Cylinder Exhaust Flanges

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ptjenkins65
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Cylinder Exhaust Flanges

Postby ptjenkins65 » Mon Nov 19, 2018 9:35 am

Hi everyone. I think I have a problem.
The push rod tubes on my r60/6 were leaking and very corroded and i had decided to replace them. As you all know, to do that, the exhaust needed removing from the cylinder. The crown nuts would not move. In the end I had to cut them off.They are cemented on. I replaced the tubes, all went well. It was only when i turned my attention to the head that i noticed the state of the threads on the flanges. The left has a copper thread, which almost screws up tight. The right has a completely chewed thread.
What should I think about doing? I would not know how to retap that thread, is there a tool off the shelf for that?
Screen Shot 2018-11-19 at 08.03.11.jpg
Screen Shot 2018-11-19 at 08.02.59.jpg
Screen Shot 2018-11-19 at 08.02.46.jpg
Thanks for the help in advance
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1998 r850r
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Neil Robertson
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Re: Cylinder Exhaust Flanges

Postby Neil Robertson » Mon Nov 19, 2018 11:04 am

Quite a common problem with old airheads.
The 'copper' thread will actually be phosphor bronze which means it has been repaired in the past.
Motor works sells a bolt on repair kit which doesn't look very original for just under£100 and one that does for just over£150.
In practice it may not be a problem, the exhaust pipes go a long way into the heads and may not leak even when not clamped firmly in place,in which case just find some way of jamming the rose nuts on and forget about it.
My own bike ran like that for many years.
I doubt you'll find a tool to recut the threads and if the threads are damaged metal will have been removed leaving them weak anyway.

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Re: Cylinder Exhaust Flanges

Postby SteveD » Mon Nov 19, 2018 11:29 am

Give the grungy threads a proper clean. Inspect.
Maybe a tool like this will clean the threads if they're not too far gone! You might get lucky. If so get some anti seize ...

https://www.youtube.com/watch?v=dYu_fl59Ztw
Cheers, Steve.
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Re: Cylinder Exhaust Flanges

Postby Rob Frankhamr » Mon Nov 19, 2018 11:44 am

That thread (the alloy one) is pretty good really, just needs cleaning up a bit. There are two ways to do it. The expensive way is to source a suitable die for the thread... They are available from engineering workshops but will cost! the thread is 52mm and I think the pitch is 1.5 but don't take that as gospel, measure it as I'm not sure.

The alternative is to obtain a thread file. This is a machine steel bar, normally square and each side has a cutting profile to match a thread pitch. Not the quickest or easiest tool to use but it will do the job. You can pick one up quite cheaply on fleabay or Amazon... you may well get one in Halfords or your local auto parts centre... The other benefit of this is that you can use it for any other unusual thread pitch you come across.

The object of the exercise is for the nut to be hand threadable onto the stub. A few missing or distorted threads won't make much difference.

The trick with these threads is to loosen them on a regular basis and to always apply a layer of copper grease when refitting to stop the thread deteriorating further.

Rob
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CaptAirhead
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Re: Cylinder Exhaust Flanges

Postby CaptAirhead » Mon Nov 19, 2018 1:37 pm

As has been pointed out, your threads are in reasonable shape and can be cleaned up. The one on my R80/7 was in much worse condition with only two of the threads holding the nut on finger tight. It was like that for some considerable time and went through an MOT before I bought the bike:-

ImageBMW R80/7 Exhaust Thread by Ian Beat, on Flickr

I had to cut the nut off the other side and managed to save the thread. I opted for the Motorworks repair kit:-

Image1979 BMW R80/7 Exhaust Nut Repair kit. by Ian Beat, on Flickr

Image1979 BMW R80/7 Exhaust Nut Repair kit. by Ian Beat, on Flickr

Happily, you will not have to resort to that option if you follow the advice of others above. Once you clean up the threads, just remember to use plenty of copper grease on re-assembly and loosen them off and re-tighten at least once a year to avoid a repetition.
Ian.
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Re: Cylinder Exhaust Flanges

Postby Nate » Mon Nov 19, 2018 9:25 pm

OK - here goes...

I expect to get shouted down on this, but my take has always been that you NEVER put copper anywhere near aluminium. Boatbuilders using both metals have always kept them as far apart as possible for the simple reason that by adding salt water (an electrolyte) you get a battery.

