Reply To: Awkward Sump Gasket

5th June 2018 at 11:21 am #22995

Bernie

Participant

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………