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How to check for air leaks - 5/2/2012 4:49 AM   
SLAYERDUDE



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Status: offline 		Here's an easy way to check if your tuning troubles are caused by an air leak near the carb or backplate.

This is on my MGT 8.0 and I had some problems recently with random flameouts (engine dies) that I initially thought were caused by a loose convergent cone in the pipe because it had come loose and was rattling around possibly blocking the stinger (outlet), I changed pipes and the flameouts went away for a while...
The pipe I have on it now has no seperate cone inside so I knew that wasn't it.
I started leaning the LSN because it seemed to 4 stroke (too rich) before it died, then I got lean jitters.
When you have an airleak you end up compensating for the extra unmetered air coming in by richening the needles, once the airleak is sealed I recommend putting the engine close to stock "rich" settings and tuning from scratch.
Tuning info can be found HERE


One shot with the nitro wash and found the issue.

I figured I'd make a vid before putting it away for the night since I suggested this to a couple people on forums and didn't get a reply whether it found their problem or not, or if they even tried it.



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RE: How to check for air leaks - 5/3/2012 3:45 PM   
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Status: offline 		That is not how you check and air leak. The engine died because it sucked in a bunch of fumes. There is no surefire way to test for an air leak. If you have symptoms, then you should start troubleshooting. RTV the back plate, replace the o-ring under the carb.

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RE: How to check for air leaks - 5/4/2012 12:00 AM   
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quote:

ORIGINAL: SLAYERDUDE

Here's an easy way to check if your tuning troubles are caused by an air leak near the carb or backplate.

This is on my MGT 8.0 and I had some problems recently with random flameouts (engine dies) that I initially thought were caused by a loose convergent cone in the pipe because it had come loose and was rattling around possibly blocking the stinger (outlet), I changed pipes and the flameouts went away for a while...
The pipe I have on it now has no seperate cone inside so I knew that wasn't it.
I started leaning the LSN because it seemed to 4 stroke (too rich) before it died, then I got lean jitters.
When you have an airleak you end up compensating for the extra unmetered air coming in by richening the needles, once the airleak is sealed I recommend putting the engine close to stock "rich" settings and tuning from scratch.
Tuning info can be found HERE


One shot with the nitro wash and found the issue.



I heard of this method a while back and decided to try it on an engine with a suspected front bearing leak.  Sure enough, the engine died.  Then I tryed it on a friends engine which was running well.  His engine died. 

I've also tried the bubble test,.  Pressurize the engine and submerge the front bearing under water.  Two of my good engines bubbled more than expected.  I had a new engine, which had never been run, and it bubbled only slightly less.  At this time, I only consider replacing the front bearing is the shield is missing or all other remedies have failed.

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RE: How to check for air leaks - 5/4/2012 1:01 AM   
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Status: offline 		Actually there is a way to check for air leaks and it's pretty simple to do.

Remove engine from car/buggy and clean it the best you can.

Get a small paint brush and a cup of soapy water. 

Put a 6-10 inch piece of fuel tubing on the carbs fuel inlet.

You need to plug the exhaust and the carb venturi (intake), the best way I have found to do this is to put a small balloon over each of them, but you can also just use your fingers to cover them as well.

For the next step it's easier if you have a helper,  what you need to do is blow air into the fuel tubing, making sure that the throttle is open.  While air is being introduced you will notice the baloons start to inflate ( you only need about 8 psi to do this) Take the soapy water and start brushing aroung the front bearing, carb orings and screws or nut that holds the carb on and also check around the rear plate.

I bought a little air duster from a computer supply store that takes regular c02 cartridges and I use it, but you have to be careful on how much air you inject at a time, you just want the balloons to inflate a little bit.  You can also apply the soapy water first then give it a shot of air too.

What you are looking for is little bubbles or foam to appear where you put the soapy water, if you get some that means you have an air leak and that area needs to be resealed, or in the case of the front bearing it would need to be replaced.  You would be surprised at how many brand new engines come from the factory with air leaks.

