crappy day - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DeputyDan · 07-10-2011, 02:04 PM

so I went to put a new harmonic balancer on using the "proper"

tool and it tore the threads out of my crankshaft. I should have stuck to the old way of knocking it on with a hammer! Anyway to make a long story short I need to retap the crank and it has only a few threads left in it. What is the best way to go about this? I was thinking drill out the threads with a 1/2 bit then tap it for 1/2-20 as I believe 1/2-20 is the next size up. Or should I drill it out with a 7/16 (the OEM size) and try to retap it as a 7/16-20? Also has anyone ever seen a thrust bearing actually go out by tapping it on with a hammer? Reason I ask is because grandpa was a GM mechanic for 30+ years and he says he never saw one go bad and they actually used a wood block and hammer at the dealrship to put them on. He says he has seen the rubber go bad and seperate the balancer but not the thrust bearing go bad if the pistons and crank are already in.

PanelDeland · 07-10-2011, 03:19 PM

I don't hve the answer.I have never seen the threads be damaged by using the tool to install a HB.I will warn you to not drill the hole.1/2 taps do not thread holes drilled 1/2 nor do 7/16.There wilkl be a smnaller drikll size recommended for the tap.It may even be printed on the tap.

Wrenchbender Ret · 07-10-2011, 04:08 PM

I used to pound them on the old ones that weren't threaded & never damaged anything. Like Panel says ive have never had a problem pulling them on with the threads. Yours must have been almost pulled out to begin with. I agree with him about starting with the approprite drill size or you can get a Heila coil kit for the 7/16 size.

DeputyDan · 07-10-2011, 05:09 PM

hmm it was a harmonic balance install tool loaned from autozone. The end screwed into the threads then I screwed the nut looking thing against the balancer like the directions said and started to turn it. The balancer started to go on fine and when it neared bottom all of a sudden all tension was lost. I loosened the nut and went to unscrew the tool from the crank and it pulled out without screwing. I looked down and the threads from the crank were in the threads of the tool. Now a 7/16-20 screw will freely push in and out of the hole without having to screw. Can I just use a 7/16-20 tap without drilling out the old threads?

67_C-30 · 07-10-2011, 05:15 PM

Quote:

Originally Posted by DDixon1000

hmm it was a harmonic balance install tool loaned from autozone. The end screwed into the threads then I screwed the nut looking thing against the balancer like the directions said and started to turn it. The balancer started to go on fine and when it neared bottom all of a sudden all tension was lost. I loosened the nut and went to unscrew the tool from the crank and it pulled out without screwing. I looked down and the threads from the crank were in the threads of the tool. Now a 7/16-20 screw will freely push in and out of the hole without having to screw. Can I just use a 7/16-20 tap without drilling out the old threads?

No, you are going to have to use a 29/64" drill (.453") and then tp it with a 12 - 20 tap. 7/16 is .4375" so you still need to remove about .018" even if all your threads are gone.

EDIT: You will need a BBC crank bolt after you do that (I forgot to mention that!)

eightbanger · 07-10-2011, 05:39 PM

That is a pisser man sorry it went south on you.....It is one of those jobs like fitting a new center support on a drive shaft, yes you can hammer on these things...but! your gonna have to take your time think about how your going to tackle it, using a block of wood on anything you lump with a hammer is going to protect it and give an even spread from the impact. But it is also true that using the correct tool will always take the what if factor out and make things simpler...I used this tool the other day on mine and it worked a treat, came with four adapters to fit different cranks, did you have the adapter threaded in far enough to begin with?

DeputyDan · 07-10-2011, 07:44 PM

Quote:

Originally Posted by eightbanger

That is a pisser man sorry it went south on you.....It is one of those jobs like fitting a new center support on a drive shaft, yes you can hammer on these things...but! your gonna have to take your time think about how your going to tackle it, using a block of wood on anything you lump with a hammer is going to protect it and give an even spread from the impact. But it is also true that using the correct tool will always take the what if factor out and make things simpler...I used this tool the other day on mine and it worked a treat, came with four adapters to fit different cranks, did you have the adapter threaded in far enough to begin with?

That is the same tool I used I don't know what I did wrong but I took out all the threads. Crazy part is the crank should have been threaded ok as I had it machined along with the block. This engine hasn't even been turned over yet! My neighbor has a helicoil 7/16-20 kit would that still work even though my threads are pretty much gone? I am afraid to tackle the project now.

eightbanger · 07-10-2011, 08:03 PM

I'm thinking they damaged the threads in the end of the crank in the machining process...maybe?
I would go with what 67_C-30 has said...it's a pain in the ass for ya, but it's fixable, and yes don't for get the larger BB bolt.

Sammy · 07-10-2011, 09:30 PM

When I used that tool from Autozone I only went far enough to engage the bolt threads of what I thought was about 3. Then removed the tool. Installed the bolt looked up the torque. Torqued it to what the book said was good to go. No problems. If I ever do it again, I would go the same route. Nice n slow. Really sucks a big one to have FUBARRED those threads on a crank. I almost feel your pain.

DeputyDan · 07-10-2011, 11:11 PM

so I have to tap the hole a size bigger and use a BBC bolt or can I use a helicoil kit that is the current hole size 7/16-20 or is the hole too shot if I've lost the threads?

Pick · 07-11-2011, 06:03 AM

You can either use a heli-coil kit for a 7/16-20 and use the original sized bolt OR you can step it up to 1/2-20 and use a BBC bolt. Either one should give you a serviceable bolt hole as long as you're careful and make sure you drill and tap the hole straight.

Either way, you're going to need to drill the original hole up to size for the correct tap, so the easiest and cheapest would be to use the 1/2-20 and the new bolt as 67_C30 posted.

