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Crankcase breather/. 4stroke

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fly boy327/03/2019 20:49:44
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3498 forum posts
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Hi all, my 4stroke engine will be buried in the wooden cowl when completed. Is it important that the crankcase breather be accessible with a small piece of fuel tube vented to the outside ? Thanks

Denis Watkins27/03/2019 20:53:52
3806 forum posts
52 photos

You have to vent it FB or you will oil line the internals

More modern solutions are to pipe the crankcase vent to a newly tapped and fitted nipple on the intake manifold

fly boy327/03/2019 21:18:36
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3498 forum posts
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Thanks Dennis, do us modellers modify the system, or do new engines come with this new mod ? Cheers

Steve Hargreaves - Moderator27/03/2019 21:33:08
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Which engine is it FB? Some engines already have the breather pipe connected to the inlet manifold. Many of the OS engines breath through the castings so have no external breather.

If yours has a breather nipple in the crank case simply add a length of fuel tube long enough to clear the cowl & vent to atmosphere. Excess oil is discharged through the breather so if you don't vent this you'll be amazed at how oily the inside of the cowl becomes.

Frank Skilbeck27/03/2019 21:44:39
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4430 forum posts
101 photos

For neatness on a scale model with an ASP91 FS, I have connected the crankcase vent to a short piece of brass tubing which is fixed to the firewall and discharges out of the bottom of the cowl. Looks neater than some fuel tubing flapping in the wind.

Steve Hargreaves - Moderator27/03/2019 21:48:28
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I have done exactly that on my Pitts Special fitted with an ASP61 Frank....thumbs up

Denis Watkins27/03/2019 21:54:14
3806 forum posts
52 photos

See the nipples here on a MK 2 ASP70Fs, v poor pic

asp70_fs_mp2.jpg

Martin Harris27/03/2019 22:22:01
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8735 forum posts
214 photos

A major function of the breather is to encourage airflow (and hence oil mist) over the camshaft and followers. Some early engines had a simple breather in the backplate but OS moved to a nipple under the cam/front bearing area, assumedly to improve lubrication and the clones went further with the recirculation option. Later OS engines moved to internal recirculation so you won't see any pipes or nipples on them.

Beware of providing too long a pipe or too much restriction - this can result in restricted flow and therefore inadequate lubrication.

Ron Gray27/03/2019 22:25:47
1431 forum posts
359 photos

Hmm, not too sure about feeding breather into intake as oil from breather will alter fuel mixture. I would always try and vent to out side. Of course some manufactures design the recirculating system presumably so their users see less ‘mess’, still don’t like it!

Bruce Collinson27/03/2019 22:44:01
384 forum posts

It will drip oil after use, so I try to remember to bung mine before putting in the wife’s car and of course open it before starting.

BTC

ASH.28/03/2019 00:55:54
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300 forum posts

flyboy, yes, the crankcase breather tube is very important. Keeo it simple and attach a lenght of fuel tubing to nipple which exits ouside of the cowl. Don't worry about the lenght, Secure it loosely to the engine mount and also zip tie to end of silencer leaving an inch or so hanging. Excess oil will be ejected out clear of the fuselage. Just make sure tubing has no kinks so oil and pressure can move freely This tube also allows you to inject After Run Oil into the crankcase after a flying session, something which is Best Practise - to preserve bearings & cam from corrosion etc. Plug the end after to keep sealed.

Happy flying. Hope you enjoy your fourstroke as much as I enjoy mine.

SIMON CRAGG28/03/2019 06:43:29
401 forum posts
5 photos
Posted by ASH. on 28/03/2019 00:55:54:

flyboy, yes, the crankcase breather tube is very important. Keeo it simple and attach a lenght of fuel tubing to nipple which exits ouside of the cowl. Don't worry about the lenght, Secure it loosely to the engine mount and also zip tie to end of silencer leaving an inch or so hanging. Excess oil will be ejected out clear of the fuselage. Just make sure tubing has no kinks so oil and pressure can move freely This tube also allows you to inject After Run Oil into the crankcase after a flying session, something which is Best Practise - to preserve bearings & cam from corrosion etc. Plug the end after to keep sealed.

Happy flying. Hope you enjoy your fourstroke as much as I enjoy mine.

After run = very important, how many of us forget? I always drain the fuel tank, run the motor flat out and pinch the fuel line to expel any residue from the crankacase before adding after run. Always try and store the model "nose up" so any xxxx in the system will drain onto the backplate and not the bearings. I have been using lawn mower 2 stroke oil for over 20 years as an after run, not the labelled stuff (silly money) from your LHS. Never had a bearing failure yet.

