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Front bearing: myths and mistakes

Front bearing: myths and mistakes

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Old 07-26-2015, 06:01 PM
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Questions?? Front bearing: myths and mistakes

Here is dry stat from engines near me:
- Picco 5TR (mine): replaced fr bearing went away after 1gal
- Another Picco 5TR: stock fr bearing went away at 1.3gal mark
- Werks B6: went away after 1gal
- Nova KeepOff4: went away at approx. 1.5gal mark

All engines running Byron 25/11 fuels, vaccum hole is not plugged. Maybe sometimes they used to run lean mixture (we're not very experienced tuners here), but nothing really criminal - no 300F checkpoints, no angry pingpong sounds.
So i'm curious about two things:
1) What can cause premature fr. bearing fail?
2) What is the proper way to maintain fr. bearing? How to keep it healty, how to remove dirt from it's facing, etc. etc.

Oh, and here is another one engine from our nitro league: Trackstar redhead, frequently hitting 300F mark, handmodded with dremel, beta-tester for various chineese fuel and so on. No leaks

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Old 07-26-2015, 06:05 PM
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How are you determining the bearing is going bad ? is it getting gritty ?
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Old 07-26-2015, 06:23 PM
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Originally Posted by Maximo View Post
How are you determining the bearing is going bad ? is it getting gritty ?
Idle is not stable at all (with good tank and fuel lines), and carbcleaner test ends with flameout.
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Old 07-26-2015, 06:36 PM
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wouldnt u see fuel coming thru the bearing surface if it was bad?
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Old 07-26-2015, 06:46 PM
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Originally Posted by stoney452 View Post
wouldnt u see fuel coming thru the bearing surface if it was bad?
I'm not talking about bearing sweating, i'm talking about air leaks
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Old 07-26-2015, 06:53 PM
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I have been running a nitro buggy for over 20 years now and have never once had an air leak. At least not on the engine. Just my opinion.
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Old 07-26-2015, 09:31 PM
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Originally Posted by merdith6 View Post
I have been running a nitro buggy for over 20 years now and have never once had an air leak. At least not on the engine. Just my opinion.
Agreed.
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Old 07-27-2015, 12:50 AM
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Again, an airleak does not come from a bad bearing, but from tolerance between crankshaft and crankcase. If a bearing would be completly airtight, it would have ALOT of friction. Remeber, 1:8 track engines runs with a steel shiled bearing for less friction..

Use a Buku cap, and the problems goes away :-)
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Old 07-27-2015, 06:52 PM
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Originally Posted by am View Post
Again, an airleak does not come from a bad bearing, but from tolerance between crankshaft and crankcase. If a bearing would be completly airtight, it would have ALOT of friction. Remeber, 1:8 track engines runs with a steel shiled bearing for less friction.
But afair that vacuum hole starts before crankshaft-case contact area, therefore crank seal has nothing to do with leaks thru vacuum hole. Or i'm missing something?

Anyway, what is a proper way to clean outside of the uncapped front bearng? I know there shouldn't be air compressor, but what about soft brush?
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Old 07-28-2015, 12:12 AM
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Use a wet napkin, like for babies :-)
Yes, the vacumhole is before the crank seal, so i see what you mean. Still, i belive that the moast important seal is between the crank and cranksahf. The sealing erea is the distance from the front bearing to the front of the intake on the crankshaft. I have tested and plugged vacumhole on 2 engines, but they still stopped when spraying front bearing. That tells me it can not be bearing or vakumhole, but crankshaft seal.

A bukucap solved it:-)
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Old 07-28-2015, 03:39 AM
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It's the front bearing.

The very thin oil seal between the crank journal and crankcase has to be interupted by something .......... That something is the disruption caused by pressure (air) entering or escaping through the front bearing.
Air can be pulled into the engine under negative crankcase pressure (vacuum) or expelled from the engine under positive crankcase pressure.
Either of these by virtue of them happening will break down the very thin oil seal around the crank.

Plugging the vacuum oil return gallery helps a lot, but it will not stop air passing if the bearing is very worn - hence why your brake cleaner test stalled the motor despite the vacuum oil return gallery being blocked.

Check and replace your front bearings regularly (as they ingest dust and start to deteriorate after only a few tanks from new).
I personally believe blocking the vacuum oil return gallery is a good idea - the only down side is the front bearing can weep a little after use.
I also seriously endorse running the oil gallery return mod in conjunction with the Buku front bearing caps.

