Guys I almost lost my patience with my RB S5 yesterday. It was running way too lean with a fast uncontrollable idle. But anyway I think my front bearing is trash. I can't see any wet oil because of the dusty track condition, but I do see caked up dirt around the fly wheel. So my question is...could it be a leaky bearing or is dirt going to cake up around this area anyway? Guys I would really appreciate your input.

The front bearings often weep as they are not a proper sealed bearing and the crank is designed to "pump" oil to the bearing using primary compression, so its often forced out the front...

The actual seal to the crankcase is made by the oil around the crank and the close tolerance, however, if the front bearing is shot then the crank will be wearing away at the tight tolerance crankcase..

[X(]

uhhhh....

Take the crank out and hold the engine up to the light, look through from the rear and if it looks like this, then it's screwed.

And yes you do get a little dirt build up. But if it's damp that is a sign of front bearing seal failure.

Galifreys (trying to look smart) answer is a little all over the place, but it is correct (if you know what he's on about).

My hyper also has the same problem,what can happen to it if i don't put a new bearing?
How can i tell if it's time for change without "opening up" the engine?

Hmm, well normally it gets damp under the front of the engine, Idleing becomes eratic, loss of smoke from the exhaust gasses (due to over leaning), they cut out at high revs, temps shoot up and eventually this...

421B

And you'll never get it to hold a tune either.

Wow, I never thought that could actually happen. I'll rip it out and see what I can find.

Well as a lot of engines use a metal shielded front bearing instead of a rubber sealed (on one side) which have a bigger gap than the shot rubber one you've shown, I think my all over the place experience of 26 years of model engines explanation is pretty spot on...

Although some engines do use a spiral on the crank rather than primary compression in the crankcase...

Galifrey, your post was informative but it was way over my head. You said the oil is meant to aid in sealing the engine, but I still don't know how oily the bearing should be. The bearing, flywheel etc is wet with oil, so is this normal or not?

Yep, my bearing looks just like that one.

If its wet with oil its a problem... if its just a slight damp patch with dust stuck to it then it's ok...

Well just my opinion then but your bearing sounds shot.

A little tip here is to find the same size bearing from a cheaper brand, more than likely it' was made on the same line in the same factory, it's stupid what a brand name can cost. i.e. Ho Bao 8 port pro bearings are the same as the NR 421Bs and cost 1/2 the price. I learnt that from my 25 years in this hobby. Maybe one more year and I'll think I'm god too?

Can i get the bearing from a bearing store!
I have one at my town and they sell all kinds of bearings.Will it work if i find the right size or these are specific for nitro engines?

They're usually standard sizes, but if it's an imperial size, you may have some troubles finding one in greece/cyprus. Everytime I ask for something in imperial sizes, they look at me like I am an alien.

Short answer, yes. Measure the dimensions of the bearing with calipers and see what they have at the shop. Take imperial and metric measurements, just in case...

Now that you mention it,i never understood the imperial numbers.How do they go???
And the manual of the hyper is in metric(mm) so is my country and Greece.I think "imperial" are in US and don't know where else...!!!!

It's not a matter of how they go, simply that they are measured in feet, inches, 1/8in, 1/16in, etc., rather than metres, cm, mm, etc.

Also, even though the car is built metric, doesn't necessarily mean the engine is too. Pull it out and size it up, I'm sure your shop can help you out. Oh, yeh, make sure you get shielded bearings.

Ah we thought you already did...



Seriously tho, the way to see if a bearing is shot is if the race is gritty, loose, noisy etc, not the amount of oil it leaks...

If it leaks a lot of oil, it may be because the engine has been run excessively with a bad bearing at some stage and the crankcase is worn...

The crankshaft sits in the crankcase with a very tight tolerance, it has to to seal the primary compression up through the rotary valve... if a back bearing fails (the usual but no always. first one to fail) the the crank wobbles in the crankcase and wears it away... that allows excessive oil to the front bearing where neither the rubber seals or the metal shields will hold it in...

Just look at any greased bearing with a rubber seal thats been run for a short while, they weap, the seals are not proper oil seals, they are there to keep dirt out...

However, once it gets to the state of the one you pictured, then the seal is no longer achieving that, and the dirt will quickly spoil the bearing race..

VTI-Chris, take the bearing with you, and ask for the same bearing of the best quality they have... If its rubber shielded, ensure you take the inner rubber shield off (pick out with a fine knife blade) if its metal shielded it will allow oil into the bearing anyway.

According to the some shops that sell it,hyper engines have the 7x19mm front bearing,
but i'll take it with me when it's time for change?