FRONT BEARINGS
05-30-2013, 01:20 AM
#16
I know stories about people using very rich engines or after racing using a huge amount of afterrun so when standing still the oil will drop out through the front bearing and then they think the bearing is bad. As mentioned before, the seal is a dust cover and not an oil seal.
The frontbearing can go bad on several reasons. One of them is a to close mounted flywheel. The sticking out pins for the clutch shoes can touch the crankcase giving a bad vibration. And all axial forces are only on the front bearing. Also in this situation dirt can be pushed in to the bearing due the small gap.
The difference in expansion of the crankcase and crankshaft needs to have some axial play on the main bearing. With no play the crankshaft can lock itself up and a to tight fit of the crackshaft in the mainbearing can cause some forces during heating up and cooling down.
The frontbearing can go bad on several reasons. One of them is a to close mounted flywheel. The sticking out pins for the clutch shoes can touch the crankcase giving a bad vibration. And all axial forces are only on the front bearing. Also in this situation dirt can be pushed in to the bearing due the small gap.
The difference in expansion of the crankcase and crankshaft needs to have some axial play on the main bearing. With no play the crankshaft can lock itself up and a to tight fit of the crackshaft in the mainbearing can cause some forces during heating up and cooling down.
05-30-2013, 05:47 AM
#18
engine tolerances play a big role in how long the front bearing lasts...... some engines are built with a very tight tolerance between the crankcase and the crank...these engines seal quite well and bearings will usually last fine...however other engines are built with very poor tolerances between the crank and the crankcase, because of this the engines are unable to make a reliable seal inside the crankcase....this causes the engines to leak and suck air thru the front bearing...when they do this they also usually take in dirt which ruins the bearing.......
05-30-2013, 05:58 AM
#19
A lot of front bearings fail due to people's laziness! No telling how many engines I look at that are full of dirt. Too lazy to change air filter, too lazy to take their engine apart and clean, too lazy to take the clutch off and clean the caked up dirt on the front seal.
There are more reasons than that but simple maintenance goes a long way.
05-30-2013, 05:51 PM
#20
Tech Master
Houston, aren't you going to come give us the final verdict here?
While you're at it, can you tell me the answer to this lifelong question; Inner front bearing seal, remove or keep? Seems there's no final decision. I tend to remove.
While you're at it, can you tell me the answer to this lifelong question; Inner front bearing seal, remove or keep? Seems there's no final decision. I tend to remove.
05-31-2013, 03:08 PM
#21
Tech Master
Well, there are many reasons for seals to og bad. One i really know of is using a shim between the collet and the front bearing. That kills bearingseals quite fast.
I for one, am not hysterical when my front bearing is a bit moist or have a drop underneath it. it is not imporatant. I was always tought that the seal should come from the case/crank seal , not the bearing itself. When you see onroad engines, the use steel shild bearings and works awsome :-) With no leaks or strange tuning issues. They have less friction too.... I Wonder how a steel shiled bearing would work With the Buku cap?... hhhmmmm, need to test that :-)
I for one, am not hysterical when my front bearing is a bit moist or have a drop underneath it. it is not imporatant. I was always tought that the seal should come from the case/crank seal , not the bearing itself. When you see onroad engines, the use steel shild bearings and works awsome :-) With no leaks or strange tuning issues. They have less friction too.... I Wonder how a steel shiled bearing would work With the Buku cap?... hhhmmmm, need to test that :-)
05-31-2013, 03:27 PM
#22
Does anybody pressure test, or pressure/vacuum test their engines before or after a rebuild?
If so what pressure do you test it at? 5 psi / 8 - 10 in-hg? I know that may sound like a lot,
or it sounds similar to pressure specs for a mx bike. But model engines spike to 4 psi, and 4 to
7 in-hg.
I was aware that close tolerances were used seal some model engines, and that the tight
tolerances would help engines equipped with a labyrinth seal. Given Maximo's comments, it
must work much better than other engines, but how well does it work? I mean, it can't be
pressure tested (at least I have never tried to pressure test a labyrinth seal) Does anyone
know how effective they actually are?
If so what pressure do you test it at? 5 psi / 8 - 10 in-hg? I know that may sound like a lot,
or it sounds similar to pressure specs for a mx bike. But model engines spike to 4 psi, and 4 to
7 in-hg.
tolerances would help engines equipped with a labyrinth seal. Given Maximo's comments, it
must work much better than other engines, but how well does it work? I mean, it can't be
pressure tested (at least I have never tried to pressure test a labyrinth seal) Does anyone
know how effective they actually are?
Last edited by wmazz; 05-31-2013 at 03:42 PM.
05-31-2013, 04:51 PM
#26
The issue with running a overly tight head on the car engines is they wont idle down correctly when you let off throttle.... With a tight head they always want to "ring-a-ping ping ping ping" when you come off a high speed pass.......... And the only way to get rid of it is to drown it out by running a overly rich mixture, which substantially reduces the power of the engine............ Some engines these days come with as low as 0.014" clearance and will ring-a-ping ping horribly if you try to tune then to the edge.,...They run like scalded dogs tho , but only if your willing to put up with the ring-a-ping ping when you idle down after a hard pass....
