Stuck bolts - newb needs help

[TorronnaPwr]

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

[Cheechako]

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.

[Chili Palmer]

There are a few things you can try. Keep going with the penetrating oil, it won't hurt. Spray once or twice a day for as many days as you can. You can also try an impact wrench (Harbor Freight has a 120v for around $30-40 that would definitely have enough power but my break the bolt/stud. I would try to heat the nut up first then while it's hot hit it with an impact wrench.

[sandy stone]

All good advice so far. I've had the best luck with Kroil or PB Blaster and letting it soak, and I also recommend using an impact wrench. If nothing else works, I once used something called CRC Freeze-Off and it did the trick. The only place I know that sells it is Autozone. Follow the directions on the can for best results.

[Reefmagnet]

Definitely use a "rattle gun" (impact wrench). You don't need air, there are cordless options and they make a very useful addition to the tool kit if you don't already have one.



When I had to remove six rusty engine mount bolts recently, the first two I tried to undo with ratchet and both sheared. I then came at it with my cordless rattle gun and the remaining four rattled out without too much effort and, most importantly, without breaking. If course there are never any guarantees, but the rattle gun is your best chance of success.

[TorronnaPwr]

Thx for your replies, really good advice. Gives me confidence to do the job

[RaymondR]

If they are nuts on studs it is sometimes better to sacrifice the nuts rather than take a chance on breaking off the stud. It there's room to work with a power drill you can drill through both sides of the nut parallel to the stud then split the nut with a chisel.

[NYSail]

Be careful using pb blaster or similar on engines. It will destroy gaskets..... second the use of impact driver

[GWilly]

Nothing more to add to what’s already been said. Let us know how it goes, what worked for you.

[wingless]

Welcome to the forum.

The method that works well for me is to first attempt to tighten the bolt, just until it moves. Then to loosen until resistance increases, then to go back and forth, until tight then loosen a little more each time.

When I did the first replacement on my Mercruiser exhaust manifolds, I discarded the OEM bolts and replaced them w/ ultra corrosion resistant hardened fasteners from McMaster-Carr. These have been terrific for well over a decade and many replacement cycles.

Note that the manifolds have clearance holes, so if a bolt is difficult to remove then the head may be ground off, permitting the manifold to slide off, leaving exposed studs that may then be removed using lubricant and lock jaw pliers.

The retention bolts include a pair of specialty studs that permit retention of the heat shield. Those may be replaced w/ OEM parts if they have degraded.

[wingssail]

I have had success with PB Blaster. Spraying it on and letting it soak repeatedly over the course of a few days might work wonders. An impact wrench is also good. Heat from a propane torch may help, I've put on more PB after heating.

Finally, If nothing gets the bolts out you may want to force it even at the risk of breaking the bolt. Get a 1/2 socket drive and 12 point sockets and put a big extension on and force it, even hit the extension handle with a big hammer.

If you break the head off the bolt, once the riser is off you will see the bit of the bolt. Some times that broken bolt will then come out easily with a vice grip.

AND, if it does not, you can drill that bolt. Not fun, and not easy, but carefully drilled to keep the drill in the middle of the bolt an easy-out will usually remove the bolt. I've gotten to that stage with riser bolts, and in the end I drilled them out and now the new bolts have non-seize on them.

[Gaia]

Many good suggestions here. Combine them. I once had some luck heating the nut and then applying PB blaster as mentioned above but while it is hot. Careful as the stuff is flammable. I would do several cycles of that while trying not to directly heat the stud as you want the nut to expand. Then while hot rattle it. Again be careful of flammability of the releasant.

Jim sv GAIA

[Scubaseas]

Heat and penetrating oil is your best bet. Impacts are OK but you can break a bolt or stud with them. I would spray with PB Blaster or Kryoil or atf/acetone and let sit. Feel free to smack the nut with a hammer is accessible. Try tightening then loosening. If no movement, heat nut with a MAP torch or borrow an electric induction bolt heater. Have an extinguisher at hand and a spray bottle in case you heat up something you shouldn't. If possible heat to dull red then carefully remove nut. Note Capt. Obvious says the bolt and nut will be hot. Just get it to move, let cool and then spray and remove. If replacing use copper clad split interference nuts and do not over torque the bolts and use a proper sequence.

Induction heater would be my choice as a professional mechanic but they ain't cheap. Mine cost $800 about 20 years ago but I see they are a lot "cheaper" now. Maybe rent one from your local mechanic? They do however work really well for exhaust manifold nuts.

[wingless]

Originally Posted by wingssail

I have had success with PB Blaster. Spraying it on and letting it soak repeatedly over the course of a few days might work wonders. An impact wrench is also good. Heat from a propane torch may help, I've put on more PB after heating.

Wow!

The usage of an open flame in a gasoline engine compartment is not a brilliant idea and should not be attempted!

The application of lubricant onto the accessible fastener head, angled downwards away from the thread, 1½" deep into the exhaust manifold casting will have limited / zero utility.

Originally Posted by wingssail

Finally, If nothing gets the bolts out you may want to force it even at the risk of breaking the bolt. Get a 1/2 socket drive and 12 point sockets and put a big extension on and force it, even hit the extension handle with a big hammer.

Wow!

Intentionally applying excessive torque to a fastener stuck in the cylinder head to break the fastener is a really bad idea and should not be effected.

Originally Posted by wingssail

AND, if it does not, you can drill that bolt. Not fun, and not easy, but carefully drilled to keep the drill in the middle of the bolt an easy-out will usually remove the bolt.

Unless replacing the damaged cylinder heads is part of the plan this is also a really bad idea.

If the bolts are somehow broken flush to the cylinder head and cannot be removed, then remove the cylinder heads and have the problem professionally repaired, so the cylinder heads don't require discarding because of damage to the fastener holes.

[wingless]

Originally Posted by wingless

The application of lubricant onto the accessible fastener head, angled downwards away from the thread, 1½" deep into the exhaust manifold casting will have limited / zero utility.

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.