Exhaust bolt hole not only stripped, but almost completely destroyed by PO

[roeme]

So, when I took off my exhausts in order to change the oil pan the other day, I got a funny feeling about a PO bodge:



I don't have too many pictures from unmounting everything, so I have to use a bit of text here. Later pictures will help understand what's going on though.

All bolts came out without fuss. The nut used on the #2 collar was very loose, and not putting any force on the collar. The only reason I didn't vibrate off is because it's a nylon locknut.

After sucessfully removing the exhaust, I found the bolt hole around the stud you see in above image almost completely gone. The stud was hanging on to only a few threads of a helicoil in there, whose existance I only discovered later on. The stud could be easily moved sideways by hand, with obscene play. So I removed it carefully.

When I put everything back on, I used new stainless bolts, and torqued them to spec, erring on the lower end of the specification (methinks it was around 1-1.6 kg⋅m), making sure that the threads matched up good. When it came to the the bad hole, I made sure the new bolt did find thread, and began to carefully screw it in, only by finger force at first, and then using a small wrench lightly.

Snap.

Helicoil disintegrated:


State of the hole:


Needless to say, I was frustrated beyond any measure at this point.

How the hell does one f$!ck up an exhaust bolt hole this badly? How much of a kludge must one be? I wished the responsible PO's bloodline to dry out, and other non-printable cussing.

Timeout.



Comparing the used stud to a regular bolt:


gave me the idea that the helicoil was further in to begin with, and that the shorter bolt only grabbed to an exposed part of the helicoil. So I tried to reuse the stud, but no dice.

Well, the good thing is that the re-drilled hole doesn't seem to penetrate all the way into the block.

After calming down enough and getting over my frustration, I fastened the collar enough with the remaining bolt in order to be able to get home:


It worked, I got only very minor blow-by. I think. At this point it was cold, dark outside and I just wanted to get home, get my mind off things.

You'll notice that I reused the fat spacer PO used on the stud. Reason was that I found the bolt hitting spec torque way before holding the collar. That could be either due to the now slanted position of the collar, or that the factory drilled the holes on #2 badly. I'm leaning towards the latter, it would also give some explanation to PO's screw-up.

After pondering this for a while now and winning a bit of motivation back, I think I getting a time-sert in there, with something "lock-tite-ey" (not sure what would stand up to the heat there) could be a viable option. Welding would be better, but as far as I understand welding aluminium is very challenging.

Other than that, I can't think of anything else short of disassembling the engine and swapping the head. But as far as I understand, that's a delicate operation, I have never done it before, and I don't think I'm properly equipped.

Your thoughts?

 

[Cipher]

its ugly but appears to work.
Did they use an over sized bolt to replace a stripped out hole?

 

[roeme]

its ugly but appears to work.
Did they use an over sized bolt to replace a stripped out hole?

I think so, and while at it, they broke off the wall of the bolt hole.

So they decided to drill another hole, smaller, further in, and put a helicoil in it, and compensate with a longer stud.

It's a mess.

 

[Cipher]

I imagine that spare heads are hard to get where you are. THey would also be a large cost to ship.

 

[bonanzadave]

Welding would be better, but as far as I understand welding aluminium is very challenging.

Finding a guy who knows how to, and has a TIG welder, may be the challenge. That would be a easy task for the guy I know.

 

[roeme]

To confirm, exhaust bolts are M8, right?

 

[Nessism]

Finding a guy who knows how to, and has a TIG welder, may be the challenge. That would be a easy task for the guy I know.

Agree. Have someone weld on some material and build the boss back up. Then dress down the weld, drill and tap the hole. M8 is correct.

 

[dem3500]

I agree with welding the hole. It seems that that's your only option at this point

 

[roeme]

Finding a guy who knows how to, and has a TIG welder, may be the challenge. That would be a easy task for the guy I know.

Agree. Have someone weld on some material and build the boss back up. Then dress down the weld, drill and tap the hole. M8 is correct.

I think I may be able to find some capable welders.

But I'm going to have to take out the engine, take off and disassemble the head, don't I.

That intimidates me a bit. From what I have read so far, working around the camshaft and valves doesn't tolerate sloppiness.

Is it possible to do for someone new to taking engines apart, but capable of following and understanding instructions?

