Awkward Sump Gasket

[189Participant]

I’ve just wasted half a day trying to fit a new rear bearing cap sump gasket and shim. Is there some knack to this that I don’t understand?

The old style cork gaskets were both compressible and semi-circular, the new synthetic rubber ones are neither. With the engine still in the car this means that by the time I’ve manoeuvred the sump into position the ends of the gasket have sprung out of the bearing cap channel. So I’m reluctant to bolt it up and hope it just might successfully seal.

Frustrated David

[BernieParticipant]

David,

This is the crib-sheet I prepared some time ago to answer questions similar to yours ….

Sump Gaskets  – 4-cyl 11CV Engine

In the past, a few members have made the TOC aware of difficulties experienced when fitting the crankshaft gaskets which seal the ends of the sump.  Their feedback suggested four different problems:

1.    Seal too brittle

2.    Seal too narrow for the groove in the bearing cap

3.    Seal too wide for the groove in the bearing cap

4.    Sump assembly leaks.

The original design is simply a strip of agglomerated cork – a basic mixture of pure cork crumbs mixed and cooked with a bonding agent to hold them all together. 

Today there are three types available: 

·       Plain cork (as original)

·       A cork/polymer mix (much less brittle)

·       A 100% moulded polymer (relatively indestructible). 

Some are supplied as a straight strip whilst others are pre-moulded into the finished “half-round” form.

An investigation of samples of each of the above taken from TOC Spares stock showed none were too small for the groove and all were of adequate length to protrude at the sump gasket face of the bearing cap (where they must then be trimmed to length).  

The 100% polymer version was probably the easiest to handle but there was no difficulty fitting any of three types supplied by the TOC into a set of bearing caps.  They ought to be a fairly tight fight in the bearing cap and a tried and tested fitting method is to lightly oil or grease the groove then start in the centre of the cap/seal and work around in each direction.  Bending the gasket (very carefully in the case of cork parts) in the opposite direction to the curve of the cap will reduce the seal’s width slightly and therefore facilitate fitting it into the groove.  Finally, the seal must be fully bedded into the groove and this can be achieved by gently tapping it with a smooth wooden block, again working away from the centre to each end. 

I have the advantage of having spent my working life in the gasket industry but anybody with a little common sense will realise such parts should not be subjected to sharp bends and need to be eased into position to avoid damage.  As stated above, a little oil or grease will help if they seem too tight.

So, why have there been problems …..?

Even with a correctly manufactured cork gasket, points one and two above can still arise and both are generally caused by the simple fact that cork is a natural plant product.  Depending on where and how it is stored, cork is inherently prone to drying out and, when this happens, component will shrink and become brittle.  Dried-out seals are therefore not only likely to be more loose in the bearing-cap groove but are much more prone to being damaged during assembly.  However, any shrinkage should be no more than a temporary inconvenience because a cork gasket in this condition can be rejuvenated by soaking in water (but not for too long or it could then swell too much – but if that happens it can always be dried again!).  An alternative is to soak in oil but, unless an extremely light oil is used, it is likely to take a very long time for the gasket to recover sufficiently – especially when it is as thick as the parts in question here.

A cork gasket that is too wide for the cap is very rare but may have absorbed moisture since it was manufactured.  In that case – or if the gasket has indeed been made oversize – the problem can be simply overcome by carefully shaving a little material from one side with a razor blade or similar sharp tool.  Providing a cork component is secure when assembled, the subsequent compression and exposure to oil will ensure it will remain a good fit and hence, seal.

I have never personally come across a gasket that would not securely fit into the groove and, although all the types of gasket available from TOC Spares are fit for purpose, more care will always be needed when fitting the more delicate cork items.  

 

Finally – why do some leak? 

Assuming all the hardware is in good condition – it is worth taking special care to ensure the sump pressing itself is not distorted – sump leaks are almost invariably due to the way the gaskets have been fitted.  

