Gads, disaster! 2GM20 exhaust elbow bolt sheered off!

MagicalArmchair

MagicalArmchair

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After ten years of ownership I have never taken off the exhaust elbow. As part of my engine service plus plus plus this year, I figured it was long overdue a look.

The first bolt, 7mm I think, felt a little tight, so I applied moderate torque and boom, it sheered clean off. I paled, slumped and wandered off to the local coffee shop to lament on this one step forward and twenty back.

jjAUhHIl.jpg


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1AL3FtBl.jpg


I didn't dare approach the other two bolts, I have left them soaking in WD40.

So this leaves me with two problems:

1 - How do I get the studding out? Access is not great, not terrible, but not great.
2 - How do I get the other bolts out limiting the chance they will sheer too? Heat from a soldering iron then some freeze spray? Impact driver?

I can't injure my lovely 2GM20, perhaps this is one PBO step too far and I should call in a marine engineer to get the studding out without shagging the thread in the block? Any recommendations for someone local to Chatham marina?

Whilst its easy to regret trying to get the elbow off at this stage, if there is this much corrosion on the bolts, I can only wonder at the corrosion of the elbow itself...
 
My "tame" engineer ( a retired toolmaker) has often told me not to try any amateur fixes to sheared off studs; such attempts invariably make his life much harder after I give up and pass the job to him.
You won't need a "marine" engineer, any experienced engineer will be able to do the job. but it is quite possible that the casting containing the sheared off bolt may have to come out of the boat.
 
One of mine is also sheared off. The good news is that the other three came out easily after a squirt of Plus Gas. Not sure what I'm going to do either, Stillsons but there's only 1/8" to grab. Be interested to hear what others suggest.
 
stuey_two said:
My "tame" engineer ( a retired toolmaker) has often told me not to try any amateur fixes to sheared off studs; such attempts invariably make his life much harder after I give up and pass the job to him.
You won't need a "marine" engineer, any experienced engineer will be able to do the job. but it is quite possible that the casting containing the sheared off bolt may have to come out of the boat.
Click to expand...

Unfortunately the casting will probably be the cylinder head so what should be a simple job will not be simple. :(

However, the OP should not get too despondent yet. Its quite surprising but the stuck bit of stud can sometimes be removed after plenty of penetrating oil had been left to soak as now the access to the thread is much better provided there is enough stud to grip with a mole wrench. Some heat applied with a fine gas torch, the gas soldering iron type is ideal, will help to drive the oil into the threads.

Once it's hot and well oiled it might well move once you clamp a mole wrench on the end, provided that you have enough stud to grip.

Obviously the other studs need to be removed (or sheared!) to get access to the sheared ones.

If there's not enough stud to grip then drilling and a stud remover is the only way. This will probably be very difficult without removing the head but I would see if an engineer might have the tools to do it in situ before resorting to head removal.

Richard
 
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I did pretty much exactly the same with an outboard motor cylinder-head bolt last winter: http://www.ybw.com/forums/showthread.php?411529-Cylinder-head-bolts-for-4hp-Johnson-twin

First thing is to ditch the WD40 (or rather, keep it for its intended purpose, as a water-displacer on HT leads, stored tools, etc) and get some Plus-Gas. Much more effective. Give the other bolts a dose of it and then see if they'll come out, it will be easier to extract the sheared one if you can get the exhaust elbow off and so gain access to the sides of the bolt. Obviously try not to shear these too, which should be ok as you'll be more careful now :)

Be prepared to give the Plus-Gas plenty of time to work, looking back at that other thread I see I left it 24 hours. It wasn't free the next morning, but was by that night. I gripped the sheared bolt by filing flats in two sides of it to fit a spanner; you could also use an external stud extractor, or failing that (and especially if you can't get the elbow off first) an internal one that goes in a drilled hole.