Getting on to airheads... I've had high mileage bikes with perfect exhaust threads where the only lubrication has been the approved BMW grey grease - Optimol TA - available from 'Bins. I've also had low-ish mileage bikes with wrecked threads where the lubrication has been copper grease - sold by 'Works for just this purpose... Some of these bikes were ex-police, who seemed to love the stuff, and don't generally stint on maintenance.

My point is that if grease containing copper dries out in a high temperature environment like an exhaust port, and is then subject to an electrolyte (salt water - easy to get sprayed on an airhead used in bad weather...) then the copper will electrolytically react with the aluminium and the result is a welded exhaust nut and wrecked threads.

I never use copper grease on exhausts, and in over thirty years of owning airheads, after cleaning and greasing with Optimol TA, I have never witnessed more damage than was originally there on any of the exhaust ports on any of my bikes however long I've subsequently owned them for.

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Re: Cylinder Exhaust Flanges

Postby Mjolinor » Mon Nov 19, 2018 10:52 pm

Copper grease does not conduct, no electrolysis will take place. It also does not dry out. I have removed bolts from aluminium that were copper greased twenty years or more ago and they were as though they had been screwed in yesterday.

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Re: Cylinder Exhaust Flanges

Postby Nate » Mon Nov 19, 2018 11:15 pm

Thought I'd hear how wrong I was...

Did a quick Google - as I suspected there's a lot of advice on not using copper grease on outboard engines and then I spotted this piece of advice regarding automotive applications on Apec Braking's website:

"Copper grease is not suitable for the brake environment as a galvanic reaction is likely to occur. Galvanic corrosion is caused
due to 2 dissimilar metals reacting with each other. All metals have galvanic qualities. This is a measure of a metal’s resistance to
corrosion when in contact with another metal. A greater relative diff erence in galvanic quality between the two metals in contact
indicates a greater corrosion potential. Galvanic corrosion (also called bimetallic corrosion) is an electrochemical process in which
one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte. Since
copper has one of the highest galvanic numbers or nobility of the active metals, it will not be harmed by contact with any of them.
It will, however, cause corrosion of the other metals if in direct contact. Thus preventing the pad from moving freely in the caliper/
carrier. The electrolyte may be rain water or moisture from the air containing enough acid to cause it to act as an electrolyte.
This results in the deterioration of the metal with the lower galvanic number. Contact in a saline environment or salty water will
accelerate corrosion."

I know loads of people "swear" by copper grease, and in its place it's brilliant, but I've seen extensive damage to exhaust threads on airheads that I firmly believe was not caused by neglect, but rather by using the wrong anti-seize.

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Re: Cylinder Exhaust Flanges

Postby Rob Frankhamr » Mon Nov 19, 2018 11:29 pm

Thought I'd hear how wrong I was...

Did a quick Google - as I suspected there's a lot of advice on not using copper grease on outboard engines and then I spotted this piece of advice regarding automotive applications on Apec Braking's website:

"Copper grease is not suitable for the brake environment as a galvanic reaction is likely to occur. Galvanic corrosion is caused
due to 2 dissimilar metals reacting with each other. All metals have galvanic qualities. This is a measure of a metal’s resistance to
corrosion when in contact with another metal. A greater relative diff erence in galvanic quality between the two metals in contact
indicates a greater corrosion potential. Galvanic corrosion (also called bimetallic corrosion) is an electrochemical process in which
one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte. Since
copper has one of the highest galvanic numbers or nobility of the active metals, it will not be harmed by contact with any of them.
It will, however, cause corrosion of the other metals if in direct contact. Thus preventing the pad from moving freely in the caliper/
carrier. The electrolyte may be rain water or moisture from the air containing enough acid to cause it to act as an electrolyte.
This results in the deterioration of the metal with the lower galvanic number. Contact in a saline environment or salty water will
accelerate corrosion."

I know loads of people "swear" by copper grease, and in its place it's brilliant, but I've seen extensive damage to exhaust threads on airheads that I firmly believe was not caused by neglect, but rather by using the wrong anti-seize.


Never had any problem either on brakes or exhaust stubs. It's also my 'anti-seize' of choice for stainless bolts in alloy... still never had a problem. I think, as has already been said, the 'grease' element means it is non-conductive and without an electrical flow you won't get a galvanic reaction.

Rob
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Re: Cylinder Exhaust Flanges

Postby Mjolinor » Mon Nov 19, 2018 11:47 pm

I have tried to make it conductive, I could have used it for a lot of things if it were possible but it is not possible so no dissimilar metals reaction can take place.

