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Coolant Pipe Bolt Hole Stripped! 850 Topic is solved

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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Dmck
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Coolant Pipe Bolt Hole Stripped! 850

Post by Dmck » Thu Jul 05, 2018 2:24 pm

Man am I screwed, or should I say I wish I could screw!

So after a full head gasket job on volvo 850, the last bolt I put in, I managed to strip the lower bolt hole of the coolant pipe on the back of the head next to the exhaust. It just spins and spins! I think I cross threaded it and mashed the threads.

Is there any possible bolt replacement that has slightly larger thread than the M7 x 1 that goes into the coolant pipe hole?

has anyone done this and found a fix that doesn't require complete tear down and a helicoil or similar? What a mess!



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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by MDK » Thu Jul 05, 2018 4:03 pm

I wouldn't worry about it too much. Get some high temperature tape and wrap the bolt and put some lock tight in the hole. Or find the American equivalent next size up,...



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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by SuperHerman » Thu Jul 05, 2018 5:44 pm

As you can kill your engine with a coolant leak I would fix it right. How much space do you have to get a tap in there?

As MDK suggests using an American equivalent may be an option. You need to see what the biggest bolt you can get into coolant pipe is or better yet enlarge the coolant pipe hole before installing it - then pick your bolt size. Make sure what ever size you pick - the bolt head can be seated all the way down without interfering with the pipe. You may have to switch to an allen or torx head here.

Visualize and dry fit the scenario before electing any approach. Right now is the time to think everything through.

Measure the depth of the current hole and the length of the current bolt. If the replacement bolt is too long it will strip out the head threads(this could have been your original issue).

Just measure the depth and take your time. The tap should go in straight without much issue. Due to limited space it may take a little longer. Clean out the hole with some carb cleaner or equivalent.



Dmck
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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by Dmck » Thu Jul 05, 2018 6:08 pm

I went and got a few different bolts

Some m7, m8, and 5/16th (7.9mm)

If you were to clean strip a 7mm hole does that mean it is ready to tap to 8mm?

I will see how deep hole is and do some testing and go buy the tap.

has anyone ever just bolted in an 8mm into a stripped 7mm hole with now tap?

It looks like Home Depot here has a lot more options for 5/16 taps..

Is there any reason to not make it a 5/16 hole over an 8mm
Last edited by Dmck on Thu Jul 05, 2018 6:14 pm, edited 1 time in total.



Dmck
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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by Dmck » Thu Jul 05, 2018 6:10 pm

SuperHerman wrote:
Thu Jul 05, 2018 5:44 pm
As you can kill your engine with a coolant leak I would fix it right. How much space do you have to get a tap in there?

As MDK suggests using an American equivalent may be an option. You need to see what the biggest bolt you can get into coolant pipe is or better yet enlarge the coolant pipe hole before installing it - then pick your bolt size. Make sure what ever size you pick - the bolt head can be seated all the way down without interfering with the pipe. You may have to switch to an allen or torx head here.

Visualize and dry fit the scenario before electing any approach. Right now is the time to think everything through.

Measure the depth of the current hole and the length of the current bolt. If the replacement bolt is too long it will strip out the head threads(this could have been your original issue).

Just measure the depth and take your time. The tap should go in straight without much issue. Due to limited space it may take a little longer. Clean out the hole with some carb cleaner or equivalent.
There is a pathetic amount of space to work with but if I can put a bolt in I can tap it I would think. Hopefully the coolant pipe itself can support and 8mm or 5/16th bolt



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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by SuperHerman » Thu Jul 05, 2018 6:25 pm

I don't know the answer to your question about "clean strip", but if one looks up the specs of the bolts they will find the answer. I have never looked at the question from your question perspective, but I have looked up specs and seen cross sections and measurements for the various bolts. The piece of information I would imagine is relevant is the thread depth and dimensions.

I have mangled larger bolts into ATVs in the past, only to regret the move and have to retap and helicoil later.

I am not sure you understand my coolant pipe clearance - it may be a non-issue. On my turbo return line I was thinking of swapping the torx head to a 10mm head, but it will not work as the head will hit the pipe line (too wide). Not sure on your coolant pipe you may have plenty of space between flange holes and the pipe. What ever bolt size you elect to use - dry fit and enlarge as necessary the coolant pipe hole and the gasket hole.