I wanted to wait with digging into an engine until both bikes were in working order, but oh well. Imma stick my nose in the manual and youtube now. Seems fate has other plans for me.

 

[jsandidge]

You seem to be taking this misfortune very well. Good luck to you.

 

[tatu]

I had a similar thing last year, one of the ex bolt holes had been mashed up from when I'd got the bike and I had the hole filled up with weld and retapped, it worked ok till I changed the pipes for the big UK show and the weld just pulled out.

It was never nice and I've deleted the photos I had of the repair but this is what I did: First drilled out the hole to I think 12mm to original depth, you have to be careful because you can go too far, I made a solid round plug which was a snug fit into the now clean hole, while it was in the Lathe I centre drilled to make sure all was..centre, turned a small chamfer and tapped it home into the hole. I took the bike to a mate of a mate and he welded it in, took him about 15 minutes. I then drilled it to size (I forget now, maybe 6-6.5) tapped it to the M8 and that was it. All done without taking anything off except the fuel tank.
I would be very reluctant to use stainless studs bolts into ally most especially where it gets hot, stainless and ally don't go together well and likely it's what has caused the thread problems in the first place by 'binding' especially where it gets so hot as to cook off any thread lube. This was in fact an easy, quick fix and is permanent.

 

[roeme]

You seem to be taking this misfortune very well. Good luck to you.

Thanks, man. I'm quite bummed out to be honest. But at some point you gotta get back up. The problem won't solve itself. Coincidentally, there's a small plate above my monitor, it roughly translates as follows:

?If you're neck-deep in sh!t, you shouldn't hang your head!?

(...)I would be very reluctant to use stainless studs bolts into ally most especially where it gets hot, stainless and ally don't go together well and likely it's what has caused the thread problems in the first place by 'binding' especially where it gets so hot as to cook off any thread lube.(...)

I don't know. I wasn't yet able to find definitive, robust knowledge on the topic of differing alloys between screws and holes,i.e. cold-welding. A lot of fear though. I think I'll create a separate thread to pick the collective GSR brain.

For whats it's worth, I have applied anti-seize on the bolts. It's of german origin, the manufacturer rates it up to 1200?C (~2192?F). I hope it stays for a moment, and if anything, I'm not really moving the bike now

I had a similar thing last year, one of the ex bolt holes had been mashed up from when I'd got the bike and I had the hole filled up with weld and retapped, it worked ok till I changed the pipes for the big UK show and the weld just pulled out.

(...)

It was never nice and I've deleted the photos I had of the repair but this is what I did: First drilled out the hole to I think 12mm to original depth, you have to be careful because you can go too far, I made a solid round plug which was a snug fit into the now clean hole, while it was in the Lathe I centre drilled to make sure all was..centre, turned a small chamfer and tapped it home into the hole. I took the bike to a mate of a mate and he welded it in, took him about 15 minutes. I then drilled it to size (I forget now, maybe 6-6.5) tapped it to the M8 and that was it. All done without taking anything off except the fuel tank.
(...) This was in fact an easy, quick fix and is permanent.

It took my a moment to understand what followed what here But it's very reassuring to know you got out of a similar predicament, and coincidentally, with something similar I have in mind.

So if I understood correctly, at first you had the screw directly into the welded hole, and that broke, i.e. the threads got out. But walls remained.
- After that, you created at insert, press-fit (or almost), into the remaining hole, and had it fixed for good with a weld.
- Then, drill & re-tap.

So essentially, the threads are now a separate "sleeve" inside the head's body/weld.

My initial idea was to put a timesert into the half-remaining thread, and weld it in.

Hrm.

I think my next steps will be

1. Clean up the hole
2. Find somebody who can weld that
2. Have that somebody weld it up
3. Either go with a time-sert or the plug like tatu did (Have also to find out someone with a lathe)
4. If plug, denn drill/tap

 

[tatu]

Exactly, Just one thing else, if you go big enough with the drill diameter you will break through the actual exhaust port where the pipe slides in that will allow the welder to run a bead and make the plug fit even firmer, then clean it up with a die grinder.
Just to ask, what are the timeserts made of that you have in mind?
I just looked again at your pics again, yours is slightly different but it will lend itself well to the above, with ally welding the metal has to be completely and perfectly clean.
All this is finally down to the welder, perhaps take the job to him and ask what he is able to do and work around that?

