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BOLT head in the Bilge...

4K views 27 replies 17 participants last post by  blutoyz 
#1 ·
So we're off cruising, finally, and we've had a few issues with the boat and engine, but nothing major. But today I found a head of a large bolt in the bilge. Searched for the place it came from and found that it was from part of a engine mount. (see photo)
So, I realize it's not good, to say the least...but is it an urgent problem? I mean, fix immediately problem...fix before proceeding any further?
And, how am I to remove/replace that bolt?
Currently we are on a mooring in Marathon, FL.
Any advice would be appreciated... Thanks!
 
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#2 ·
It is something you need to fix, sooner rather than later. Each time you start the motor it is going to flex that mount, and with only one bolt holding it if it breaks the whole motor will be useless, plus if it shifts because it broke you could bend or break other parts. If you are lucky you might be able to use a screw extractor to get it out. Put a lot of penetrating oil on it first and let it work. then drill a small hole for the extractor too bite into. It should just back out. If that doesn't work then you will need to drill out the bolt and re tap the hole.
 
#3 ·
Looks pretty urgent to me. Looks like the engine allignment will shift if the bracket swings. It doesnt look to difficult to repair, there may be enough bolt sticking out to get ahold of with a good pair of "visegrips" (no substitutes). If it does not you will have to drill and use an extractor. Bluepoint makes the best one. See a $nap-on dealer
 
#4 ·
Is the stud still in there? From the case thru the mount I mean . . .if so, not so crucial . . .if you just lost the head of the bolt you'll still have rigidity in the mount. You just don't want a pivot point at the top bolt in the photo, if there is a piece of bolt thru the mount bracket I would relax . . .
 
#5 ·
I would recommend removing the broken bolt and replacing both bolts as the remaining bolt with the head may have been compromised and may also lose it's 'head' (pun intended)... I would not trust the loads imparted on one bolt all that time (may be ready to shear off too)... good thing you spotted it sooner than later... :eek:
 
#6 ·
Monkey,

If you can manage to get a scissors jack under the engine, you can fit it up to support it when you remove the bracket. If your luck holds, there might be a bit of the bolt still sticking out of the block -- hopefully enough that you can gain a purchase on it with a pair of vise grips or a small pipe wrench. If not, then you'll need to try an easy-out.

Like mentioned before, pretreating with a good penetrating oil should be your first through third steps (apply, tap lightly and wait; repeat; repeat).
 
#12 ·
Monkey,

If you can manage to get a scissors jack under the engine, you can fit it up to support it when you remove the bracket.
Otherwise just use wedges - you can exert an amazing amount of force with wedges so be careful to just make them snug, don't pound them in. If the engine does settle a little - enough to make lining up the new bolts a problem, just tap the wedges some more until it rises into position - you can be very precise with them.
 
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#9 ·
I should add that we did an engine alignment when installing a new prop shaft and coupling back in October. From my notes, the opposite corner was raised 5mm. That was probably 125 engine hrs ago. I'm thinking that may have something to do with the stresses that caused this eventual failure.
 
#13 ·
As others have said you need to fix it now.

Replace BOTH bolts. If possible get aircraft quality bolts.

The broken bolt might very well come out easily but if not heat is your friend. Get someone with a gas axe to come along and heat up the casing. Fire extinquishers at the ready of course [or a water hose].
 
#14 ·
The good news is that you found the head and it was in the bilge. I once found a 3/8 washer on my deck while sailing off the coast of Baja California. Heads popping off on steel bolts is usually not due to direct stress, but due to hydrogen embrittlement (a manufacturing/processing defect). Other bolts that may have come from the same lot should be considered suspect.
I have made this type of repair several times, and it is unlikely that you can back out the bolt with vice grips, but its worth a try if you can do it while leaving a good bit of the broken bolt protruding. In any case you will need to remove the bracket first. In drilling for a screw extractor (easy out), the hard part is drilling a hole in the broken bolt without running it out into the surrounding part. I would make two drill bushings. Each of these would be a short piece of steel rod with a shallow hole in one end that would fit over the broken bolt extension (there needs to be an extension left) and the first would also have a hole the rest of the way through that would be a close fit for a center drill. This would be used to drill a center into the broken bolt. The second drill bushing would be the same but with the through hole the size to guide the drill for the easy out and used to drill an appropriate sized hole deep into the broken bolt. If you end up just drilling out the broken bolt, it is extremely important to keep the hole as centered over the original bolt as best possible. Good luck
 
#15 ·
Another couple of options: Oddly enough, an old basketball or soccer ball makes a decent air jack. Deflate, stick under the engine, pump up until it starts to lift.

Once you remove that engine mount, and put some PBlaster or other real penetrant on that stud, you may also be able to unscrew it by cutting a slot in it (with a metal saw blade or dremel bit) and then hitting it with an impact hammer and a "screwdriver" tip. If the penetrant has done its job, that will spin right out with the impact hammer. If not...you can still use the screw extractor.

