Head Bolt threads in block pulled out / stripped

[Chuck Leeper]

I pulled the top 3 or 4 threads out of one of the outer most holes.

These are the threads that carry 80% of the fastener load.. The threads further down, are almost "along for the ride".
Counter sinking the threads is a good idea, as it removes the problem w/ pulling the deck up, causing the gasket to leak....The LS engines are that way...

 

[ek02]

If Time Serts are used, be sure the machine shop has the fixture to drill and tap the block so the inserts go in perfectly square. If not, the head bolts or studs will not line up properly. They can not be installed freehand. The threads will be stronger with the inserts than before.

 

[84BuickGNYorkPA]

Thanks for the reply's, the machine shop said that they will buy the fixture so they have it for future projects. I believe that all threads in the block for the heads are at the end of there, life cycle or close to it. I can get the 7/16-14 Time Certs at many different lengths longer than the 1" length of the ARP stud engagement length, thinking of 1.5" length so that the base metal will have 50% more contact over stock to ease my mind of future thread failure.

Chuck,
The Buick blocks are countersunk for the head studs/bolts 1/2" from the factory, at least my two blocks are.

 

[Chuck Leeper]

Chuck,
The Buick blocks are countersunk for the head studs/bolts 1/2" from the factory, at least my two blocks are.

Now that you mention it, I do remember that... Been a while!

 

[84BuickGNYorkPA]

Ok, let's assume I go with the "Time-Cert" system

and knowing that the machine shop is generally slow as crap, thinking of doing it myself. Today I did a through inspection with my machinist tools and sent the information to the machine shop to get him engaged.
The base metal is on average 1.38" long for the top row of through holes (all holes go into the coolant cavity of the block, hence the reason to use thread sealer when installing studs or bolts for the heads) on both banks and the bottom holes are 1.87 average lengths, the clearance counterbores are .465 diameter x .56 deep (so .56 length of gripping power is given away). The ARP studs have .875" of full threads, if you measure with a scale it appears to be 1" long at 1st glance, but when you look close, it's 7/8" or .875 of full engagement. The hole that is stripped out has approx .435" of good metal below the stripped threads, not enough to entertain the thought of getting a longer stud IMHO.
So my thought process is to not use the install tool that pushes out the bottom threads of the insert to lock the insert, which I'm afraid may damage the thin wall of material the threads go through (what we in the machine shop would refer to as an internal Boss). But to rather buy the longer inserts and just lock tight them in with the permanent 271 "red" Loctite, which would eliminate the need to expand the bottom threads of the inserts to lock them in place and I would gain some surface area over the 7/8" length of the ARP stud engagement in the cast iron material.

Chuck

 

[Jerryl]

Have you considered helicoil repair?

 

[ek02]

Trust me on this, if you do not get the Time Sert inserts perfectly square to the block, your studs will be way off and the head will not go on. The Time Sert kits that come with a plate that bolts to the block are expensive, and you may have to adapt one for a V6. The tap guide sold for a big block Chevy's 7/16-14 thread fits in a hole in the plate. You cannot hold the tap guide square to the block by hand. The stud will be crooked. It also helps if you can find a drill bushing to fit in the tap guide with an ID the size of the drill bit and an OD that will fit in the tap guide, or if you can find someone with a magnetic drill that sits flat on the deck to drill the hole out. A little off at the insert turns out to be way off at the top of the stud.

 

[84BuickGNYorkPA]

Yes, I have access to a magnetic drill press, I just bought (16) 1.5" long Time-Serts and the special 7/16-14 STI tap. I also have all drill sizes in 1/64 increments up to 1". The plan is to rotate the engine in the engine stand so the work surface is flat, easy since it's already on the stand. Insert an ARP stud in the stripped hole, line up the mag drill to the stud (clamp to the stud and turn the magnet on). Take out the stud, put the 29/64 drill in and drill through, put the STI 7/16-14 tap in and tap through. Now I have to mic the head of the time-sert and drill that diameter down .5 deep so it clears or grind the outside diameter to clear the factory counterbore. Then clean the hole and "Time-Sert" with electric cleaner and an air hose, put some permanent "red" Loctite in and turn the insert in with an ARP stud, done. At that time, I will put the head on and decide if I want to do all the holes or not.

