How to build an oil tight twincam?

Elan Discussions
1

Hi friends,

before anyone starts joking, I’m also not quite sure wether this goal is at least possible. But I’m on my 3rd attempt in getting my engine oil tight and it’ll definitely be my last one before I give up and push the hole thing over the cliff or fake a carburetor fire. What I’m trying to do here, is to sum up the known points to pay attention to in one (hopefully) helpful thread. Also I want to lern more about issues that lead to oil leaks and where to pay attention to avoid them.

My engine has been rebuilt some years ago, but it suffers from catastrophic leaks ever since. As said, meanwhile I did two attempts in re-sealing (including nearly complete disassembling before), no effort. Leaks are mainly around all areas where the engine is able to push oil through. There are is a bit difficult to source, because the engine is drenched in oil just aft half an hour and of course all is dripping from the sump in the end. For sure is:

  • oil is going coming out of the dipstick tube (despite of adding a spark plug rubber)
  • oil is leaking around the crank case breather, either through the rubber block/head connection or where the breather to airfilter-box tube is connected to the block (that push-fit rubber thing)
  • oil may also leak through the crankshaft oil seals, difficult to see when all is drenched in oil anyway
  • oil leaks at the front timing chain cover, where that cork gasket is squeezed out because of its wrong thickness
  • oil leaks through the oil filler cap

So far. First I’d like to discuss the reasons and options for the describes leaks. Obviously there is excessive crank case pressure going on. I just don’t know why yet. Right know I have taken the head off and may also take the block out again to see what’s going on. Before dismantling I measured compression at all 4 cylinders (cold engine). Got readings from 13.5 to 14bar (all around 200psi). So, that seems a bit high, but also indicates that the pistons rings are holding the pressure quite good (?).
My block has been skimmed at the time the rebuilt was done (don’t know how much), but pistons sit still under the blocks surface, I will try measuring the nip exactly later on. Heads thickness is roughly measured (caliper) 117.4mm (4.62’‘).
Head gasket used was a 0.051’’ (87.5mm) composite from QED. Block is bored to .060’’ oversize and has +060 pistons fitted by a previous owner in the 1990s. I have fitted a new set of piston rings from Burton (#FL151S/060). I paid attention to piston ring gaps and ring to groove tolerances at the time and also to piston to bore clearances and as far as I can remember I got it all in spec.

Apart from the idea of adding a second crank case breather to the valve cover at the front, what options are there to avoid excessive crank case pressure? Any ideas what could have went wrong?

I have quite a comprehensive list of where to pay attention to on reassembling and will try to list/sum it up later here - but first I’d really like to talk about the possible root causes that facilitate leaks like in my case. Many thanks for your help in advance.

cheers
Matthias

2

Many many issues

A few starting points - all easier said than done unfortunately :slight_smile:

  1. use the right gaskets and sealants… a whole topic for separate debate :slight_smile:
  2. make sure all the joining surfaces are flat… they all distort
  3. assemble to not squeeze out the gaskets and sealants and torque correctly, takes care and knowledge to bolt up correctly
  4. hone the bores and properly bed new rings in, if so the standard breather is Ok for road use… use the right honing, oil and right running in procedure
  5. align the front and rear crank seals with the crank
  6. ensure the oil level is correct and the dipstick correct and the dipstick tube properly installed

In the end it is a 50 year old British engine design not a modern Japanese or German engine and will still probably leak especially if used “enthusiastically”

It is possible to make a road twink reasonably oil tight for a reasonable period (a vague enough statement haha), I still struggle with keeping one oil tight at 8500 rpm on the track :frowning:

cheers
Rohan

3

Hallo Matthias,

I certainly can relate to each of these with my street S4, coming from a slightly different angle since I did not rebuild the bottom end myself.

I have considered the hypothesis of too much back blow at some point, which should be confirmed with a leak-down test before embarking in heavy mechanics (in my case, it actually was the early onset of a head gasket failure, seeping in tiny amounts of coolant under some circumstances, but not blowing into the coolant yet).

I eventually did make up a “fast road” breathing system with a small oil fume condensor, a catch and recuperator, to be on the safe side if/when the problem surfaced again, but for the moment there is very little oil collected in the tank, even after “spirited” use.

Still, some oil is making it’s way out as you describe (possibly less, or most likely I have a higher tolerance level … and a nurtured relationship with my TÜV inspector)

More specifically, I’m also wondering

  • if I can/should attempt to change the seal of the oil cap on the camcover (minimal leak imho, but the cap is old and a bit shaky)
  • as for the front, I’m not sure I sealed well enough the cork at the front, it was very late/early when I did the head gasket just before taking off to a track day…
  • the crankshaft seal I’m almost sure would benefit from being changed, it is 4 decades old … I’m not sure if this can be attempted in situ, or if it is worth it considering other potential leaks, but I suspect this is the main one: I’m waiting for the next occasion to take the engine out and couple that with other things (like the broken speedo cable on the 5 speed gearbox…) - the oil coming out of there does get spread around by the pulley…

also at some point I had a bit of oil seeping from the oil pressure fitting, I had fitted a T system to install a tell-tale warning at 20PSI on the dash, and this is no so easy to access in situ… but this tell-tale oil light certainly is worth the price of a rebuild (I once popped out the oil filter rubber seal at the end of a straight)

4

I was told that high pressure oil pumps can be the cause of many leaks on a twin cam. Fitted a standard pressure replacement when I rebuilt mine with no real problems.
Just a bit from the rear of the sump, despite converting to a xflow rear crank seal.