Note the position and alignment of the motor mount carefully, try to match it back up since that affects shaft alignment. In theory, engine mounts should be replaced about every five years as the rubber stiffens up or cracks over time. In practice...that's something else again.

Could be that bolt sheared because it was improperly torqued, so if you have a torque wrench, use it. If you don't, this could be the time to buy one anyhow. And I suppose if you were really compulsive, you mght want to replace both bolts on both front mounts while you're in there. Using Loctite or antiseize on all of them as well.

Or just replace the one and go sailing.
 
#16 ·
most of the time heads come off bolts because the bolt was loose in the first place. this usually occurs because of poor engine alignment. The stud in there may back right out buy hand if you get the mount off. You can take the weight off the mount many ways. The wood blocks and wedges is most likely the easiest. Have a experienced tech inspect your mounts and replace them if needed carefully inspect your shaft & cutlass brg. then have your engine aligned. It needs to be within .003 tolerance. When running your engine in gear a good alignment will have no noticeable vibration. One trick to checking vibration is to set a cup of water on the cockpit sole if you see concentric rings in the water you have vibration. The better you get the alignment to longer all your machinery will perform & last.
 
#17 ·
one other way of getting a bolt out is to freeze it, coke also eats rust, a butane torch really doesn't get it that hot. it may be a stud and once you remove the bracket you might have enough to grip it. you can drill out a hole in the center and use a screw extractor set.

one trick is try to tighten the bolt then spray wd40 on it then try to loosen it.
 
#18 ·
depending on how much of the bolt shoulder is sticking out, you can use a chisel and hammer to make it turn. you want to walk it around you do not want to use it as if you were using a screw driver to turn it. basically the chisel would be flat against the block so when you hit it with the hammer it turns the screw.
 
#19 ·
Sometimes simple is better. If you have a bit sticking through dremel a slot or an 'X' and take it out with a screw driver (of course penetrating oil etc.. first)

As others have said, I'd replace all of the bolts, but first I'd call the service who did the realignment and tell them they have some explaining to do, followed by a refund or repair. This didn't happen because they did the job right, not in a couple of months.
 
#20 ·
I'm betting the shaft of that bolt is stuck really tight. I've found over the years that the single biggest reason for bolt heads failing is over tightening - someone leaned on the wrench until they felt the bolt head start to give and called it good enough. :)
 
#21 ·
Yes... overtightening a bolt can compromise the strength of the bolt but this is unlikely as Grade 8 bolts have a tensile strength of 150,000 psi... that's quite a bit for hand tightening... but if the bolt was over torqued I could see it failing... I believe it was more due to an overload condition on the engine causing the over torqued bolt head to break off... which is why you must change not only the two bolts shown on the photo but all bolts holding this engine... bolts are cheap... ruining your alignment is more costly... The preload, or thread tension in a fastener is higher when the type of steel being used is grade 8 in quality which if you can get aircraft bolts that would be the best overall grade.
 
#22 ·
THANKS EVERYONE... Sure got a ton of replies and advice, and I appreciate all of it! Here's what I did...
Lined up the local boat yard to do the work if what I was going to try failed. Then, walked to Home Depot. Bought a bottle jack, a breaker arm (long socket wrench), PB Blaster Penetrating, and a big Visegrip (I only had the medium size). Last night I PB Blasted the bolts. This morning I put the jack in the bilge under the stern end of the engine, jacked it tight, but not enough to move it. Then with my fingers crossed I put the big wrench on the remaining upper bolt and slowly cranked. Woohoo, it moved. I removed it. That was probably a 5 inch bolt with threads only at the end (odd since the broken head had threads right to the head). Next I removed the bracket by taking off the upper nuts on the mount. Then I got the big Visegrips and put it on the end of the now revealed broken bolt. It moved so easily I thought the wrench had come off. I removed it with my fingers. It was only about 1.5" long and all threads. So the two bolts were different. I thought I would be visiting a hardware store or the boat yard for a new bolt, but a quick look in my stock and I saw I had three SS bolts that were identical to the broken one. I used a lock washer and one of those bolts to reassemble.
I suspect that the bad bolt was very tight, and then when the opposite corner was raised during the alignment it stressed the neck of that bolt and it eventually gave way. I'm just glad I found it.
Thanks again!
 
#23 ·
:cool:

:thewave:

Sounds like the correct bolt got lost and something that was at hand got substituted.

Congrats and now head out and buy a lottery ticket. :)
 
#25 ·
Monkey,

Congrats on the success!

Just a thought: If your replacement bolt is identical to the one that snapped, then keep a close eye on it. From your description it seems to differ from the others, and it sounds like it may not be up to the task for long. You might want to consider finding a bolt that's identical to the one that didn't break.

Best,
PF
 
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