Stripped thread in aluminum engine block...

IRideASlowBike · 09-25-2011, 09:04 PM

I was in the process of installing front tip-over bars today on my old Concours. I've had these bars laying around since January.

As I was tightening the bottom left mounting bracket (the bolt goes into the radiator mounting bracket), with the torque wrench set at 35 ft-lbs (instructions for tip over bars say 30-40), of course, the aluminum engine block threads got stripped.

I am now unable to screw anything into that hole now, even the original, shorter bolt. The thread in the engine block is fucked.

Is there anything that can be done now? How does one go about rethreading a stripped hole in an aluminum engine block, if this is even possible? Is it possible to do something without having to rethread?

God I hate wrenching.

beemerkid · 09-25-2011, 09:09 PM

I would go for a helicoil. Ive had good success with them in the past.

henrymartin · 09-25-2011, 09:16 PM

Helicoil OR finding a SAE bolt that is just enough larger in dia, then threading the hole for SAE bolt.

I did this with a drainplug on a motor once. 12mm bolt was stripped (PO), and I did not feel like doing the helicoil route. A 1/2" thread is just enough larger to allow for new threads, and small enough not to have to drill or cause any structural issues.

Now, I don't know what size metric is the thread now, but I imagine there is something pretty close to it.

IRideASlowBike · 09-25-2011, 09:20 PM

Quote:

Originally Posted by henrymartin

Helicoil OR finding a SAE bolt that is just enough larger in dia, then threading the hole for SAE bolt.

I did this with a drainplug on a motor once. 12mm bolt was stripped (PO), and I did not feel like doing the helicoil route. A 1/2" thread is just enough larger to allow for new threads, and small enough not to have to drill or cause any structural issues.

Now, I don't know what size metric is the thread now, but I imagine there is something pretty close to it.

Pretty sure it's a 17 mm bolt right now. So basically you're saying that you'd find a slightly larger SAE bolt and just force it in the hole, cutting a new thread with the bolt itself?

troidus · 09-25-2011, 09:25 PM

I did the same thing. Fortunately, the threads are not in the engine, they are in the radiator support. The TO bar instructions shouldn't say 40 ft-lbs for those fasteners, 'cause the threads in the radiator support can't hold that much. It would help if the factory service manual specified a torque for those bolts, but it doesn't. To fix it, get a bolt that's a little longer and a matching nut and sandwich the radiator support to hold it and the TO bar to the engine.

IRideASlowBike · 09-25-2011, 09:35 PM

Quote:

Originally Posted by troidus

I did the same thing. Fortunately, the threads are not in the engine, they are in the radiator support. The TO bar instructions shouldn't say 40 ft-lbs for those fasteners, 'cause the threads in the radiator support can't hold that much. It would help if the factory service manual specified a torque for those bolts, but it doesn't. To fix it, get a bolt that's a little longer and a matching nut and sandwich the radiator support to hold it and the TO bar to the engine.

Good idea, I'll be dropping by Home Depot and Auto Parts store tomorrow to explore both options. THanks.

GreaseMonkey · 09-25-2011, 09:39 PM

Quote:

Originally Posted by IRideASlowBike

Pretty sure it's a 17 mm bolt right now. So basically you're saying that you'd find a slightly larger SAE bolt and just force it in the hole, cutting a new thread with the bolt itself?

Unfortunately in your situation I do not think it will work. When you mention 17mm, that would be a pretty big bolt (bigger than a lug nut stud on a car!), so I suspect you mean you need a 17mm wrench, which makes it a 10mm bolt if the standard configurations are followed. Now a 10mm bolt is 0.393 inches, and a 3/8" bolt is 0.375 so it would not work. (however, if you had a 3/8" bolt that stripped you could run a 10mm tap in just fine without drilling first). So your option is to drill it out and re-tap to 12mm, or 7/16 X 20 if the local hardware store does not have metric taps and bolts.

They do have a specific purpose, but I cannot figure out the fascination with helicoils. Basically, you have to drill and tap a hole bigger, then add an extra part that can fail, then reinstall the screw. Why not re-tap the hole and just use a bigger bolt in most cases.

beemerkid · 09-25-2011, 09:48 PM

Quote:

Originally Posted by GreaseMonkey

Unfortunately in your situation I do not think it will work. When you mention 17mm, that would be a pretty big bolt (bigger than a lug nut stud on a car!), so I suspect you mean you need a 17mm wrench, which makes it a 10mm bolt if the standard configurations are followed. Now a 10mm bolt is 0.393 inches, and a 3/8" bolt is 0.375 so it would not work. (however, if you had a 3/8" bolt that stripped you could run a 10mm tap in just fine without drilling first). So your option is to drill it out and re-tap to 12mm, or 7/16 X 20 if the local hardware store does not have metric taps and bolts.

They do have a specific purpose, but I cannot figure out the fascination with helicoils. Basically, you have to drill and tap a hole bigger, then add an extra part that can fail, then reinstall the screw. Why not re-tap the hole and just use a bigger bolt in most cases.

