BlackB12

My Feedback: (9)

I'm confused. Are you running muffler pressure or not? Also it looked like on your pics that you have the crankcase vent line running back into the tank. That prolly ain't gonna work. It's not like a closed system with a regulator like on a YS. Have you run the engine with stock muffler?

Mike

blw

My Feedback: (3)

Am I the only one wanting to hear the girlfriend story???

w8ye

My Feedback: (16)

Yes, let us see your tank stopper and where you have the lines going
Looks like one blue line goes through a filter and to the fuel inlet on the carb
Looks like the one clear line goes from the tank and is plugged with a fuel dot
Looks like maybe a third blue line coming off the tank and going where?
Looks like your crankcase pink line goes where?

Is your tank vented or where is it getting pressure?

proptop

My Feedback: (8)

Maybe she had a "crush" on your airplane, but just had an odd way of showing it?

highside

Hellewww.

Firstly the (ex) girlfriend story. The model was a lightly built example, unlike the girlfriend. She came flying with me for the first time to see "what it is you saddos actually do". She sat in the car whilst I assembled the model, then got out to walk up to the strip. It was muddy. Whilst we were faffing around, she stepped back, realised she was about to step on the plane, overbalanced, waved her arms in a comedy fashion for what seemed to be an eternity, tried to take a big backwards step over the model, slipped and sat plumb on it. To be fair, she was mortified, whilst I thought it was absolutely hilarious and couldn't stop laughing (probably suffering from shock). In the spirit of every cloud having a silver lining, in that instant she effectively refunded a huge pile of Brownie Points, the stock-in-trade of modellers who fancy going flying instead of visiting family/painting the bathroom/worming the cat etc.

Secondly the ring gap. I measured by sliding the ring back in the bore and using feeler gauages. The .2mm guage would go in but was tight, .15 was a clear fit. Hot compression isn't mega, turning over by hand it has that sort of vacuum feeling after TDC which suggests it as leaked some on the compression stroke. But it's not much and if I flick it over it certainly has compression.

Finally the plumbing. In the pictures with the hatori system:

: The blue line with the filter is the feed from the clunk.
: The clear line is one of two tank vents used for filling and is blocked off during running.
: What you can't see is a second blue line from the second tank vent (it's routed to the other side of the tank so isn't in the picture) which is open to the atmosphere
: The pink line routes the crankcase vent into the inlet manifold (actually into the carburettor body on the inlet manifold side*). This is a mod I've done to all my big block saitos because I hate fuel mess. Worst case effect I've seen is about 100rpm loss. I did, of course, undo this mod when I had problems and there was no change in behaviour.

So with the hatori system there was no pressure feed but the tank was vented to atmosphere.


Then I replumbed the test stand with a new tank Dubro 20oz tank which I only put one vent in. I reverted to the OEM muffler:
: Clunk to feed the engine
: Vent to muffler pressure tap
: Fill tank by disconnecting feed to engine

I also tried disconnecting the muffler pressure and venting to the outside world.

I'm off to look at Reivers Prop Power :-)

HS

* First time I did this, I put a tap in the inlet manifold itself. Worked fine for a short while, but then the extra mass caused it to leak a bit around either the O ring at the carb or head end. If it turns out to be something related to this mod that is causing the problem on the 125, I shall run naked down the road singing I've got a lovely bunch of coconuts. Possibly.

XJet

One thing to be aware of is that Saitos tend to spit a *lot* of oil out the breather far more than any other 4-stroke I've ever owned.

I'm wondering if that amount of oil may well be interfering with the engine's operation these engines just aren't designed to have the oil recycled like that.

It's a shame you didn't try to establish a base-line *before* you made the mods it might also invalidate any warranty claims.

How are you connecting the crankcase vent line to the carby and how did you "undo" this mod?

Given that the crankcase pumps an amount of air equal to the displacement of the engine, I can't see how hooking the crankcase breather up to the carburetor isn't going to result in some major screwing up of the air/fuel mixture.

highside

Hmmm, it's an interesting question and one I've chatted about on other threads.

You're right about establishing a baseline - usually I would have but I've done it on other engines and it's been OK, so I didn't worry this time.

