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Stripped thread on exhaust stub
Well, bugger me.
Took the pipes off my '82 airhead today and to my horror found that one of the threads was stripped on exhaust stub on the head. I mean the one under the finned nut where the pipe comes out. I do know it happens, but I always use Copperslip and slacken them off just a fraction of a turn and retighten them again just to keep them from seizing once a year or so. So I was particularly miffed to find that it had happened to me. So. My questions are therefore (1)Why me, Lord, why me? and (2)How do I make sure that the other one doesn't seize also? John |
Same happened to my girlfriends 94 GS. Before moving to England from Germany to be with my good Self in Jan 2002, the bike had always been dealer serviced.
Imagine my horror when I found both heads had stripped, hardly a thread in sight & not a trace of lubricanr/grease/CopperSlip anywhere? We ended up buying two second hand heads with valves & springs from Sherlocks. By the time you added gaskets etc & VAT, the bill was over £300.00. Time was tight, hence not opting for their re-furbishing service which was cheaper. I now clean & lube the threads twice a year. |
And I only touch mine when I absolutely have to, (3-4 times so far) and use lots of Never-sieze, and have had no problem in 19 years.
Have I been lucky? Dunno! http://www.horizonsunlimited.com/ubb/smile.gif But not complaining! Mostl;y when removing I am VERY careful that they come off smoothly - slightest resistance (after the initial big grunt) I turn them back on and work them by hand a bit until it omes smoothly. Once damaged, they are repairable. Any good BMW shop should know who to send them to for the repair. Should look good as new when done. ------------------ Grant Johnson Seek, and ye shall find. ------------------------ One world, Two wheels. www.HorizonsUnlimited.com |
Hi, Grant,
What is miffing me even more is that I'm now in a bit of a quandary as to how much work to do on the heads; now is a golden opportunity to have the seats upgraded and guides and valves replaced and fit the hush kit and twin-plugging. Like everybody else I hate being in a corner with obvious but expensive options available. Actually, the way I'm feeling at the moment is 'Sod it' and to put everything back, there's a good bit of useful thread left. As I see it the pipe is most unlikely to come out on the trip as it is held in position by the rest of the exhaust system anyway. Is Never-sieze a graphite compound, by the way? I was given some by an aircraft engineer for plug threads, this seems a similar application but in a hotter place. As always, many thanks Grant, John |
http://www.horizonsunlimited.com/ubb/biggrin.gif
always a problem - go for the whole hog, or just what you really need right now... good luck whatever you decide! I THINK never-seize is a graphite based compound - grey and horribly gooey and stringy and impossible to get off your hands. Sorry don't have it here to check - I'm in London at the moment. One can has lasted me 15 years... I carried a 35mm film can full on our rtw trip and it made it all the way. I use it on plugs and exhaust and anything else that might be hot or easily corroded. ------------------ Grant Johnson Seek, and ye shall find. ------------------------ One world, Two wheels. www.HorizonsUnlimited.com |
...Bostik Never-seez Regular:
-Aluminium -copper -petroleum distilates -hydro-treated heavy napthenic -residual oils (petroleum) -demaxed solvent -synthetic graphite -zinc oxide ...These are the ingredients from the can. You can also get a high-heat silver grade, but i don't have a can at the moment. I had to remove my r/h pipe for an oil-filter change. After 8000 miles, all threads were lined with copper. Removal of the nut was a little-bit tight, but didn't require a wrench after the first gunt. Threads were easily cleaned with a copper-wire brush and looked like new in no time. http://www.horizonsunlimited.com/ubb/smile.gif ...John, i recently had the exhaust threads renewed on one of my heads last year. The machinist did a brilliant job, boaring out the old threaded insert, machining a new insert from aluminium pipe and pressing it in. The job looks flawless, no welding and better than new.The prices for me in Canadian is: -dual-plug 2 heads...$170 -port and polish...$200 -repair one exhaust thread...$180 -new valve-train...100 pounds (aprox.$250??) -Assembly and grind...$160 -The look on my face first time starting my bike...priceless http://www.horizonsunlimited.com/ubb/smile.gif |
Mr. Ron,
