Snapped bolts on ali outboard block

slimtim · 23 February 2009, 18:39

As far as bad days go, this one is fairly well up there. I have managed to snap not one, not two, not even 5, but a depressing 10 bolts off while trying to get them out.

(hhmm, thats a new smiley since I was last around)

I won't go into why I felt the need to go on this rampage of bolt snapping brutality, perhaps my DIY mechanical mind had turned to mush after a year of no ribbing and dossing around in canada or maybe I was day dreaming of hot summer days and glassy flat seas while each bolt went crack under surprisingly little load

Anyway, the engine as many of you will know is a 70hp tohatsu 4-stroke (1996 if I remember correctly) and I was trying to take the plate off the side to gain access to the cooling ducts that feed the tell tail so I could unblock it all. Each bolt screws through the plate, a gasket, a spacer plate and then another gasket (as far as I can tell) before screwing into the block. Each bolts appears to have snapped at the point where the plate meets the first gasket so if I do get the plate off there should be a little stump of each bolt left.

The plate is still on because there are 4 bolts at the bottom that I have not yet touched. If I snap these off too then the plate will come off but I would need to strip the engine and take the block off to access the broken bolts with a drill. For this reason I have left these intact and am hoping to get all the other broken bits out, stick new bolts in and unblock the cooling clog by some other means.

Does anyone have any experience of snapping bolts off and how did they get the bits out? Over the next few days I'll be squirting everything with plusgas but I have a feeling it won't be enough. I really don't want to have to buy a new engine because of this, not that I could afford to anyway.

I think I've probably thought of every possible option but the knowledge on this forum never ceases to surprise me so thought I'd give it a go.

Thanks in advance

Dirk Diggler · 23 February 2009, 18:47

Blow lamp and mole grips

codprawn · 23 February 2009, 19:03

Some photos would be great.

What size are the bolts?

You may need to snap them all to take the cover off - then either the mole grips or maybe even put slots in them and use an impact driver.

Another solution is to run a die down them the opposite way and stick a nut on them.

jwalker · 23 February 2009, 19:51

Tap (hit) the ends of them to shock the dross around the threads and attempt to make just a little space to break the seize.

slimtim · 23 February 2009, 20:00

bolts are 6mm.

Considered the heat option, but not sure how far I can take it though before melting or distorting something. Using mole grips obviously means I need to get the plate off which will probably result in the other bolts being snapped as well.

Whats an impact driver? Dad and I were just discussing the options with respect to using tapered stud extractors and have come to the conclusion that the one of the most difficult things will be drilling a decent straight hole to begin with.

Thanks for the replies so far

PeterR · 23 February 2009, 20:04

Quote:

Originally Posted by Dirk Diggler

Blow lamp and mole grips

Its the way to go also spray with easing oil.If you use heat gun instead of a blow torch it will be better and heat the ali and hopefully it will then pop off

JSP · 23 February 2009, 20:07

http://www.screwfix.com/search.do?fh...NJ1Q&source=aw

But make sure you get decent bits to go with it.

Nasher · 23 February 2009, 20:14

Welcome back Tim, I hope the trip was all you expected, I'll have a look on your website later to see if you've uploaded any images of the last year.

Regarding the bolts, and to answer your specific question, I've had lots of experiance snapping bolts off

You know you have to do it properly, and that I'm afraid involves trying/breaking the other 4.

Once the plate is off, if you have a little stub of each one you can soak it in WD40 or Plus-gas for a few days then grab each one with a pair of mole grips to carefully wind it out.

6mm isn't very big to use a stud extractor with a left hand thread, you'll only be able to drill a 3mm hole and use a very small extractor, which in my experiance will snap off and leave you with a bigger problem as you now have a very hard piece of metal stuck in the hole.
You'd be far better off drilling out bigger in the first place and heli-coiling the holes.

Don't be afraid to remove the powerhead, it's really not that big a job to sort your problem out properly.

Nasher

Dirk Diggler · 23 February 2009, 20:15

Believe me, we do this all day long, heat and mole grips, and as peter says, a squirt of oil, we prefer wd40, but that's coz we buy it by the barrel load.

Get the burner on it, and get it really hot, it won't do any damage, it doesn't even harm the paint on a merc!