We offer both the oil gallery mod and the Buku caps to our customers. On engines with both, the tune stability and idle stability of engines is greatly increased, and front bearing deterioration is also greatly reduced along with the period between bearing replacement.
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Old 07-28-2015, 03:50 AM
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Originally Posted by grizz1 View Post
It's the front bearing.

The very thin oil seal between the crank journal and crankcase has to be interupted by something .......... That something is the disruption caused by pressure (air) entering or escaping through the front bearing.
Air can be pulled into the engine under negative crankcase pressure (vacuum) or expelled from the engine under positive crankcase pressure.
Either of these by virtue of them happening will break down the very thin oil seal around the crank.

Plugging the vacuum oil return gallery helps a lot, but it will not stop air passing if the bearing is very worn - hence why your brake cleaner test stalled the motor despite the vacuum oil return gallery being blocked.

Check and replace your front bearings regularly (as they ingest dust and start to deteriorate after only a few tanks from new).
I personally believe blocking the vacuum oil return gallery is a good idea - the only down side is the front bearing can weep a little after use.
I also seriously endorse running the oil gallery return mod in conjunction with the Buku front bearing caps.

We offer both the oil gallery mod and the Buku caps to our customers. On engines with both, the tune stability and idle stability of engines is greatly increased, and front bearing deterioration is also greatly reduced along with the period between bearing replacement.
So how do you explain all 1:8th track enignes to run for many gallons without changing front bearings with metal shield? Thoose engines run good because they do not suck dirt and ruin the fine torlerance between the crank and crankcase :-)
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Old 07-28-2015, 04:06 AM
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So I am a little late to the party here, been super busy in the shop and haven't stopped long enough to post here much..... Anyways the bearing doesn't have anything at all to do with sealing the engine, the bearing contains no seal and its job is to just keep the crank centered and spinning free..bearings have a dust cap on them, but its not a seal..... When a front bearing goes bad its almost always from ingesting dirt....running a engine rich will not blow the seal, that is absolute rubbish as first there is no seal and secondly if anything being rich seals the engine better.....Oil and fuel do not ruin bearings, running dry ruins bearings.........

Anyways the engine is sealed by a fluid ring seal that encircles the crankshaft, if you look you will see there is a machined channel that encircles the crankshaft either machined into the crankcase, the crankshaft or both...at the top of this machined channel is the bypass port previously mentioned..then at the bottom of the crankcase there is a shallow oil galley that runs along the crankshaft.... The bypass port uses engine vacuum to draw fluid up from the galley into the machined channel that encircles the crankshaft kike a drinking straw.... This fluid filled channel is what actually seals the engine.....The system works great as long as there is enough fuel in the galley to supply the bypass port, however when guys run their tune too lean the galley cannot keep up with the fluid demands of the bypass port and the ring seal ends up running dry causing the engine to lose its seal and start sucking vacuum thru the front bearing and in the process often bringing dirt into the engine...This is why pushing for crazy runtimes is not a good idea, as it will often lead to the engine filling itself and its front bearing with dirt.... even the Buku cap won't help if you push it to far as you will just suck the grease right out of the cap....blocking the bypass helps as it floods the front section of the engine and allows for a leaner tune without losing the crankcase seal, however its downside is it can cause leaking out the bearing.....In the end the proper solution is to stop running the engines so lean and keep enough fuel in the crankcase to retain the engines ring seal....... If your constantly killing front bearings then it means you are running your engine too lean and the only real solution is to fatten your tune..
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Old 07-28-2015, 11:31 AM
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How does the oil content of the fuel play into this ? If the fuel is 11% oil , then 11% of the fuel mixture going into the engine is available for this seal correct ? How would that compare to 9% fuel ? Or is the amount of oil required for this seal less than even that and is metered by the orifice of the supply hole ? I assume when the engines are designed , they are imagining a certain amount (cc's ) of oil being present every cycle .
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Old 07-28-2015, 11:34 AM
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Originally Posted by wittyname View Post
How does the oil content of the fuel play into this ? If the fuel is 11% oil , then 11% of the fuel mixture going into the engine is available for this seal correct ? How would that compare to 9% fuel ? Or is the amount of oil required for this seal less than even that and is metered by the orifice of the supply hole ? I assume when the engines are designed , they are imagining a certain amount (cc's ) of oil being present every cycle .
the liquid mixture of the fuel and oil is what seals the engine....I am not sure how much viscosity difference there is between 9% oil and 11 % oil and if that small change would have much effect on the sealing capacity but my gut tells me there wouldn't be any significant differences....
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