Exhaust nut torque spec?
- Thread starter BrianK
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You must have a "C" spanner with a 1/2" drive to be able to get a reading. I always smeared a little anti-seize on the threads and torqued it until it bottomed. Never had one come loose and never stripped one out. Do your exhaust nuts have one thicker lug (fin)? That's for tapping with a hammer and drift. Not sure what weight hammer is called for on that one, though. :lol:
Hi Danno. I have a proper nut attachment and a fairly good torque wrench. I do put antiseize on each time the nuts are out - airhead owner's habit. 750 nuts on an 850 (with unbalanced head pipes), they don't bottom but do go in there a good ways. Just wondering if there's an official torque spec. Thanks - Brian
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BrianK said:
Hi Brian,
The NOC Commando Service Notes say the exhaust threads in the head cannot be stripped using the standard large service C ring - the fins on the nuts bend first. Tighten them, heat up the engine and repeat. To get them off again, you'll need to heat up the head once more. There are two types of exhaust nuts - 750 and 850 types. I just switched to the 850 type on my '72 750 as I have a tool left over from my '83 R100RS BMW that fits these nicely.
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So the 750 nut threaded area is shorter than the 850? I guess my 850 has 750 nuts since it takes 3 gaskets to keep the 750-style pipes from rattling in the port with the nuts screwed in until they bottom. Guess I'll have to look at the parts manual to see the actual difference. New CNW ones would, I assume, work perfectly...
I use antizeize and tighten them "fairly tight" with the tool that's sold for that purpose and then safety wire a fin to the lower exh rocker cover nut. I don't tighten them again after the engine's hot. With the safety wire they can't loosen and since they are not super tight (and have antiseize), there is never any trouble at all removing them.
I use antizeize and tighten them "fairly tight" with the tool that's sold for that purpose and then safety wire a fin to the lower exh rocker cover nut. I don't tighten them again after the engine's hot. With the safety wire they can't loosen and since they are not super tight (and have antiseize), there is never any trouble at all removing them.
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Oh, OK so then I guess the 750 pipes have a much narrower flange than the 850 pipes? I don't like running all those gaskets either and, at some point want to correct it. As I said, I'm assuming the CNW nuts would work on either pipe but I'll confirm that before I actually order them.
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AHA! I see. Thanks Bill.
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MexicoMike said:
I think the idea is that they can settle against the gaskets with the heat cycles and then they will be loose and rattle and you think everything is ok because it's safety wired. I wonder where in Mexico you have have the inserts installed in your head. :?
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The head has the inserts from a PO so that's a good thing!
Rather than buying new CNW nuts (not that I object to that per se but I'm not interested in "dressing up" the engine). So just buying the collets should take care of the problem. I see them shown on the parts diagram for the 850; I had never looked at it before. Old Britts stocks them so that's an easy and relatively cheap fix.
Rather than buying new CNW nuts (not that I object to that per se but I'm not interested in "dressing up" the engine). So just buying the collets should take care of the problem. I see them shown on the parts diagram for the 850; I had never looked at it before. Old Britts stocks them so that's an easy and relatively cheap fix.
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OF COURSE THEY DON"T! What the heck was I thinking... 
maylar
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Go here:
http://www.mrcycles.com/
Select Suzuki motorcycle parts, and enter this part number: 14181-01D00
Order two of them, plus a spare. These are the absolute best exhaust crush washers for a Commando. They are thick enough that you only need one and the 850 finned nut will not bottom out. This tip came from a Norton Tech Digest years ago.
http://www.mrcycles.com/
Select Suzuki motorcycle parts, and enter this part number: 14181-01D00
Order two of them, plus a spare. These are the absolute best exhaust crush washers for a Commando. They are thick enough that you only need one and the 850 finned nut will not bottom out. This tip came from a Norton Tech Digest years ago.
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On that site the search turned up NA. But on that same site if you go to Suzuki motorcycle parts than plug in 1977 for a year than the GS750B as a model (fourth one down)than the drawing for muffler it is item 4.
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Thanks guys, certainly seems like the easiest/cheapest way to solve the problem. I Checked it out and will order two pair to be sent to a friend where I'll be in the US in May and June. So the bike will have to live with the 3 gaskets in each side for the next few months.
I use 850 nuts on my 750 with the Suzuki exhaust washers (1 per side). I have slighty less than an 1/8" to spare. Big fins, better cooling, nicer crome.
As to the threads on the nuts, I believe that the casting of the head 750 and 850 are basically identical and the larger bore of the 850 leave less area for internal threads.
As far as the clearance from the balancing pipe, my arguement would be that the 850 nut is much thicker and wider with much more mass then the 750.
My 2 cents, some one set me proper.
As far as tightening, don't be puttin a breaker bar or nothin on it, snug them down real good after every run for 3 or 4 cycles and check once in a while. Don't go crazy with it, it's a feel thing that you will get.
As to the threads on the nuts, I believe that the casting of the head 750 and 850 are basically identical and the larger bore of the 850 leave less area for internal threads.
As far as the clearance from the balancing pipe, my arguement would be that the 850 nut is much thicker and wider with much more mass then the 750.
My 2 cents, some one set me proper.
As far as tightening, don't be puttin a breaker bar or nothin on it, snug them down real good after every run for 3 or 4 cycles and check once in a while. Don't go crazy with it, it's a feel thing that you will get.
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