Exhaust Port Repair

This seems a decent method and cheap enough:

http://www.rgmnorton.co.uk/buy/exhaust-port-helicoil-repair_3807.htm

The above is for the big twins but make a phone call to see if they can do your head as well.

Les

Hi Ian,

I had the same problem with my Wideline Model 50 head earlier this year. I was told that, unlike with the twins, there is insufficient wall thickness on the singles head to machine for a threaded insert or oversize rose nut. I had to bite the bullet and have a welding job done and then re-machined to take a new rose nut.

It was expensive,just over £250 including two way courier, a new nut and customised multi-tooth nut spanner to fit, but it was a good job and restored it to as new condition. I had mine done by Seager Engineering in Ipswich.The head was away for a couple of months and numerous calls necessary to chase it up, but they had a back log ofwork at the time and staffing problems,things might now have improved. Suggest you call Patrick Seager on 01473 232908.

My stripped thread incidentally was caused by a Norvil exhaust nut fitted new 4000 miles previously which continually worked loose and subsequently measured to be 50 thou undersize compared to an original off myES2.

Georges wise words were as follows"

.All aluminium cylinder heads exhaust portswith internal threads, where the exhaust âNutâ or âRingâ screws in are liable to damage. Over the years, the combination of vibration, lack of maintenance and âwear and tearâ means that one day the set up gives up! Here are a few tips. It is best to undo the âExhaust Ring Nutâ (ERN) when the cylinder head is hot or at least warm, so that the relative expansion of the alloy cylinder head allows some loosening. If you have a cold engine and the ERN appears tight then use a Hot Air Gun (a very useful tool to have in the workshop) to heat the adjacent area. If you are working on an engine which has stood for many years, the inevitable carbon deposits in the exhaust port will have foundthereway onto the threads of both male and female components. In combination with other dirt and muck, this acts as a âgrinding pasteâ and undoing a tight ERN under these conditions can cause a lot of damage.

If on inspection the internal thread is damaged and/or worn and consequently the ERN is either a sloppy or poor fit, then a repair is required.

I mount the head on an angle plate on the Mill and bore out all the old and damaged threads. I then measure the ID of the smooth bore left; add two thousands of an inch to this dimension. Now make up a sleeve which has its OD to the same numerical value; in other words it will be 0.002 inch larger than the hole! Internally screw cut a new thread which compliments your ERN, which will be in perfect condition; if notyoumust make or buy a new one. The length of the sleeve should be about 1/8thof an inch longer than the depth of your hole. When your new sleeve is finished, shove the cylinder head in the oven for ten minutes and then drop the sleeve in and finish off with three (120 degrees spacing) small welds to âbelt and braceâ the job. The reason for making the sleeve 1/8thinch too long will become apparent when you do the welding!

Your ERN should be a perfect fit. When tightened up, finish the job with lock wire or other locking device and your pipes will never dangle!

Previously Ian MacDougall wrote:

Thanks Pete, Seager had popped up in my internet search, I will speak to them tomorrow. It helps to know that someone has had a (mostly) good experience. Any chance of a picture of the finished job and spanner?

I didn't photograph the finished job but it looked pristine, accurately cut thread and no obvious sign that it had been repaired. Their custom nuts and spanner are shown on the Norton page of their web site, a bit pricey at £50. I ordered the nut and spanner to ensure an accurate fit in the newly cut thread but with hindsight a decent standard replacement nut (not Norvil's !) fits just as well. The spanner seemed a good idea at the time but is a bit fiddley to fit and short on leverage. I tendthereforeto stick nowwith my standard wrench, although theSeager one would fit in a tool kit and save some burnt leather gloves -- don't ask !. At the time (May/June) they were working on an oversize version of this nut but problems with a CNC machine meant that the flutes to fit the spanner could not be cut on the threaded blanks available, this situation might have changed and could save the welding costs.

Hope this helps.

Previously Ian MacDougall wrote:

My 1956 19S (Alfin head) has stripped the threads in the exhaust port. Has anyone had this type of repair done recently, and if so who did you use? Did they do a good job?

It seems that the best way (maybe the only way) to repair the port is to insert an aluminium alloy sleeve, threaded internally to suit the standard exhaust rose nut. What alloys are suitable for this application? Should the rose nut be steel or would it be better to make it from a material with a similar coefficient of expansion to the head material so that it is less likely to come loose when hot?

Cheers, Ian McD

Dear Ian,

The advice given so far is absolutely spot-on. I would however recommend that you drill a 1/16" dia hole in three of the collar fins and then a 1/16"dia hole in the top aluminium fin adjacent to the exhaust port. You can then wire lock the sealing ring with galvanised garden wire to the cylinder head once you have tightened it (whilst hot) and it will never vibrate loose again. Mine has been that that for three years now and is solid as a rock. The reason for drilling three holes is only so that when you tighten the ring you have a choice of how long you wish the locking wire to be and to make ease of access when wiring it all up.

