K4.6 Bearing Help!

[savageweasel]

Well I decided to check my motor for air leaks while I had it out.
With very little pressure (blowing through fuel tubing) the front bearing leaks. I then heated the motor and tried again and it still leaked. bad word

Now the funny part is that it never spit any fuel out? cornfused

I was wanting some input on a good replacement bearing. I'm looking for the best that money can buy because if it's gonna be a pain in the a** to change i don't want to do it twice. And if the only metod for changing it is by baking it?


😛eace:

 

[Jeremy]

Yea the only method for changing the bearings is heating the block .

As far as the best that money can buy .. BOCA bearings are one for the best. Heat the block and put the bearings in a freezer for like 10 min the put them in.
www.bocabearings.com

 

[savageweasel]

Is it safe to use ceramic bearings for a engine?

 

[Jeremy]

Yes it is .....

 

[Purenitro]

There is a misunderstanding when it comes to front bearings, they are not air tight and do not seal the engine. The seal that stops an engine from leaking is made just behind the front bearing between the crank and the block. The front bearing has a "light contact" seal, it's main job is to keep dirt and grime out of the bearing, not to seal it. Heavy contact seals are "more" airtight but can not handle the rpm and soon wear the rubber seal resulting in a light contact seal again. The main reason for a leaking front is slop in the main bearing, this causes the crank to wobble and results in the tolerance being taken out between the crank and block. Once this wear has happend it does not matter what bearing you put in, it will leak.

If you have ever looked behind the front bearing you will see a little hole that goes through into the throat just under the carb. this little hole is there to suck the little bit of oil that makes it's way through the seal back into the engine keeping the front clean and oil free. If this hole get's any sort of blockage, the result will be a buildup of oil leaking out the front bearing. A little cleaning of this hole can fix a leaking front end as well. People sometimes think this hole is to lube the front bearing but that is not the case, it uses the negative pressure in the carb to suck oil back.

Many engines use metal shielded bearings in the front, my P9R for example has a metal shield. Looking from the back side of the engine, you can see right through it at different points, far from sealed (airtight) yet it is bone dry at the front. It is a good idea to check and replace bearings when they get worn to prevent them from taking out the internal seal of an engine. I hope this doesn't confuse anyone, but if it does just ask, I will try and explain better.

 

[savageweasel]

Ty for the info, but now i'm lost :istupid:

Does this mean I have a bad rear bearing or is this ok to blow out air? If it's ok... then how do you check for air leaks? All my air just blows out the front.

I don't think I have a air leak, but I figured I would check while it was out and noticed this.

It does not leak any oil/fuel out.

 

[Jeremy]

Great Post Robin thanks bro

 

[Purenitro]

Air will easly blow past when it is all clean, when oil from the fuel is present, it acts like a seal (fills the void). If it does not leak when running, there realy is no issue. If you are concerned about bearings, I would replace the main bearing for safety. The main bearing has a tendancy to fail, the ball retainer is very weak and if run too lean, it will fail sending balls through the engine (worst case) or it may just take out the tolerance leading to leakage. I don't mod these engines anymore unless the bearing is upgraded due to this fact. Here are a couple main bearings for a decent price, I would look at replaceing the main bearing just for peace of mind, it wouldn't hurt to upgrade the front one as well.

http://www.amainhobbies.com/advanced_search_result.php?keywords=14X25X6

 

[savageweasel]

Ty again... all clear now.

I will change these out for the bocas over this winter.

The motor has about 1 3/4 gallon ran through it. Mainly sidewinder 20%, I did use a quart of traxxas 33% but noticed the oneway bearing slipping alot.

 

[Shaun]

There is a misunderstanding when it comes to front bearings, they are not air tight and do not seal the engine. The seal that stops an engine from leaking is made just behind the front bearing between the crank and the block. The front bearing has a "light contact" seal, it's main job is to keep dirt and grime out of the bearing, not to seal it. Heavy contact seals are "more" airtight but can not handle the rpm and soon wear the rubber seal resulting in a light contact seal again. The main reason for a leaking front is slop in the main bearing, this causes the crank to wobble and results in the tolerance being taken out between the crank and block. Once this wear has happend it does not matter what bearing you put in, it will leak.

If you have ever looked behind the front bearing you will see a little hole that goes through into the throat just under the carb. this little hole is there to suck the little bit of oil that makes it's way through the seal back into the engine keeping the front clean and oil free. If this hole get's any sort of blockage, the result will be a buildup of oil leaking out the front bearing. A little cleaning of this hole can fix a leaking front end as well. People sometimes think this hole is to lube the front bearing but that is not the case, it uses the negative pressure in the carb to suck oil back.

Many engines use metal shielded bearings in the front, my P9R for example has a metal shield. Looking from the back side of the engine, you can see right through it at different points, far from sealed (airtight) yet it is bone dry at the front. It is a good idea to check and replace bearings when they get worn to prevent them from taking out the internal seal of an engine. I hope this doesn't confuse anyone, but if it does just ask, I will try and explain better.

awsome info bud!! its good to have your expertise here with us at the forum!!!:resp:

 

[Purenitro]

Thanks Nitro.

 

[Shaun]

no problem my friend.. I'm always willing to give credit were its due and i've been meaning to say thanks for all the help you have been giving out here.. its truly appreciated.. because i know what its like to try and figure out things on your own, if i had of known about this forum when i bought my x it surely would have saved alot of headaches.. i was terrified to mess with my sav x for fear of screwing it up somehow, and I'm sure alot of people have felt that way so its nice to have a place to go to for help, and you always seem to be there with advice so thanks again!!