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This engine never fails to surprise. Some time ago, for no very good reason, I gave the manifold new Club gaskets plus new Club brass nuts. I did the usual things that have always worked: cleaned surfaces, checked for warping, pulled up the gasket with plain washers under the nuts. And tightened again after the first thermal cycle.
On the recent Fougeres, I sprang a gasket leak unlike any other I’ve known – so noisy I at first thought the little ends had gone. No gas could be felt around the manifold. Tightening the nuts cured matters for a few tens of km but then the cycle would repeat. Eventually, I contrived to strip a couple of the brass nuts but replacing these with steel ones got me home reasonably quietly.
Opening up, the gasket is intact – no splits or cracks. Is there any particular technique for the 2 Litre that I should know about? Spring washers over the plain ones have been suggested but the efficacy of spring washers seems to be in doubt these days. I would really welcome any guidance on the sequence for tightening the nuts and the permissible torque. I’ve never used “goo’ on exhaust manifolds but one of the Loctite products has been suggested though its upper temperature limit is only 350 celsius which I would have guessed would be inadequate.
I really never thought an exhaust manifold joint would present problems. Only on a 2 Litre…
John
Hi John,
We got home safely also from Fougeres, although soaked to the skin in seconds due to the deluge encountered. Given the weather forecast, we got off more lightly than hoped!Surprised to hear your gasket is intact. If it was blowing one would at least expect a burn mark. You seem to have taken care that everything is true, so perhaps the gasket is faulty internally, ie the exhaust is passing through the gasket, between its outer mating surfaces? The only other possibility I can think of is, I hate to say it, a crack in the manifold.
Have you tried my Redex suggestion? You may need to blank off, partially at least, the tail pipe, but white smoke emerging will hopefully identify the culprit.
Laurence
Hi Guys,
Can I make another suggestion? The exhaust goes through the head gasket and if this blows it would make a horrible noise without affection the compression or water flows. I almost suspect the one on my 2 Litre has the same problem which is why I mention it.
Agree with comments about burn marks as tell-tales.
Colin
I just had my manifold off to replace the water jacket cover plate. When I went to re-fit it, the lugs on the bottom of the manifold fouled the new aluminium plate, which stopped the manifold going fully home. This was easy to spot with the engine at eye-level, so I just ground a bit off the bottom of the manifold.
Unless you have replaced the side plate it is difficult to see how this could be your problem, but I thought I’d mention it.
Another long shot – I don’t suppose it’s possible that the new gasket is thinner & the nuts are bottoming out before pulling the manifold home?I apologise for the late reply Laurence – we took a short holiday to recover from the short holiday. I’m sorry the evil orages caught up with you – we somehow ran between them though had the hood not been up (which I hate) I’m sure we would have been also soaked under Dr Sodde’s Universal Law.
I think I described the gasket condition poorly. There are no cracks or tears but plenty of soot marks on both sides marking the blow. Nothing I could call a burn though. All the evidence is that the brass nuts just kept on loosening off, something I’ve never encountered before.
I didn’t try your Redex ploy as having got home I just charged in and removed the manifold. Great idea though.
My thanks to Colin and Hugo for excellent ideas but I think now that the problem is simply brass nuts refusing to stay tight. As yet, I don’t have a cure for this. Something called a Nord-Lock washer has been suggested to me as being better than a spring washer but I’ve yet to investigate.Thanks to all for the help,
John
Hi John,
We had also planned a short “holiday” to follow, but the hotel charging an unexpected extra ?66 for breakfasts (since refunded) and the overlooked cost of petrol to get home left us with no money to pay for it, whilst we still wait for money from our investments to be released, Don’t invest with LMEP / AG2R!Still find your nut loosening odd. Usual problem is totally the opposite, brass nuts appear to age-shrink onto their studs in this application. Not come across a Nord-Lock washer. Locking (or at least, spring) washers are unusual in this application, either because of corrosion or more likely, heat de-tempering the washer.
I think a far superior solution would be a suitable grade of Loctite. In fact, as that might prevent corrosion, could be a major benefit in that eventually undoing them in the future could actually be viable without stripping threads etc.
All this said, I think we are talking of addressing the symptom, not making the cure here. Firstly, I’d check that all your exhaust mountings are secure and effective. If that doesn’t reveal anything untoward, perhaps there is some resonance/vibration within the engine causing this. I suspect the 2 Litre engine will be solidly mounted, so engine mounting unlikely to be a culprit, but worth checking mounting bolts. An unlikely contender could be cracked chassis or loose rivets, but I suspected you’d have encountered other problems in that case.
One final thought, could there be a problem with the thread form on the Club-supplied nuts you are using? Unlikely, as surely others would have encountered the same problem. Possibly the stud threads are worn; if rusted as they often are, de-rusting may have removed enough metal to cause problems, especially if what is left of the threads has effectively been polished smooth.
Laurence
Laurence, I think I have it. Or at least a major contributing factor. The manifold is held by 8 studs and 5/16 BSF nuts. It turns out that two studs have 1/4 BSW threads so it’s quite obvious why the soft brass BSF nuts being forced onto these rogue studs failed.
And the engine was “professionally” rebuilt at great expense a few years ago. Ouch.
Thanks for all the help, very much appreciated.
John
Hi Folks,
My thoughts on 2 Litre studs – both exhaust and engine water plates.
What a vile job! The studs rust in or simply jam. They are all BSF and may end up needing to be drilled out if they snap. Stud extractors can help but then they can snap as well, the you are in big trouble trying to carefully drill out studs under the camshaft tunnels.
Heat can help.
