Front engine bearing leaking?

[Coach Z]

So I COMPLETELY tore apart my lst2 to get it super clean and after about three tanks of fuel I'm seeing some fuel residue under the carb and around the bottom of the engine. I've sealed the carb and back plate but can it be leaking between the crankshaft and the inside race of the front bearing?? Any ideas would be much appreciated. oh and all the fuel lines are new as well as fuel filter etc.

 

[bourney2006]

replace front bearing.

 

[beason]

i dont know the layout of the lst2 but i wouldnt jump to the conclusion of the front bearing being bad just yet, you could have spilled when refueling, or the tank cap leaked on a rollover. clean it all up really good and run it around slowly, maybe a tank or so. then check and see if its wet there again.

how much fuel have you run through the truck?

 

[bourney2006]

check sor air leaks.
Get a bucket of warm soapy water and a tooth brush. Then get a piece of fuel tube and attach it to the carb (as normal). Block the carb venturi (hole) with your thumb. Brush water all around the crankcase and blow into the fuel tubing. If you see any bubbles then you have a air leak in that place and you need to seal it

 

[jetmechG550]

Technically you shouldn't have a front bearing leaking. You may be running too rich on the bottom end. People always suspect it's a bad bearing when they see residue in that area but the fact is fuel doesn't get up there.

 

[bourney2006]

Technically you shouldn't have a front bearing leaking. You may be running too rich on the bottom end. People always suspect it's a bad bearing when they see residue in that area but the fact is fuel doesn't get up there.

then how does the bearing get lubricated?

 

[jetmechG550]

Look at how it operates, fuel comes through the carb into the opening in the crank and through the face of the crank into the lower chamber, up the ports and into the combustion chamber. You may get residual into that compartment between the inner and outer bearings but nothing that will indicate a leak. The bearing really isn't sealing anything off.

 

[olds97_lss]

You sure about that JM? Most (if not all) engines I've had have a pin-hole leading from the bottom of the carb neck to the front bearing to help keep it lubed. Granted, if your running rich, it may seep out, but if your front bearing seal is worn, it will suck air through there and throw your tune off.

 

[jetmechG550]

Yeah, it will get lube but if it shouldn't be getting so much through it that it will be leaking out the bearing unless you are running too rich on the bottom. Maybe I'm not splainin' it right.

 

[olds97_lss]

Did you check your carb neck cinch bolt? A buddy of mine has the LST2 with the stock engine. His carb neck leaked as did the cinch bolt. I tore it all apart, cleaned the neck, cinch bolt, cinch bolt hole and carb with DA then smeared RTV all over it and it hasn't leaked since.

 

[Coach Z]

Total of about 2 gal. through it so far.
Yeah I sealed the carb, cinch bolt, and back plate. When I say I cleaned it I mean like with a Q-tip. Chassis entirely apart. All new fuel lines, filter, tank. Truck was spotless for the test.
edit:
I've been reading about this a bit more and have heard some people have better success with Avid bearings over the stock. Anybody tried these?
http://http://www.avidrc.com/

 

[olds97_lss]

I've used them, but for other things than engine. For an afermarket high speed engine bearing, I'd suggest acer or boca's engine bearings.

Avid's are ok for general use, but they aren't all that "tight" as far as the seals are concerned. Boca and Acer will cost you more, but they will be less problematic.

 

[jetmechG550]

TKO Ceramics for the engine. I do use avid's 8x16x5 and they are a good bearing.

 

[olds97_lss]

Do you have a link for TKO? I've never heard of them.

 

[jetmechG550]

http://www.tkocompetitiondev.com/shop/
They have been around MX for a long time. They carry some good products and their starter box plates are the shizzle.

 

[olds97_lss]

Thanks JM.

I saw these in XtremeRC mag I believe: http://tkocompetitiondev.com/shop/product_info.php?products_id=341

As soon as I went to the site, I realized I did recognize the name. Just couldn't figure out why.

They sell GO engines... Someone was asking about those recently too.

 

[jetmechG550]

They do a lot of bearings for MX engines, I know two of my buddies that ran MX for a long time ran their bearings.