wikitjuggla

Where is the bypass or "vacuum" port located on a nitro engine and how do i seal it shut?

controlliner

If you remove the front bearing, You will see the port @ 12:00 in the back of the bearing seat. it is drilled upward (at an angle) toward the intake where the carb mounts.

wikitjuggla

do they have these on all nitro engines? i have a .21 engine out of a redcat aftershock

controlliner

Not all engines have this. It is questional whether or not this has any benefit.

Barracuz

It's a little slit above the front bearing runs parallel to the crank or it would go in a diagonal direction to the carb does not give any performance benefits. Its there to lube the bearing and serve as "pressure valve" to help let any excess mixture escape either out thru the bearing or either loop back to the carb.

It supposedly prevents hydrolocking the engine.

wikitjuggla

Well I don't want to do it for performance benefit. I just hear it plugging it up makes the front bearing push oil out, keeping it from drawing in air. Last time I used my engine though it actually seemed to be running alright without plugging the port. Now its been cold out, like -10 and its sitting in the corner collecting dust.

downunder

When the engine is running there's an average positive pressure inside the crankcase and this tends to push oil along the crankcase to the front bearing where it can fill up the space behind the bearing and eventually leak out and make a mess. The port opens up at the base of the carb where the low pressure (when the inlet port is open) helps to draw excess oil back from the front bearing. It doesn't draw in air because the port is full of oil. The actual seal against too much oil being pushed along the crankshaft is a very close fit between the crankshaft and the crankcase.

supertib

We are indeed having issues with it causing the engine to suck air thru the front bearing............ easily tested by spritzing WD-40 behind the flywheel while the engine is running..it will stall instantly............ I block that bypass port and the engine will no longer stall from the WD-40...............

Also these ngnes can see lower then negaitive 15 PSI while running......even higher if the engine was at WOT and the throttle closed...

we were seeing hundreds of engines pack the front bearings full of dirt during operation...by blocking the bypass port it stopped this from happening.........

Anthoop

So, I have to ask why you think this is?
Do you think primarily, the drilling should not be there or do you think it is a consequence of how the engine is being run (mixture) and the fuel used (oil type/content) ?
Of course when an engine is modified with different timing and/or altered crankcase compression I could understand that problems may arise, but with a standard engine (of reputable manufacture), I would not expect problems when used as recommended.

supertib

unfortunately I have seen it happen with quite a few stock engines as well as modifieds....

Anthoop

Yes, I have heard you say that before, hence the question "So, I have to ask why you think this is?".

wikitjuggla

Opinion on why it is happening isn't really relevant. Fact is, it is happening. The manufacturers probably put the port there on purpose so it draws in dirt and destroys engines as a marketing ploy, who knows, who cares. The solution to the problem is all I care about. If my engine starts acting up again, I'm definitely plugging that hole though. Don't really have anything to loose except a few droplets of extra fuel/oil out of the front bearing and a little extra mess. It's not like it is going to hurt the engine. I haven't seen a single post saying it can cause damage. And if this wasn't a problem, then that company wouldn't make those BUKU caps or what ever they're called.

downunder

While you're at it, how about explaining this? Sounds like nonsense to me.

supertib

I am not sure 100% why it is happening, but I think it has been happening to all sorts of nitro engines for many years....the WD-40 test shows that these engines are not sealed very well and almost all of the engines will stall if WD gets anywhere near the front bearing....... Blocking the bypass allows more fuel to puddle in the oil galley which I believe helps make a stronger seal.....I also believe blocking the bypass also reduces the amount of vacuum behind the front bearing, which also helps with reducing the issue.............

In airplanes and boats its not as big of a deal as the air the engines operate in is ralatively clean.... same with onroad racing...... However in offroad racing its an entirely different story.....As we are often racing in extremely dusty conditions, with high amounts of fine airborne contaminants...So what this means is a airplane or boat engine could be breathing thru the bearing and we wouldn't see much issues., however in offroad the dirt gets sucked right into the engine , destroying the bearing and sometimes even the engine............ ever wonder why offroad engines go thru so many front bearings ?

Anyways the ultimate answer is the buku crankcase cap...

supertib

thats your opinion...But we have some really good testing done on thsi, but I am not going to let the cat out of the bag just yet.... so you will just have to take my word on it...But I will say these engines produce far more vacuum then any of us initially thought......This is especially seen when you close the throttle after a full speed pass....engine spooled up, full power and RPM..throttle closes to idle...that instant there the vacuum spikes extremely high ..........

Barracuz

Supertib I can sense the knowledge in your posts but I simply can't put in order what you're trying to say. Why don't you make a thread discussing your experiments and findings. I'll really be interested in reading.

The bypass/vacuum port in a 2 stroke glow engine is there to serve as a bearing lubricator and pressure valve. No rocket science here and no need to make it so.

Wikitjuggla that port won't suck up dirt or mud unless you're purposely stuffing a cubic yard of dirt thru the front bearing and you purposely bored out the port. The guys you see plugging up the port own really worn out engine. By plugging up that port you may get to use that engine for another gallon or so...

So in conclusion I recommend you don't fiddle with your engine. Don't worry about getting dirt in the engine. A little dirt won't kill it. As long as have a fuel filter and an oiled air filter you will be fine.

Anthoop

We have been through this a few times I think.... http://www.rcuniverse.com/forum/car-...ur-engine.html

supertib

by blocking the bypass I increase the amount of lubrication, not decrease............ and a person would be a fool to willingly let dirt into their engine..thats the fastest way to destroy a engine there is.......

the only bad thing blocking the bypass does is increase the amount of leaking out the front bearing......... other then that, all else is positive...more lubrication, better idle, longer bearing life and no more dirt getting sucked into the bearing.......

downunder

One way to both block the oil return port (if that's what you want to do) and avoid getting any dirt/dust into the front bearing is by fitting a fully sealed bearing. These are packed with a grease which is held in by rubber seals on both sides of the race so never need any other lubrication. However the grease limits the (still very high) max revs and I don't like the idea of grease as a lubricant at these high speeds so I remove one seal and wash out the grease before fitting the bearing with the remaining seal on the outside. It's cheap and easy, especially if you were fitting a new bearing anyway.

nitroexpress

There are several companies selling front bearing protectors. With a bit of grease between the cap and the bearing, no leaks. No need to replace a bearing or limit high RPM's.

http://www.amainhobbies.com/product_...Engine-Protect

supertib

We already run rubber sealed bearings packed with grease.... we even have bearings with dual rubber shields on the outside........unfortunately this doesn't help...the bearing packs with dirt regardless........the rubber shields do not stop the dirt, they barely slow it down.....

supertib

so I willl gather up some photos so you guys can see what kind of dirt we are seeing.....

this is the engine with bypass open







and this is a engine with the bypass blocked



this is the inside side of the bearing...pulled right out of a engine,,,

supertib

supertib

another dirty bearing

downunder

http://www.avidrc.com/product/1/bear...-bearings.html