Thanks for that. Bostik, you say, now that's something to go on, I can look it up on the web. I'm intrigued though when you say that the thread insert was bored out by the machinist, um... are we talking about the same thing here, I mean, the thread I'm having grief with is on the OUTside of the exhaust stub on the head, whereas on the inlet side there is a short length of pipe threaded INto the head. I can see that there is indeed an internal thread in the head here and am wondering if this is the one you had bored out. Sorry if I'm being obtuse- it HAS been known! Say- How come there seems to be such a high concentration of Hubbers in BC, then? (A hive of Hubbers? A horde? A host? How about a Hubbub of Hubbers, perhaps?) There's yourself, Grant & Susan, Timo, somebody else in Nanaimo (spelling?)(I think he's the guy that enjoyed his trip up to Whistler in a recent thread) and a few others whose names come up from time to time. Been there once in Feb '99, not TOO cold (Vancouver side, anyway) but wet. Was most impressed with the Fraser Canyon. One of the photos I took of one of your miles-long trains lugging along in falling snow down at the bottom on the other side of the canyon (it might have been just a little way down from Hell's Gate- now there's a name.) When I first got the photos back from the lab I was disappointed, it was all dull and washed out with no contrast at all and it took me a couple of years to appreciate it. Thing was, that's exactly how it was at the time, it was cold, miserable, with little colour, and there was this bloody monster of a train growling its way up the canyon on a ledge cut into the rock at the side of the canyon in the snow. Impressive, or what? Many thanks, John |
Hi John.
...i think some of us might call it a gaggle of airheads, but i'm really not sure. I thought about it after i posted my last reply"...hmmm, that sounds confusing..." Your right. The exhaust thread is not an insert like i said, but part of the casting. The machinist cut off the thread, bored out the port to accept an insert which he skilfully turned on a lathe. I'm not sure how he pressed the sleave into the undersized hole, but i guess he froze the insert and heated the head in an oven and slipped them together. The end result is a nearly flawless fix. You can only tell by looking very carefully whats been done. BTW...next time you come to BC, i believe there is a train you can ride north through the Fraser Canyon. Haven't done it myself, but i here it's a brilliant ride!! Take care. |
Sherlocks offer a similar service to the one Ron describes. I believe that it's also keyed in to place?
http://www.james-sherlock.co.uk/service.htm |
John a similar thing happened to my R80ST afew years back despite lubing the threads twice a year with coppaslip. I sent both heads off to MOTORWORKS in yorkshire,(also had them put new valves, springs guides and seats in) they put some type of brass thread replacement in, looks like it will last forever. I can't remember what it cost, but I think it was worth it.
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Mr. Ron and Steve:
Now this is interesting. I had assumed that the stub around the knackered thread would be built up by welding and then re-machined with a new thread. It isn't because I'd been told or that I'd worked it out- I just took it that that was the way to do it. I'm not that familiar with welding alloy, but I suppose it could be done like that. Hence my interest in hearing how the job is actually being done. Yes, Steve, it would seem that the new tubular insert would have to be keyed into the head in one way or another or it would sooner or later work itself loose- just think of the initial force - the grunt- (good word, that!) you need to undo the finned nut. Hmmm... perhaps a Left Hand thread would be better where the sleeve screws into the head so that it would further tighten in the head (rather than unscrewing) when you tried undoing the finned nut. Oh, then on the other hand there would be a tendency for it to UNscrew when you tried tightening the finned nut. Swings & roundabouts. You are probably right there, Steve, it would have to be keyed (or pegged) to be reliable. I still think that threading would be an added bonus compared to a shrink fit, though, but if that's the way it's done then it must be good enough. Thanks again, J |
Or, you could just weld up the seam once threaded in. http://www.horizonsunlimited.com/ubb/smile.gif
just to throw another thought on the fire... |
Yes, of course! Right again, Grant!
J |
I believe the specs call for a torque value of 120Foot lbs or some huge number like that ... There is no way the exhaust nuts have to be that tight.
I clean the inside of the exhaust flange and make sure the pipes and sealing washer fit well, then clean the threads (chase them with a thread file if necessary)use high temp never seize and make sure the nuts go on smoothly all the way by hand, then tighten 1/16th to 1/8th of a turn. I remove my right exhaust to change the oil in my 1984 R80RT (it's just easier)and have never had the exhaust nuts come loose or stick on. |
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