It's that easy and it works everytime.  Just be sure not to put too much air pressure into the engine or you could actually damage the front bearing seal.  Just 8 psi is all that you need.

If you have any questions you can pm me or ask them here...

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RE: How to check for air leaks - 5/4/2012 4:38 AM   
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Status: offline 		I hate being told I'm wrong so here goes lol.

8MILLSNIPER007 - that's the more common way to check airleaks.
The front bearing will leak air out on that test no matter what, it's just a rubber lip on the crank and isn't too hard to force air past, Robin from Extreme RC Mods (ERCM) taught me that.

I learned this method by mistake on my friends truck, his wouldn't tune out and had lean jitters and caked fuel/dirt all over the engine, we sprayed the nitro wash on there while it was running and it idled way down so we sealed it and it tuned like a dream afterwards.

I've been struggling with this 8.0 (.50) so I tried the same and you saw what happened, but the census is that my method is bunk.

In the process of sealing it now, and I'll post a daylight vid of the results.

But I had to get the easiest engine I had running and put what Nitroexpress said to the test, compared to the .50 with the air filter that's 10 X's the diameter and a couple inches away from where I was spraying, I tried the HPI MT1 .18 with a motorsaver filter that is less than an inch from the carb.

Hmm, it stayed running until I sprayed a steady stream for more than a couple seconds.
You can see in the .50 vid it dies when I sprayed at the exhaust instead at the bottom of the carb, then resprayed more towards the carb, which is still far from the actual air cleaner.

This vid don't prove much because you can't see it, and can't really hear the spray either, but an .18 getting doused with an air filter that's open just centimeters from where I was spraying, compared to a .50 with the air cleaner inches away tells me something.

I'll absolutely post another vid of the .50 after it's sealed up, I'm fairly certain this will show that I can douse the engine without it dying.



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RE: How to check for air leaks - 5/4/2012 7:39 AM   
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Status: offline 		If you put 15-20 psi of course the front will leak.  I said 8 psi for a reason the normal pressure inside  running nitro engine is close to 7.5 psi so if your front seal will survive 8 psi youre good to go.  I have been working with two stroke engines big and small for over 17 years now.  I have been doing performance mods now for the last 8 years and my way of testing has not failed me yet.  I am not saying that your way could not work, but your way does have some holes in it.  You cannot postively say that the reason the engine died is because the gas you sprayed went into the air leak, it is an invisable gas and for all you know the carb could be sucking it in.  Dont get me wrong, I use your method all of the time on larger engines only with propane.  It's called a propane enrichment test.  Propane works well because it is a heavy gas and is less likely to be drawn up through the intake, it will stay low and against the part I am testing.  On larger engines when you find a leak the engine will speed up until you stop the flow of propane.  I was not saying your metohod was wrong I was commenting on the remark that there is no way to check for an air leak...

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RE: How to check for air leaks - 5/4/2012 7:44 AM   
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Status: offline 		By the way alot of older engines didnt even bother to use a seal on the front bearing, all of my OPS marine engines do not have one as well as most older K&B engines.  They seal from the crank and the bearing housing, a film of castor oil is enough to keep the engine sealed

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RE: How to check for air leaks - 5/4/2012 10:43 AM   
Argess



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Status: offline 		I use the soapy water method too, but never the less, good effort to the OP for making a helpful post.

The OP's method is similiar to checking intake and carb leaks on full size engines, where home mechanics try WD40, unlit propane (methinks that's dangerous) and various other flammable sprays. Maybe it needs a little tweaking, but it should work. Hope your "after-the-fix" test shows your method works fine.