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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by Dmck » Thu Jul 05, 2018 7:31 pm

SuperHerman wrote:
Thu Jul 05, 2018 6:25 pm
I don't know the answer to your question about "clean strip", but if one looks up the specs of the bolts they will find the answer. I have never looked at the question from your question perspective, but I have looked up specs and seen cross sections and measurements for the various bolts. The piece of information I would imagine is relevant is the thread depth and dimensions.

I have mangled larger bolts into ATVs in the past, only to regret the move and have to retap and helicoil later.

I am not sure you understand my coolant pipe clearance - it may be a non-issue. On my turbo return line I was thinking of swapping the torx head to a 10mm head, but it will not work as the head will hit the pipe line (too wide). Not sure on your coolant pipe you may have plenty of space between flange holes and the pipe. What ever bolt size you elect to use - dry fit and enlarge as necessary the coolant pipe hole and the gasket hole.
It looks like I am majorly screwed. The coolant pipe hole that you go through to bolt it down is too small to take an 8mm or a 5/16th. To fix this problem I am either going to have to remove the coolant pipe and drill the hole bigger in it, then tap the hole in the head, or remove the head, OR drill through both and hope I line it up right (not worth it)... my only true/safe option it to start completely over and do a full head gasket job.

I'm going to try the idea with tape above before I throw in the towel for a few days and do the whole job over. This is my car so I'm not on a deadline.

luckily I have my t-5r as my backup, but I don't like that being my dependent daily driver car.

Once I get back to having the head off I'll start recording the process in this thread so if any sorry sob does what I do they will see what is needed.

Doh!
IMG_0311.JPG
IMG_0231.JPG
IMG_0233.JPG
And what I will need to drill bigger once back down to the block.
IMG_0235.JPG
You do not have the required permissions to view the files attached to this post.



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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by JimBee » Thu Jul 05, 2018 9:08 pm

I ran into a similar problem on my 855 turbo. I think at factory assembly those bolts are dipped in a heavy sealant / locker type stuff. After you remove the bolt, a lot of that stuff remains in the bolt hole, so when you reinstall the bolt you run into it. The hole is effectively too short to bottom out the bolt head firmly enough on the flange to get a good water seal.

I got the tap for the factory bolt but had to borrow a driver chuck from the local shop to run the tap in to clean out the threads. The tap wasn't square cut at the end, it was tapered, so I still couldn't clean out the hole to its original depth. Rather than risk what you did, after cleaning the threads as well as I could, I "shortened" the bolt with a couple of flat washers and gently torqued it tight enough so it doesn't leak.
I feel your pain.
BTW: if you drop the pan to do your oil pickup o-rings (while you're in there) watch out for that same problem on the pan bolts. Clean out those holes with your tap as well, especially the long bolts by the rear main.



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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by Dmck » Thu Jul 05, 2018 9:35 pm

JimBee wrote:
Thu Jul 05, 2018 9:08 pm
I ran into a similar problem on my 855 turbo. I think at factory assembly those bolts are dipped in a heavy sealant / locker type stuff. After you remove the bolt, a lot of that stuff remains in the bolt hole, so when you reinstall the bolt you run into it. The hole is effectively too short to bottom out the bolt head firmly enough on the flange to get a good water seal.

I got the tap for the factory bolt but had to borrow a driver chuck from the local shop to run the tap in to clean out the threads. The tap wasn't square cut at the end, it was tapered, so I still couldn't clean out the hole to its original depth. Rather than risk what you did, after cleaning the threads as well as I could, I "shortened" the bolt with a couple of flat washers and gently torqued it tight enough so it doesn't leak.
I feel your pain.
BTW: if you drop the pan to do your oil pickup o-rings (while you're in there) watch out for that same problem on the pan bolts. Clean out those holes with your tap as well, especially the long bolts by the rear main.
Thanks for the oil pan tip.

I realize if I pull the head I don't have to drill the coolant pipe hole and just have to helicoil the hole in the head back to fit the original m7 x 1. So at least there is that!

I have also never worked with helicoil so ill get some practice in.



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Re: Coolant Pipe Bolt Hole Stripped! 850

Post by SuperHerman » Thu Jul 05, 2018 9:54 pm

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.



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