5

Like Nick I think the easiest thing to do to start with is a leak-down test, “Druckverlusttester”.
Easy, cheap and - in a quiet enviroment - gives very interesting results

6

Good point, but isn’t the oil from a high pressure pump only under pressure when it’s doing its job? Once past the bearings its not under pressure or is it the increased volume that’s the issue?

I struggle with leaks from the round oil filler caps, I’ve tried various thickness gaskets and a splash guard, which probably should have been longer, but it still leaks when the engine is used enthusiastically.

7

As you say it appears there is too much blow by pressurising the system. Did you use a ‘glaze breaker’ when you fitted the new rings?

8

My engine is now (very nearly) leak free. It has about 30K miles on it. To get it that way I’ve done 4 things:

  1. I use Right Stuff on both sides of the cam cover gasket - not the cork one. The cover has to be cut off with a thin box-cutter now, and it is a bear of a job, but to me worth it. You have to think about this one.
  2. I use an “o” ring oil filler cap that I got from RD Ent. The adapter ring is Right- Stuffed to the cover.
  3. I sealed the rubber head to block drain fitting with Right Stuff.
  4. I gave up on spark plug boots etc. on the dipstick and am now using a stick with an “o” ring.
  5. I replaced the front crank seal.

Those were the 5 main leaks my engine had. The block is always essentially dry now using a high pressure pump. There is an occasional drip from the bellhousing and the speedometer gear but that’s about it. Basically, I don’t use silicone or RTV type sealants anywhere near oil or fuel.
Good luck, with perseverance you can get pretty close.
Victor

9

Sorry for nor responding lately, forgot my glasses at the workshop for the second day and there is not much I can do (see) in front of my computer without them. But I’ll try… You gave multiple helpful hints and I’ll try and respond to everyone.

Start with is a leak-down test. Good advice, stupidly enough I haven’t done that and now it’s too late because the head is already off and the block out of the car. All I have done before is measuring compression as said above (13.5 to 14bar / around 200psi).

Concerning “I have a higher tolerance level … and a nurtured relationship with my TÜV inspector”. I really don’t expect the engine to be oil tight like a modern car. But catastrophic oil leaks is the right way to describe what’s going on in my case. Since the failed first attempt to get it tight, I run a second sump under the hole engine area, where oil fleece is catching what comes from above. Otherwise I couldn’t use the car or park it anywhere on public roads. For the TÜV (MOT) inspection (I have a very nurtured relationship to the guy too) I clean the mess, remove the second sump, drive until 100m round the corner of the inspection garage and wipe again. Then drive the last 100m and hope to leave no spots on the inspectors garage (doesn’t work out always). Then I get the certificate, drive back to my workshop and install the second sump again. My goal is to end that sort of behavior, feels silly. The diaper of my car has of course to be changed regularly (spots under the car indicate when it’s time), depending of the use every three month or so and I’ll find like a pint of oil bound in the fleece. Concerning the correct dipstick level I will measure again, but I can say that after draining the sump I got roughly 3.5 liters out there. I have ran the car with the oil level at the minimum, because filling up to the max has lead to even more oil loss.

Oil pressure: my car has a standard pressure oil pump, readings are within normal limits.

Squeeze out of gaskets / torque correctly: I only have had that problem at the front cover cork gasket, where you have no choice then to torque to the given spec of the head bolts. But for this try I have cork gaskets in different heights at hand, sourced extra from Australia from Steve at lotusmarques.com

Hone the bores and properly bed new rings in / Did you use a ‘glaze breaker’ when you fitted the new rings? I was relying on the work the machine shop did at the time. Had not much of an idea about engine building, this had been my fist engine rebuild. What I can say from the records is that we have found the block to be bored to 84.03mm, where the pistons I have found in there (labeled as ASSO-W 339 +060) have been (and most likely still are) 83.93mm. So mathematically that gives .009mm clearance. There was a bit of a discussion going on at the time what would be correct, the workshop manual states 0.076 to max. 0.09mm for “C-type” pistons. Whereas QED and also the math tells you, that the the correct bore for +060 pistons would be 84.074 (3.310’'). But that would mathematically result in 0.144mm clearance - at least in my case with that pistons purchased by the previous owner from Burton in the year 1990. In the end the workshop machined my block to 84.05mm. I have attached a picture of the block how it came back from the machine shop after removing two hundreds of a millimeter from the bores. This is how I had assembled it afterwards. Any comments welcome. I have pulled the block from the car yesterday and will measure again after dismantling. I wouldn’t bother buying a new set of +060 pistons from QED, if that would help to end the oil disaster. Another option would be to fit liners and start with standard sized pistons again or of course fit the susceptive existing pistons again.