 

[sam000lee]

Is there any reason to not just get a new cylinder head? I see that the OP is in Switzerland but an ebay head can be had for less than $100 and even after international shipping could be less than the welding, drilling, tapping, etc.

 

[Grimly]

I'd be inclined to go with Sam's idea - buy a good condition head, quick valve job, new seals, bang it on, and use the old one as a paperweight.
Otoh, the extra cost of a gasket set, etc... hmm...

 

[bwringer]

There are a few more things you can try before giving up and pulling the cylinder head.

What size are the large threads here? I'm talking about the threads that are only present for about 2/3 the circumference:

If I'm understanding things correctly, these would be the exterior of a failed Helicoil.

Is the diameter a bolt size or an external Helicoil size? Is the thread pitch 1.25mm or 1.5mm?

If you can get a bolt to thread in, then you could make a plug. Drill and tap the center of the bolt, thread it into the cylinder head, then cut off the head of the bolt. Then you have solid steel M8 threads.

If the OD isn't a bolt size, then you could possibly do the same with a bolt inside a helicoil.

For example, if that mess was an M10 helicoil, then install a helicoil (it'll be janky and loose, but a bolt inside will help keep it in place), thread in an M10 bolt, then cut off the head of the bolt and drill and tap it. Or, thread in a double-ended stud that's M10 on one end, M8 on the other.

Or, you could use a metric step stud that's M10 on one end, M8 on the other:
https://www.belmetric.com/metric-step-studs-6810mm-c-9_73/?zenid=9v433cpio60i79g6o97hnlmvl3

If the threads are loose, you might also be able to make a sort of expanding anchor out of a bolt or a slug of aluminum.

 

[roeme]

That would make a spectacular paperweight

(...)buy a good condition head, quick valve job, new seals, bang it on, (...)

(...)but an ebay head can be had for less than $100 and(...)could be less than the welding, drilling, tapping, etc.

I'm not ruling out replacing the cylinder head. I'm currently leaning towards welding the old one up since I may be able to find a welder who is willing to do it for a reasonable price. And apart from welding, I'm able to do the rest of the work by myself.

Not so, or not yet, for replacing the head. What I'm missing for this route is experience, a head, a clean, heated working space and quite possibly some tools.

Well, I could have a shop swap the head for me, that would leave me with the task of getting a head (while the shop owner knows the bikes well, he doesn't acquire second-hand parts, but will use what I bring him). I don't know the head compatibility between the various years, I have only found heads for later years so far.

This will easily exceed the price of the welding option. I'd expect the shop to charge at least $750, if not $1000 for swapping the head. While I can manage that...it's more of a fall-back option.

Just to ask, what are the timeserts made of that you have in mind?
(...) with ally welding the metal has to be completely and perfectly clean.
All this is finally down to the welder, perhaps take the job to him and ask what he is able to do and work around that?

I have no particular timesert selected yet. Regarding the clean-up I will ask the welder, as soon as I found one. But I'm sure one can't properly weld the way it currently is.

What size are the large threads here? I'm talking about the threads that are only present for about 2/3 the circumference:

(...)If you can get a bolt to thread in, then you could make a plug. Drill and tap the center of the bolt, thread it into the cylinder head, then cut off the head of the bolt. Then you have solid steel M8 threads.(...) If the OD isn't a bolt size, then you could possibly do the same with a bolt inside a helicoil. (...)

I really like your idea! This would give me enough time to prepare for a proper, permanent fix, while still being able to ride the bike.

I have to measure them again for the diameter and thread pitch. I think it was 9-10mm when I checked it out of curiosity.

To recap, my options at this point, pending further research:

1. Repair with a weld & insert
2. Have a shop swap the head
3. Try to re-use "external ⅔ (more like ⅝) remaining" threads (temporary fix)

Does anybody know which years' heads would fit on my '78 engine? I would expect until '81, '82 look a bit different...

Thanks y'all so far your input.

 

[Guest]

As Tatu says, stainless and ally do not go together well. There is a reaction that happens between these two with heat. I thought of doing the same thing a few years ago then read a thread here that explains what happens when these two are combined. It has been a long time now but I ended up using steel inserts instead of stainless.