What Tap for the CrankShaft Balancer Bolt

I have extracted a broken bolt out of the crankshaft. This is the Balancer Bolt that holds the Harmonic Balancer in place. I was trying to determine the proper tap that I need to use to clean the thread out. I have figured out it is an M16 Tap but am not sure whether it is 1, 1.5, or 2. I have looked everywhere and can not find any information online about what this is. The dealership of course wont help. Im gonna try and contact 800 GM TOOLS on Monday and will post the information if they know it. Otherwise im hoping someone on here might definitively know what the correct tap to use is....

I'm pretty sure it is 1.5.
I would look at ARP's web site for a replacement bolt and see what the thread is that is listed.

Thanks! I will look into it and post a confirmation either way to try and help other people who may run into this. I appreciate you taking the time to answer me. Does anyone know where to get custom interior products for the 98-02 F-Body. I wanted to do something neat and custom with the dash so that it could be blue or any other custom color. Doesnt seem like there is anyone prominent in the market that has custom products for looks like these.

I wish I could be some assistance, but I only have spare bolts sitting around if you want a measurement.


Mind me asking how you broke it? Not starting anything, just curious. I put everything I had into it and had no issues. And I am no little guy.
Did you maybe re-use a bolt or something?



EDIT: I take that back.
Highly Recommended: Longer crankshaft pulley bolt, M16 x 2.0 pitch x 120mm long...this is not the stock size, but it is the same other than length.
www.ls1howto.com

Here is what happened....

First of all I made a bad purchase when I got this car and trusted that the previous owner had done all his installation work properly. Since owning the car ive had nothing but problems and have had the car 4 months and driven it about 2 weeks. First I ended up rebuilding the transmission which wasnt too hard. Got a kit from www.danddperformance.com

For the life of me I couldnt bleed the system so I took it to a GM Goodwrench shop. THe guy there had trouble bleeding it also but was able to get it done. I had experienced people that tried to bleed it and couldnt. Its easy to point fingers here but I think design flaws in the stock master or slave must have been the culprit. Anyway when I got my car back the dealership told me that it would shake violently over 90MPH. They ripped me off charging $200 to rebuild the driveshaft which I requested. Now this was done and then the vibration problem occured. I noticed that they had definitely put the driveshaft in a vice because there were two dents offset by 180 degrees. I then had that rebuilt at a shop that cut the entire driveshaft and welded a new one on AND rebuilt the bearings for $160. Anyway I know im getting off subject but I finally have people that I can talk about this with. My girlfriend probably could give two hoots about this stuff, (;.

The Harmonic Balancer was an underdrive ASP performance part with an aftermarket Balancer Bolt. While I was driving one day I started to lose battery voltage (it was erratic, charging full and then draining and then charging again. I also quickly started losing Oil Pressure and in a 5 minute span of driving on the highway I had 0 Oil Pressure. I got my car safely home and noticed the underdrive pulley was loose. The belt was riding over the alternator in a way that explained the battery voltage problems. At that point I realized I would have to take out the harmonic balancer. I purchased a breaker bar because after locking up the flywheel in my own custom way I broke a 1/2 inch drive ratchet because there was so much force on trying to loosen that bolt. I sprayed Zepreserve on the inner part of the bolt in a hope to free it up a bit. It took my hands around the passenger tire and two feet pressing against the breaker bar with all my strength and the bolt started to turn very slightly. It was unfreaking believeable how much force this was taking and it was obvious this bolt was seized in there. I got the bolt to turn about 2 -3 full revolutions and then it snapped. Now at that point I ended up trying to use an extractor to get the bolt out and that snapped inside the broken bolt. Final solution was to drill a small hole in the center of the balancer bolt and working up one size up until 1/2 inch. Eventually when the outershell of the balancer bolt was very thin I revved the drill at full speed and cracked the remainder of the bolt out of the thread. After looking inside the shaft I noticed a small piece in there which I used a pick to get out. After that I used an Earth Magnet to get out all the debris inside the thread. Now the thread looks pretty good and im relieved that it can definitely be saved. I have the balancer bolt that broke and had purchased a new SLP underdrive pulley with balancer bolt. It came with a GM Bolt that is factory. The GM Bolt looks ugly and costs $4 but my impression is that it is the best bolt to use. THe guy that installed the aftermarket pulley used a different style bolt that looks really nice but unfortunately was installed wrong. Furthermore that aftermarket bolt has some type of coat on it that I feel may have contributed to the bolt seizing. Anyway I have been very unlucky with this purchase but I feel that after I fix this I will have corrected most of the screw ups that the previous owner had done to the car. I havent listed most of the problems ive had. Little things like a very loud bang when I hit bumps which I found was due to the transmission mount bolt not being tightened. Not only was it not tightened. It was halfway down the thread. THe guy that had this before was a real piece of work. Anyway I love the car. Looks just like the one you have. Its black, Z06 rims, WS6, blah, blah...

You guys were both very helpful. It is an M16 X 2.0. I alreay have the new ARP Bolt here but I didnt know how to check it. I gave it to my brother and he told me he didnt have the tool to measure the pitch but he coult tell it was an M16 Tap. I can confirm that it is what I have listed below. I bought my bolt from Thunder Racing along with the new SLP Underdrive pulley. They didnt have the specs listed but ARP did have them listed. That information is below.


LS1 & LS6 Gen III 4.8,
5.3 and 6.0L
1-1/16 M16 x 2.0

Make yourself an install tool. It'll keep you from yanking the threads putting it on with the bolt. A lot of people just use the bolt to pull the pulley on with but it wasn't a risk I was willing to take. Go to a good hardware store and buy some m16 x 2.0 pitch metric all thread with 3 bolts and a bunch of washers. Thread the all thread into the crack and slide your pulley on and put the washer stack on then hold the bolts on the end to keep the all thread from turning and push it on with the other bolt. Much safer and cheap to make.

NO PROBLEM GLAD WE COULD HELP!!:cheers:

Orion is also right about using a installer. When installing make sure to use antiseize to prevent gulling.
Afterwards you can clean threads out with brake clean and install new bolt with RED locktite and tq to spec with a GOOD tq wrench NOT a swap meet lou.

Oh yeah. I know its overkill to spend tons of money when you dont have too but I sprung and got the recommended J-41665 GM Tool to install it. The install seems rather easy. You have to torque it on there to 240 ft lbs. with the used bolt. Then you remove that bolt and put in the new bolt and torque it to 40 ft lbs. After that you are supposed to use a torque angle wrench to turn the bolt 120 degrees. I opted not to spend $1200 for that through GM TOOLS. That is ridiculous. For that I will estimate 120 degrees. I really put alot of research into making sure I do it by the book because it was such a pain in the butt to go through what I did that I never want it to happen again. I did plan on cleaning that out really good inside and using locktite also. No one should go through what I did. WHat a pain in the butt. Im feeling like im getting close to having this baby run again.

P.S. - I got the 2007 GM Performance Parts manual and I was reading that they put those complete drop in motors through 300 straight hours at maximum RPM/Torque. That is freaking nuts. A pretty good indicator why these are popular motors to play with.