cylinder head exhaust threads stripped

[judah]

first of all, a huge thanks to all on this amazing forum. i recently acquired a 1972 norton commando roadster and found this site. great folks and great info in here.

the bike is basically in pristine condition. I've had to fix a few odd things here and there but nothing major. so far… currently i have a big problem. when i got the bike the left exhaust pipe would vibrate loose after every ride. read the forum, applied the sauce and nipped it up when warm. over and over. the last time i did it i felt it give. nothing major as far as force. just my hands. seems i got to it too late. too loose for too long. damage already done. its stripped.

now, what to do? my first move was to just to remove the washer to gain a little more thread. nothing to lose at this point. so far its worked. also applied a heavy spring from a hole drilled in the wing nut to a bolt on the head to keep constant clockwise tension on the wing nut. i think its working for the time but expect a failure any time soon. theres just too damn much vibration here and (its probably norton heresy, but this particular part was engineered piss poor, as is testified by the number of commando owners with the problem) it will no doubt vibrate the threads off at some point and over tightening will just strip what i have left.

soooo… I've looked at all the posts i can find on here. one showed a bore and replacement of new steel threads. other than that can't find much.

any idea who might do this kind of work? is it possible to take the head off and send it to someone who can refit it?

should i just buy a new cylinder head? expensive but probably the most sure. there seems to be several sizes out there (valve sizes i guess?). any advice on the right size for a stock 1972 commando roadster? is this a huge task to replace? where best to buy?

any help appreciated.

 

[Fast Eddie]

There are various specialists who can repair this. where in he wolrd are you?

 

[comnoz]

first of all, a huge thanks to all on this amazing forum. i recently acquired a 1972 norton commando roadster and found this site. great folks and great info in here.

the bike is basically in pristine condition. I've had to fix a few odd things here and there but nothing major. so far… currently i have a big problem. when i got the bike the left exhaust pipe would vibrate loose after every ride. read the forum, applied the sauce and nipped it up when warm. over and over. the last time i did it i felt it give. nothing major as far as force. just my hands. seems i got to it too late. too loose for too long. damage already done. its stripped.

now, what to do? my first move was to just to remove the washer to gain a little more thread. nothing to lose at this point. so far its worked. also applied a heavy spring from a hole drilled in the wing nut to a bolt on the head to keep constant clockwise tension on the wing nut. i think its working for the time but expect a failure any time soon. theres just too damn much vibration here and (its probably norton heresy, but this particular part was engineered piss poor, as is testified by the number of commando owners with the problem) it will no doubt vibrate the threads off at some point and over tightening will just strip what i have left.

soooo… I've looked at all the posts i can find on here. one showed a bore and replacement of new steel threads. other than that can't find much.

any idea who might do this kind of work? is it possible to take the head off and send it to someone who can refit it?

should i just buy a new cylinder head? expensive but probably the most sure. there seems to be several sizes out there (valve sizes i guess?). any advice on the right size for a stock 1972 commando roadster? is this a huge task to replace? where best to buy?

any help appreciated.

I repair them just about daily using a threaded hard al-bronze insert. CNC installation, Lifetime warranty. Normal turnaround in about a week. I am in Colorado. Jim

PS, seager-engineering does a similar repair in the UK.

http://www.ebay.co.uk/itm/Norton-cylind ... 0292507828

 

[Beach]

Highly reccomend Comnoz repair...Better than original...

 

[Snorton74]

Highly reccomend Comnoz repair...Better than original...

Same here.

 

[judah]

thanks so much. i live in ms, usa. will pm comnoz about the repair. would like to get it to last till winter but its already getting a bit loose. prob will have to bit the bullet and do it soon. thanks again all.

 

[drp]

Comnoz did mine too. Great job but I'd recommend doing both sides even if the other doesn't seem to need it. Most likely over time it will.

Dave

 

[petejohno]

Bronze insert is the way to go. I was told that the problem occurs because the exhaust nuts and the cylinder head heat and cool at different rates causing the nuts to loosen. The insert heats at the same rate as the nuts therefore they stay tight - problem solved.

I had mine done in Melbourne Aust. 10 years ago and have never had an exhaust nut come loose since.

johno

 

[dynodave]

"I was told"

It seems to me that the problem is almost exclusive to commando and is almost unheard of on aluminum head featherbed and gardengate framed NHT. At least I have never yet seen a stripped head from one of them.....though I have repaired over a dozen commando heads for local norton club members

Same head and same nuts!

Why not the same resulting failure?

 

[JimNH]

"I was told"

It seems to me that the problem is almost exclusive to commando and is almost unheard of on aluminum head featherbed and gardengate framed NHT. At least I have never yet seen a stripped head from one of them.....though I have repaired over a dozen commando heads for local norton club members

Same head and same nuts!

Why not the same resulting failure?

Perhaps because of the isolastic mounts and all the movement against the exhaust system suspended many feet away?

