Factory Fault Or Designed To Fail?

[samy]

Hello all,

i have just picked up my 2010 Sherco 250 after needing new crankshaft bearings and seals. The bike was 18 months old when the seals and bearings decided to go belly up. I did not do the work myself, but had a great fellow trials rider & mechanic do the work for me. He stated that when the factory put the crank shaft bearings in, they did not remove the seals in the bearings and therefore after 18 months of easy clubman riding they ran dry and failed. Apparently the bearing's seal needs to be removed before installing the bearing to allow the gearbox oil to lubricate the bearing. If the bearing remains completly sealed, unless you crack open the engine on a regular basis, crankshaft bearing failure is inevitable.

Apparently there was a batch of Beta's which had this problem back in 2000/2001.

My mechanic has replaced the bearings (and leaving the seal out), and after giving the bike a full service and going over is confident that the bearings will not have a catastrophic failure again in the future in the way it was designed from the factory.

My question is, is this normal for the bearing seals to be left in place? Does the factory expect the average clubman rider to tear down the engine every 6-12 months to replace/regrease the crankshaft bearings? Is this an oversight on Sherco's behalf? Was the person on the facotry floor who installed the bearing simply being lazy?

I was under the assumption that as i only ride 1-2 times per month (and very easy at that) that i would have been able to get years out of my bike without having to tear the engine apart. I did not plan to have to tear down the engine as part of basic servicing!

Anyway the bike is back, it is running VERY nice and has more power than i remember!

I think my next trials bike will be electric...

cheers

[copemech]

Shercos have been coming with pre-lubed sealed bearings for many years now('05??) with no great issues. Not sure what your original problem was.

Crank seal issues due to alcohol induced fuel can be an issue, yet these seals can be replaced externally. Reports on bearing issues seem actually less over the years with the sealed units, as they seem to mitigate dirt entry through the intake tract, although dirt is the prime culprit here and I suppose may wipe out any bearing. With your seals being removed you are now at the mercy of your own maintenance for prevention I would think. If one was going to opt for that the bearings may have been had for a lot less dosh.

Did he install the Viton(alcohol resistant) seals as well?

My seals have been replaced on my '07 bike, but no bearings.

Seems your mechanic has opened a different set of worms for you.

[lineaway]

So, Cope is the bearing lubed some other way like the gasser?

[copemech]

So, Cope is the bearing lubed some other way like the gasser?

No, apparently just pre lubed and sealed. Now although I have my own questions about all that, I quess it works for the most part.

I have a couple of compressors at work with 20,000 hours on the motors with no added lube! Go figure?

I can only presume from there, but I still think DIRT is the worst enemy!

[chewy]

I had a 2011 Sherco from new which had a failed water pump seal after 40 hours , had to do it myself as this problem would have ruined a weeks riding holiday... found the seal put in on the p***. this was one of several manufacturing faults I had to sort out with my new Sherco....I say I because I received poor service from the importers here. Most trials bikes are a collection of the cheapest components put together by the cheapest means wrapped up and marketed as dream fulfilment in a leisure industry. you pay your money and you take your chance.

[gasgas249uk]

Shercos have been coming with pre-lubed sealed bearings for many years now('05??) with no great issues. Not sure what your original problem was.

Crank seal issues due to alcohol induced fuel can be an issue, yet these seals can be replaced externally. Reports on bearing issues seem actually less over the years with the sealed units, as they seem to mitigate dirt entry through the intake tract, although dirt is the prime culprit here and I suppose may wipe out any bearing. With your seals being removed you are now at the mercy of your own maintenance for prevention I would think. If one was going to opt for that the bearings may have been had for a lot less dosh.

Did he install the Viton(alcohol resistant) seals as well?

My seals have been replaced on my '07 bike, but no bearings.

Seems your mechanic has opened a different set of worms for you.

Copemech , you obviously have a lot of knowledge on this matter , but a number of things things would worry me about sealed bearings. Firstly when the engine gets very hot , the seal has to be very efficient and keeping the lubricant in , for all of its life, showing no wear at all. I can just imaging the lube getting out and being burnt and the bearings running dry.

I would have thought Samy would be far better off for long term reliability with open bearings . As long as the design as such, allows the mixture can come into contact with them , then the lubrication is there.

Samy ,like copemech says the reliability of the bike is down to your own maintenance. Im sure you do this already , but just keep your fuel cans spotless internally and clean your air filter after each trial. But this is no more than we all have been doing for decades.

I dont think you've got anything to worry about and are better off now.

[naichuff]

I had an 02 200 Sherco with a main bearing failure the bearing was not sealed Water had came in true the timing side seal The bearing was the same as the old Bultaco My old Bulto still runs on the bearings fitted at the factory My Beta also has mains and these were sealed I think that problem started when it used to flood if the fuel was left on when parked at sections This washed out the bearing lube

[dadof2]

Perhaps the manufacturers could shed some light on why they have switched to shielded / sealed main bearings.

I wondered if it was to increase crankcase compression or to enable leaner oil to fuel ratios to be used.

Sealed bearings do last many thousands or running hours in industrial applications but usually at lower temperatures than 2 stoke crank cased and without the vibration.

Cheers

[tony27]

The bearings being sealed isn't their only change over the older non-sealed bearings, the cage material changed to polyamide for noise reasons although also have the advantage not doing as much damage if they fail

I think the reason for going to sealed bearings was to try & extend their life after lots of owners were finding very short lifespan due to water damage

How hot do 2 stroke crankcases honestly get?

[baldilocks]

you may want to ask your friend how the gearbox oil gets to the bearing in a two stroke ? it does on the gas gas pro because there is a oil circulation passage to the bearing but generally on a 2t the mains are lubed by the pre mix oil you add to petrol. my 2011 sherco did the ssdt and numeous other long distance events and was still on original mains when i sold it.