The whole point of anti-seize is to prevent the two close fitting pieces from actually touching. This is why you should also cover the underside of a bolt head and both sides of any washers, shank and thread then both sides of the nut.

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Re: Cylinder Exhaust Flanges

Postby SteveD » Tue Nov 20, 2018 1:31 am

If when you do an oil and/or filter change, loosen the star nuts, clean the threads, reapply the antiseize of your choice. It adds 10 minutes to the job and save a lot of future heartache and money for you or the next owner.

If those nuts get left for years then the outcome can be different.
Cheers, Steve.
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Re: Cylinder Exhaust Flanges

Postby krankshaft » Tue Nov 20, 2018 10:51 am

I like to loosen and grease my exhaust nuts when I check/adjust my valve clearances,
it makes the 10mm nuts on the back easier to replace when the exhaust nuts are off.
Ride safe
Jim

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Re: Cylinder Exhaust Flanges

Postby Rob Frankhamr » Tue Nov 20, 2018 10:57 am

It's also worth mentioning, although I think that the thread owner already knows this from earlier posts, if you try to remove a finned nut and it won't move, don't force it. If the nut starts to move but then seizes and doesn't release easily... equally don't force it. There's a tendency to think "well it was moving a second ago so it must be OK if I just push a bit harder"... bad move! Once it galls, forcing it will destroy the thread.

Cut the nut through. The chances are you'll be able to salvage a useable thread on the stub. You'll have to buy a new nut , which isn't cheap but substantially cheaper than any of the other options...

Rob
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Re: Cylinder Exhaust Flanges

Postby Mjolinor » Tue Nov 20, 2018 10:58 am

Those 10mm nuts seem like a right faff to me. I didn't bother fitting them and it seals OK.

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Re: Cylinder Exhaust Flanges

Postby SteveD » Tue Nov 20, 2018 1:46 pm

Those 10mm nuts seem like a right faff to me. I didn't bother fitting them and it seals OK.
The centre ones have been known to disappear. It might be safer to use the 10mm nuts just in case.
Cheers, Steve.
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Re: Cylinder Exhaust Flanges

Postby Rob Frankhamr » Tue Nov 20, 2018 2:38 pm

Those 10mm nuts seem like a right faff to me. I didn't bother fitting them and it seals OK.
The centre ones have been known to disappear. It might be safer to use the 10mm nuts just in case.

+1 I've lost a couple of the middle nuts over the years and been saved by the 10mm ones. Belt and Braces is good sometimes...

Rob
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Re: Cylinder Exhaust Flanges

Postby Mjolinor » Tue Nov 20, 2018 3:00 pm

But ti wouldn't be proper motorcycling if one didn't have one oily shoe.

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Re: Cylinder Exhaust Flanges

Postby krankshaft » Tue Nov 20, 2018 6:09 pm

I have been tempted to leave them out also ( the 10 mm nuts) as the rocker covers on my Dnepr seem to seal ok with
just a 14 mm centre nut (well , more or less!) but I came to enjoy the challenge of getting them back on, good for manual
dexterity and good excuse to remove the exhaust nuts and grease them.
Jim

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Re: Cylinder Exhaust Flanges

Postby Rob Frankhamr » Tue Nov 20, 2018 8:17 pm

They are available from engineering workshops but will cost! the thread is 52mm and I think the pitch is 1.5 but don't take that as gospel, measure it as I'm not sure.

Rob

FWIW, I checked today... the threads are 52mm x 2mm.

Rob
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Re: Cylinder Exhaust Flanges

Postby John Marshall » Tue Nov 20, 2018 8:57 pm

Such a die is on fleaybay for about £250 so certainly not a viable prospect.
I use the old Optimol grey grease I bought 20 years ago.

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Re: Cylinder Exhaust Flanges

Postby Mjolinor » Tue Nov 20, 2018 9:38 pm

An M16 or M14 metric course die (or tap) will do to clean up the thread, same pitch and tooth shape just a bit more work on your cutting tool splitting the die.

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Re: Cylinder Exhaust Flanges

Postby Rob Frankhamr » Wed Nov 21, 2018 10:28 am

I would recommend a thread file. Prices between £6.00 and £30.00 dependant on whether you buy it with a name. Much easier to use and will treat a variety of thread profiles so it's a useful tool to have in the box anyway.

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Re: Cylinder Exhaust Flanges

Postby SteveD » Thu Nov 22, 2018 4:35 am

It's a cheap and easy way to assess the threads correctly before lumping too much cash on someone else's bench top.
Cheers, Steve.
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