IMS, whilst the engine is out and the trans is off

Get the seal removed?

It's a 1998 dual row, 62,000 miles, based on the wisdom of the Internet my understanding is that if I ask Precision to pull the seal the bearing should get enough splash lubrication to live a longer and happier life than if the seal is left in-situ?

I had the outer seal removed, and checked the bearing for play on my 997 during a clutch change.

I will also have it checked again on the next clutch change - it provides at least a small window of opportunity to have it checked at little extra cost.

I read a soundly-reasoned article which said that the centrifugal force of higher RPMs would empty the lube from the bearing without the seal.

Their view was that the seal served to allow the oil to seep in, but keep it in there when it was needed.

If you have one of the better earlier dual row bearings, I'd leave it alone.

I'd like to see how centrifugal force would empty oil out of a concave external ball race :?:

Ball bearings only need a tiny amount of oil to function as all moving parts roll against each other instead of rubbing like a solid bearing.

When the engine's off the ims bearing is submerged in oil as the level when static is higher than the ims.

Whoever wrote that article is obviously not an Engineer.

i wold leave it alone...

To not have it checked out whilst you have the opportunity would be a bit naive & ignorant IMHO. Also my opinion, if you want to check there is no wear in the bearing, the only proper way to visibly do it is to remove the seal and check that the ball bearing cage is rotating at half the speed the spigot rotates at when manually turning it. If they cage can be held still whilst the spigot is turning, then it's had its day. Once you've pinged the seal off, there's very slim chance it'll go back on.

They are going to remove the dust seal, they've not expressly said that they'll check it for wear at the same time but given that they've found over four grands worth of work to do at what was, initially, a minor service I'm going to assume that they will do so.

Keep us posted on what they find once it's off.

What were the issues discovered that necessitated pulling the engine?

Engine had to come out as they couldn't get the AOS off/out with it in-situ, and the AOS "pipe had collapsed". I suggested (and paid for) the time required for them to break the engine and trans in order to examine the clutch, my thinking being that whilst we had the engine out we should look at all other jobs that could only be done at this point - we're also replacing the fourth chain tensioner that you can't get to with the engine in place.

I'm sure they'll check anyway but ask them to inspect the front to rear brake pipes. They run up past the gearbox and are much easier to renew without the box in. :thumb:

The problem here is who to believe and who to listen to.

Dealing with the original design and lubrication arguments - the sprocket next to the IMS bearing is much larger in diameter but rotates at the same rotational speed in an oil bath but therefore a higher surface tangential linear speed and the chain moves in the oil bath at speeds up to 40mph at high revs.

The combination of these two forces oil everywhere at much higher force and velocity than the small amount inside the bearing (the centre of the bearing also remains stationary so any oil reaching there has no rotation forces to try and expel it). There is therefore a continual flow of fresh oil being effectively pumped/forced into the bearing all the time.

Ball bearings run best with a small amount of fresh replaced oil (it's what they are deigned to operate with) but if the seal gap is too small it starves the bearing.

This is why some fail early and some last a long time because when they are new the grease remains inside and does the lubrication job. The seal is barely more than a dust shield and so when it wears the grease (that becomes like a thick oil when hot) gradually leaks out.

The seal wear that allowed the grease to seep out then doubles as an entry gap for spray oil resulting from the external forces flooding/spraying oil everywhere enabling some oil to seep back into the bearing.

If this is sufficient to keep it cool and lubricated then as time goes by the seal gap increases and the oil flow increases with it until is sufficient to allow the bearing to last a very long time but if the amount getting inside after the grease has gone is too small there is a critical time when it may fail prematurely.

If the majority of bearings that last through that initial critical period can then last for high mileages (as statistics have proven) by being lubricated through a small seal gap - imagine how much more they are lubricated and cooled by fresh oil sprayed all over the bearing continually (which is how they were designed to be lubricated).

The original bearings were a little too small to survive with a limited oil supply and even with new bearings and no seal - although most last for tens of thousands of miles - they are marginal on design suitability for the application which the larger and later bearing solves and therefore lasts even longer.