Regards,

Peter Bolton

I have dealt with Seager for my T120 head using their oversize inserts and can recommend them.

Hi Dan...Nice description of how to make and fit a new exhaust thread insert and also impressed that you can do the job yourself... The only thing that I wasn't too happy with is that you suggest making the insert slightly too long to enable 3 small welds to fix it. Surely the slightly protruding sleeve would be noticed with close inspection and spoil the job slightly? ...Hoping you don't mind but as a suggestion I would make the sleeve about 2-3mm too short leaving it in effect countersunk...(not sticking out). The "countersinking" would then leave room for the small tack welds* to be done internally, leaving them mostly out of sight when the Ring Nuts are fitted and tightened... do you think this could be done?

Les

* As the welds would now be out of site it would seem that you might as well take the weld all the way round the entire insert making the fix unable to shift in any way, yet still remain invisible....Les

Les, sadly not my words but those of George Cohen, thevNorton Doctor. I'm guessing he filed it away after welding, making it too short might mean the weld could be too thick and foul the threads?

but possible tho.

dan

Hello Ian

I have made the jig to mount the commando head in my lathe to turn the knackered exhaust thread out and fit a bronze threaded sleeve so restoring the thread to a better than new material.

If you send me some pictures of your exhaust port i will see if there is enough material to accept a threaded sleeve. bear in mind these sleeves are not a standard thread size and can be made to whatever dimension is required.

Steve Maney does commando head exhaust repairs at very competitve rates and when speaking to him at squires one evening he said to me why did you bother making that jig? i can do the job for x amount of pounds. I could have but i like the challenge of doing stuff like this i replied!

I have just read the late George Cohen's description for alloy head exhaust port thread repair and not wanting to denigrate George in anyway i disagree with his repair method. I have seen quite a few alloy sleeved exhaust thread repairs start to pull out of the head breaking the welds in the process. The very act of tightening the nut is wanting to jack the welded sleeve out of the head.

Much better to screwcut the head to accept an external and internal threaded sleeve. No chance of the nut jacking the sleeve out then

Regards

Peter Shand

I had my exhaust port threads on my '61 Model 50 done by Mike Pemberton a number of years ago. I cannot remember exactly how he did it (bored and inserted I think) but It has been trouble free ever since.

Looks a good repair, glad he pinned it as the one that came on my Commando eventually started to turn in the head and that was unpinned. That had a permanent repair done by Mick Hemmings, he welded the head and recut the thread.

Previously Ian MacDougall wrote:

Hi Peter, your approach to this makes sense. I think it is also Seager's preferred method although their inserts are stainless rather than bronze. I dropped the exhaust off this afternoon; it looks to me as if there is not enough material for a threaded insert so it will probably have to be welded. The port threads had already been recut oversize 30 odd years ago, and after the thread failure last week I rode another 500 miles so plenty of opportunity for the loose nut to inflict more damage. The copper sealing ring was missing entirely and the top half of the pipe flange has also broken (or maybe burnt) away. I was travelling between the Kendal & Applecross weekends, hence the mileage. Maybe I could have abandoned the Applecross event but even then I was almost 200 miles from home. Photo attached so you can give me your opinion.

Cheers, Ian McD

Ian,

I had a rash of copper sealing ring issues some years ago on my own model 19S. My solution was to obtain a length of 1/8 th inch soft copper tubing from a plumbing supply store. I copied the spare sealing ring I had in this material and simply butted the two ends closely together, figuring on carbon depositing to fill the very small end gap. My reasoning was that the tubing being hollow, would simply crush slightly and seal the exhaust port. It worked beautifully and I haven't had that problem since. I also put a thin coat of anti-seize compound on the threads and have drilled a small hole in one of the fins on the rose nut to allow a spring to be hooked over one of the rocker box bolts and have the tension pulling the nut closed at all times so it cannot loosen.

Cheers,

Albert

Previously Ian MacDougall wrote:

Hi Albert

Those sound like useful ideas, I would have used anti-sieze compound anyway. I think Peter also mentioned the spring - on the Commando head a single spring can be hooked onto each exhaust nut, each one tightening the other. With the differential expansion loosening is inevitable and I think the spring should be more effective than lockwire as you describe. I shall see what I can come up with, maybe a brake shoe spring?

Cheers

Ian McD

Hi Ian,

Glad you liked them. The spring I used was one I got at a local hardware store. Obviously I had to do a little jiggery pokery to make it work, but one about 3 inches long was sufficient. Not sure if going to a brake shoe spring is necessary.

Cheers,

Albert

P.S. I also made a head gasket out of 0.020" sheet copper just because I could.