Most importantly, the end seals must first be correctly located without any damage or over-trimming.  They must be fully seated in the cap and the half-round shim (on the inside of the rear cap) must also be correctly positioned or the seal will almost certainly be distorted and possibly dislodged as the sump is tightened down. 

Final cutting-to-length is an equally important step and can only be done properly once the seal is correctly seated in the bearing cap.  Both ends should be trimmed just a little proud of the bearing cap to ensure the seal will fully engage – and just interfere – with the sump gasket.  It is enough to just be able to feel the seal protruding above the surface of the cap.  It is equally important that the sump side gaskets are also correctly trimmed to fully fill the cut-away areas under the bearing caps before those gaskets are securely clamped between the caps and block casting.  The point at which an end seal meets the main sump gasket and the adjacent area where the sump gasket sits under the bearing cap is one of the very few places in which I would advocate the use of a very thin layer of a non-hardening jointing compound such as Blue Hylomar – but not much and never use anything along the length of the main sump gaskets.

Smearing a very light trace of grease on the inside curved surfaces at the ends of the sump will help the sump to slide over the seals as it is tightened into place thus minimising the danger of the digging into and dislodging or damaging the seals during assembly.  With the two reinforcing strips in place to spread the clamp load, the sump bolts should be tightened up evenly and in sequence to draw the sump squarely into place.

It may seem obvious but, in my opinion, replacing a sump is a job that is unlikely to be carried out successfully without removing the engine from the car. 

As I said, I have never personally come across a gasket that would not securely fit into the groove” and they have always been tight enough in the groove to be retained by friction.

However, although this does talk you through the process of sump gasket fitting, you will see, in the very last paragraph I state “It may seem obvious but, in my opinion, replacing a sump is a job that is unlikely to be carried out successfully without removing the engine from the car“.  That is not to say it is impossible without removing the engine but you definitely increase the risk of something not being aligned quite as it should.

I hope this helps.

B………

 

 

 

[189Participant]

Dear Bernie

Thanks for such a comprehensive reply.

I’ll persevere for a while longer in the hope that I get lucky and the b*gg*r finally fits.

Frustated David

[BernieParticipant]

David,

Fortunately the information was already prepared so it was no big problem to reproduce it here.

I wish you luck – but before you do try again I suggest it might be worth trying different seals in the bearing cap – and fit the shim before you attempt to fit the seal.  (I know that is not easy when you are working overhead).

As I said, all those that I have worked with have been tight in the cap groove and have remained in situ – some for months on the shelf here following my numerous tests on the various seals available.  I have never seen any myself but I wonder if you have some of the “undersize” ones that some members have complained about in the past? …. but they were usually cork items that had dried out after having been stored for a very long time in hot/dry conditions.

If they are clearly “undersize” and from the Club Spares, please let both me and Chris know and request replacements from Chris.  If you don’t mind, please let me have the old ones in due course because I would like to see them for myself.

B……………..

[189Participant]

Dear Bernie

The problem is that the synthetic rubber gasket is too thick rather than too thin. I can get it to stay in place without the shim but not with it.

So how important is that shim? And is the rear bearing cap the most badly designed component on a Citroen?

David

[BernieParticipant]

David,

At least the seals are not too small – that is good news.

So, …….. are you trying to fit the seal with the bearing cap in place?  If you are, I believe it will be virtually impossible to get the seal perfectly seated.  Not only will the seal need to be persuaded into the groove but it must then be accurately cut to length at each end once it is correctly located (per my earlier notes).

If I read your initial posting correctly you are not attempting to replace the main sump gaskets …..?  However, I fear you may have to disturb the ends because you will almost certainly have to remove the bearing cap in order to fit the seal on the bench.  When you remove the cap there is a strong likelihood of damaging the ends of the main gasket strips where they are pinched between the block and the cap.  If you are very careful, you may be able to cut across the width of both sump gaskets (using a scalpel or similar) at the points where they disappears under the cap.  Having done that, when you reassemble you will need to reuse (or replace) the small pieces of gasket trapped under the cap and you will also need to apply some sort of sealant to ensure you fully close the joint you have created.