Pete
 
If all else fails, weld a nut onto what's left of the stud bolt.
if you can get the casting off, apply lots of heat with a gas blowlamp and quench with plus gas several times.
Agree; ditch the WD 40.
 
from memory the three studs on our 3gm30f are onto the exhaust manifold, not the cyl heard, so (slightly) easier to get it out the boat if required

also pretty sure they are bolts not studs - with some access behind for plus gas

and easier to drill out if needs be

(all assuming yours are bolts not studs!)

to get you home mole grips should hold on the exhaust mixer elbow at the one sheared bolt, tho clearly check often that they haven't fallen into the bilge...

good luck
 
Don't even think about drilling and Easi-outs at this stage, nor Stilsons. You need a stud extractor, like one of these http://www.uktoolcentre.co.uk/Shop/...6_1445851583_65b6170784e74d24af2030c557618504 There will be plenty of stud showing when the manifold is off, and space to swing the tool. Not cheap for a single use but mine has come in very handy over the years. I will even lend it to you if the logistics are suitable.
 
Thanks chaps, Plusgas on order! Bikedaft, all that remains is the studding after the top of the bolt has come off :) and it appears from the below that the exhaust elbow is indeed in the head, so it would be a full head off job if I need to drill it out. Drilling in situe would be a recipe for knackering the thread in the head as access is awkward.

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I never knew there was such a beast as a stud puller - Those bolts are M8 bolts, so an 8mm puller might do the job? Something like this? How do they work?

I should have a good 5mm of thread exposed once the exhaust elbow is off.

So I can use the Plusgas immediately after applying heat? Is it not too flammable then...? I'll keep my fire extinguisher handy regardless :)

Edit: Posted at the same time as you, vyv_cox :). Great, I'll get one of those if that will work on M8 - another tool in my arsenal and a whole lot cheaper than a new head...
 
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Yes, you can apply Plusgas to the hot stud. Not talking about red-hot here of course. 100 degree type heat so just too hot to touch. Heat up the other studs whilst you're at it and get the Plusgas on those.

Vyv's extractor looks very good although I've never used one of those. I don't know about the one you have linked to as I've never seen one. However, with heat, Plusgas, 5mm of thread and a good Mole wrench I think you'll get it sorted.

As far as I'm aware those exhaust manifold studs on any engine always screw directly into the cylinder head, almost by definition I suppose.

Richard
 
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I would wholeheartedly recommend the extractor as shown in Vyv's link - It works when the mole grips wouldn't stand a chance!

Photos at the links below showing the tool in use...
Exhaust manifold removed (and a number of studs sheared)
http://1drv.ms/1LwuBg1
A close up..
http://1drv.ms/1LWuAn0
And you will see that the tool doesn't need much room around it..
http://1drv.ms/1LWuHz9

Lots of PlusGas first though and heat if possible. The hot parts cooling should even suck the PlusGas into the threads.
 
Gosh, great photos Martin_J. I may try my 240V soldering iron to apply heat to the bolts/thread as it may be tricky getting my small blow torch into that space safely. Then lots of Plusgas and time for it to work. Fingers crossed...
 
Martin_J said:
I would wholeheartedly recommend the extractor as shown in Vyv's link
Click to expand...

It does look like a useful piece of kit - but I'm a bit puzzled by the "impact" part. That implies you hit it like an impact driver - but it also has a 1/2" drive on the back. Surely you're not meant to welly the back of your ratchet with a hammer?

Pete
 
prv said:
It does look like a useful piece of kit - but I'm a bit puzzled by the "impact" part. That implies you hit it like an impact driver - but it also has a 1/2" drive on the back. Surely you're not meant to welly the back of your ratchet with a hammer?

Pete
Click to expand...

No, I don't recognise any impact suggestion. The great thing about the tool, which I don't see in the Halfords one, is that the more you turn the tommy bar the tighter it grips. It can sometimes be quite difficult to get the extracted stud out of it. I usually put the stud in the vice and reverse the turning, sounds simple but the stud can be so wedged in that it resists strongly.
 
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