This technique is used by other 4Cyc manufacturers, included OS and me-toos such as ASP. Firstly they routed the breather into the inlet manifold much as I have done. On the latest alpha engines they have actually drilled through the head connecting the volume inside the rocker cover to the inlet tract by the valve. This creates a path from the cranckcase, past the camshaft and up the pushrod cover tubes and finally back into the inlet. It's neater, doesn't rely on external tubing and being as far as possible from the carb probably disturbs the flow inside the carb itself much less.

I've just put an M3 nipple into the carb body on the manifold side of the barrel but before the O-ring. It needs a small notch filing in the end of the manifold to clear the outlet of the nipple, but results in a reasonably flush finish with nothing protruding into the inlet tract. Yep, it would have invalidated the warranty. But seeing as they wouldn't honour it anyway seeing as I bought the engine in the US, no loss there.

To undo the mod during testing I first just replaced the silicon pipe with a short bit on the nipple on the carb which was blanked off with a dot; the breather nipple in the crankcase was left open. No difference, so I took the M3 nipple out and blanked the hole with a M3 bolt cut to the right length to be flush on the inside face, sealed with hermatite.

I can't explain why, but there is no way that a full swept volume worth goes out the breather and down whatever silicon pipe you have connected on every stroke. Just watch the progress of the oil down that pipe. Also, the only oil that comes out is that which has made it past the piston ring. My WAG is that this would be less than 15% of the oil entering the engine, roughly a 2.5% increase in oil in the mixture. Not a big deal, especially given that I usually run 18% oil not 20%. I can envisagethat it does horrible things to the inlet tract flow tho...

In terms of modding engines in general, I can see both sides of the coin. Yes, they are designed by people far sharper than me with huge amounts of experience. It seems stupid to interfere with their lovely, efficient engine. On the flip side, having a play expands one's understanding; at times it has yielded an engine more appropriate to what I want, other times it resulted in rubbish!

Man, if it turns out that the problem was due to this mod, I'm gonna be so embarrased!

:-)

togatoga

My Feedback: (42)

I channeled the oil from the breather to the inlet manifold for my 125 too.I am pleased with the result.Less mess and no loss of performance.

airbusdrvr

XJET, explain this statement a little more thoroughly, "Given that the crankcase pumps an amount of air equal to the displacement of the engine." That would seem like a lot of air being pumped out of the vent.

gkamysz

My Feedback: (19)

The piston displaces that much volume, but that doesn't mean it all makes it to the intake manifold. OS Surpass 2 engines use a small orifice to control the volume of gasses passing through to the intake. When Magnum copied this feature, they missed it and used regular muffler sized fittings. This doesn't seem to make then run any worse. The only time the volume of gas displaced in the crankcase is a problem is when you try to choke the engine by turning it over. If the engine is turned over slowly, the flow through the orifice is high enough that there is little manifold vacuum created and weak choking action. If you flip briskly, it still draws fuel into the carb. That has been my experience with my FS-52 with the Alpha type oiling mods I added.

rlmcnii

My Feedback: (3)

abd,

Each time the piston moves from top-dead-center to bottom-dead-center, it displaces an amount of air equal to the displacement (swept volume) of the engine. Strictly speaking, I guess one would have to subtract the volume of the metal from which the piston is formed,since this volume is occupied by metal and not by air. It is this volume of air that is forced out of the crankcase vent.

When the piston moves from bottom-dead-center to top dead-center a vacuum would be created. Air at atmospheric pressure is then forced in through the vent to fill that void. Nature abhors a vacuum???

I have no idea how efficient this process is. Is all of the air expelled on the down-stroke replaced on the up-stroke. Don't know. However, at some differential in pressure between ambient and the interior of the crankcase, an equilibrium must be reached. If not, the pressure in the case would continuously increase or decrease when compared to ambient.

All of this up and down stuff is happening pretty rapidly and the net outflow from the vent must be the volume of gas that blows past the piston into the crankcase. Were there no gasses passing the piston from the combustion chamber to the crankcase, there would be no net outflow through the vent.