Usually a larger bolt will work. My fascination with helicoils is that working in the engineering department on a ship you have things that you are opening every day, and then somebody (usually you) strips it out, and you want to use the same size wrench for all of the 20 bazillion bolts you have to undo. my $.02, you get your moneys worth

henrymartin · 09-25-2011, 09:49 PM

Quote:

Originally Posted by IRideASlowBike

Pretty sure it's a 17 mm bolt right now. So basically you're saying that you'd find a slightly larger SAE bolt and just force it in the hole, cutting a new thread with the bolt itself?

NOOOOOO! Never. You got the concept right, but I would tap for the SAE bolt. Never force a bolt into aluminum case to cut its own thread. Please.

GreaseMonkey hit it head on.

Riley #494 · 09-25-2011, 09:50 PM

Timesert......

http://www.timesert.com/

Check their online retailers or a local store.

concours · 09-26-2011, 03:15 AM

Quote:

Originally Posted by beemerkid

I would go for a helicoil. Ive had good success with them in the past.

+1 Helicoil is the answer.....

NC Scott · 09-26-2011, 08:18 PM

Quote:

Originally Posted by concours

+1 Helicoil is the answer.....

The helicoil is the only proper fix. Done correctly you will have a stronger, more reliable thread than the factory threaded aluminum.

Langanobob · 09-26-2011, 08:40 PM

Quote:

Originally Posted by NC Scott

The helicoil is the only proper fix. Done correctly you will have a stronger, more reliable thread than the factory threaded aluminum.

Scott,

Have to take issue with the statement that a Helicoil is the only proper fix. There are competing products such as Timeserts that are just as good or better.

Bob

Pokey66C23 · 09-26-2011, 09:17 PM

Timesert beats hc every time.

troidus · 09-26-2011, 10:32 PM

I'm sure both products are fine, but the OP misunderstood which threads were pulled out of what and there isn't enough meat to do thread repair. The threaded part of the assembly he's talking about is a steel stamping (~14ga) with maybe three threads in it. It's supposed to steady the bottom end of the radiator, not carry any kind of a load. The longer bolt with a nut is the way to repair this, unless you want to disassemble the bike and weld a nut on the back side of the tab.

09-25-2011, 09:04 PM	#1
IRideASlowBike ^OP Banned Joined: Feb 2010 Location: SE PA Oddometer: 1,244	Stripped thread in aluminum engine block... I was in the process of installing front tip-over bars today on my old Concours. I've had these bars laying around since January. As I was tightening the bottom left mounting bracket (the bolt goes into the radiator mounting bracket), with the torque wrench set at 35 ft-lbs (instructions for tip over bars say 30-40), of course, the aluminum engine block threads got stripped. I am now unable to screw anything into that hole now, even the original, shorter bolt. The thread in the engine block is fucked. Is there anything that can be done now? How does one go about rethreading a stripped hole in an aluminum engine block, if this is even possible? Is it possible to do something without having to rethread? God I hate wrenching.

09-25-2011, 09:16 PM	#3
henrymartin Mr. Tourguide Joined: Sep 2010 Location: South of the Great North Woods Oddometer: 2,552	Helicoil OR finding a SAE bolt that is just enough larger in dia, then threading the hole for SAE bolt. I did this with a drainplug on a motor once. 12mm bolt was stripped (PO), and I did not feel like doing the helicoil route. A 1/2" thread is just enough larger to allow for new threads, and small enough not to have to drill or cause any structural issues. Now, I don't know what size metric is the thread now, but I imagine there is something pretty close to it. __________________ My motorcycle projects blog My Goodreads Profile This is what I do when I'm not here!

09-25-2011, 09:50 PM	#10
Riley #494 Studly Adventurer Joined: Nov 2004 Oddometer: 670	Timesert...... http://www.timesert.com/ Check their online retailers or a local store. __________________ "The object of life is not to be on the side of the majority but to escape finding oneself in the ranks of the insane." Marcus Aurelius, Emperor

09-26-2011, 09:17 PM	#14
Pokey66C23 Gnarly Adventurer Joined: May 2008 Location: wetside Oddometer: 365	ts is best Timesert beats hc every time.

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09-25-2011, 09:25 PM	#5
troidus Beastly Adventurer Joined: Sep 2010 Oddometer: 6,915	I did the same thing. Fortunately, the threads are not in the engine, they are in the radiator support. The TO bar instructions shouldn't say 40 ft-lbs for those fasteners, 'cause the threads in the radiator support can't hold that much. It would help if the factory service manual specified a torque for those bolts, but it doesn't. To fix it, get a bolt that's a little longer and a matching nut and sandwich the radiator support to hold it and the TO bar to the engine.

09-26-2011, 10:32 PM	#15
troidus Beastly Adventurer Joined: Sep 2010 Oddometer: 6,915	I'm sure both products are fine, but the OP misunderstood which threads were pulled out of what and there isn't enough meat to do thread repair. The threaded part of the assembly he's talking about is a steel stamping (~14ga) with maybe three threads in it. It's supposed to steady the bottom end of the radiator, not carry any kind of a load. The longer bolt with a nut is the way to repair this, unless you want to disassemble the bike and weld a nut on the back side of the tab.