Blowing exhaust manifold

Holeshot · Post by **Holeshot** » Sat May 30, 2015 10:13 am

Hi guys.
I've developed a small, irritating blow on the rear LH side exhaust manifold.
It's difficult to see exactly where or why it's blowing but I thought I'd try to take a closer look.
I've had a look in the workshop manual which as always seems to make things seem straight forward........but in real life, what are the things which are really going to cause me gip in stripping down to inspect the manifold and possibly remove it?
I don't have specialist tools or a ramp.
Any advice would be great before I embark on something I won't be able to finish

Thanks fellas :D

Post by **Heuer** » Sat May 30, 2015 10:33 am

If you have the cast manifolds it is likely to be one of the four brass retaining nuts has come loose or fallen off. Basically the down pipe has a flange which squeezes a sealing ring between the pipe and manifold.

Unfortunately the nuts have a different coefficient of expansion to the steel studs so the come loose. Only fix I have found is to use stainless steel Nord-Lock washers under the nuts. Reach down a check the nuts are still there (sometimes the stud drops out with the nut attached) and tighten them up. Can be difficult to reach the ones nearest the engine block so you may need an array of extension bars with wobble ends from underneath.

PeterCrespin · Post by **PeterCrespin** » Sat May 30, 2015 11:08 am

He's talking about a V12 David.

Not that the technology is miles different but the setup is.

I'd say in the absence of a ramp, very good jack stands and wheel chocks would be needed.

Post by **Heuer** » Sat May 30, 2015 11:57 am

Sorry, V12 drawing but the principle is exactly the same:

Holeshot · Post by **Holeshot** » Sat May 30, 2015 1:39 pm

Wow! Thanks for the quick reply David & Peter :)
I've been lurking on this forum for a while now and so impressed with the pleasant atmosphere & knowledge.
Sorry to just wade in and ask for answers without any prior contributions :(

Thanks for understanding!

Anyway, yes, mine's a V12 2+2.

Stripping off the carbs & inlet manifold seems straight forward enough as does the cooling system components(I'm guessing). Are there any sneaky booby traps I should know about .....other that seized bolts etc?

Also, once the above are stripped away, should I be able to get good access from above to the manifold?

Can the manifold be removed (or released enough to pull away from the engine) to replace the gasket without having to access from underneath?

Hope I'm making sense here?!

Thanks again,
Hilton

Holeshot · Post by **Holeshot** » Sat May 30, 2015 1:44 pm

David,
Great diagram, thanks.

The blow appears to be from where the manifold clamps against the head.
The manifold that connects to the top of GEX1663.

Cheers, Hilton

MarekH · Post by **MarekH** » Sat May 30, 2015 7:07 pm

Dear Hilton,

You should be able to diagnose where and how exhaust gas is getting out with a combination of two methods:- firstly if there is a crack or a gap, you ought to be able to hear it and see a thin black line which will be a carbon deposit. Secondly, also whilst the engine is running, you can place your hand close to the manifold and feel the hot exhaust gas pulsing through. Don't get too close - the gas temprerature will be about 350'C at idle.

If there is a breakage of one of the ears where the stud attaches, then this can be brazed. If there is a genuine proper breakage, then it'll be easier to remove the manifold in as many pieces as it'll break into. If some of the nuts are loose, then it can simply be tightened up.

If reusing old or fitting new gaskets, make sure that the whole lot is flat before you do the nuts up. You can easily overtighten one of the edge nuts and crack the cast iron manifold on reassembly against the alloy head.

If you find access very tight, then you can remove and refit the manifold by taking out the studs with it, turning each of them in turn. The centre top stud will be the one which cannot be removed easily. You have to turn the studs out either with the nuts attached (good & easy) or use vice grips (bad & tricky). You can get a bit more access by loosening the engine mounts and raising or tilting the engine a bit, but I find it isn't usually necessary.

Holts makes a product which you can use as a gasket dressing if the manifold surface is rough.

kind regards
Marek

42south · Post by **42south** » Sun May 31, 2015 7:48 am

Those rearmost studs/nuts are the ones that cause problems with refitting.
Not sure how mechanical you are but a couple of important points.
Buy new studs and brass nuts if you are replacing the manifold.
Clean out the thread in the head with a suitable thread cleaning tool.
Get the surface of the head super clean and flat with a hardened scraper before fitting the studs.
apply some anti seize to the studs prior to refitting.
I found for the rearmost top and lower stud that it was better to put up the manifold loosely first and then put the stud through the manifold and use a pair of pliers on the smooth area between the threads on the stud to screw it into the block, it doesn't need to be super tight.
If you loosen the engine mounts and jacking at the front of the engine you may find it easier.
You may need to take off the lower drip tray and the starter motor on the right side to get spanners etc up in there.

christopher storey · Post by **christopher storey** » Sun May 31, 2015 8:47 am

The easiest and safest way to locate a blow is to use a longish tube in your ear and with the other end of the tube go round all the joints until you hear the unmistakable blowing sound

Holeshot · Post by **Holeshot** » Sun May 31, 2015 12:52 pm

Well, I'm overwhelmed with the help you guys are giving: thanks Marek, Mark and Chris. Much appreciated.