On another note, this entire conversation about routing exhaust gasses to the intake side of the engine has intrigued me. The oil in our model engines is not burned, and all of the oil that goes in must come out. I know, a small volume is retained in the case; but another equilibrium must be reached here also. Putting the oil vented from the case through the engine and out the exhaust may keep the plane a little cleaner, but the oil comes out somewhere. And, regardless of restrictive orifices, the net volume of gasses and oil displaced from the crankcase must pass into the intake side of an engine so plumbed (minus that which blows out around the front seal or through some other leak). If not that engine would accumulate oil and gas pressure in the case.

It will be interesting to see if highside's difficulties are related to his replumbing of his 1.25.

My apologies for jumping in. Merry Christmas.

gkamysz

My Feedback: (19)

The gasses in the crankcase are compressible. If there is a restrictor in the flow path, only so much gas can get out before the piston reverses direction. This high frequency and the restrictor means the gas volume quickly attain equilibrium where the gasses inside the crankcase should be roughly equal to the crankcase volume at half stroke. Blow by is basically the only volume exiting the crankcase when the engine is running. Engines with a lot of blow by emit a lot of oil through the breather. The comments on Saitos during the rich break-in support that the unseated ring and a rich setting result in a lot of oil through the breather. I think Saitos put out more oil in general due to the short piston skirt which results in more piston rocking and blow by.

OS made the car versions of the FS-26 and FS-40 without breathers at all. The only way for oil to get out is past the front bearing. I don't hear too much about these engines. But I don't think they ever changed them to the Alpha style even though they already had the passages in the cam follower bores. I have a couple of these engines, but only a few minutes of bench time on them. OS warned not to run the engine excessively rich in the manual.

XJet

You're right that the choking effect of the breather nipple and tubing means there won't be a gas-flow equal to the displacement of the engine but there will be pressure pulses hitting the carb (from the breather) that it wasn't designed to handle.

And, as I said, the Saitos tend to blow a *lot* more oil than any other 4-stroke engine I've used so whereas the OS and Magnum engines might get away with a closed system because the oil volumes are low, I wonder if that might not be the case with Saito where the oil volumes are high.

Also remember that anything on the manifold side of the carby will be subject to a partial vacuum which means that instead of the crankcase breather exhausting to the atmosphere, the engine will effectively be *sucking* on that pipe. I wonder what that will do (over time) in the case of an engine where the breather is on the backplate so there's already very little incentive for the oil to travel past the rear bearing, down the crankcase and into the cambox area?

I know that quite often the Saito 100s will run very dry in the cambox because the oil prefers to travel out the breather on the backplate rather than find its way to the cambox. Eventually this can cause the cam bushes to dry out and "squeal". I suspect that's why the breather nipple on the 72/82 was repositioned to part-way along the crankshaft.

It'll be interesting to see what the ultimate resolution is. It's been my experience that simply drilling holes in the carb/manifold of an engine to introduce new flows can do very odd and unexpected results. Compressible fluid flows are extremely tricky and not always intuitive.

gkamysz

My Feedback: (19)

That is an interesting question. I'm looking for another larger Saito (I only have one each FA-80, FA-30, FA-40) to convert to spark ignition and attempt some crankcase breathing modifications. I'll have to look at the 80 to see if I can do what I'm thinking.

As far as the original problem. I think it's going to be a cylinder issue as was mentioned by someone already. A few thousandths more end gap of the ring won't cause this sort of issue.

highside

It's true that all the oil that goes in must come out somewhere. In practice, I tend to route the exhaust so that as much as possible of the exhaust fumes miss the airframe. It's harder to do this with the short breather tube.

Have a look at:

http://www.rcuniverse.com/forum/m_71..._1/key_/tm.htm

for another thing I tried to enable me to run a long piece of pipe on the breather, down the inside of the fuz and down to the bottom of an undercarriage leg, thus getting it away from the airframe. It worked fine, but eventually I went back to piping it into the inlet manifold.

I hadn't considered the fact that the inlet is, in fact, sucking on the breather. But this only occurs for 1/4 of the time i.e., on the induction stroke. So I think this, combined with the added restriction of the M3 nipple (which has a smaller hole than the breather nipple in the backplate), will mean a generally positive pressure in the crankcase.


Any of you that have had a YS DZ series engine to pieces will appreciate how big an aperture is needed to vent the crankcase properly. These engines use the pumping action of the piston in the crankcase, combined with a crankshaft driven disk valve, to "supercharge" the inlet mixture i.e., to physically pump it up the manifold and into the engine. The apertures to enable it to do this are several square cm in area. So the breather nipples are relatively extremely restrictive.

