Has anyone drilled and taped the intake on an older 4 stroke to attach the breather tube? What size engine and how does it work?

Why?

Any opening in the intake will change the air/fuel mix. Not a good idea. Also, a vent in the intake will not depressurize the crankcase.

Dr.1

If I ever end up with an engine that has the vent plumbed to the intake it will promptly get undone. That is simply overkill.

Venting the crank case to the intake is similar to shoving a hose into your posterior orifice, and putting the other end in your nose. The engine doesn't like it any more than you would.

Bill.

Such eloquence, well said.

I modified my OS 61FS, 2- OS 120FS, and my OS 120 Twin. In each case a severely restricted nipple was necessary in order to not upset the idle mixture and low end acceleration. This had to be determined thru trial and error and was quite time consuming. The 61 required a restrictor of .0145", the 120's a restrictor of .020" and the Twin a restrictor of .040". The intake pipe on the 61 and 120 FS is too thin to tap so to provide a nipple, I soldered a piece of 1/8" copper tube containing the restrictor, to the intake pipe. On the twin I tapped into the manifold tee.

The 61 proved to be sensitive to temperature change adversely affecting the idle and midrange. The 120 FS engines were not similarly affected. The 120 twin suffered from engine failures on approaches when the fuel level was less than about 1/4 . All engines had approx double the rate of carbon accumulation in cylinders and on exhaust valves as compared to when the breathers were vented to atmosphere.

After experimenting for a couple of years and many hours of test flying, I returned all the engines to their stock configurations, and all engines perform better.

Waco:

You have just reinforced my previous statement.

Bill.

LOL!! Very well put.

I've never seen anybody put their used car engine oil in the gas tank, this amounts to the same thing.

That "recirculation" idea was dumb. Made even worse by the fact that it does not work...at least not like some granola eating, tree-hugging, enviro-nazi visionary intended.

Let the crankcase vent overboard and be happy.

'Race

Magnum engines are designed like that, and (at least the one I have) runs exceptionally well. However, I suspect this is because it was engineered this way--and all variables were kept to a minimum. However, I have not, nor would I ever, retrofit my other four strokes for this kind of application--simply asking for trouble.

Here is my rationale for modifying my 4 strokes to incorporate the breather mod.

In 21 years of repairing OS 4 strokes, I have always found that high time engines with 50 or more hours running time have significant wear on intake valve faces where the valve contacts the seat. In one case the outer circumference of the valve face was completely cut away from the valve which allowed the valve to be swallowed into the intake port. This was on a 120 Surpass engine.

This wear is not found on the exhaust valves due to the hard carbon build up on the valve face protecting the face from wear.

My thought in incorporating the breather mod was to increase the amount of lubrication available to the intake valve to preclude this wear. I do not know if this was also the intention of OS in introducing this breather setup on their latest engines. I do know that their latest engines run beautifully as their carburetors are flowed to adjust for the introduction of air downstream of the carb. Unfortunately I did not have access to their flow bench equipment.

Waco:

Fallacious reasoning sir. Every bit of fresh oil going into the engine flows past the inlet valve seat, along with the rest of the fuel. All you would add with the case venting into the intake is contaminated oil and other combustion products that have leaked past the piston.

Bill.

Exhaust gases are replumbed into the combustion cycle to clean the air in automobiles all the time, not to far from what is being done to the newer four cycle model engines. You can bet the manufacturers would not do it unless there is some benifit (since it must add cost for the parts and machining). Crankcase vents have been plumbed back into the intake maifold of cars for years.

Get real guys, I would not do it unless there was some technical information. But all the new four cycle engines are being plumbed that way. If done correctly will ensure positive lubrication to the bearings, especially the cam bearings. It would seem improved negative crankcase pressure would enhance lubrication of the low end of the engine, especially the bearings. By scavaging the crankcase back to the intake provides that improvement.

Might as well get use to it since all the new engines are so configured.

Cheers,

Chip

That is not even close to what is being discussed here and what they do in cars is for whole different reason that is Off Topic for here.

If done correctly will ensure positive lubrication to the bearings, especially the cam bearings. It would seem improved negative crankcase pressure would enhance lubrication of the low end of the engine, especially the bearings. By scavaging the crankcase back to the intake provides that improvement.

Might as well get use to it since all the new engines are so configured.

Cheers,

Chip
[/quote]

That is not even close to what is being discussed here and what they do in cars is for whole different reason that is Off Topic for here.


Isn't that the reason O.S. and others are doing it that way.
So,do i need to take it off my O.S.?

Bill

I'm glad to see that your crystal ball is working so well.

I personally will wait to pass judgment on the the demerits of oil recirculation until I have had a chance to inspect the intake valve wear on a high time factory configured OS engine.

Waco:

Quote:

..glad to see that your crystal ball is working...

No Crystal ball needed. As I said, and is obvious, every bit of fresh oil going into the engine flows past the inlet valve seat. If you want more oil in the intake valve use a higher percentage oil in your fuel. Simple.

I have never, even in the highest time Saito engines (or OS for that matter), seen a model engine valve worn to the extent you mentioned in your 50 hour OS. Since I have an OS brand crystal ball with a blown transistor I can't be sure, but I think an inlet air filter would help you more than additional oil.

So why haven't I fixed my crystal ball? OS wants too much money for the replacement part.

Hobbsy:

This is ALL on topic. Exhaust emissions are a hot subject. As stated in another thread California has already outlawed two stroke engines in lawn equipment, they're probably putting the eyeball on model engines as we speak.

Bill.

This is ALL on topic. Exhaust emissions are a hot subject. As stated in another thread California has already outlawed two stroke engines in lawn equipment, they're probably putting the eyeball on model engines as we speak.


Are you serious, Bill? That's scary...

Dr.1

DR.1:

Dead serious. The garden shops in Reno love the California Air Resources Board, many Cal. residents are finding it less expensive to drive into Nevada to buy the two-stroke weed eaters than to buy the "Legal" four-stroke powered local stock.

Or maybe the CARB will outlaw synthetic oils in model fuel - then all the exhaust products will be "Biodegradable." But I doubt it. Thinking that any '"Eco-Nazi" would do something that even approaches sensible is a pipe dream. To them, "Two-Stroke" is a vulgarity.

Bill.

No way Bill, the recirc. valve in a car allows a small amount of exhaust into the intake to dilute the fuel air mixture to reduce combustion temps. Not what we're talking about here at all. Back to the RC question the original poster asked or it will be locked up. Please

Car engines have a very similar setup to the model four strokes under discussion - a breather pipe into the carb/manifold. I think the main reason for doing it in cars is to re-direct the exhaust gases out the tail pipe instead of having them contaminate the engine compartment.

I think that it is done in the later model four strokes for exactly the same reasons. No science - just keeps the place cleaner.

So William if you were me, would you disconnect the hose from cam bearings to the intake manifold? The engine pictured is a Magnum 91. Curious minds want to know.

John

Leave it. Magnums are engineered with that design, and changing it could cause tuning problems. My magnum runs great--until, that is, I beat it up one fine day (landings are better with the wheels down!)

Don't worry, though, as soon as global gets valve covers in, mine will ride again. Good, strong engine. You will like it. It's a steal for the price!

Leave it as is. What most people on here are saying is don't make your engine recycle crankcase exhaust if it wasn't designed to in the first place.

John:

No, I'd leave it connected. If it were from the back of the crank case it would be different, but the way Magnum has done it greatly increases the oil to the cam and tappets.

Bill.