The smaller bearings outer ring also distorts more when press fitted into the housing (as it is relatively thin and weak) and results in different clearances inside from new - some wearing quicker than others and even some being a little too tight to start with.

The sprocket and shaft are subjected to considerable lateral forces that designers find difficulty calculating (caused by chain flap) which most roller bearings options are not designed to restrain sufficiently and may wear.

The lager ball bearing has sufficient designed in stress limits to survive both radial and lateral forces.

We are continually testing and analysing different solutions to find the best alternatives and over many years we have recommended replacement with a std small bearing running with no seal. This is not however the ultimate last forever option but a good compromise of cost against life expectancy. In many cases it will last a very long time but is a little small for the application in our opinion.

The only ball or roller bearing combination we are happy with therefore is a version using the later larger bearing without a seal.

The only other solution that would be acceptably reliable in my opinion (and could be fitted without stripping an early engine) would be a pressure fed plain bearing.

As soon as we are happy with our analysis of and the testing results of a plain pressure fed bearing solution that can be fitted without stripping the engine we will say so.

Some of the many optional replacements on the market rely on oil fed from a small hole in the other end of the IM shaft filling the shaft and suggest it pressure feeds the bearing. Ball bearings do not need pressure fed oil nor does this solution supply pressurised oil as the outlet is insufficiently sealed and it also does not compare in supply volume to the amount naturally sprayed everywhere at the business end. Ball bearings filled with oil and under pressure from a reliable sealing system would create a lot of oil sheer inside the bearing, absorb power and also run hot as a result.

For engines with the smaller bearing - I would currently only recommend a larger ball bearing version during a rebuild (without a seal) or accepting an improvement of a std small ball bearing without the seal (until we are happy with the alternative of a suitable pressure fed solid bearing option (that can be fitted without stripping the engine) or during a rebuild.

Although we have experienced no problems with the larger ball bearing, because it can only be retrofitted while the earlier engines are apart - we will continue to explore alternatives that can be fitted to earlier engines without stripping them until we find something we are happy to recommend and supply.

Baz

Baz, my engine has the dual-row IMS bearing, the engine is on 62,000 miles.

The received wisdom (from aggregating information from posts from those who would appear to know what they are talking about) is, I believe, that in my situation (not rebuilding the engine, bearing seems ok at present) to remove the dust-shield.

Is that inline with what you would advise?

For clarity - I'm not going to rebuild the engine at this point, or put a new IMS bearing in, the options are remove dust-shield or leave in place.

It is a very difficult one to answer and I may have been guilty of confusing you because I was responding to questions about what it theoretically best and not necessarily what you should go and do yourself - because there are dangers in removing the spider that has the three bolts in (to hold the assembly in place) which you need to do in order to remove the seal. I was referring more to the situation as we see it every day with an engine already stripped.

Even if the crankshaft is correctly locked in the TDC position and the tensioners removed, when the spider is also removed the chains pull the IMS sideways. On re-assembly the shoulder on the spider lines up with the bore in the crankcase at the same time as the centre spindle lines up with the bore and this makes it necessary/likely to put a small strain on that shaft which is weak because it has a machined groove in the centre where the 'O' ring seal sits.

The dangers are that it could initiate the start of a fatigue crack or that the chains may still jump a sprocket.

When we fit a new bearing we also replace that weak shaft with a high - tensile solid one but you can only do this with the bearing removed.

When the bearing has been running in the IMS bore with an interference fit for many years the surface between the 2 parts can develop "fretting" (or Brinelling) deposits that leave high and low spots in the bore that can alter the shape and when that bearing is removed and replaced it may not fit back as nicely (nor with the same tolerance) as it did when it was new. Once again this is an easy job if the engine is apart and the shaft is on the bench - to check, measure and smooth out - but in situ it is a different story.

Movement of the IMS during bearing removal and re-fitting can also put strain on the chains and crack small parts of the plastic guides (because the chains create grooves in the surface of the plastic during their lifetime that any sideways movements can crack). So my arguments about the benefits of removing the seal should be read in connection with the differences in doing it with the engine apart or in situ - for which my advice is different.

