Lotus Elan

Rope Seal Distress

PostPost by: Ross Robbins » Thu Apr 19, 2012 4:16 pm

Not a question, just a story.

After living with oil leaks, not seeps but actual leaks, for over 5,000 miles of driving over the past year, I decided enough was enough and pulled the engine for a complete reseal. Now I know that no twin cam engine is fully dry, but I had a vast gap to cover to tolerable. After replacing the front crank seal and adding an oil slinger that was missing I had confidence that things would be better there by far. At the back of the engine we replaced the rope seal and couldn't get the rear oil seal housing on because the new seal was so much thicker than the tired old one. Anyway, we had to loosen the main caps to get the rear oil seal housing on and then tighten the main caps to compress the seal enough.

Finally after putting all the bits back (with a detour for a fuel pump rebuild and a lot of "two steps forward one step back") it was time to turn the engine without plugs to build some oil pressure before firing it. Double check everything and it all looks OK. Turn on the battery switch, twist the key and...clunk. The starter engaged but just made a sickening clunk. Ahh..duff battery? No. Starter in wrong? No. Then what?

My friend Roy Poague who was so helpful and has built two racing Sevens that are meticulously prepared, said the rope seal was binding on the crank and just needed a bit of break in. I challenged that by saying, "How can a quarter inch wide seal around a polished crank journal create that kind of force?" We tried to turn the engine with a long handled socket on the front crank bolt. No joy. We put it in fourth gear and tried to turn it by pushing the car. The only thing that happened was the tires squeaked on the polished floor. We then tried rolling it forward down a slight grade and dumping the clutch. It turned, but only a bit and brought the car to a halt as if the brakes were on (they were not)!

Roy decided that the only way to get it to move was to tow it down the block and back in gear and let it break in a bit. So, plugs out, fourth gear, twenty miles an hour I was towed down the street chugging like an old Model T Ford. Got oil pressure and things seemed to smooth out. Try it again with plugs installed and switch on halfway down the block. She fires!!

IT'S ALIVE. My relief was palpable and when I got back to the house, I started it on the key quite easily. At last I could breath.

My point in this post is to make others aware of the powerful effect a new rope seal can have on the ability of the crank to turn. If I had not experienced it I never would have believed it myself. Oh, and not a drop from the engine or transmission whose seals we also replaced. Now I'm happy and it was worth it.
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PostPost by: Mazzini » Thu Apr 19, 2012 5:11 pm

I've got to ask - did you soak the rope seal in oil and roll it in with a 'roller' for want of a better word? I used to use Graphogen on the rope seal as well. I gather the problem is if the rope seal is dry it can burn on start up and will never properly seal.

My experience of rebuilding Twincams is twenty years out of date, I'm sure our fellow posters will have much more up to date advice.
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PostPost by: Ross Robbins » Fri Apr 20, 2012 11:45 pm

We rubbed white lithium grease on it and tapped it in with a pipe whose diameter was just a bit less than the crank as that was what we had. And what is Graphogen, a graphite grease?? And why isn't all this in the manual? It said nothing about soaking it in oil.

I guess I'm stuck with what i have done now and will live with it. I doubt it would have turned over much differently with an oil soaked seal as the grease is slippery enough isn't it? 20 miles and no leaks yet :D :D
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PostPost by: Mazzini » Fri Apr 20, 2012 11:58 pm

Ross Robbins wrote:We rubbed white lithium grease on it and tapped it in with a pipe whose diameter was just a bit less than the crank as that was what we had. And what is Graphogen, a graphite grease?? And why isn't all this in the manual? It said nothing about soaking it in oil.

I guess I'm stuck with what i have done now and will live with it. I doubt it would have turned over much differently with an oil soaked seal as the grease is slippery enough isn't it? 20 miles and no leaks yet :D :D


You have the magic! Shame you're not closer, you could have re-sealed mine :) :)
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PostPost by: gjz30075 » Sat Apr 21, 2012 11:52 am

Wow, great story Ross. I would have never imagined that either. Now hopefully it's not wearing a groove in the crank. :shock:

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PostPost by: SJ Lambert » Sat Mar 05, 2016 6:01 am

Should the rope seal be a couple of millimetres proud of each end if its housing?
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PostPost by: SJ Lambert » Fri Jan 06, 2017 5:22 am

Or maybe even less than 1 mm proud at each end?
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PostPost by: Mazzini » Fri Jan 06, 2017 7:14 am

I just refitted my rope seal sump. I used Hylomar on the rope seal to metal face, very firmly rolled the seals into the housings, fed oil into the seals over a few days. I trimmed the seals to slightly more than the thickness of the sump gasket. I then put Graphogen on the crank seal, RTV on the sump and bolted it all together. I then rotated the crank to make sure it wasn't binding, it wasn't.

Does it leak? I don't know as I haven't finished the cylinder head work yet, but I think it probably will leak in time.
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PostPost by: SJ Lambert » Fri Jan 06, 2017 7:50 am

I've been rolling a seal in with an old coil - your procedure sounds good Mazzini!


I've recently "discovered" Blue Hylomar - I love it!! - I wonder whether it would assist the Cometic Cam Cover Gaskets to seal over the top of the rubber half moon plugs??
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PostPost by: englishmaninwales » Fri Jan 06, 2017 4:44 pm

I've stopped using hylomar after I stripped my Twin Cam and found the oil strainer badly clogged with it (overused by PO, not me).
img_1638.jpg and


There was loads more in the sump waiting to be sucked up. It had been used on the cam cover gasket.

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PostPost by: SJ Lambert » Fri Jan 06, 2017 11:09 pm

I am using Blue Hylomar on the Hewland/VW gear box end cap as a "flange" sealant - I'll be sure to be very careful in any engine applications..........
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PostPost by: Mazzini » Fri Jan 06, 2017 11:28 pm

I recently pulled apart an engine built by an ex-QED employee, he too used too much sealant, it wasn't as bad as whats shown in the photo, but I guess it shows it's not the sealant but who applies it and how much they use.
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PostPost by: englishmaninwales » Sat Jan 07, 2017 10:05 am

I agree that operator error in applying too much is part of the problem, but the curing of extruded sealant, like Hylomar and especially silicone, and then breaking off is also a significant part of the problem. For undamaged, well machined casting flanges I use anaerobic sealant, so that extruded sealant will not cure and generally wash away. I have used this to good effect on the timing case joints when the castings are new.
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PostPost by: SJ Lambert » Sat Jan 07, 2017 12:08 pm

dsc62351.jpg and


dsc62321.jpg and


dsc62331.jpg and



Soaked, trimmed and having a "size appropriate" overnight squeeze!!
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