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Old 11-08-2020, 10:00   #16
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Re: Stuck bolts - newb needs help

Lots of ideas and cautions, which is great. I have one riser off - it was the one which felt hot while running, and its badly corroded - strangely the dash temp gauge never rose? I used penetrating oil, tapped the wrench to tighten and to loosen in sequence with patience and finally got some small movements.


Am I understanding the comments properly that its mainly the head of the nut which bonds with the riser, and less the actual male/female threads?

Do you think the overheating of the riser compounded the bonding issue, or was it just age/corrosion (hoping it did and so other risers will be easier to take off).
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Old 11-08-2020, 10:19   #17
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Re: Stuck bolts - newb needs help

Great news.

The internal raw water passage corrosion was the reason the part felt hot. A quick / easy test is to verify it is possible to continuously hand hold the exhaust while the engine is running.

My salt water engine would destroy OEM Mercruiser exhaust parts every 3-5 years until I redesigned the exhaust. Now it looks like these parts will last the life of the engine.

Assuming the manifold is also raw water cooled, then those raw water passages also suffer from that problem.

The threads are typically the part making removal difficult, from corrosion over time.

When the manifold is off it is then possible to perform a visual inspection of the exhaust valves and port for corrosion, to determine if head work is required.
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Old 11-08-2020, 10:23   #18
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Re: Stuck bolts - newb needs help

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Originally Posted by wingless View Post
...Unless replacing the damaged cylinder heads is part of the plan this is also a really bad idea...
Are not the exhaust risers bolted to the exhaust manifolds on the 454 Magnum, not the heads?

And, yes, I have successfully drilled out broken bolts without damaging the aluminum exhaust manifold.

To the OP, good work, keep it up.
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Old 11-08-2020, 10:31   #19
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Re: Stuck bolts - newb needs help

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Originally Posted by wingless View Post
Here is an image of the exhaust manifold on a 4.3L Mercruiser showing the distance between the accessible head and the manifold surface having the threads. It looks to be about 3" away from the exposed head, uphill from the head when in normal orientation.


Seems like that is not the type of motor or the type of exhaust manifold, or the type of riser, but good advice I guess.
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Old 11-08-2020, 11:04   #20
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Re: Stuck bolts - newb needs help

Heat with propane torch until bright red, let cool for 15 minutes, tap with ballpeen hammer for 2 minutes, Spray w/ PB blaster. Repeat, Repeat. Put socket wrench and try to tighten. Repeat heat, hammer & Blaster. Use socket wrench, try to tighten then try to loosen. If it starts to budge, repeat as needed until you get a good full turn
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Old 11-08-2020, 17:57   #21
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Re: Stuck bolts - newb needs help

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Boy I'm not sure. This is mostly a sailboat forum, but many here have had powerboats with those risers. The bolts on those arent that big, so I too would worry about too much force. Hammer shocking is done often on various things and can help.
What often works is an air wrench/air hammer. The rattling shocks from that will often loosen up bolts like that where a wrench wont. You can rent one if you have access to a compressor. They are adjustable for force.

They have electric ones now days but I dont know if they are any good.
Air impact wrench is very good, try going both ways... loosening and tightening. Electric impact wrench is very good,
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Old 11-08-2020, 19:57   #22
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Re: Stuck bolts - newb needs help

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Originally Posted by TorronnaPwr View Post
New to working on engines but decided to replace risers and manifolds on my 18 yr old mercruiser alpha one's because one was hot to the touch, unlike the other three. Have had boat 3 yrs but i don't think they have ever been changed although i am in lake water.
The riser bolts won't budge, and are too tight to get penetrating oil in. I'm afraid if i extend socket wrench for more leverage i could snap bolt head off.
I've heard of "shocking" the bolt with a hammer blow but don't know if this is safe to do. Also heard of heating the area - is this a good idea and if so what would be the best way to do it?
Any other ideas would be great