Personally I would advocate completely replacing the gaskets as well as the cap seals but I appreciate this will entail additional work you would probably rather avoid if possible.

I note you live about an hour from me.  If it helps you will be most welcome to bring the cap, shim and seal here and I will be pleased to at least assist you to assemble and trim the joint to length.

B……………….

[189Participant]

Dear Bernie

Well it’s in.

I finally realised that not only was the gasket too thick but it was also too short.

To install it I had to outwit it. That meant stretching it between two G clamps on the bench and leaving it for a couple of hours under tension. I then slipped it into the bearing cap before it realised what was happening.

It seems that the synthetic rubber gasket material isn’t stable and regresses over time, in this case the twelve months since I bought it.

Finally thanks for your all advice but this must be the silliest way to seal a sump.

David

[Richard LarterParticipant]

Have just spent several hours on the sump gasket, who thought it was a good idea to trap the ends of the gasket under the main bearing end caps. A professional restorer had bodged the last gasket by not removing the main bearing caps and using gasket cement rather than a gasket which lead to the sump distorting and damaging the end cap seals and leaking lots of oil.  It is possible to do this with the engine in the car but I found the trickiest part was knocking back the tab washers on the timing cover bolts. The new neoprene end seals are a nice tight fit in the bearing end caps but should they be fitted with any sealant?

Cheers

Richard

[BernieParticipant]

Richard,

I would refer you to my June 2108 post above, in this same thread.  If you don’t want to read it all, I think the relevant bit to your question are :

• Final cutting-to-length (of the bearing cap seals) is an equally important step and can only be done properly once the seal is correctly seated in the bearing cap.  Both ends should be trimmed just a little proud of the bearing cap to ensure the seal will fully engage – and just interfere – with the sump gasket.  It is enough to just be able to feel the seal protruding above the surface of the cap.  It is equally important that the sump side gaskets are also correctly trimmed to fully fill the cut-away areas under the bearing caps before those gaskets are securely clamped between the caps and block casting.
• The point at which an end seal meets the main sump gasket and the adjacent area where the sump gasket sits under the bearing cap is one of the very few places in which I would advocate the use of a very thin layer of a non-hardening jointing compound such as Blue Hylomar – but not much and never use anything along the length of the main sump gaskets.
• Smearing a very light trace of grease on the inside curved surfaces at the ends of the sump will help the sump to slide over the seals as it is tightened into place thus minimising the danger of the digging into and dislodging or damaging the seals during assembly. 
• With the two reinforcing strips in place to spread the clamp load, the sump bolts should be tightened up evenly and in sequence to draw the sump squarely into place.

Hope this helps.

B…………..

[Richard LarterParticipant]

Thanks Bernie. If it had been a cork gasket I would have given it a smear of grease but wasn’t sure what to do with the synthetic seals. Sump now back on hopefully without any oil leaks.

Cheers Richard

[BernieParticipant]

Richard,

First of all, not everybody is fortunate enough to have the facility to remove an engine easily but, as I said in my earlier post, in my experience this is not an easy job with the engine in situ –  so well done for having succeeded.

And, just to explain why I do not recomend “lubricating” a gasket when fitting … I spent the greater part of my working life in the gasket industry and experience there showed that a lubricated gasket was more prone to slide over the component face(s) leading to possible extrusion and hence reduced clamping load.  This is less of a problem with a rigid material such as a metal/soft mat’l sandwich but pure cork is one of the most susceptible to it.  Cork/rubber mixtures are a bit more resistant but not immune to being compromised in this way.  Therfore, if a cork joint does have grease added to the surface it should literally be no more than a smear for that reason.

Sorry if this sounds pedantic  …. but that is because I am a pedant!

B………….

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