Sump Gasket - Rear Seal

[Roland]

I just started to sort out refitting my sump (engine still in car) to my Elan Sprint and was checking out the cork gasket half moons at the front and rear . The front one is fine and fits reasonably snug in the seal carrier gap. However the rear cork seal is 5 mm wide and the gap in the seal carrier is just under 7mm wide. Phoned Kelvedon who supplied the gasket set and they indicated the rear seal should also be a snug fit in the carrier.

A cork seal was fitted at the rear but it was covered in silicone and did leak but not badly.

So I am thinking that someone has changed the rear crankshaft seal carrier for a Ford X flow type carrier that takes a neoprene seal?? Would this be a likely explanation.

Tks

Roland

[types26/36]

Sounds like it has the Xflow seal carrier, have a read of this thread.
viewtopic.php?t=30104&p=200751

[types26/36]

Rear seal.

https://www.burtonpower.com/sump-seal-r ... fp763.html

[Roland]

Brian,

Thanks for highlighting that thread, I hadn't found it.

Just reading it confirms that my rear seal carrier with an approx. 7mm groove is correct for my engine. So it is not a later x flow carrier as far as i can judge.

The problem seems to be that the rear cork seal in the Kelvedon sump gasket kit is 5mm wide and is rattling in the groove which doesn't seem right. The front cork seal is thicker and sits nicely in the front groove.

[types26/36]

Brian,
The problem seems to be that the rear cork seal in the Kelvedon sump gasket kit is 5mm wide and is rattling in the groove which doesn't seem right. The front cork seal is thicker and sits nicely in the front groove.

Well both the front and rear cork should be the same thickness......sounds like a bad cork seal?

[Roland]

Brian,

It's exactly the same problem on the thread you sent me, rear gasket too thin. I think Graham on the previous thread had bought an unbranded gasket set and then sourced one from Burtons which was correct.

My sump gasket set came from Kelvedon so not exactly a minor supplier these days in classic Lotus world. I even spoke to the mechanic there today and he was indicating it was my seal carrier.

I'll maybe just order from Burtons which will hopefully be correct.

[Roland]

So I have consulted two more main classic lotus suppliers and it seems the sump gasket kits have a rear half moon seal that is narrower than the front seal. My conclusion is the the rear seal width of 5.1mm is correct by design and not snug in the carrier gap.

I guess that if the longer rear cork seal was wider then the forces to crush it would be 'too high' and would start impacting on the sump (distortion?).

[Roland]

So just to counter that last post. Just had a discussion with Clive and Classic Team Lotus and he measured up their half moon gaskets, front and rear half moon seal widths are 6mm and will be snug in the gaps. So I am assuming this is correct and that last post of mine was not correct.

I have spent a bit of time on this with a few suppliers, there seems to be stock out there amongst more than one supplier in the UK where that rear seal is too narrow. Now it could easily be fitted by using a load of sealant but I doubt it would seal for long.

[2cams70]

The cork seal is designed to seal on the top and bottom surfaces so the width is not that important. What is important is that you don't trim the seal too short and that you tighten and torque the sump bolts in the correct sequence so that the seal is forced into the groove with the correct preload. I've posted on here somewhere before about the correct tightening sequence.

[Roland]

I actually have your tightening sequence post printed out in front of me.

My concern with that narrow seal is that it will move laterally when it contacts the ridge in the sump half moon. Anyway I have a wider seal on its way to me and one of the ex Paul Mattys mechanics was advising it should be snug in the gap. No idea how it was originally designed.

Roland

[david.g.chapman]

Years ago when I replaced the sump seals I trimmed them and couldn't understand why they seemed too long. The last time I fitted the sump I bit the bullet and did not trim the seals. They compress nicely as long as the sump bolts are correctly tightened.

Once the sump is in place it's hard to see if the seals are correctly positioned. I used one of those telescopic small inspection mirrors to see the seal in situ and give me peace of mind.

Cheers,

Dave Chapman.

[Roland]

Dave,

I got the seal kit from Matty's today with the correct width rear seal (6mm) wide.

Regarding the half moon seal lengths they do seem way too long, I doubt they would be able to be set properly without some trimming. Having spoken to a couple of mechanics in the week who do these seals regularly they have advised to trim them but be very careful not to trim them short (similar to your advice). I know they land onto the sump gasket and need to press into the sump gasket to form a seal. So the advise I seem to be getting is to leave them overlength each end by approx. 1.5mm so they can seal against the sump gasket.

I have two setting formers made (like Col Croucher uses from Elantrikbits) so I can set the seals in the grooves with my chosen sealant. I can then remove the setting formers and I should be able to see any issues with seal length before the sump goes on, at least that is the plan.

[david.g.chapman]

I think the idea with having the seals too long is so they can compress sideways and lengthways as the sump is tightened up, moving against the still liquid rtv.

The question is, how long does the seal have to be? Perhaps the percentage compression lengthways is similar to the percentage compression sideways. That would need a large excess length of 15mm +, more than you actually get!

So it's up to each one of us to decide.

Cheers,

Dave Chapman.

[Roland]

Dave,

I've not cut anything yet.

My thinking is that a normal cork gasket between flanges spread sideways as it is compressed. These half moon gaskets are almost fully restrained on all sides. So I was thinking that the seal is compressed radially as the sump is tightened and it will spread sideways and lengthways (but not by much). The lengthways spread will then load up the joint between the sump gasket and end of the half-moon cork which is already approx. 1.5 mm over length.

My concern is that I leave the halfmoon gaskets fully over length (they are 6mm over length each side) is that I end up with excess cork at the corners which is either difficult to compress or overloads the sump gasket at the corner.

You of course may be right, I am going to take some more advice before cutting. I don't want to leave these seals short.

Tks

Roland

[rgh0]

Personally I leave the seals about 3mm long and with a small dab of RTV on the ends this seals well to the flat cork gaskets and enables the gasket to seat properly in the carrier. I use Loctitie aviation gasket cement on the gasket and carrier

cheers
Rohan