Stripped SBC ( Gen I) Head Bolt Holes

Putting my heads on my 350 I stripped two of the head bolt holes.  Both were where the short bolts go next to the exhaust ports.  It would be an easy fix with timeserts or helicoils, but I don't think you can install those without taking the heads off and I don't want to take the heads off because I think more holes will be stripped when I put the heads back on.

I did see a post in another forum where someone suggested tapping the holes for 1/2 inch bolts and using some Oldsmobile 1/2 inch head bolts.  Has anyone ever tried this or does anyone know someone who has?

Thanks.  

Try running 7/16" NC tap down the hole.
If the threads further down are good, then go to a good hardware store and get a longer grade 8 bolt.
I have had success with this method before.  

Low11, the bolts run all the way through the holes so that there are no threads left that a longer bolt could grab.

Thanks.  

How about tapping it to the next metric size?
Make a stud then loctite and use a nut and washer.
Probably if you cut up a Helicoil installation tool you could get one installed.
You are going to have to flush the block so as not to have filings floating around the cooling system.  

Low11, thanks for the helicoil idea.  I will look at that.

As for the metric size, I looked at that idea, but the stripped hole is too big meaning I would only get about 50% thread contact.  That's why I'm looking at 1/2".  The other problem is that a standard nut will not fit into the bolt head area of the head.  The nut is too big.  But then the question in my mind is; I know some builders use studs so how do they get the nuts to fit in the bolt head machined areas of the head?  

if the other bolts are stripped when they were installed.. there will not be enough clamping force to stop the head gasket from blowing in the first few minutes of start up...    then you will be into that much more problem...

it is easiest to install multiple heli coils with the engine on an engine stand...     tape the  deck completely off with masking tape...   tape paper over the rest of the motor.. taping the edges down...

for double sure... after you tape off everything.. use duct tape over the masking tape..  the masking tape will pull off cleanly.. the duct tape stuck to the top of that makes it strong..  just over the decks

rotate and lock the block so the deck is vertical..   |   then you can drill  the head bolts holes that are stripped out completely .. and tap them oversize with the helicoil tap...  and get them straight in..  have someone watch from the side.. or use a level to adjust the motor on the stand... some power drills are factory equipped with levels..    most of the time.. i recommend. that tall helicoils are installed.. or in double deep.. put a paint mark on the side of the tap... and on the side of the installer tool..  that way you know how many turns you have gone in..

oh...   and if you put the medium length bolts in where the long ones go..  you might have only damaged the top few threads.. ...  run a tap it.. carefully...    there are 3 normal types of taps... a tapered tap has  very few threads on the end so it lines up in the hole well and cuts a little at a time..    a regular tap.. which has a short taper to get it in the hole...  and a bottoming tap... this has no taper.. it is almost as blunt as a bolt.. and is used with care to cut the last few threads in the bottom of a blind hole.. and are really easy to cross thread when used for thread cleaning.. but do a really great job at it...

warning... warning.. warning..   taps.. can also cut whats left of the threads out of the hole..  if the tap does not start straight and catch the threads properly.   disaster..  experience will help...

if the threads are damaged down more than one or two threads.. you might really think about putting in the heli coil...

the helicoil size is 7/16- 14...   you need to look at the package and buy a drill that matches ... shown on the top corner of the package...  get a good one.. 5 to 10 buck... and an extra package of heli coil inserts...

if you have a good industrial  hardware store... or a grainger.. store near by.. they may have the tall heli coil inserts...     it is also better to start the heli coil tap with a chuck type tap handle..  not a cross bar type.. unless you have some skills..  less chance of getting it crooked in my opinion..

and you want to follow instructions.. i knew of a shop who stripped the head bolts out of a benz 450 block...   they did not want to spend the money on the drill and tap jig..  they knew what they were doing.   and drilled and tapped them all perfectly straight..  except.. benz head bolts go in at a slight angle.. hence the reason for the drill and tap guide..    

oh.. i forgot...  buy some long 7/16 -14 bolts at the hardware store...    put them in near by head bolt holes when drilling and tapping.. as a reference.. so you can see if it is lining up properly...


best of luck...  

Wayne, thank you so much for taking the time to write the long reply and for your thoroughness.  I've copied and pasted what you wrote into a word document for future reference.

I'm still not sure what I'm going to do.  Because there are only two bolt holes stripped all the way through (one on each side of the engine) and because I read in some other forum about a guy who tapped the stripped holes for 1/2" bolts and used 1/2" Oldsmobile head bolts and it worked, the 1/2" head bolts are still a tempting alternative. But I'm still not sure.  It's a tough call.

So you know, my primary reason for starting this thread was to try to find someone who has used or heard about someone using the 1/2 bolts.  It seems reasonable to believe it will work and it can be done without removing the heads.  If I have to remove the heads I feel certain more holes will fail when the heads are reinstalled. Thus, if I have to remove the heads I'm just going to go out and get a new block.

Thanks again Wayne  

how much torque are you putting on the bolts? (60-65)  ft-lb. I dont know of a tap long enough to tap the hole with the heads on anyway. the heads will have to be removed to fix it no matter how you fix it.  

Chevelle, the bolts were torqued to 65#.  As for the tap length, the bolt holes that were stripped were where the short bolts go, which are just below the exhaust ports.

I've already tapped the holes for 1/2" - 13 bolts. It went extremely well and I was able to prevent most of the drill and tap chips from going into the block by greasing up the drill bits and tap with a heavy coat of grease. The minimal amount of chips that got into the water chambers came out when I flushed the block because they were coated in grease, which helped them to flow out.  I'm now waiting for the 12 point flanged bolts I've ordered.

Again, about the tap: Had I needed a longer than standard tap, they are available.