Personally I can't stand engines that do the ring-a-ping ping on idle down... I have spent years playing around with head buttons trying to find the perfect balance that allows my engines to reach warp speed RPM"s, carry crisp throttle yet still idle down smooth and silky after a hard run...... I see far too many engines at the races that ring-a-ping ping piing, to the pint where I believe some people assume its perfectly normal and acceptable....
In the end its a very fine line finding the perfect balance in the head button that allows the engine to make full power and RPM, yet still retain the ability to idle down quick and smooth after a hard pass........
Personally I can't stand engines that do the ring-a-ping ping on idle down... I have spent years playing around with head buttons trying to find the perfect balance that allows my engines to reach warp speed RPM"s, carry crisp throttle yet still idle down smooth and silky after a hard run...... I see far too many engines at the races that ring-a-ping ping piing, to the pint where I believe some people assume its perfectly normal and acceptable....
In the end its a very fine line finding the perfect balance in the head button that allows the engine to make full power and RPM, yet still retain the ability to idle down quick and smooth after a hard pass........
There seems to be tons of different ways to explain the same things on this forum.
The brake cleaner test isn't new, neither was the solvent test. But they only
test for vacuum.
After so many years of dealing the same problems, and nobody does the standard
kind of tests?
Maybe a few people?
Sorry Houston
Last edited by wmazz; 05-31-2013 at 05:01 PM.
05-31-2013, 10:18 PM
#27
No offense, but "ring-a-ping ping on idle down" isn't anything new.
There seems to be tons of different ways to explain the same things on this forum.
The brake cleaner test isn't new, neither was the solvent test. But they only
test for vacuum.
After so many years of dealing the same problems, and nobody does the standard
kind of tests?
Maybe a few people?
Sorry Houston
There seems to be tons of different ways to explain the same things on this forum.
The brake cleaner test isn't new, neither was the solvent test. But they only
test for vacuum.
After so many years of dealing the same problems, and nobody does the standard
kind of tests?
Maybe a few people?
Sorry Houston
Its an open forum , its a discussion , git r dun
06-01-2013, 07:47 PM
#28
Suspended
iTrader: (7)
No offense, but "ring-a-ping ping on idle down" isn't anything new.
There seems to be tons of different ways to explain the same things on this forum.
The brake cleaner test isn't new, neither was the solvent test. But they only
test for vacuum.
After so many years of dealing the same problems, and nobody does the standard
kind of tests?
Maybe a few people?
Sorry Houston
There seems to be tons of different ways to explain the same things on this forum.
The brake cleaner test isn't new, neither was the solvent test. But they only
test for vacuum.
After so many years of dealing the same problems, and nobody does the standard
kind of tests?
Maybe a few people?
Sorry Houston
06-02-2013, 09:11 PM
#29
Here is a follow up on the caps in regards to engine tune and tuning window.Over the last 2 weeks I have been running caps on new,old and also rebuilt/pinched engines. My conclusion is this. These engines suck the highest amount of vacuum through the front bearing directly after a WOT pass immediately followed by breaking or completely off throttle.
Detonation can occur in a narrow rpm range as an engine transitions from low to high speed circuits, before
peak hp, and it can occur at wot.
Let me hold a dollar!
A lot of front bearings fail due to people's laziness! No telling how many engines I look at that are full of dirt. Too lazy to change air filter, too lazy to take their engine apart and clean, too lazy to take the clutch off and clean the caked up dirt on the front seal.
There are more reasons than that but simple maintenance goes a long way.
A lot of front bearings fail due to people's laziness! No telling how many engines I look at that are full of dirt. Too lazy to change air filter, too lazy to take their engine apart and clean, too lazy to take the clutch off and clean the caked up dirt on the front seal.
There are more reasons than that but simple maintenance goes a long way.
My point is that these engines are not special. They suffer from all the same problems as any other
2-stroke engine. The engines geometry creates the same positive & negative pressures as any chainsaw,
mx bike, watercraft, snowmobile, outboard, and 2-stroke Subaru's
That is why the exposed front bearing is so important.
This is why Houston's thread is important, why do front bearings fail, and what are the signs? They
fail for the same reasons as any other 2-stroke engine. By recognizing that fact, it will simplify diagnosing
and tuning your engines.
Here is a product I like: Suzuki 1207b sealant. It is made by Three Bond, but it isn't available anywhere
except from a Suzuki Motorcycle or Outboard Dealer. It has been used as a case sealer for Honda,
Kawasaki, and Suzuki, PJS engines. It is heat resistant (my experience, about 800' to 1000'), It works great with nitro,
it's expensive $20 per tube, it is not user friendly, it is messy - like ink, and it is buy far the best sealer I have ever used.
Last edited by wmazz; 06-03-2013 at 11:12 AM.
