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For various reasons i need to get a thread chaser and tap for the crank on a 2000 (as far as i can tell W Code) 4.3L, and a new crank bolt, Pretty much whats on the tin really, i need the specs for thread type, depth and size, and in the case of the bolt its grade and size.
First we have to make sure we know which thread you are talking about.
The cranks in the 4.3 V6 have different locations with threads.
There is the thread in the nose of the crank (front) which holds the pulley onto the nose.
There are the threads in the rear flange of the crank where the flywheel or flexplate is mounted.
First we have to make sure we know which thread you are talking about.
The cranks in the 4.3 V6 have different locations with threads.
There is the thread in the nose of the crank (front) which holds the pulley onto the nose.
There are the threads in the rear flange of the crank where the flywheel or flexplate is mounted.
I Should have specified Crank snout, if it was a flywheel bolt i'd be in much bigger trouble.
Stock crank bolt is 7/16-20 x 2.25 grade 8 - so there is your bolt and tap size.
For replacement might as well just buy an aftermarket one with washer for a SBC, rather than going to a hardware store for it.
Hint...... IMHO an even better strategy than just cleaning up the threads and replacing the bolt...... The original bolt doesn't use all the threads in the crankshaft, and the crank bolt hole is usually significantly deeper than the damaged area, so a longer bolt may work fine to get some bolt screwed into some undamaged original threads (after you straighten up the damaged ones with the tap). Afterwards flush out the metal shavings with spray cleaner and a plastic nozzle placed as deep as possible into the bolt hole - yes this will be messy, but blow all of those little particles out - dry with compressed air and then oil liberally. Be careful to measure how much depth you have available in the bolt hole before trying this and don't bottom out the bolt. Use a 2.5" or 2.75" long bolt, depending on the depth of the hole (longer is more original threads engaged if you can make it fit). You can screw the bolt in without the washer and see where it bottoms out as a final check.
Stock crank bolt is 7/16-20 x 2.25 grade 8 - so there is your bolt and tap size.
For replacement might as well just buy an aftermarket one with washer for a SBC, rather than going to a hardware store for it.
Hint...... IMHO an even better strategy than just cleaning up the threads and replacing the bolt...... The original bolt doesn't use all the threads in the crankshaft, and the crank bolt hole is usually significantly deeper than the damaged area, so a longer bolt may work fine to get some bolt screwed into some undamaged original threads (after you straighten up the damaged ones with the tap). Afterwards flush out the metal shavings with spray cleaner and a plastic nozzle placed as deep as possible into the bolt hole - yes this will be messy, but blow all of those little particles out - dry with compressed air and then oil liberally. Be careful to measure how much depth you have available in the bolt hole before trying this and don't bottom out the bolt. Use a 2.5" or 2.75" long bolt, depending on the depth of the hole (longer is more original threads engaged if you can make it fit). You can screw the bolt in without the washer and see where it bottoms out as a final check.
Good luck either way.
Should probably include a bit of info on the damage
The last person who worked on this motor was on some type of drugs, had to have been because they used JBweld on the bolt and then forced it in, im not even sure if a tap will do this right and i may end up having to ream the center out for the next size up of the same grade, Any tips for removing JBweld without damaging anything? (any worse then it already is). Going to go with a 2 1/2" bolt from McMaster, its effectively the only thing keeping it from running at this point.
Should probably include a bit of info on the damage
The last person who worked on this motor was on some type of drugs, had to have been because they used JBweld on the bolt and then forced it in, im not even sure if a tap will do this right and i may end up having to ream the center out for the next size up of the same grade, Any tips for removing JBweld without damaging anything? (any worse then it already is). Going to go with a 2 1/2" bolt from McMaster, its effectively the only thing keeping it from running at this point.
You do know that you don't "really" need that bolt. The interference fit will keep the balancer on, and the pulleys have their own. Some SBCs in the 1960s actually didn't have this crankshaft bolt. Only thing is if you need to pull the balancer back on the snout of the crankshaft without beating it on...... Using the bolt (instead of a proper puller tool that screws all the way into the threads from the start) to try to pull it back on is how the threads usually get stripped.
I would think the tap is about the only thing that would clean out JB weld, so you might just try drilling the center slightly undersize (same size that you would for tapping new 7/16-20 threads) and use the tap to clean it up. You can always go bigger size.
Don't forget the size I quoted was using the thick factory washer under the head of the bolt. If the outer threads are very damaged, you may want to go with a 2 3/4 to try and get 1/2" of good original threads past where the original bolt reached. I would have one of each bolt on hand when I did this job - but then again I would probably not put the bolt in and just run it as-is, if the balancer is still on the engine and is fully seated. Whatever you do, don't beat a balancer back on the crank snout with a BFH.
You do know that you don't "really" need that bolt. The interference fit will keep the balancer on, and the pulleys have their own bolts. Some SBCs in the 1960s actually didn't have this bolt. Only thing is if you need to pull the balancer back on the snout of the crankshaft without beating it on...... Using the bolt (instead of a proper puller tool that screws all the way into the threads from the start) to try to pull it back on, is how the threads usually get stripped.
I would think the tap is about the only thing that would clean out JB weld, so you might just try drilling the center slightly undersize (like you was tapping a new hole) and use the tap to clean it up. You can always go bigger.
Don't forget the size I quoted was using the thick factory washer under the head of the bolt.
Good luck and let us know how you come out!
For peace of mind reasons i'd like to have it on there anyways, and one way or another im chasing the threads on the crank to install it balancer so i may as well go all out and get it back to a semi-OE state. If i get it running i'll be sure to post a link to her first run.
Picked up a tap and some bolts from Ace today, cover is installed and the balancer is on, Thanks for the help folks, while installing the balancer the motor turned over until it bounced off Number 2 which still has its plug in, heat shielding is warped so i cant get a socket on it.
When would it be appropriate to start a build thread?
Picked up a tap and some bolts from Ace today, cover is installed and the balancer is on, Thanks for the help folks, while installing the balancer the motor turned over until it bounced off Number 2 which still has its plug in, heat shielding is warped so i cant get a socket on it.
When would it be appropriate to start a build thread?
12-22-2019, 09:30 AM
2000's 4.3L/W Crank Bolt thread count/type