Apart from that - just imagine what the situation would be if the bearing that may be looked OK never the less failed shortly after someone had removed the seal - even with the greatest care possible. The owner would obviously blame whoever did the job with potentially unpleasant consequences, unfair damage to reputations - and/or costs.

For this reason my advice about what is best for the situation technically (remove the seal and allow splash lubrication) is not something we like to do and will not guarantee. Most will get away with doing it OK but as we are so busy repairing engines (and because the smaller bearing of any type we think is marginal for very long term reliability) we prefer not to do the job and to either replace the bearing with the latest larger IMS (when the engine is apart) or remove the seal and fit a new bearing while the engine is apart (if the customer will not pay for the former).

If your bearing has covered over 60K and still works Ok the seal is probably sufficiently worn for enough oil to splash past it and into the bearing to last a lot longer (but I cannot guarantee it). Certainly - that is what feedback suggests - that they either fail early or last a very long time.

Removing the seal is more advice about what would technically be a better solution and is not necessarily an offer or recommendation to do so in situ.

With care and an experienced technician - with the right tools - it will probably be Ok but there are still some risks so it may not be any more reliable than leaving it alone.

It is a very different scenario if the engine is apart.

Because the crankshaft shells wear, chains stretch, bores go oval and crack (in most models) or can score (in the later plastic coated piston examples) - we prefer to advise owners to have the engines reconditioned overall rather than just take the risk of removing the seal.

But that doesn't alter the fact that - if you want to do it and/or get it done carefully - it may extend the life of the bearing.

The question is whether it is worth that risk when something else may well go wrong in the future that requires an engine rebuild when a better solution can be offered.

This is one reason why we continue to research and test alternative solutions that could be fitted with the engine in situ but without any of the concerns and potential pitfalls and hope to be able to offer a better solution one day.

To put it a different way - if I were scoring the potential reliability of the outcome 0 to 10 I would probably give the following scores (not scientifically researched just my of the cuff opinion that others may well disagree with and I am not guaranteeing is reliable or accurate).

ASSUMING THE ENGINE WILL NOT BE STRIPPED (using experienced technicians and the right tools).

Over 60K leave alone 6 or 8, remove the spider and remove the seal retaining the original bearing and spindle 3 to 7, Replace the original type of bearing and spindle and remove the seal 6 to 8, Replace the type of bearing with a ceramic or roller bearing and the seal 4 to 6.

If the engine was already stripped - replace the bearing and spindle without the seal with a suitable steel ball bearing 8-9, Replace with a different shaft to fit the larger ball bearing with no seal (or if and when a suitable solid pressure fed bearing system has proven suitable under test by us) 10.

Sorry if my technical original answer was misleading it's a really difficult subject to be firm about.

Baz

I removed my seal when having the clutch done. My IMS 'spider' (as Baz calls it) was leaking oil, so it had to be removed anyway to re-seal it. If this is the case, then removing the seal off the bearing is a no-brainer as all the issues Baz states could still have affected me even if I didn't remove the bearing seal.

This could well be the deciding factor for you when they split the gearbox and engine:

If the ims 'spider' is weeping, have the bearing seal removed.

If it isn't, leave well alone.

ps. If your RMS is ok, leave well alone.

alex yates said:

I removed my seal when having the clutch done. My IMS 'spider' (as Baz calls it) was leaking oil, so it had to be removed anyway to re-seal it. If this is the case, then removing the seal off the bearing is a no-brainer as all the issues Baz states could still have affected me even if I didn't remove the bearing seal.

This could well be the deciding factor for you when they split the gearbox and engine:

If the ims 'spider' is weeping, have the bearing seal removed.

If it isn't, leave well alone.

ps. If your RMS is ok, leave well alone.

Click to expand...

Did you need to lock the cams/remove the tensioners to do that? I plan on doing the clutch on my 72k C2 (dual row) in the summer, and am likely to remove the dust seal.

[edit] ignore me, I have just scrolled up and seen Baz's post.