 

[comnoz]

I would break it down to :

1. engine movement/vibration 50%
2. thermal expansion issues 25%
3 sloppy thread fit from the factory 25%

I did loose the threads on my N15 back in the 70's. I sent the head to Scholtz for his oversized nuts. Jim

 

[Hobot]

Huh, some of us, like the big parts dealers instructions, think its 100% d/t not banging the rose nuts on ridiculously tight enough then putting on some half fast retainer that only keep the nuts from falling off on road but not from losing the tight clamp pressure, so slack beats the ally to dust. The Cdo exhaust hanger set up puts the vibrating leverage force to work like shoe eves taking out stitches instead of sewing em up tighter. I've 3 well used heads with pipes on/off dozens of times yet the threads still good. My buddy Wesley '71 threads are still good after 35 yrs constant use going through sets of pipes fractured by our rough paths. Wesley was the one to impress me with wisdom to get all fasteners ridiculously tight. Milk of Magnesia has proven its worth in my riding mower exhaust manifold bolts and a few times on '72 Trixie. Wes still has the steel nuts that rust, Trixie has the bronze cuties and Peel gets machined aluminum I'll not put on ridiculously tight but will have springs to finish the nip up on the fly. Peel will also get a different muffler hanger that will support the floppy mass w/o straining the head connections. Our mufflers guts get banged apart routinely and pipes fracture at front but not our ridiculously tight threads.

 

[norton73]

I sent the head to Scholtz for his oversized nuts. Jim

Seeing as he was in CO, I guess it would make sense that you would be familair with his repair. I had him do my head way back in about 1998 or so.

I chose his repair because I thought he was boring the port and recutting the threads oversize and installing the matching nuts. Then there would be no insert to come loose.

About 4-5 years ago I was cranking down on the exhaust nut and a insert came out! I drove it back in and had someone local weld a bead around the periminter, but it pulled out again. Any chance the inserts you do can be installed to replace the oversize ones? I'd guess I'd have to go back to stock size nuts. Which I already have because I am currently running another head, but I'd like to repair the old one as a spare for future use.

 

[comnoz]

I sent the head to Scholtz for his oversized nuts. Jim

Seeing as he was in CO, I guess it would make sense that you would be familair with his repair. I had him do my head way back in about 1998 or so.

I chose his repair because I thought he was boring the port and recutting the threads oversize and installing the matching nuts. Then there would be no insert to come loose.

About 4-5 years ago I was cranking down on the exhaust nut and a insert came out! I drove it back in and had someone local weld a bead around the periminter, but it pulled out again. Any chance the inserts you do can be installed to replace the oversize ones? I'd guess I'd have to go back to stock size nuts. Which I already have because I am currently running another head, but I'd like to repair the old one as a spare for future use.

I have inserts with two different OD's . The large ones will usually take care of repairing heads that have already had an aluminum insert installed.

If you want to send a nut along I can thread my insert to fit. The ID is threaded after they are installed in the head so a simple change to the CNC program will accommodate oversized nuts .

I have never seen Scholtz install a welded insert. He would normally just tap the head for his oversized nut. There is a good possibility that he may have tapped an insert that had been previously installed.

I have had a couple heads here that had an aluminum insert that was installed so clean that you could not tell it was there. I installed a bronze insert inside of a welded aluminum insert one time and the insert ended up pulling out.
Funny thing is the man said he had owned the bike since new and had never had an insert installed. Makes me wonder if it was a factory fix. It was done so well I did not know it was there. Jim

 

[Hobot]

Funny thing is the man said he had owned the bike since new and had never had an insert installed. Makes me wonder if it was a factory fix. It was done so well I did not know it was there. Jim

Hm with the infamous slip shod factory items I'd suspect an American vender fixed a blunder early on. On the factory level of production numbers it would be counter productive to spend so much time on such exquisite repairs than just scrap it. The new discoveries and variations of existent Nortons continues to surprise us.

 

[swooshdave]

Comnoz did mine too. Great job but I'd recommend doing both sides even if the other doesn't seem to need it. Most likely over time it will.

Dave

Do not ignore this wisdom. Comnoz, both sides. Done.

 

[norton73]

I have had a couple heads here that had an aluminum insert that was installed so clean that you could not tell it was there. I installed a bronze insert inside of a welded aluminum insert one time and the insert ended up pulling out.
Funny thing is the man said he had owned the bike since new and had never had an insert installed. Makes me wonder if it was a factory fix. It was done so well I did not know it was there. Jim

I'm the second owner of this bike, but I got it in the mid-80s from the second owner, who parked it in 1976 after riding it only one summer. It only had 6K miles on it when I got it, so I'd assume neither of the POs had that insert done. I was disappointed to find an insert in there. All this time I was thinking I'd been mislead by Scholtz, or maybe misunderstood what he did. But I guess it must have been done by someone else.

I'll send you a PM about my head.