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Getting broken bolt out of engine block

wannabecraig

One of the two bolts that hold my starter motor in place on my 3trl boat engine has broken inside the engine block. This is on the underside of the engine, about 6" from the floor, so I can't get a drill at it to drill out the bolt. If I were to drill it out, I'd have to remove the engine,. This is a nightmare and I'm not up for it.

I was thinking of putting in another screw with Araldite for steel or Gorilla Glue Epoxy on the top and hoping it would catch the broken piece of the screw and bond, then I could remove the screws.

Is this likely to work? Do I have any other options?

TIA

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Sharpyshoot

stratowide wrote: »

Its a 10mm bolt sheared off in a position that can only be seen with a mirror.

I wouldn't even plug in the welder let alone try to weld something onto it.

Did I suggest the op should follow my proposition? I was offering a very successful generic solution to a common problem. I couldn’t be reading four pages of drivel. After the suggestion of a text screw I had enough.

wannabecraig

stratowide wrote: »

Its a 10mm bolt sheared off in a position that can only be seen with a mirror.

I wouldn't even plug in the welder let alone try to weld something onto it.

Jesus, that's an amazing idea... I have a decent size magnifying mirror I use for shaving, this will be the savior of this job, I can feel it!

wannabecraig

Sharpyshoot wrote: »

Did I suggest the op should follow my proposition? I was offering a very successful generic solution to a common problem. I couldn’t be reading four pages of drivel. After the suggestion of a text screw I had enough.

Hey, 1/4 of those are mine... But I ask again, this wouldn't work given my situation right?

crosshair1

There is no way that bolt failed from vibration, it was either yielded when fitting the starter or failed due to seized threads on removal.
Are you certain that this is a metric, the sheared bolt does not look correct type, the starter looks recent - is there more to this than meets the eye.
If its failed due to incorrect thread or cross threaded on tightening the engine will need to come out.
If this is not the case I would drill from above into the casting with a 3mm drill to find the depth of the bolt in the casting and if this looks correct, die grind the casting to expose the bolt end and try an automatic centre punch to rotate it out.

Corbally

What type of boat and which engine OP? Prop driven or saildrive? I work on boats but I'm flat out at the minute too. Where are you based? PM me if you prefer. I can give you a few ideas or a few names of people that might be able to help.
Engine not need to come out. A cheap block and tackle and a home build gantry/frame might get you enough access.

wannabecraig

@crosshair
I don't know the answer to the question re' how it happened. I assumed it was vibration, I don't know how bolts break in engines to be honest. I am not certain of anything regarding this, I bought it with that starting motor in it, so don't know anything about its fitting.

Does the last two sentences of your post mean drill through the engine from above? If so I'd ideally like to avoid it.

The Continental Op

crosshair1 wrote: »

There is no way that bolt failed from vibration, it was either yielded when fitting the starter or failed due to seized threads on removal.
Are you certain that this is a metric, the sheared bolt does not look correct type, the starter looks recent - is there more to this than meets the eye.
If its failed due to incorrect thread or cross threaded on tightening the engine will need to come out.
If this is not the case I would drill from above into the casting with a 3mm drill to find the depth of the bolt in the casting and if this looks correct, die grind the casting to expose the bolt end and try an automatic centre punch to rotate it out.

If the bolt was loose then its possible the extra movement in the starter motor could have snapped it?

back to welding after rooting around I rather like this MIG welding approach, but any welding method will need room to get the tip in place.

crosshair1

wannabecraig wrote: »

@crosshair
I don't know the answer to the question re' how it happened. I assumed it was vibration, I don't know how bolts break in engines to be honest. I am not certain of anything regarding this, I bought it with that starting motor in it, so don't know anything about its fitting.

Does the last two sentences of your post mean drill through the engine from above? If so I'd ideally like to avoid it.

Yes if i was certain that it wasnt cross-threaded I'd drill a pilot from above, wouldn't have to be vertical as its only to confirm that the bolt looks like it was the correct length to begin with.
Unfortunately my guess is that this has been messed up when fitting the starter and perhaps a metric bolt fitted to a 3/8w hole possibly having to be cut short because it wouldnt thread fully in etc...
I dont have much boat experience but have seen imperial threads on a mercruiser, while the bolt looks very similar to a japanese car front shock absorber lower mounting one.

gutteruu

Why not make a new mount bracket which is fixed to the big bolt/thread above it and hole in block just above.

wannabecraig

crosshair1 wrote: »

Yes if i was certain that it wasnt cross-threaded I'd drill a pilot from above, wouldn't have to be vertical as its only to confirm that the bolt looks like it was the correct length to begin with.
Unfortunately my guess is that this has been messed up when fitting the starter and perhaps a metric bolt fitted to a 3/8w hole possibly having to be cut short because it wouldnt thread fully in etc...
I dont have much boat experience but have seen imperial threads on a mercruiser, while the bolt looks very similar to a japanese car front shock absorber lower mounting one.

IT's a good point about it being the wrong bolt to begin with. But there is a replacement that looks exactly like it: https://www.nlamarine.com/products/mercruiser-120hp-140hp-2-5l-3-0l-starter-bolt-set-10-94435001-94435-10-805343-3 so I think it's a legitimate bolt for this block. This is the serial number, don't know if there is more info on the bolt in those number, I dont know how to break it down. Short Bolt (1 15/16"): 10-812509184 10-805343

wannabecraig

gutteruu wrote: »

Why not make a new mount bracket which is fixed to the big bolt/thread above it and hole in block just above.

