Exhaust Removal -Help!!

[peterc]

I'm sure many others have been here: The castellated exhaust rings on my bike are absolutely refusing to budge - they are the original bronze type and whilst I have the correct C spanner it is not a great fit as the rings have been bashed round in the past. No amount of 'persuasion' is proving of any use. What's my 'last resort' solution? I have a complete new set of pipes so am not worried about damaging the old exhaust, but obviously need to avoid any damage to the heads/exhaust threads.

Have now found this thread:viewtopic.php?f=4&t=857, which gives some useful suggestions, so no need to repeat the advice given there. Think I will take the heads off and see if a few days soaking the threads in Plus Gas works.

[John Bunting]

Hi Peter,
If the exhaust nuts are already bashed about a bit, try to move them with a drift, a little shock may do it after plenty of WD40.
The worst case scenario is that the threads are damaged and have to be welded and the threads recut, ouch!!
If you want to get the heads off to soak them you will have to cut the pipes.
Good luck
John

[MarkB]

Have you tried the NLM exhaust spanner? Rather than just being a C spanner, it has three teeth which fit into the castellations. This may give you more purchase on the nut.

Good luck, Mark.

[72degrees]

Plusgas is the one true penetrating fluid. Leave it to soak for 24 hours. If the bike is a runner get it really hot before trying to shift the nuts. Differential expansion of head and nut might help - though if brass it might not, anyone know for sure?

I use a Brotool articulated 'hook' spanner. It tightens on to any surviving bit of castellation as you heave. Otherwise it's lump hammer and drift time.

The worst one I ever had to do was for the founder and vice president on his 74 Sport. Someone had codged it with loads of white exhaust assembly paste. As you might guess the head had to have the port thread repaired.

[EVguru]

As a last resort if you're going to scrap the pipes anyway, you could stuff the port with rag and then split the exhaust nut with a grinder, or by drilling. It's not uncommon for the nut to have a broken part of the port thread embedded in it and you simply won't get it out without damage to the head, although the port thread may still be usable with care.

I've got very stuborn nuts out eventually by using a collar clamped onto the pipe to make sure the nut key couldn't jump out of the castellations and then used the pipe itself for extra leverage.

I've repaired stripped ports threads and it'd not too hard, but it takes me long enough that I'd charge more than NLM. I bore the port out, press in an insert with the new thread cut in it (It's a close tolerance thread, not standard) and weld the insert in. I think NLM thread the head and screw in the insert, then weld it and then cut the new thread. It would be much faster to do it on a CNC mill (thread milling) and there's a youtube video of the work being carried out on a Bultaco (as I recall) head.

[peterc]

Much obliged to all for the above. The NLM Morini specific C spanner is great if the Castellations are in reasonable shape, but as I'm discovering the nuts are pretty soft and once damaged the spanner cant be held in place effectively -even with a clamp around the exhaust pipe chocked up against the nut to hold it. I had the engine hot yesterday before starting so I'm now going to try plus gas and patience for a few days before cutting the pipes and removing the heads if they still wont shift.
I'm fairly confident its just a case of the nuts having been over tightened rather than damaged threads as the bike had been well maintained and used regularly before my ownership started - in fact I'm pretty sure the exhausts were last off in the NLM workshop a couple of years ago. At least from the comments above I know I can get the threads restored if it comes to the grinder.
Thinking about the replacements for the nuts I'd be interested to know if others do use the Stainless ones successfully, I know there is a potential issue with reaction between the alloy/stainless but wouldn't a good application of copper slip and routine maintenance avert serious problems?

[EVguru]

Alex does like to do the nuts up very tight!

Mine don't seem to come undone with moderate tightening, but my preferred approach if they did would be to take a good quality stainless pipe clamp and weld a tab to it to engage with one of the castellations.

[72degrees]

Alex does like to do the nuts up very tight!

Mine don't seem to come undone with moderate tightening, but my preferred approach if they did would be to take a good quality stainless pipe clamp and weld a tab to it to engage with one of the castellations.

I seem to recall seeing some bikes that went on the first factory visit to Bologna that returned with such devices. I have small holes drilled in a head fin and lockwire tightly round one of the castellations. Your solution is more elegant

[adrian650]

After PlusGas and heat cycles, I decided the head was more valuable than the header pipe and managed to extract the header and nut in many pieces by careful work with cut off discs in a Dremel.

I must stress that this took ages. Well, probably not that much time, but repeated spells of 30min to an hour. Every bit out was a bonus and then I took a break so as not to get impatient. I cut through the header into the brass first and then far enough through the brass to be able to fold it in.

By not unscrewing the nut there was enough thread left in the head to be able to reuse it without a repair. I'm nervous of over tightening it however and find after a few thousand miles that it needs a tweak. I should make some of Paul's locking clamps.

Whatever approach you take, be patient!

Good luck,

Adrian

[robinh44]

Hi,

You did well to keep the cylinder thread intact. I had lots of problems with my rear cylinder thread in the head, in the end it was so badly worn and I could not get the exhaust to seal. I decided to carefully drill and heli-coil a couple of stainless studs and used an old Moto Guzzi V35 collar along with a modified Guzzi split collet. The exhaust now seals a lot better and stays tight, fortunately the front cylinder is still in good shape. Picture below:-



Regards

Robin

[peterc]

After reading your accounts I've clearly been very lucky - 48hrs soaking with Plusgas and some almighty larruping with the hammer and drift and they are both off tonight, with no apparent damage to the heads/threads.
No posts on the subject of using the stainless exhaust nuts - I'm sure with regular maintenance and care not to overtighten these would be ok, but open to being told otherwise....
Thanks again to all for advice.

[MarkB]

I've got stainless exhaust nuts on my Strada which haven't given any problems - touch wood. A bit of copaslip stops them seizing in the threads.