In the end it might be easier to pull the engine out and do them all upside down. If not, I think you may find it useful to remove the steering box as well as the dynamo.
I seem to recall that we had a discussion about undesirability of stainless steel bolts/studs so perhaps the new studs could be made from bright zinc plated high tensile BSF set screws which seem to be readily available, possibly dipped in Copper-slip grease so they never seize again!
Brass nuts are then good.
I wish you luck and hope there are not to many broken studs and you get to enjoy the car again quickly.
Colin
(Duplicate deleted)
Hi John,
Hope it wasn’t the “professional vintage engineers” who “rebuilt” my LG6 for the previous owner so appallingly. What a daft thing to do, hope you can replace the rogue studs without too much difficulty.
LaurenceAgree with Colin :
1. Exhaust manifold studs need to be high tensile steel. A decent HTS should have a UTS ( ultimate tensile strength) of about 1100 MN/sq.metre and will be affected less by the heat. Stainless will be only offer about a third of the tensile strength, depending on grade.
If you use ordinary steel studs or stainless it is highly they will stretch when they get hot which will reduce the end load in the stud and of course the face stress of the gasket. If the pressure in the exhaust is more than the minimum face stress on the gasket as it heats up and cools down then it will blow.
2. Brass nuts are good as they will be much easier to get undone. Putting coppaslip or John Crane Thread Guard or similar graphite based compound, as used on steam pipework etc will also help to stop the nuts falling in love with the studs! If you come across any nuts made from Nickel aluminium Bronze or Kmonel ( Copper/ Nickel /Aluminium alloy) these are even better but expensive.
The amount of end load you put on the stud for a given torque applied to the nut also varies a lot depending on whether the thread is lubricated.
I did some tests on this once at work using strain gauges to measure the end load in the studs over various sizes……too many years ago now to remember the figures but I do remember that, in general, we found that the end load in a dry, unlubricated thread was about half that of a thread lubricated with thread guard or coppaslip and that threads lubricated by oil of normal multipurpose grease were in between. (Of course the loads also vary with thread diameter and thread form as well as the number of threads per inch and the thread angle, as well as the grade of thread… all have some impact.
As a result of these tests we amended the company’s manuals and stated that all threads must be lubricated with thread guard and adjusted the torque settings specified as it was the only way to ensure a consistent result!I would use new best quality spring washers under the nuts.
Hope the above helps
Bill 😉Colin, Bill many thanks. I think this very educational thread will be of interest to a lot of people.
I’ve no way of knowing what grade of steel Mr Lagonda used for his studs but I doubt whether it was too fancy in 1927 so perhaps the pressures in the manifold aren’t all that great. But it’s clearly safest to use HTS. Onwards we go…
John
Interesting – I think you mean you have 5/16 Whit studs, not 1/4 Whit; the confusion arises because Whitworth nuts used to be one size larger across flats than BSF. Then, I think it was in WWII, they ‘shrank’ the Whitworth nuts to the same size as BSF nuts, in order to save metal. Hence you have dual markings on spanners; 1/4W = 5/16 BSF etc. Except that this is no longer accurate either, since ‘modern’ 5/16 Whit and 5/16 BSF nuts are the same size across flats. That in itself is a very weird size, 0.513″ or some random figure like that.
Anyway, to return to your problem – presumably you have just been tightening the nuts on the (incorrect) threads, rather than pulling the manifold up tight against the block? In a way I’m surprised they still managed to work loose. If it were my car, I think I would try to rescue the threads on the studs if possible. Can you run a die-nut down the studs to retrieve a passable thread? Either BSF or Whit, whichever is most likely to work. Then get some long brass nuts & hope they will tighten up ok. If it doesn’t work, you’re only back where you are now anyway.
I’ve just had the job of drilling out all fourteen bolts that hold the water jacket side-plate on. The previous owner had started removing the steering box & dynamo to do this (it had corroded through) but sadly he did not live to complete the job. I pulled the engine out & did it at eye level.
I also had one of the exhaust studs snap off when I pulled the manifold, & I managed to drill it out ok. It had to be a top one too, right up against the cam housing, and I JUST managed to drill it straight by putting a drill bit in the chuck about 1/4″ deep and then the drill bit was JUST long enough to go in there before the chuck fouled the cam housing. It really needs an extra-long drill bit to do the job properly. I got away with it, but more by luck than judgement!Hi Hugo
I think you would agree it’s vile job much better done with the engine out! Glad you got all the studs out OK.
By the way Lagonda seldom used Whit, they almost always used BSF on the smaller studs and then 20 TPI on the larger ones.
This equates to either UNF or 20 TPI cycle thread variants. Not sure about the thread angle used by Lagondas on the larger 20 TPI bolts but I think it was 60%. Tracy Tools sells taps and dies in these lovely obscure sizes. You will end up with drawers full of them, just like me….
I think low chassis floor bolts are BSW for some strange reason.
Colin
Yes I’m debating whether to change the two 5/16 BSF – 1/4 BSW studs to new all BSF ones or just slap a couple of 1/4 BSW brass nuts on them and forget about the whole annoying episode.
Interestingly, the BSF HT bolts readily available on the Internet (following through on Colin’s suggestion) are Grade R or 8-8 (seem to be synonymous terms) and, if I have it correctly, will have a UTS of at least 800 Mpa or MN/m^2. This is much less than the 1100 that Bill recommends. Also the stainless studs available are of grade 303 and these have a UTS of about 750 i.e. very little different from the HT ones. I’ve learnt quite a lot about megapascals but am increasingly of the view that keeping the rogue studs and using BSA nuts is the obvious if cowardly thing to do.
Thanks for the help, this is why this forum is so great.
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