[samy]

Hi guys, thanks for the replies!

To try and answer a couple of things, we don't get a lot of mud/water here so we don't have to deal with what i'm sure are very dirty bikes in the UK But on saying that, i usually change my gearbox oil after every 1-2 trials so that's about once per month or two. I also clean the airfilter after every trial, only use fairly new but very clean plastic petrol cans and have an additional inline fuel filter between the tank and carby.

Copmech, the mate mechanic is the state authorised repair/service mechanic for Sherco and Beta and knows his stuff very well. He did mention something about the Viton alcohol resistant seals needing to be used.

naichuff, it has been said to me by many an opinion in the paddock at the last 2 -3 trials that the Sherco's crankshaft seals are one of the worst in any modern trials bike and you should expect at least the timing side seal to fail within 12 months. Therefore the seals should be replaced every 12 months as part of routine maintenance. I am now aware of a 2010 290 Sherco in my club that was when 9 months old, knocking, pinging and running very lean like mine due to failed crank shaft seals. The seals were replaced and it was as good as new.

baldilocks, i am unsure how the bearings will be lubed by gearbox oil if at all (i just assumed) but as i mentioned above the mechanic is the authorised Sherco repair/service rep and he stated that sealed crank bearings were a factory design fault. He said something along the lines that a fully sealed bearing inside a hot 2 stroke engine is never a good idea. I'm not a mechanic so don't quote me

Well the bike is running very well, too well in fact. It's now very snappy of the bottom so i need to get used to all this power or somehow calm it down. It's about to hit 2 years old and finally running great

cheers

Edited August 1, 2012 by samy

[copemech]

Copemech , you obviously have a lot of knowledge on this matter , but a number of things things would worry me about sealed bearings. Firstly when the engine gets very hot , the seal has to be very efficient and keeping the lubricant in , for all of its life, showing no wear at all. I can just imaging the lube getting out and being burnt and the bearings running dry.

I would have thought Samy would be far better off for long term reliability with open bearings . As long as the design as such, allows the mixture can come into contact with them , then the lubrication is there.

Samy ,like copemech says the reliability of the bike is down to your own maintenance. Im sure you do this already , but just keep your fuel cans spotless internally and clean your air filter after each trial. But this is no more than we all have been doing for decades.

I dont think you've got anything to worry about and are better off now.

To be honest, I was a bit put off by the concept of the sealed bearings when I heard all this. Sometimes the engineers who develop things can be wrong, and only time will tell.

Well, over time it seems the sealed bearings have held up well, in both my personnal experience on long term testing of the Sherco and from general reports from others on this forum.

The trials motors are generally lightly loaded and water cooled, so excess heat would not be an issue. Most have bigger issues keeping heat in the motor as they cool quickly!

I still believe one of the big problems in earlier years was the fact that if one ever even approached a Sherco with a water hose, one would wash enough dirt and water through the filter to induce damage. The only way to stop this is to plug the airbox prior to washing the bike or similar. This does not neccessarily happen with riding wet areas alone, yet may if the rear mudguard and such is not properly sealed, mostly self induced as it is easy to do. This would apply to all years through '09, and at least you will fill the lower airbox with muck for your next trip!

Crankshaft seal issues with the standard issue nitrile seals poor resistance to the introduction on alcohol in our fuels is another issue. Yes, I give them a couple years maybe. This is a fuel issue, not a design issue, yet I do believe they should adapt for the sake of longevity.

Samy's motor will now be more conventional in a sense, and even though less costly bearing may have been had, possibly it is all OK, but even today I must ask myself the question of which way I would go on all this, I am leaning toward the newer sealed units as I have found no real reason to condem them.

[kris]

^{2010 250 Sherco main Bearings}

^{Not trying to rubbish any manufacturer the comment's about samy's main bearings were made by myself.}

^{The crank seals do require replacing due to heat, fuel and lack of lube}

^{Normaly the stator side seal fails first because it only gets lube on one side (fuel oil mix) and hot dry dust on the other, the gearbox side seal lasts longer because it gets lube on both sides ( fuel oil mix & gear box oil) the fuel/ oil helps cool as well as lubricating helping them seal.}

^{I think they are using sealed bearings to reduce air volume in the crankcase and increase the air pressure from the bottom to the top end between strokes, but i also think it causes a lack of lube and cooling to the rear of the seal and increased wear, when the seal starts to fail the bearing will then fail from excess air and dirt induction}

^{all fuels and 2 stroke oils are different some better than others and may cause a different service life of the seals , but we should change the more often than we do its a cheap way to stop big failures}

^{The bearings and seals replaced in samy's bike are genuine sherco parts but I removed the dust seals from the bearings}

^{Just my opnion.}

Edited August 1, 2012 by kris

[atomant]

^{2010 250 Sherco main Bearings}

^{the gearbox side lasts longer because it gets lube on both sides ( fuel oil mix & gear box oil) the fuel/ oil helps cool as well as lubricating helping them seal.}

I have not stripped a sherco engine but I am intrigued how what you say can be the case. The crank chamber is under pressure and I would therefore assume that the bearings are open on the inside and are lubricated using the oil/fuel mix and are sealed on the outside to contain the pressure. I cant see how a single bearing can be lubricated using both the oil/fuel mix AND the gearbox oil as the gearbox oil would just be drawn into the crank chamber?

Edited August 1, 2012 by atomant

[kris]

The bearings get lube from fuel/oil mix only. Leaving the dust seals in the bearings restricts the flow of fuel/oil mix behind the crank shaft seal. The crank shaft seal on the g/box side gets oil on both sides fuel/oil on the inside of the seal and g/box oil on the outside of the seal. So cooled and lubed on both sides.

Edited August 1, 2012 by kris