Coolant Pipe Bolt Hole Stripped! 850 Topic is solved

[Dmck]

You should be able to buy a tap set for about $10 - or the specific tap for a few bucks. Don't give up on a proper repair so easily. You could blow a leak in a year and be out in the middle of no where. Just not worth it.

You just need to pull up the specs for the existing bolt and the proposed bolt. Take a look at this as a starting point:

https://en.wikipedia.org/wiki/List_of_d ... _tap_sizes

or this one -(Which sounds exactly like yours)

https://mechanics.stackexchange.com/que ... t-drilling

Drilling through the coolant pipe is pretty easy - just remove the gasket, tape up the hole and drill. If you have to borrow an angle drill or angle drill adapter (you can get these at Mendards) and you should be able to do it in car. A flexible shaft adapter would also be an option for drilling out the coolant pipe.

Thanks I will look into it. Not having an angle drill is what was holding me back from this.

This sounds like the best scenario. It would be great to not have to see the cylinders for a little while.

[SuperHerman]

I have something like this: https://www.harborfreight.com/38-in-90- ... 69337.html

Before buying make sure it will fit into your space. Mine has come in handy a number of times.

[Dmck]

I have something like this: https://www.harborfreight.com/38-in-90- ... 69337.html

Before buying make sure it will fit into your space. Mine has come in handy a number of times.

Thanks you so much! I can really visualize this now. That looks like it should fit either with a long enough bit or with an drill bit extension/holder. Also your other link answered the question about a clean stripped m7 hole is ripe for m8 tapping, but since I have to drill through the coolant pipe hole anyways I should just give it a good clean out.

So here is how I'm understanding it laid out

1) buy drill adapter that you linked (get drill bit extension if needed)

2) buy proper drill bits, your link says buy a 7.1mm drill bit for M8 x 1 tap (should I get an extra bit, a little larger diameter, to drill out the coolant pipe hole to be even bigger than the new head hole for easier tap?)

3) measure how deep the coolant pipe hole is, measure how deep the hole is into the head using the original bolt. Double check using a smaller drill bit, or thick wire.

4) mark the drill bits with a sharpie where the stopping points should be so I don't over/under drill

5) buy an m8 x 1.0 tap (most likely one that can fit onto a ratchet, because I need the extension and there is no space for the T handle?)

6) mark tap with sharpie for proper depth so I don't over tap and ruin everything or break tap in hole

7) buy proper m8 x 1.0 bolt with proper length (use original m7 bolt as guide for length)

bolt the sucker in and torque it down to spec


Am I missing anything here?

Also would you buy a new gasket for this? Getting the "old" gasket out and putting in a new one would be an undertaking of its own. I just put in the gasket on the rebuild.

Thanks so much SuperHerman!

[abscate]

Reuse the gasket from your new set, if it isn’t a compression type it will be fine.

Sometimes a day away from the crisis gives you new wind under your wings.

[SuperHerman]

I think your approach is solid. Couple of thoughts.

You can get different 90 degree drill adapters from most the major sources (Lowes, Harbor Freight ...) It appears some are even able to swivel in 5 degree increments. So shop where convenient and the price is right - a quick on line search may be fruitful.

For drilling the coolant pipe two items: 1) the hole only has to be slightly larger than the actual bolt going in, so see what you have on hand as far as drill bits (of course way too big is not ideal); and 2) I would try to reuse the gasket that is in place as it appears you sealed it to the pipe. Just put some masking tape over the coolant passage and on the bolt hole - and drill through it. Clean it up and see if it survived. If not you have answered your question.

How you want to approach the tapping of the stripped hole depends on how much you want to spend. From the articles I linked it looks like you can just tap the hole as is - best practice would be to drill to match the tap requirements (but again right now you are basically there). The thread pitch of the new bolt is also determinative of the hole needed.

Tap type - some are pointed tips and some are slightly tappered. A slightly tappered may allow you to get threading deeper. You will have to look at what is available - to be honest I don't think it really matters. From what I have read the top 4-5 threads do 80% or so of the gripping - plus you are going with a bigger bolt. Your approach of taping or sharpie marking the depth is smart. If you bottom out the tap it could strip the threads. Related to this - make sure you clean out the swarth every few turns as their build up can have the same effect as the swarth builds up on the bottom of the hole. You can use carb cleaner or air spray to clean it out every so often. I have used a vacuum cleaner. Use oil while doing the tapping. Tape up or cover any holes or places the small swarth may fall into if you don't use a vacuum cleaner.

I have turned taps in limited space with a 1/4 ratchet and a socket that accepts the square tap end. I don't recall which size fits - try an 8 point or a 32 point - one will accept the square tap.

Finally - make sure the tap goes in straight. Due to the limited space this may be tough. Using a pointed tip tap will help it go in straight.

Thinking it through and sourcing the items is most of the hard work. The rest will be pretty easy. Good luck.

[Clemens]

I might have missed that, maybe someone already suggested this, but what about a heli coil? Enlarge the hole so that a helicoil that will accept an M7 bolt.
That should work.

[SuperHerman]

Helicoil option discounted because OP doesn't want to pull head again.

[Clemens]

Sorry, I had a wrong idea of how the coolant pipe attaches. Taking the head off again is definitely something to avoid.

[JoebobNLacey]

When you're dealing with a dead-end hole, and presuming you don't have a lot of extra depth to play with, you should have two taps to do the job properly, if not three. The taper tap is the starting tap to get the threads started, and can be used to cut thread for as deep as the tap will go. There is a "plug tap" which is tapered some but not as much and will thread closer to the bottom of a hole. Thread as much of the hole as you can with the tapered tap or plug tap but be very careful not to jamb the end of that tap in the bottom of the hole or else you could damage the threads or worse yet, break off the tap (which is a nightmare to deal with--ain't gonna drill a broken tap out). The second tap you want is called a "bottom tap." It is not tapered. Its use is specifically for this application: once the threads on the top half of the hole have been cut with the tapered tap, the bottom tap follows those threads and the tip of the bottom tap can cut the threads all the way to the bottom of the hole.

[SuperHerman]

Joebob - Excellent information and advice. I learned something about tapping I didn't know. Thank you.