HT4100 4.1, 4.5, 4.9 Discussion, Stripped Head Bolt Threads in Cadillac Engine Technical Discussion; You can do it with the engine in the car.
Check out http://jadz.com/2007/01/24/cadillac-...sket/#more-431...
There is plenty of room to get tools in there to install inserts and so on? What about studs? Enough room, perhaps, for studs? I ask because I'm seriously considering dumping my '97 Eldo for a '89 to '91 Eldo because my Northstar has been such a pain in the a**. As nice a motor as it is I'm sick of the bull s**t I've put up with from it.
The factory manual for my '85 shows all the inserts, tools etc for repairing the stripped threads. Looks like it would be a real project to do a major overhaul on one of these engines, specially if it need a bunch of the holes fixed.
I've had the pleasure of having to throw heli coils into a 4.9 while still in the car. All the threads i had to fix were thankfully on the side closer to the radiator. I dont think you'd be able to repair any on the opposite side with the limited room back there. Getting the propper tools to get the job done, was the hardest part of the install. If i can remember correctly you have to drill out the threads with a 31/64 drill bit, then tap the threads with the appropriate tap, then use the insert tool to insert the heli coils. it honestly took me about 2 weeks to find all these tools. drill bits had to be bought online, a 9in 31/64th is non existent in any local hardware store. the tap and the insert tool were bought online as well. the insert tool i bought was a 4 inch long platic t-handle looking thing. so i had to cut off the handle, and ghetto fabricate a way to make it longer so that it could reach the threads deep in the block. finding half inch long helicoils took an entire week of calling every fastener shop in the state, and i had to buy a bag of fifty. its been about a year and a half since ive done this but i would be more than willing to give any advice to anyone who has to knock this out. in my personal opinion; id do it to every head bolt, because they are all extremely weak. im pretty sure i still have the tap tool, and plenty of heli coils for anyone who is interested. if you guys have any questions about the process, email me at firstname.lastname@example.org. ill post on here later the exact tools and sizes needed once i check my FSM. GOOD LUCK!!!!!
I helicoiled 2 head bolt holes on the back side of my 4.9 while the engine was still in the car with no problem. Yes getting the drill bit and tap extension were a pain to find. Note the the bolt holes that had the problem were on the rear head, but it was two of the upper holes (two of the 3 that call for the highest torque. I dont think the lower holes can be done inside the car.