advice for rusty bolts on manifold - gasket replacement

[Dave_BG]

Hello everyone,

I have a 1986 Mk3 that suddenly has bad fuel economy and lost some of it's power, especially driving uphill. A friend helped me the other day to change the oil and sparkplugs plus new sparkplug-leads. The car runs a bit better now, but not great yet. He noted there's an air-leak at the manifold below the sparkplugs and suggested it needs a new gasket there, but was concerned about doing it because the bolts are quite rusty.

I drove into town to get my mechanic to look at it and he was also reluctant. From what I understand they're afraid they'll break or strip the bolts, which would then mean half the engine needs to come out for a much bigger repair.

So I wonder what to do now. Has anyone here been in a similar position? Would there be something I could do to loosen those bolts safely?

Below are some images of the situation. Thank you for any advice you might be able to give.

[V184]

looks like the oil leak is from the rocker cover/gasket

[joinerman]

Plenty of penetrating fluid on frequently then get the hot spanner out.

[dumper]

If you do snap them off not the hardest head to remove but when you try make sure you use a 6 point socket if I was doing it I’d start with a die nut to clean the exposed threads so if they do start to undo your not going to have to force the nut over rusty threads

[Chug]

Plenty of penetrating fluid on the them as its cooling down, not when first stopped or it will smoke away, do this a couple of times then a good session with a wire brush and then get it hot again and try to turn them, work them back and forth and more penetrating fluid as you go.

[Adam mk1]

not an easy job if your not a hands on man, garages think of time and it could go wrong unless its done in certain way and not rushed with poor fitting sockets & ham fisted inpatients, id remove air filter to give better access, id use an angle grinder with a 1 mil cutting disc (dont use if in experienced) they can kick back and take your fingers off, id cut through excess thread of bolt, the heat from grinder may help a bit, there 13 mil spaner size bolts, try beating a 1/2 socket on nut, if that fails cut across bolt with grinder splitting nut in half, the idea of this is to remove manifold and replace manifold studs, once manifold is removed, if studs shear at head then head will have to come off anyway but id try this first, i had a similar problem with a Bentley all bolts we're rusty and access was tight, i had to remove steering column to get grinder under manifold, and then i placed grinder were i wanted it, put my gloves on full face mask, lay under car, then flick the switch and hold on to that grinder, cut bolt switch grinder off, let it stop, then remove grinder, took me 2 afternoons to get it off, im a panel beater and welder by trade, and have been using grinders for over 30 years, so my advise is dont buy a grinder and have a go, let some do it that knows what there up to

[Dave_BG]

Thank you everyone for your advices, I really appreciate it.

It sounds like you all would try it (I guess not much choice), but very carefully and bit by bit. I'm reluctant to do it myself, because I'm not the most hands-on person.

I went to a different mechanic and they said they'd do it very carefully: first lots of wd40, then try a bit, more wd40, etc. slowly slowly. They also do bodywork there and so I think they have plenty of experience dealing with rust.

They said if it was a diesel they'd be able to heat it with a flame, but not a petrol engine. So the advice on letting the engine run for a bit to warm up makes sense then, I'll be sure to respectfully pass that on.

Thank you again and I'll post back when I know more - have to wait now for the car to be booked in.

[Kjeles]

Just to be clear: Replacing the exhaust manifold gaskets will not fix your problem of bad fuel economy and loss of power. A leaking exhaust manifold gasket will cause a more noisy engine (like a leaky exhaust pipe) and exhaust fumes in the engine bay that may find their way into the cabin.

If your concern is the fuel economy and power -- and not engine noise or exhauset fumes -- then it might be best to leave the manifold alone.

To solve your problem of bad fuel economy and loss of power, you will have to look elsewhere. Start with simple checks like clogged air filter, faulty carburetor, ignition timing and cylinder compression. The looks of your spark plugs will indicate what the problem is. If you have the original VV carburetor, the automatic choke may stay on and cause low fuel economy. Leaky valves or a broken cylinder ring may occur suddenly and cause low compression and, consequently, poor fuel economy and loss of power.

Make sure you have the right diagnosis before fixing anything.

[Dave_BG]

Thank you Kjeles, that's very valuable advice.

I'm not too concerned about the noise to be honest. And fumes don't seem to be an issue at the moment. My main concern is fuel economy - which seems to have dropped about 20% - and loss of power. I'm not overly concerned about these two things, only worried it might get worse or indicate a bigger problem.

The first mechanic I went to did hint at compression, so thank you for pointing that out. I know the air-filter is new, so I can rule that out, but I don't know about the other things, so I'll try to get a good diagnosis and go from there.

[V184]

Always replace the studs, very rare for them to snap when removing, wouldn't like to say why someones put a bolt in one

[MinorMatt]

Get the engine hot before attempting to undo...

[hetman]

Great advice by Kjeles (and all others... ). I wouldn't touch that exhaust manifold at all since it's not the cause of the poor fuel economy, and you're really asking for trouble by messing with those rusted bolts (and nuts - good catch: why is there a bolt in there anyway?).

But if you insist on taking off that manifold, I've found that using old brake fluid instead of WD40 as a penetrating oil is more effective. Let it soak in a few days, applying it a few times. Then get the engine hot; that will help. Be very careful trying to unbolt those nuts and bolts; they can strip very easily. Use a 6-point socket only, not a 12-point. Tapping it on with a hammer for a good fit is a good idea. And seeing how rusty they are, I'd be tempted to go the angle grinder route and cut them off to free up the manifold (and replace the studs later). But I usually leave the cutting as a last resort. I was able to free the tow hitch bolts recently of my Transit using the brake fluid penetrating oil and flame-thrower trick though the bolts looked hopelessly rusted together.

[Kjeles]

Dave, please tell us how it's going with your engine. Many of us will appreciate learning from your experience.

I had a similar case with sudden increase of fuel consumption and loss of power. The problem was the carburetor. I replaced it with a Weber 34 ICH with manual choke. The van has been running like a charm ever since.

[Dave_BG]

Thank you again everyone for your advice. I really appreciate you all sharing your experience. And thank you Kjeles for following up.

So a quick update:

I spoke with my friend who replaced the oil and spark plugs and in his opinion this manifold really needs to be done. It's broken, because it blows in 2 places and he strongly recommends getting it fixed. He's not a mechanic, but does work on his own engines a lot (motorcycles and cars), plus he's seen the engine and driven the car so I trust his advice.

He also mentioned that the old spark-plugs looked like they had gotten very hot, which to him indicated that the fuel mixture going through the engine is clean. So he doesn't expect big problems there.

So I'm going to get the manifold done at a garage where they've already said they'll do it slowly slowly and I'll make sure to pass on the advice you all gave here. I'm bringing in the car tomorrow and then we'll have to see how it goes.

The plan is to first get the manifold done (because it's the biggest thing that needs doing), and then re-evaluate and look at the smaller things like carburator and timing.

Thank you again everyone and I'll post back when I know more.

[Kjeles]

Interesting. Each case is different.

Since your spark plugs indicate lean fuel mixture and excessively hot combustion, you may have burned -- and hence leaky -- exhaust valves. A compression test would be useful.

If the head has to come off for a valve job, it might be easier to separate the manifold from the head after the two parts have been removed as a unit from the engine block. And if any of the manifold studs break and you will have to drill them out, it will certainly be an advantage (and maybe a necessity) to have the head/manifold out of the engine bay.