Fascinating stuff. Glad I haven't gone electric yet :-)


HS

DarZeelon

Quote:

ORIGINAL: rlmcnii

Each time the piston moves from top-dead-center to bottom-dead-center, it displaces an amount of air equal to the displacement (swept volume) of the engine. Strictly speaking, I guess one would have to subtract the volume of the metal from which the piston is formed, since this volume is occupied by metal and not by air. It is this volume of air that is forced out of the crankcase vent.

Rlmcnii,


One would have to subtract nothing...

The volume of the piston's structure is there, whether the piston is at BDC, or at BDC (and everywhere in between), so the amount of air displaced is EXACTLY equal to to the displacement of the engine - Half the bore squared, multiplied by π (Pi), multiplied by the stroke.

No other calculations necessary...

And this volume is not forced out of the crankcase... Only a very small percentage of it is. This volume is not drawn into the crankcase as the piston rises either.

As Greg wrote, air is compressible and behaves like an air-spring. The average pressure is slightly over-atmospheric, changing from slightly higher pressure, with the piston below mid-stroke, to a slight vacuum, when the piston is near TDC...

What does make the average pressure a bit over-atmospheric, is blow-by gasses that blew past the piston-ring, during compression and combustion (and carried with them oil for bottom-end lubrication).

Sport_Pilot

When the inlet is sucking the breather will be blowing so there will be no or very little differance in manifold pressure.

XJet

But the problem is that some of the air going into the engine will have bypassed the carburetor (coming straight from the crankcase) and what's more, if that route contains "globs" of oil, the *amount* of air that flows by this alternate route will vary depending on whether the breather tube has a lot of oil or only a little oil (since oil is far more dense than air an will tend to dampen the pressure pulses and resulting flow).

This *could* (at least in theory) make it far more difficult to establish a reliable/consistent mixture setting.

________
When I'm not here, I'm at [link=http://rcmodelreviews.com]RCModelReviews[/link]

rlmcnii

My Feedback: (3)

Thank you for the correction.

I assumed not, thus the statement concerning the efficiency of the process. If you are correct, and I do not doubt that you are, the process is very inefficient.

Thank you, again.

Cherokee Flyer

Have you pulled the cylinder to see if it is carboned up?
L.

gkamysz

My Feedback: (19)

I have noticed that my FS-52 with these mods tends to jump around a bit at idle. Mixture setting doesn't seem to be an issue, just that it idles at a slightly irregular speed. This was installed in an airframe and I haven't investigated it on the bench.

The benefit to the Alpha system is cleanliness. I was very impressed with my FS-52 after I did the mods. I'm also running very low oil content, but the airplane and engine was extremely clean after a day of flying. I do wonder a bit about corrosion but the OS engines supplied with this system have sealed bearings, and plated steel parts. There is nothing to corrode. I think it's mainly a way to keep the mess down.

XJet

Yes, and it's partly because of the bearing seals that they spit less oil in the first place (assuming the breather is/was previously on the crankshaft portion of the crankcase).

One of the reasons that Saitos spit so much oil out the breather is because it's often located on the backplate so doesn't have to find its way past the rear bearing and crankshaft and also because (on the 72/82 and others where it's not on the backplate) these engines use unshielded/unsealed rear bearings.

w8ye

My Feedback: (16)

I might add that on the OS Surpass II and Alpha engines with the sealed bearings that the crank shaft is cross drilled just in front of the rear bearing to let oil come into the timing cavity through the center drilled hole from the rear of the crank.

togatoga

My Feedback: (42)

Most crankshafts have that hole. If you look at the rear bearing fit to the crankcase, that hole is the most expedient way for tranferring oil.
Channeling oil from the breather to the inlet manifold causes no drop in performance. Its like having a fuel with a higher oil content.YS engines behave that way by channeling the supercharged air into the inlet. The oil/fuel goes to the combustion chamber and is subsequently expelled.
Automobile engines do the same thing,the crannkcase breather is routed back to the carb although the oil expelled is more like vapour.

w8ye

My Feedback: (16)

The OS Surpass I original crank does not have the cross drilled hole