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RE: How to check for air leaks - 5/4/2012 7:39 PM   
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The front bearings in RC engines are not airtight by design. The front seal on the bearing is more to keep dirt out of the bearing, not air and fuel in the engine.  If the tune is too rich, especially on the bottom end, fuel can push out thru the front bearing. If you are pressure testing the engine statically, the front bearing will very rarely show a seal, even in a perfect engine. Sometimes, if you are checking an engine that has been stored with after run in it, it might seal without running - but not usually

Bearings make their seal when they spin, utilizing the oil film.... no bearing will seal if its not spinning.... the soapy bubble test is actually quit pointless as pretty much every bearing will leak

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RE: How to check for air leaks - 5/4/2012 8:09 PM   
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Status: offline 		The seal is most certainly there to help seal the engine up, if you believe what you say then go ahead and pull the front seal and try to keep that engine tuned.  I have been using this method for years and I would say that 95% of the bearings I install in customers engines pass this test.  I have tested many used engines a well and they have passed this test as well, like I said if you are putting more than 8-10 psi in the engine, then yeah it will leak, but the running engine will never reach those kinds of pressures unless it is forced inducted, but that is a whole different issue. anyways if you have fuel leaking out your front bearing like you say it does while its running, youve got some other issues, if there is a leak there it would be sucking air in not pushing fuel out.  There is a reason why they sell "engine bearings" They are meant for high rpm's but they also have a renforced seal. 

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RE: How to check for air leaks - 5/4/2012 8:12 PM   
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Nitro-
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RE: How to check for air leaks - 5/5/2012 12:29 AM   
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Status: offline 		The front bearing does not seal the engine. The seal is made behind the bearing between the crank and block, just in front of the induction opening. The tolerance is such that a skim of oil is all that's needed to make it air tight. A little oil will get past this point and that's what the little hole behind the bearing is for, to suck back any extra oil that's sitting behind the bearing. If the tune is too rich then more oil will flow and the little hole can't keep up so at that point, the bearing starts to leak oil, lean it out and the leak will mysteriously go away.

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RE: How to check for air leaks - 5/5/2012 10:07 PM   
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ORIGINAL: 8MILLSNIPER007

The seal is most certainly there to help seal the engine up, if you believe what you say then go ahead and pull the front seal and try to keep that engine tuned.  I have been using this method for years and I would say that 95% of the bearings I install in customers engines pass this test.  I have tested many used engines a well and they have passed this test as well, like I said if you are putting more than 8-10 psi in the engine, then yeah it will leak, but the running engine will never reach those kinds of pressures unless it is forced inducted, but that is a whole different issue. anyways if you have fuel leaking out your front bearing like you say it does while its running, youve got some other issues, if there is a leak there it would be sucking air in not pushing fuel out.  There is a reason why they sell ''engine bearings'' They are meant for high rpm's but they also have a renforced seal. 

No. The front bearing does not seal in any sort of vacuum or pressure. The fit between the crank and crank case is what keeps a seal, with the help of a film of either synthetic or castor oil. The front bearing is NOT airtight by any means. Most engines have a metal dust shield on the front bearing anyways. A leaking front bearing is not indicative of an air leak, it's just a bad front seal.

Besides, why are you talking about pressurizing an engine? Leaks become apparent under vacuum, when the engine is on its upstroke. Pressurizing an engine will not diagnose anything.

These little bearings are not RC specific, let alone rc engine specific. They're usually just industrial grade abec 5 or 7 bearings. Most hobby grade bearings are manufactured by Nachi.

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RE: How to check for air leaks - 5/6/2012 1:31 AM   
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  Proanti,
First you say that the front seal is not airtight and then in the next sentence you say that if the front seal leaks you have a bad seal?? Which one you gonna go with cause you cant have both!! 

