc. so I don't totally buy into that notion

Saito did though - and went to a lot of trouble to provide the pump...but as my next engine is due to be be a Laser I must have total confidence in your opinion and Lasers' own lubrication!

Oh I know they did, I just cant really understand why. I suppose I will find out if they were right when I make my own, but for the moment I don't expect to be worrying about it.

As for our lubrication, I am running 2 of my models on 4% oil and will be running more on that mix through this year. If I can demonstrate that it is safe to use then that could be the future for us

[Tim Flyer]

Thanks Engine doc. I think I will have to tap the backplate as the oil will not easily seep past the followers as you say and it's the easiest place to fit it.  Hopefully the SKF decent quality bearing I put in will buy me time. Regarding running the engine dry I certainly ALWAYS have done that. Plus I am very careful to drain the tank. What I should not of done with this motor was to run it when I knew it was on its way out. That exacerbated the damage and was totally my decision . It is strange that the bearings last such a short time these days. My Webra Speed 40 boat engine I bought in 1979 is still on its first bearings and I can guarantee it has don't far more hours at much higher RPM than this OS 81😉

Edited By Timothy Harris 1 on 03/01/2017 11:51:16

[Tim Flyer]

Just a quick update chaps. I did put an oil lube access nipple in the back of The crankcase backplate as per Subalibs suggestion. So I now add after run oil directly into the crankcase. I keep the silicone pipe attached to it sealed while the engine is running, so I am not changing the way the internal lube system works. I have had quite a few flights now since the rebuild and the engine performs as well/ better than ever so I'm a happy chap😀.