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Align the front and rear crank seals with the crank. I’ll definitely pay more attention to that this time and probably build up an alignment tool as discibed here viewtopic.php?f=39&t=49407 by the member “2cams70”. Or, hey 2cams70, would you lend it to me?

I use Right Stuff on both sides of the cam cover gasket - not the cork one. What exactly is (the) “Right Stuff”? I guess we all want to use the right stuff, but I guess you refer to something particular. I have used a Cometic cam cover seal from Burton and that worked out ok for me (in addition with a light smear of some Loctite aviation gasket, esp. at the half moon rubbers). I also wanted to use the Cometic bottom end set from Burton while my 2nd attempt in getting that thing oil tight and in the end used all of the seals contained in there, but the sump seals. They came cut to the wrong length out of the box (see picture attached).

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So in the end I had to use cork gaskets again for the sump. By the way: I always had to cut off a bit from the cork-insert gaskets front and rear at the crank area of the sump to be able to use them as they are out of the box. Never understood wether this type of X-Flow seals could also be used on twincam Elan sumps, maybe someone can bring in some light. burtonpower.com/sump-seal-r … fp763.html

Rubber head to block / crankcase breather I will use the alloy one from Steve at Lotusmarques this time. Hope that will seal better, although the rubber tube appears to be not the main leak in that area in my case. Which leads to the question how to get away with the very optimistic design of that only push fit rubber grommet in the head, where the breather tube to the airbox is attached. I assume this has been the biggest leak in my case. Should I cut a thread in there and build up a threaded breather tube with an o-ring or something? What good is a well sealed alloy breather tube when the next leak is just centimeters away from it?

Oil filler cap: I have also fitted new seals in the past and paid attention to the cam cover surface to be flat. Still is leaking. So either I’ll add a splash guard underneath or go that route, which seems more promising. lotusmarques.com/parts/datashee … cam-engine

So far, I’m off for scraping of old sealants from the parts…

cheers
Matthias

10

You are welcome to send me a PM

11

A centering bush is a good idea

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12

What is the Clearance on the Valve Guides.
Alan

13

I am relatively new to Loti but have rebuilt many engines british and otherwise. It should be possible to get a relatively oil tight build on these. I’ve put together a couple twincams without much trouble as well as some pushrod fords. You do need to look it over carefully for warpage and other leak paths. I thought the ford part was pretty simple and not that prone to leakage. Check the tin parts for cracks.

14

You can use the rubber sump seal at the rear IF you change the rear seal carrier to the later design, however you cannot fit the rubber front seal as the groove in the timing case is narrower on the twincam (the same as early crossflow and the precrossflow ) than it is on the later 711M engines.To claim that this :-https://www.burtonpower.com/cometic-lotus-twin-cam-timing-case-gasket-set-c4491.html fits the twincam really is out of order as the sump gaskets in this kit are for the 711M style engine and will not work with the cork seals as shown in your picture.

Brian.

15

In many cases I believe leaks around the half moon sump cork gaskets is due to people trimming them shorter when fitting in the mistaken belief that they are too long.

The Ford workshop manual gives a specific method and tightening sequence for the sump bolts. It’s certainly not what you would intuitively believe it should be. The method given in the workshop manual is designed to compress these down into position so that they are installed with a designed amount of preload.

I did post about this some time ago but can’t find the link. If anyone is interested I’ll take the time again to scan and post the relevant section from the Ford workshop manual otherwise I won’t waste my time doing so.

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viewtopic.php?f=39&t=47993

So thanks 2cams70, good one. 12th post in link

17

Brain, are you referring to this part?
burtonpower.com/rear-oil-se … fp306.html

Do you think it’s worth converting to the rubber seal?

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Now I know: inlet is 0.04 to 0.05mm (in spec but a bit towards the maximum), Whereas exhaust is 0.03 to 0.05 which is s bit too narrow (should be 0.06 to 0.075).

19

That’s the part.
Is it worth changing your current cover? Probably not as you still have to use the cork seal at the front so will be unable to use the Cometic gaskets that are cut too short. :frowning: :frowning:
Brian.

20

Possibly. You can only successfully use the later design rear carrier if the raised lip inside the sump recess where the carrier fits is in the same position as the later sumps (1973 onwards) intended to be used with this carrier. It’s not something I’ve checked personally. As another poster said - the timing cover is always going to be cork anyway. Trying to convert is not something I’ve ever bothered with. The Nitrile rubber seals will harden and lose compression over time just like cork does.