   putting a positive pressure into the engine will acomplish the same thing a pulling a vaccum on it, think about it. If there is a leak it will show up one way or the other, it's just easier to find it by pressurizing it, plus you dont end up sucking soapy water into the engine.  You are dead wrong about the front bearing seal and you might be right about some of the engines are using industrial grade bearings, but you will not find those on a quality engine.  Instead of argueing with me over it why dont you do some reasearch first.  R/C engine bearings are anything but standard bearings, sure you can probally find one that would work, but you should vist a few of the local bearing companies and ask them about their rc engine bearings, the seal is thicker and made out of different materials at least it is on any bearing I would run in my engines and the mills I build for other people.  You can go to the front page at Boca bearing and he has literature right there, or if you want some really nice bearings look up Santa Clarita bearing.  aIf you actualy read my post you would of read that I did mention that some engines did use oil to seal between the crank and the block or bearing housing.  If you put a 5 ABEC bearing in an engine that is turning 30,000 +  it wouldnt last for a tank.  RC engines are built specifically for high rpms, I have yet to to see a rc engine bearing with a metal bearing cage (retainer) like ABEC 5 and 7 rated bearings have.  Look guys you can argue all you want, but I have been very successful using this method for many many years now, someone asked how to check for engine leaks so I gave him my method, just as you gave yours, if you are happy the way you do yours then carry on!  As for me I will continue to use what I know works.  I am not here to argue or make any enemies, I am here to try and help people that I can.



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RE: How to check for air leaks - 5/6/2012 1:51 AM   
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Status: offline 		 You can put a genric bearing in just about anything, but that doesnt mean that is is the right thing to do.  For instance  Ball bearings that are meant for electric motors have a "M" in the part number, why? Because bearings that are designed for electric motors need to have looser clearences so that when the motor is energized the armature can self align itself.  Putting a generic bearing in an electric bearing is a great way to shorten it's life plus it might not run as efficent as it could.

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RE: How to check for air leaks - 5/6/2012 2:06 AM   
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Status: offline 		The front bearing is a "light contact" seal bearing for off-road engines, it is not sealed as in air tight. The seal that give the barrier between crank case pressure +/- and atmosphere is created by the thin film of oil between the crank and block. I have seen engines that used front bearings that had gaps between the balls and no real shield, you could look right through it, like the nova flash marine, I would call that a high end engine. Airtight or "heavy contact" bearings would be considered "sealed" but can not take the rpm these engines push so the heavy contact seal becomes a light contact in no time.

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RE: How to check for air leaks - 5/6/2012 2:24 AM   
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ORIGINAL: 8MILLSNIPER007

  Proanti,
First you say that the front seal is not airtight and then in the next sentence you say that if the front seal leaks you have a bad seal?? Which one you gonna go with cause you cant have both!! 

   putting a positive pressure into the engine will acomplish the same thing a pulling a vaccum on it, think about it. If there is a leak it will show up one way or the other, it's just easier to find it by pressurizing it, plus you dont end up sucking soapy water into the engine.  You are dead wrong about the front bearing seal and you might be right about some of the engines are using industrial grade bearings, but you will not find those on a quality engine.  Instead of argueing with me over it why dont you do some reasearch first.  R/C engine bearings are anything but standard bearings, sure you can probally find one that would work, but you should vist a few of the local bearing companies and ask them about their rc engine bearings, the seal is thicker and made out of different materials at least it is on any bearing I would run in my engines and the mills I build for other people.  You can go to the front page at Boca bearing and he has literature right there, or if you want some really nice bearings look up Santa Clarita bearing.  aIf you actualy read my post you would of read that I did mention that some engines did use oil to seal between the crank and the block or bearing housing.  If you put a 5 ABEC bearing in an engine that is turning 30,000 +  it wouldnt last for a tank.  RC engines are built specifically for high rpms, I have yet to to see a rc engine bearing with a metal bearing cage (retainer) like ABEC 5 and 7 rated bearings have.  Look guys you can argue all you want, but I have been very successful using this method for many many years now, someone asked how to check for engine leaks so I gave him my method, just as you gave yours, if you are happy the way you do yours then carry on!  As for me I will continue to use what I know works.  I am not here to argue or make any enemies, I am here to try and help people that I can.