Mainly because I dont know how to do that. I just don't have the knowledge.

gutteruu

wannabecraig wrote: »

Mainly because I dont know how to do that. I just don't have the knowledge.

A metal fabricator/welder would wip something up fairly easily. Save the cost and wait of a marine mechanic. Simply bolts in and out then.

wannabecraig

So slight plot twist. I was down there just now and was trying to get the other bolt out, but ended up tightening it.
This held the motor in place very tightly and allowed me to start the motor easly.
I was also able to get the other bolt to grip a tiny bit. This leads me to believe that the bolt didn't break
recently and was probably in the blige a long time!

So what I was thinking was;
Take long bolt out, use Loctite Threadlocker on that when I put it back in to keep that bolt in there tight and secure.
Before tightening, use Unibond Epoxy Repair metal to bond the starter motor to the engine block.
They get a new bolt (official one on order) and put that in with a little thread lock on it.

I think this will work well. The only issue was I couldn't get the longer bolt out today,
seems like it was stuck in a loop, would loosen, then kind of go tight again, then loosen but didnt come out fully.
So I'll need to understand why that's happening.

Link to engine running with starter motor tightened.
https://imgur.com/uB3MlTi

Tokyo

There's possibly a certain amount of wishful thinking going on. If you take a look at the sheared end of the broken bolt, it will be pretty obvious (bright metal) if it's a recent break or not. Looking at the earlier photo of the bolt, there's maybe a half thread left on it at best.

Likely you should be able to snug up the second bolt enough to keep it tight (don't break that one too), but my concern would be that the torque on the starter will Quist it back out of position over time. I'd still be looking at some way to clamp the second lug of the starter in position.

The Continental Op

wannabecraig wrote: »

...
I think this will work well. The only issue was I couldn't get the longer bolt out today,
seems like it was stuck in a loop, would loosen, then kind of go tight again, then loosen but didnt come out fully.
So I'll need to understand why that's happening.

...

May mean a lack of thread either on the bolt or in the housing or both. Possibly due to the bolt being loose and getting slap everytime the motor started or because its been cross threaded. Could also just mean crap and corrosion in the thread. If you unbolt it until its loose then put a prybar on the head so as you unbolt it you can force the bolt to pick up the next bit of thread you should get it out, but as always don't force it.

Worst case senario is that the engine has to come out both threads can be drilled out and helicoils put in - example kit https://www.screwfix.ie/p/helicoil-eco-thread-repair-kit-m10-x-1-5mm-14-pieces/265FR (you need to check the pitch). Although maybe you could to that blind in situ but I wouldn't like to try. Done right the helicoils can make the threads as good as new.

wannabecraig

Tokyo wrote: »

I'd still be looking at some way to clamp the second lug of the starter in position.

Agreed and I will do this. For now, I've just to go with the single nut and metal bonding to see if that will hold. Just spoke to marine mechanic that was too busy to deal with before, he said he's come out and bone the nuts and the starter motor.

wannabecraig

The Continental Op wrote: »

May mean a lack of thread either on the bolt or in the housing or both. Possibly due to the bolt being loose and getting slap everytime the motor started or because its been cross threaded. Could also just mean crap and corrosion in the thread. If you unbolt it until its loose then put a prybar on the head so as you unbolt it you can force the bolt to pick up the next bit of thread you should get it out, but as always don't force it.

ok, just some light pressure to release the bolt? It had a odd feel to it, felt like it was going in both directions at once, didn't want to risk breaking the bolt so didn't force it.

The Continental Op

You could have an area on the bolt and the housing that has some thread then a gap with no thread (maybe caused by the bolt being loose) then an area of thread again. So you have to get it from the area with no thread back onto the area with thread as you undo it. That will require a little bit of downward pressure to get the threads to engage.

Although I'm sure someone can come up with another reason for the thread behaviour?

crosshair1

http://www.marineengine.com/boat-forum/showthread.php?410788-Broken-starter-bolt

wannabecraig

So I'm restarting this thread because there is an update! I now have 2 broken bolts stuck in the engine. This worked until last friday, when the other bolt broke off! Same thing. Seems that the new bolts aren't as good as originals and can be the wrong size! So now I have 2x broken bolts and same issue with mechanic, none about.

Ive cut the side of the engine housing out to get better access so I think I'm going to try drilling out again. I dont think I need a mechanic to get them out if I can't, just somebody with the right skills and tools. If anybody has updated thoughts I'd appreciate those!

greasepalm

Do you have enough room to get a drill in there with things out of the way. Trying to get wd40 in that far might take some time to penetrate in around the threads.

right angle chuck.jpg

wannabecraig

I have one of those so going to try it tomorrow. I think I have enough room, but it's very tight.

I just bought some different size drill bits to try get better access.

greasepalm

Are you removing the starter motor to see what you are doing?

Sometimes a sheered of bolt can be unwound by using an impact pen and wd40.

wannabecraig

The starter motor is removed yes. I'll retake better photo tonight for upload.

I will WD40 it this evening to see if it does anything for making it easier to remove.