Key things to understand:
  1. Even experienced mechanics break off bolts in situations like that. Decide whether you're willing to accept that outcome. Beyond a certain point you may have to pull the engine out and send it to a machine shop to remove bolt stubs using EDM. Generally this is after you've tried everything and broken off an ez-out.
  2. With bolts that thread into a tapped hole in the casting, usually the best strategy is to put a breaker bar and six point on there and alternatively try to loosen and tighten the bolt until it starts to move a little. It takes experience to judge the amount of movement and torque to use.
  3. Heat sometimes helps because it expands the bolt which reduces the clamping pressure and in some cases that reduce the torque necessary to break the threads loose. But it also weakens the bolt so that it will accept less torque. In a combustible/flammable environment mechanics cover vulnerable items with wet towels and have fire suppression equipment and extra people at hand depending on the situation.
  4. An impact wrench sometimes helps but rarely IME with bolts that have a long shank (more than about one inch) before reaching a tapping. The shank acts as a torsion spring and absorbs the impulse. That said, I got an air impact wrench 30 years ago when they were the only thing that was any good. The world has changed and I have a cordless battery one now.
  5. Sometimes penetrating oil will help particularly given repeat applications over a period of many days or even weeks. Use good modern penetrating oil, JB-80 is one of them but there are plenty of others that are good. WD-40 isn't particularly effective, and neither is plain motor oil.
Good luck. You'll need it.
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Old 11-08-2020, 22:32   #23
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Re: Stuck bolts - newb needs help

Quote:
Originally Posted by TorronnaPwr View Post
.
...Am I understanding the comments properly that its mainly the head of the nut which bonds with the riser, and less the actual male/female threads?

Do you think the overheating of the riser compounded the bonding issue, or was it just age/corrosion (hoping it did and so other risers will be easier to take off).
There is no "mainly" with this aspect of mechanicing; corrosion 'does' what it wants when it finds appropriate conditions.

There are many different styles of Mercruiser risers; without knowing what specific engine you have, everyone's just guessing about an effective plan of attack, though most of the suggestions are good, standard mechanical procedural advice. Most risers nowadays have long bolts that pass through a boss at the top and bottom surfaces of the riser, leaving the center 4 or so inches of the bolt exposed, which helps prevent the bolt from locking itself into a full length hole by corrosion.

As you've found out with the first riser.

This is not the case with manifolds, the bolts, roughly 5 inches long and threaded only on the last 1 - 1 1/4", not always, but often enough, have a nasty habit of locking themselves into the manifold because the bolt passes through a full length boss, where no amount of anything save drilling them out (a near impossibility, in situ) will remove them.

If this happens, no amount of heat, torque or impact will remove them; they have to be cut or broken off, and then the stub ends removed from the head and the shanks drilled out of the manifold (if you plan on reusing it).

There are several different options here, depending on your application, situation and skills.

Remove the head and manifold together and work on them on the bench. In this case it is easy enough to sacrifice the old manifold and just cut the bolt, manifold and all, close to the head (1/2" or so) and them remove the stub with vise grips.

A competent machinist with a well-equipped shop can drill the bolts out of the assembled manifold and head, without damaging either, relatively easily. Emphasis must be put on competent though, as 'easily' requires the right tools and knowledge...

Because the gasket used between the manifold and head is rather thick, depending on access, sometimes the frozen bolt can be cut in place (without removing the head [I've done it a few times]) with a sawzall, or god forbid, one of those 'hacksaw blades in a handle' contraptions. Of course then one has to worry about removing the flush-cut stub, but a left hand drill bit usually works wonders there.

So there're three ideas; hopefully you'll need none of them.

When you put the manifold back on, it helps to get a couple of 7" bolts, cut the heads off and screw them into the head as guides to hold the gasket in place (make sure it's right way up) whilst you position the (damn heavy) manifold. Once you slide it onto the cut-off bolt guides, screw in a couple of bolts hand tight (use plenty of never-sieze) to hold the manifold in place, unscrew the quides with some vice grips (or a screwdriver if one's had the presence of mind to hacksaw a slot in the end beforehand), screw in the bolts to replace the guides, and then torque to spec, alternating from the center out.
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Old 11-08-2020, 23:45   #24
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Re: Stuck bolts - newb needs help