07-10-2011, 02:04 PM	#1
DeputyDan Registered User Join Date: Oct 2010 Location: Missouri Posts: 165	crappy day so I went to put a new harmonic balancer on using the "proper" tool and it tore the threads out of my crankshaft. I should have stuck to the old way of knocking it on with a hammer! Anyway to make a long story short I need to retap the crank and it has only a few threads left in it. What is the best way to go about this? I was thinking drill out the threads with a 1/2 bit then tap it for 1/2-20 as I believe 1/2-20 is the next size up. Or should I drill it out with a 7/16 (the OEM size) and try to retap it as a 7/16-20? Also has anyone ever seen a thrust bearing actually go out by tapping it on with a hammer? Reason I ask is because grandpa was a GM mechanic for 30+ years and he says he never saw one go bad and they actually used a wood block and hammer at the dealrship to put them on. He says he has seen the rubber go bad and seperate the balancer but not the thrust bearing go bad if the pistons and crank are already in.

07-10-2011, 03:19 PM	#2
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: crappy day I don't hve the answer.I have never seen the threads be damaged by using the tool to install a HB.I will warn you to not drill the hole.1/2 taps do not thread holes drilled 1/2 nor do 7/16.There wilkl be a smnaller drikll size recommended for the tap.It may even be printed on the tap. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

07-10-2011, 04:08 PM	#3
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,204	Re: crappy day I used to pound them on the old ones that weren't threaded & never damaged anything. Like Panel says ive have never had a problem pulling them on with the threads. Yours must have been almost pulled out to begin with. I agree with him about starting with the approprite drill size or you can get a Heila coil kit for the 7/16 size.

07-10-2011, 05:09 PM	#4
DeputyDan Registered User Join Date: Oct 2010 Location: Missouri Posts: 165	Re: crappy day hmm it was a harmonic balance install tool loaned from autozone. The end screwed into the threads then I screwed the nut looking thing against the balancer like the directions said and started to turn it. The balancer started to go on fine and when it neared bottom all of a sudden all tension was lost. I loosened the nut and went to unscrew the tool from the crank and it pulled out without screwing. I looked down and the threads from the crank were in the threads of the tool. Now a 7/16-20 screw will freely push in and out of the hole without having to screw. Can I just use a 7/16-20 tap without drilling out the old threads?

07-10-2011, 05:39 PM	#6
eightbanger 454 MAKES IT ROAR Join Date: Jan 2008 Location: Essex, U.K Posts: 2,701	Re: crappy day That is a pisser man sorry it went south on you.....It is one of those jobs like fitting a new center support on a drive shaft, yes you can hammer on these things...but! your gonna have to take your time think about how your going to tackle it, using a block of wood on anything you lump with a hammer is going to protect it and give an even spread from the impact. But it is also true that using the correct tool will always take the what if factor out and make things simpler...I used this tool the other day on mine and it worked a treat, came with four adapters to fit different cranks, did you have the adapter threaded in far enough to begin with? Attached Images __________________ Nigel. An American living in a British body. 1971 Chevy Cheyenne 10 454 "In a time of universal deceit, telling the truth becomes a revolutionary act." - George Orwell "When injustice becomes law, resistance becomes duty" - Thomas Jefferson No more pain. 03.12.60 -- 12.28.10 http://www.youtube.com/Eightbanger

07-10-2011, 08:03 PM	#8
eightbanger 454 MAKES IT ROAR Join Date: Jan 2008 Location: Essex, U.K Posts: 2,701	Re: crappy day I'm thinking they damaged the threads in the end of the crank in the machining process...maybe? I would go with what 67_C-30 has said...it's a pain in the ass for ya, but it's fixable, and yes don't for get the larger BB bolt. __________________ Nigel. An American living in a British body. 1971 Chevy Cheyenne 10 454 "In a time of universal deceit, telling the truth becomes a revolutionary act." - George Orwell "When injustice becomes law, resistance becomes duty" - Thomas Jefferson No more pain. 03.12.60 -- 12.28.10 http://www.youtube.com/Eightbanger

07-10-2011, 09:30 PM	#9
Sammy Registered User Join Date: Apr 2000 Location: Bonne Terre, Mo Posts: 3,005	Re: crappy day When I used that tool from Autozone I only went far enough to engage the bolt threads of what I thought was about 3. Then removed the tool. Installed the bolt looked up the torque. Torqued it to what the book said was good to go. No problems. If I ever do it again, I would go the same route. Nice n slow. Really sucks a big one to have FUBARRED those threads on a crank. I almost feel your pain. __________________ '69 Chevy Long Fleet & '71 GMC Short Step & Project "ODD BALL" "You can wash a pig, soak it in most expensive perfume. In the end it is still just a pig." ODD BALL build thread http://67-72chevytrucks.com/vboard/s...d.php?t=478629"

07-10-2011, 11:11 PM	#10
DeputyDan Registered User Join Date: Oct 2010 Location: Missouri Posts: 165	Re: crappy day so I have to tap the hole a size bigger and use a BBC bolt or can I use a helicoil kit that is the current hole size 7/16-20 or is the hole too shot if I've lost the threads?

07-11-2011, 06:03 AM	#11
Pick Registered User Join Date: Jun 2010 Location: Fayetteville, GA Posts: 214	Re: crappy day You can either use a heli-coil kit for a 7/16-20 and use the original sized bolt OR you can step it up to 1/2-20 and use a BBC bolt. Either one should give you a serviceable bolt hole as long as you're careful and make sure you drill and tap the hole straight. Either way, you're going to need to drill the original hole up to size for the correct tap, so the easiest and cheapest would be to use the 1/2-20 and the new bolt as 67_C30 posted.



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