An oil seal is different from a pressure seal. Ball bearings used on model engines do not have a pressure seal, none of them do.

Do some research? I have been in this game a long time, kid. You really have no idea what you're talking about, which has become abundantly apparent.

An ABEC rating is for tolerance, it has absolutely zero to do with the quality of the bearing or the cage/retainer.

Here is an NTN bearing in an OS 12CV. Model W689Z. It has a unilateral closure according to one of the sites selling them. That means it has a cage. 'Local bearing companies' do not produce bearings specifically for RC applications. The only company I know of that actually does, is Boca, and engine manufactures do not use their bearings.

Besides, we're just talking about car engines. Just try to find an airplane engine with a rubber seal.

I sold these things dude, I worked for one of the largest bearing and industrial drive suppliers in the united states. You really should just stop talking.



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RE: How to check for air leaks - 5/6/2012 2:31 AM   
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Status: offline 		As I said in two of my previous posts SOME of the engines do seal by oil films between the crank and case, however not all of them do...

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RE: How to check for air leaks - 5/6/2012 2:35 AM   
proanti1



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Status: offline 		Yes, all conventional nitro engines do. This is a requirement, as the intake timing depends on it.

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RE: How to check for air leaks - 5/6/2012 2:36 AM   
8MILLSNIPER007


 

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Status: offline 		First off, I am not a kid and I have also been in this business for a long time, as I have worked with many bearing suppliers as well. I have actually worked with these engines not just sold them like you say.  I do believe you are the one that needs to stop talking.  By the way I have several airplane engines with rubber sealed front bearings.  You are the one that needs to do your reasearch!!!

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RE: How to check for air leaks - 5/6/2012 2:41 AM   
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RE: How to check for air leaks - 5/6/2012 4:37 AM   
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Status: offline 		I build engines on a daily basis, and the front bearing does NOT create the airtight seal, on any conventional nitro engine.

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RE: How to check for air leaks - 5/6/2012 4:57 AM   
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Status: online 		Front bearings do not seal the engine.... the engine is sealed along the crankshaft by a oil film.....

However........ there is a big caveat to this one....... Not all of todays fuels make a very good hydraulic seal along the crankshaft, and the front bearing then becomes a second vacuum barrier and the engine will definitely be affected by how well the bearing does seal.............. I find some of my modified engines create enough vacuum to overcome the hydraulic seal of some fuels........ Fuels like OD Speed Blend, VP Powermaster and Sidewinder Team Strike have very weak hydrauilic seals and the front bearings ability to seal is put the the test.... However with a good fuel like Byrons, Werks or S_W we have no issues with the hydraulic seal along the crankshaft............ So int he end a front bearing does not seal these engines, however if the hydraulic seal along the crank fails having a bearing with good sealing characteristics can make a big difference............. Also these bearings do not seal till they are spinning, it is perfectly normal for them to leak when static...onroad engines run open bearings, where you can see daylight right thru the bearing.............

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RE: How to check for air leaks - 5/6/2012 6:27 AM   
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Status: offline 		Are we positive that it's the fuel and not a manufacturing tolerance issue? I have still yet to see a light contact seal bearing that was air tight. I know there was that issue with that one engine but was that across the board or just a individual case.

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RE: How to check for air leaks - 5/6/2012 6:38 AM   
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quote:

ORIGINAL: purenitro33

Are we positive that it's the fuel and not a manufacturing tolerance issue? I have still yet to see a light contact seal bearing that was air tight. I know there was that issue with that one engine but was that across the board or just a individual case.



multiple engines on the same fuels... most definitely a issue with some fuels in combination with some engines...may be related to tolerance, but the increased vacuum from the mods and the thinner nature of some fuels most definitely creates some issues....... Have one here where I can clearly see the engine was drawing thru the front bearing, as the inner sheild was caked with dirty grease from inside the bearing..... those 3 fuels I mentioned definitely do not make anywhere near the seal that the other fuels I mentioned do....

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