Here's a lucky update:
Thankfully, the blow has manifested itself in the joint on the diagram that David posted up that has the gasket GEX7259. The one between the manifold down pipe and the link pipe GEX1663. Much more accessible!
I managed last night to get a socket on the outer 2 nuts from under the car and nip up a bit. It made it slightly better but it's still there. I'll have to jack the car up and try all nuts evenly and see where it gets me. Otherwise I'm guessing a simple job of gasket replacement.
Big relief all round really!

Sorry if it was a bit less dramatic than at first thought but it's been a very nice introduction to this forum. :)

Thanks again - I'll let you know the end result soon.

Cheers, Hilton

and.nox · Post by **and.nox** » Sun Jun 21, 2015 7:22 am

Whilst we're discussing V12 exhausts, I have an issue with the bottom flange of the LHS downpipe banging against the subframe under load. This flange almost touches the subframe at rest (within 2mm) with a 50mm gap on it's opposite side between the flange and the engine sump. However, on the RHS, the downpipe passes directly through the middle of the gap between the engine sump and subframe, as I expect it should. Both downpipes are bolted squarely onto the exhaust manifolds.
I suspect that the downpipe on the LHS is in fact a RHS downpipe which unfortunately bends in the wrong direction, hence it's proximity to the subframe. Any thoughts anyone?

MarekH · Post by **MarekH** » Sun Jun 21, 2015 7:44 am

Dear Andrew,

Check the height of the engine on both sides by looking at the vertical gap between the frame rails and the airboxes. You can then adjust or check the condition of your engine mounts and maybe turn them around or swap sides or put a spacer in. Bear in mind that the engine will twist under load a bit.

kind regards
Marek

and.nox · Post by **and.nox** » Sun Jun 21, 2015 8:31 am

Marek,

Engine height is the same both side and the engine is centrally located. Mounts are in excellent condition. I understand the the engine twist under load but surely the downpipe should not be almost touching the subframe at rest?

MarekH · Post by **MarekH** » Sun Jun 21, 2015 9:40 am

Dear Andrew,

If you consider that the downpipes are at the end of a lever, a long way from the fulcrum that is/are the engine mounts, then it may indeed appear in the middle but the slightest deviation from centre is greatly magnified. I'd simply experiment with the engine mounts and spacers and how it is bolted up to achieve the clearance you wish for. After forty years, plenty of stuff is twisted, sagged and bent even it all looks straight and level.

kind regards
Marek

and.nox · Post by **and.nox** » Sun Jun 21, 2015 10:26 am

Marek,

Thanks for the feedback. I'll certainly look at the mounts more closely. In your opinion, is it conceivable that a previous owner has done what I suggested initially - ie put a RHS downpipe on the LHS.

MarekH · Post by **MarekH** » Sun Jun 21, 2015 11:12 am

Dear Andrew,

Swap them over by all means, but I've never bothered with that myself. If they were somehow angled inward, then you'd see it in both sides if you were to get that the wrong way around. The only conceivable difference is how far back they extend as the front of the twin exhaust pipes is offset a couple of inches. Consider that the mounting at the top is the same for the exhaust manifolds, the manifolds are the same pairings side to side, the height above the ground should be the same for both sides and you have some leeway to adjust the front exhust pipes to the mufflers as they are joined by a flexi-pipe. Your only adjustment is to tighten the bottom four flange nuts away from the frame rail tighter because the four nearest the frame rail have been overtightened previously - that'd pull the downpipe across as it sits on a pair of big fat crush washers between it and the exhuast manifolds. In theory all eight nuts ought to be the same tightness but that isn't necessarily so.

Failing that, I'd still suspect that the engine sits off centre despite your reservations as the tiniest deviation is magnified geatly. When I dismantled my v12 front end, it was obvious that the forty year old engine frames were very subtly twisted and yours will unlikely be any different if they are not brand new. If you place a piece of angle iron along the top square sections when they are out of the car, you'd notice but you'd never see it in situ normally unless you really look.

kind regards
Marek

and.nox · Post by **and.nox** » Sun Jun 21, 2015 11:50 am

Marek,

Thanks for your suggestions - they're much appreciated.

My thinking is that they are both angled inward, and that is why they are sold as either a left or a right hand item. (Part No's C33480 right & C33481 left). As they're not identical side to side, I'm suggesting that I've got two right hand downpipes which would explain why the RHS one angles inward towards the engine (toward the LHS of the car) and bisects the gap perfectly and the one on the left side angles outward (also towards the LHS of the car), thereby coming into conflict with the frame.

I think the next step is to pull them both off and if they're identical, I think that'll prove my point.

and.nox · Post by **and.nox** » Thu Jun 25, 2015 11:51 am

Following on from my last post, I took both downpipes off and as I suspected they were identical. Both right hand items. Someone had replaced the left one with the incorrect item. A little slicing, dicing and rewelding and it's now perfect and fitted in car.

Interestingly, the nuts I removed were something I hadn't seen before - "Helicoil Nuts". They are larger internal diameter nuts with a helicoil insert designed to be lock nuts that don't loosen under heat and vibration. Can't get them in Australia even from the registered Helicoil distributor. I've replaced them with 3/8 UNF nuts and Nordlock washers. Job done.

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