Cuban828/03/2019 09:35:18
2640 forum posts
13 photos

Perhaps I'm a contrary so-and-so, but I don't follow what on the face of it, seems a common sense procedure i.e regular use of after-run oil. I used to follow the advice, but in my experience the down side of extra mess, hydraulic locks, difficult starting etc out-weighed any advantages. The regimen for my four strokes is to simply always warm them up and run them completely dry at the end of a flying session. I will load an engine with suitable oil when laying it up over winter though. I find this to be perfectly adequate and have never had a bearing failure and when I have got around to changing a bearing that started to get a bit noisy after an extended period of use, rust has not been evident.

I don't use high nitro fuel, just 5% with 15% oil content, so perhaps those using more exotic fuels will have to be more cautious.

For the breather, I just vent it out through the lower cowling - length of pipe doesn't appear to be that critical. A lot of the oil spray seems to come from fuel blow-back from the carburettor.

Edited By Cuban8 on 28/03/2019 09:41:28

Ron Gray28/03/2019 13:25:06
1431 forum posts
359 photos

Cuban8 - +1

J D 828/03/2019 14:43:12
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1227 forum posts
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+ 2. I do much the same.

fly boy328/03/2019 14:53:45
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3498 forum posts
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Thanks all, will act on information recieved. One more question, club members put after run oil in the carb.,remove the plug, or into crankcase breather nipple. Which is best practice for a 4 stroke. ? Thanks

jrman28/03/2019 14:58:01
346 forum posts
3 photos

Cuban8 & Ron +2

Denis Watkins28/03/2019 15:43:30
3806 forum posts
52 photos
Posted by fly boy3 on 28/03/2019 14:53:45:

Thanks all, will act on information recieved. One more question, club members put after run oil in the carb.,remove the plug, or into crankcase breather nipple. Which is best practice for a 4 stroke. ? Thanks

4stroke motor manufacturers do not like excessive removal of glow plugs, as cylinder heads are expensive to replace

And plug threads are not often brass inserts, but are threaded soft aluminium

So plug change once a season maybe, but it is your motor

Store motor and model, prop to the ceiling

Introduce after run oil down the carb, and turn over the motor by hand, to induct the oil into the main areas

Point the motor down for 6 revolutions, then up for six revolutions, which should coat the bearings

It is a good idea to manually oil the rockers as it can get quite dry up there and cause rust, so take of the rocker cover and inspect

Over the the winter, I usually turn motors over by hand just to be sure each month

During the flying season, with regular use, Just run the hot motor dry of fuel

Edited By Denis Watkins on 28/03/2019 15:45:57

Jon - Laser Engines28/03/2019 20:10:00
4770 forum posts
179 photos

For engines in regular use i dont bother with after run. taking off props and spinners, then cowlings, needles, exhausts and glow plugs so i can inject nowhere near enough oil to prevent rust but just enough to make it difficult to start next time....no thanks. To be honest, i dont bother with it at all any more and even engines in long term storage dont get any special treatment beyond a run/reset on the test bench before being tucked up under the bed locked at TDC to prevent stressing the valve springs.

The key is to use a good quality fuel with no castor, and then run the engine at its maximum performance all the time. All of the 'a bit rich for safety' nonsense does nothing but make engines go rusty so just tune it for maximum power and get on with it.

Dont neglect your slow run needle either. Always adjust your slow run so that it as lean as possible as this will save you a great deal of fuel, prevent flameout at idle, improve throttle response, and help keep corrosion at bay.

Denis makes a good point about rockers though. Apart from Laser and YS, all other 4 strokes should have a little oil stuck on the rockers every now and then. Laser engines have an oil way cut into the cam follower so oil is pumped into the rocker cover, and YS use the rocker cover as part of their pumping system if i recall. I also recommend oiling rockers on all ASP/SC engines from new as asp ship them pretty dry.

GrahamWh28/03/2019 20:28:58
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356 forum posts
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Thanks Jon - very reassuring - I'm a bit too lazy to do much other than run dry at the end of a session. It takes ages just dismantling and cleaning my biplanes anyway! I'll watch the rockers on my ASP and OS engines and be more careful re the low needle settings. Thanks for bringing the topic up fly boy3.

 

Edited By GrahamWh on 28/03/2019 20:30:05

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