Chuck

 

[ek02]

Sounds like you have a really good plan using the magnetic drill press. I'm sure you know to use tap fluid. You can check the stud with a small square in all directions and the head should go on.

 

[FASTV6HENRY]

Situations like this is why i try to convince my wife that i need to buy a Bridgeport.

 

[bison]

A magnetic drill press would work but you'd still need to verify its 100% square to the deck before drilling. I'd rec a 1" plate with a drill bushing installed and located by at least 2 other holes on the deck .


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[Pronto]

Maybe the kit for the Cadillac Northstar could be adapted?

 

[84BuickGNYorkPA]

There is little chance the drill will not follow the existing hole as this is the path of least resistance. However, if the drill is not perpendicular (square) to the surface, and in true position, I can get an over-size hole for the minor diameter of the special STI Tap. The tap is to be delivered Monday and the Time-Serts today, so this morning I'm going to visit some local garages and ask to borrow a 7/16-14 STI tap (I've been checking around and nobody is willing to lend it out or they don't have one). If I'm successful then I can go to my employer and borrow the mag drill from the machine shop. I'll be flat filing the base to make sure there is no raised metal, I don't need to scratch the deck of the block. I also have a spring center and plan on hand tapping the threads. Cast iron machines like butter compared to carbon or stainless materials.
Bison,
It would be nice to have a fixture made up for the "Time-Sert" or "Heli-Coil" (both same drill and tap size for inserts) thread repair systems, if you don't have a mag drill, this would allow you to use a hand held drill and get the job done as the bushing that would fit between the fixture and drill will keep is perpendicular to the surface and on true position.
Chuck

 

[bison]

I drilled a hole with a mag drill last night. With the length of the drill and the stack up of slop in everything id still want a drill bushing for a very accurate drilling. even with an existing hole it's possible for a little error. There's no room for error if using studs. A few thousandths in drilling error will be magnified at the end of the studs. Drilling oil drain back without removing front cover. Wasn't my assembly and didn't want to open it in any way.

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[bison]

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[ek02]

I modified a plate from a Time Sert kit cheap on E-Bay. It bolts to the block with 3 bolts and the tap guide sits in a hole with a tight fit. I center it over the bolt hole with a 7/16-14 bolt with a shoulder the same size as the ID of the tap guide. I install a drill bushing in the tap guide and drill out the hole. The plate is removed and the countersink tool is used. The plate goes back on lined up to the hole with the drill bit. The tap is used with the tap guide in the plate. Then I install the Time Sert with the red Lock Tite supplied with the kit. The stud is square to the block with this method. I tried it free hand at first using the head as a drill guide and then holding the tap guide by hand and the studs were way off and the head would not go on. The 4.1 block had some bad cracks anyway, so time for another block. Drilling the hole straight is critical and so is having the tap go in perfectly square.

 

[84BuickGNYorkPA]

Everything went perfect, here are a few pictures.

Bison,

The pipe tap needed for the block will make you work for the threads, they don't turn easy. I always used a center (I have a spring loaded one) to keep the tap straight also.

 

[ijames]

Chuck & Chuck, you were both half right on the recessed threads - 84-85's were not recessed, with the threads starting at the deck surface so they were prone to lifting the top thread a bit and leaving a high ring around the head bolt hole that reduced gasket seal. The 86-87's were recessed to stop this. Glad you got this worked out, Chuck; hopefully this will be your last "trial". As for thread strength, the outer circumference of the insert is about 25% greater than the 7/16-14 threads, so for the same thread engagement length there is 25% more material taking the load.

 

[84BuickGNYorkPA]

Chuck & Chuck, you were both half right on the recessed threads - 84-85's were not recessed, with the threads starting at the deck surface so they were prone to lifting the top thread a bit and leaving a high ring around the head bolt hole that reduced gasket seal. The 86-87's were recessed to stop this. Glad you got this worked out, Chuck; hopefully this will be your last "trial". As for thread strength, the outer circumference of the insert is about 25% greater than the 7/16-14 threads, so for the same thread engagement length there is 25% more material taking the load.

Yes well I have a 87 motor/drivetrain in the car, the hot air has been gone for 6 years now.