BillGrissom
Well-Known Member
Two of the 5/16-18 threads in my harmonic balancer were stripped. This describes a cheap repair. Metal inserts are only $0.70 at Ace Hardware, but you must buy the $20 special tap, often not in stock. I found a better approach.
Ace carries STI brand, as does Autozone (recall). I still recall the hurt of a $30 Heli-coil kit to fix a 1/2" tranny thread in 1980's dollars. For another stripped 1/2" thread I am set, but who can afford a kit for every size. The Autozone guy helped me determine an M10-1.5 thread is real close to the insert's OD. Of course, the manufacturer doesn't tell you that. I splurged on Harbor Freight's 45-pc metric nitride tap & die set ($65 sale). Not sure why I didn't have a metric set since 4 of my 6 cars are metric, maybe I do and didn't find it. Anyway, redundant tools are handed down to my boys (the cheap stuff).
For the metric thread, ideally drill 21/64". I used 11/32", which worked. Best to not tap all the way thru, so the insert bottoms out and can't screw thru. Loctite might help. Ideally, you get the special insert tool. On the first hole, I used needle nose pliers, but the tab broke off with 1 thread exposed. I was able to get it in w/ a 5/16-18 tap (grabbed the end). I got wiser and cut a slot in a 1/4" bolt for a homemade tool that looks like Heli-coil's plastic ones (sitting on K-frame in photo). After inserting flush, you can push in to snap off the tab, but better to use needle nose pliers and recover the tab so it doesn't wind up in your engine.
For those wondering about my engine build, this is a 1965 273. I switched to the aluminum water pump, which opened a can of worms on pulleys and accessories, especially since I rebuilt the TRW PS pump (recent revelation, thought a Federal) and found they never made brackets for the alum pump. I currently have the thin motor mounts, but haven't found if the oil pan and steering link will clear. I recently got original ones 1" thicker, which may interfere with the brake booster I will add or the magnum intake I plan to later try.
Ace carries STI brand, as does Autozone (recall). I still recall the hurt of a $30 Heli-coil kit to fix a 1/2" tranny thread in 1980's dollars. For another stripped 1/2" thread I am set, but who can afford a kit for every size. The Autozone guy helped me determine an M10-1.5 thread is real close to the insert's OD. Of course, the manufacturer doesn't tell you that. I splurged on Harbor Freight's 45-pc metric nitride tap & die set ($65 sale). Not sure why I didn't have a metric set since 4 of my 6 cars are metric, maybe I do and didn't find it. Anyway, redundant tools are handed down to my boys (the cheap stuff).
For the metric thread, ideally drill 21/64". I used 11/32", which worked. Best to not tap all the way thru, so the insert bottoms out and can't screw thru. Loctite might help. Ideally, you get the special insert tool. On the first hole, I used needle nose pliers, but the tab broke off with 1 thread exposed. I was able to get it in w/ a 5/16-18 tap (grabbed the end). I got wiser and cut a slot in a 1/4" bolt for a homemade tool that looks like Heli-coil's plastic ones (sitting on K-frame in photo). After inserting flush, you can push in to snap off the tab, but better to use needle nose pliers and recover the tab so it doesn't wind up in your engine.
For those wondering about my engine build, this is a 1965 273. I switched to the aluminum water pump, which opened a can of worms on pulleys and accessories, especially since I rebuilt the TRW PS pump (recent revelation, thought a Federal) and found they never made brackets for the alum pump. I currently have the thin motor mounts, but haven't found if the oil pan and steering link will clear. I recently got original ones 1" thicker, which may interfere with the brake booster I will add or the magnum intake I plan to later try.