I don't know how much space/access there is, but I have used nut splitters for such jobs. You could also drill vertically down through the body of the nut - ie parallel to the stud - before using the splitter at the drill hole. https://www.amazon.com/CRAFTSMAN-Universal-Nut-Splitter-CMMT14117/dp/B07R96Z6LY/ref=sr_1_3?dchild=1&keywords=nut+splitter&qid=1597 214623&sr=8-3
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Old 12-08-2020, 01:01   #25
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Re: Stuck bolts - newb needs help

An impact wrench will loosen most rusted bolts. Using force with a socket and big breaker bar will just twist off the bolt heads. From about 60 years of dealing with rusted or seized nuts and bolts.

Most rental places rent electric impact wrenches. Also some auto parts stores rent.
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Old 12-08-2020, 01:44   #26
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Re: Stuck bolts - newb needs help

All the above work it's a matter of which one is going to work for you. Something that is going to get you out of trouble is before you put everything together get some copper grease put this on everything that has a thread so you won't have this problem again. Good luck with everything
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Old 12-08-2020, 11:34   #27
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Re: Stuck bolts - newb needs help

Can you attempt to remove these frozen bolts with the engine warmed up?

In the event the bolt heads do snap, i like the use of reverse drill bits.

You don’t need to be a machinist to remove broken bolts, even if they’re in the head.

Just common sense and patience.

Make sure you centre your hole with a punch.
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Old 12-08-2020, 13:20   #28
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Re: Stuck bolts - newb needs help

Not sure how many people here are aware of how most Mercruiser manifolds are attached, but the manifold bolts are 3/8 x at least 5 inches long, probably closer to 6, with only the last little bit, maybe 3/4 " threaded into the head. The rest passes through the manifold; when they get stuck it's not usually the thread but the shank of the bolt that is rusted into the manifold. The 'heat sink effect' is usually such that it makes no difference to try heat as a removal aid. The use of an impact might help, but in bad cases the head of the bolt snaps off, leaving 5 inches of bolt in the manifold, and the manifold still securely fastened to the cylinder head.

The chances of drilling by hand through 5 inches of steel bolt rusted into a soft cast iron manifold and coming out on the other side within the diameter of the bolt, even with the patience of Methusela, the eye of a jeweler and the dexterity of a safe cracker, are so close to zero so as to be nil. Throw in the cramped space of the typical engine compartment and the abilities of the average novice mechanic and the chances of success are well into the negative range.

The last one I did, a couple of years ago, was rusted into the manifold by a slow, neglected raw water leak on a 502. The boat was big enough to give access to cut the bolt at the manifold-to-head junction with a sawzall, and then bring the manifold home, clamp it in a drill press and drill the bolt out with a 5/16" bit. Even so, the bit drifted a little into the manifold, maybe a bit less than a sixteenth, and the remains of the bolt had to be peeled out with a drift.

A machinist with a big enough milling machine could have mounted the manifold with cyl head attached and milled the broken bolt out without getting into the rust that held it in place.


If the OP is a little lucky, they'll just come out with a 6 point socket and a 12-16" handle, or maybe an electric impact, and none of this will matter in the slightest...
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Old 24-08-2020, 08:41   #29
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Re: Stuck bolts - newb needs help

As long as your plan is to replace the manifolds and risers, why be concerned about breaking the riser bolts? I was taught when removing any item with more than one bolt to break all of the bolts loose before backing any of them out. Along those lines, I’ve had success by retorquing the other bolts that were broken loose, then working to loosen the troublemaker.
When you go to install the new manifolds, cut the head off a bolt an inch or so longer than the installation bolts and use it to support the manifold while you get the installation bolts and gasket aligned and started.
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Old 24-08-2020, 09:09   #30
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Re: Stuck bolts - newb needs help

Hi, lots of good ideas. I have a new one I have never tried but was told by a mechanic. This is the same mechanic that told me about making a bolt/studs to hold the new exhaust on place during the replacement. He said to sacrifice the old riser/exhaust and just break the casting with a hammer. I have never done it but when all else fails it might be worth a try.
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