Dirk Diggler · 23 February 2009, 20:17

Quote:

Originally Posted by codprawn

Another solution is to run a die down them the opposite way and stick a nut on them.

That ain't going to work, you'd need a pair of nuts so as to be able to lock them up.

Nasher · 23 February 2009, 20:22

Another method I've used in the past is to put a nut on the top of a stud or broken bolt. Then put a blob of weld in the middle to connect the two.
The combination of the heat and the new 'head' can release it.

Of course all our methods assume you have the plate off and a small stub of each bolt sticking out.

If they break off flush its out with the extractors or Heli-coils.

Nasher

Chris · 23 February 2009, 21:07

Quote:

Originally Posted by JSP

http://www.screwfix.com/search.do?fh...NJ1Q&source=aw

But make sure you get decent bits to go with it.

I think this is what Codders meant.

http://www.amazon.co.uk/Draper-22322.../dp/B0001K9R8U

Davie · 23 February 2009, 21:26

Take the gearbox off and run the engine. After 30 seconds the exhaust plate will get as hot as you will ever get it using a blow torch. This way you are heating the whole side of the engine. If they do not come out now they will never come out without drilling. Do not try this method on Yamaha 80 /100 or the equivalent Mariner / Merc. hth.

bedajim · 23 February 2009, 21:36

Quote:

Originally Posted by Dirk Diggler

Blow lamp and mole grips

We give the stud a go with this to help after warming the area

http://uk.rs-online.com/web/search/s...94954590&Nty=1

chris123 · 23 February 2009, 21:38

As others have said, you need to be very careful if you try and drill out the bolt or use an eazi-out (tapered tap with reverse thread) as it is very easy to drift off the bolt (damaging the casting and at best requiring a bigger helicoil / bolt) with the drill or snap off the tap (requiring spark erosion to remove).

If it were me, if the heat / mole grips / plusgas / impact driver don't work, I would take it to a machine shop who should be able drill / tap out the bolts relatively painlessly (and cheaply).

Cheers

Chris

slimtim · 23 February 2009, 21:39

Thanks all for the advice. Dirk, good to know I can be fairly heavy handed with the heat, I'll try this first if I have to end up taking the plate off, which I think is actually my only option. If I do this however I will almost definitely have to remove the block which may well mean I have problems with other bolts.

Nasher, trip was great thanks but I missed the ribbing! I guess snowboarding in perfect powder and riding some of the best lift accessed mountain biking in the world made up for it a little

The welding nut thing is a good option if the mole grips don't work.

Cheers,

Tim

slimtim · 23 February 2009, 21:48

Quote:

Originally Posted by Davie

Take the gearbox off and run the engine. After 30 seconds the exhaust plate will get as hot as you will ever get it using a blow torch. This way you are heating the whole side of the engine. If they do not come out now they will never come out without drilling. Do not try this method on Yamaha 80 /100 or the equivalent Mariner / Merc. hth.

I thought about running the engine to heat it up but how long can I do it for without coolant without completely buggering up the engine?! Seems a bit risky to me

JSP · 23 February 2009, 22:00

Quote:

Originally Posted by Chris

I think this is what Codders meant.

http://www.amazon.co.uk/Draper-22322.../dp/B0001K9R8U

I was looking for a link to the hand tool version as I prefer them but I have seen some of the Drill versions work well.

Nos4r2 · 23 February 2009, 23:37

Quote:

Originally Posted by slimtim

I thought about running the engine to heat it up but how long can I do it for without coolant without completely buggering up the engine?! Seems a bit risky to me

You won't have to do it for long-there'll be no cooling water hitting the exhaust plate. Spit test it-when it sizzles when you spit on it, it's hot enough.

As Nasher said, don't use an easy-out. On an M6 thread, it'll expand the broken bolt so far it'll never come out. You may find some joy using a stud extractor, but mole grips are just as good with the proviso that it's got to be a good quality pair of mole grips of the right size. Cheap, oversized or worn mole grips will just make a mess.

codprawn · 23 February 2009, 23:52

Quote:

Originally Posted by Chris

I think this is what Codders meant.

http://www.amazon.co.uk/Draper-22322.../dp/B0001K9R8U

Yup.

Use a very thin grinding disk or a hacksaw and put a slot into the end of the stud turning it into a screw.

Heat and Mole grips are the first choice though!!!