Nuts (exhaust, castellated. Camel)

Camel, Sahara, Kanguro, Coguaro
Post Reply
Butch
Posts: 94
Joined: 15 Oct 2016 16:47
Location: Essex
Location: Mid Essex

Nuts (exhaust, castellated. Camel)

Post by Butch »

Now here’s a thing. Investigating a loose exhaust box (high level 2:1), I found in fact that the rear exhaust header was quite loose, though the castellated nut itself still seemed to be pulled up OK. The rear nut on mine is still quite pristine, the castellation on the front one has had a hard life by the look of it.

I ordered a C spanner and exhaust gaskets from NLM that turned up in time for me to pull it all off on Saturday morning. The C spanner is really quite something – good stuff. There are no collets for this header fixing (as you probably know), the nut pulls up directly onto the back of the flange on the end of the header pipe. The rear gasket was still there, though rather flaky. The front one better.

I’ve yet to refit as I’m buzzing all the rust off the Lafranconi can for a blow over with heat resistant paint. There doesn’t seem to be much here to stop the castellated nuts from working loose, accepting that the gaskets will crush up and offer some resistance, and that there is maybe some taper involved betwixt nut and header flange. Is this likely to be a problem area? Should I be considering drilling for lock wiring?

Thanks
User avatar
72degrees
Posts: 1549
Joined: 31 Aug 2007 21:24
Location: West Midlands

Re: Nuts (exhaust, castellated. Camel)

Post by 72degrees »

Butch wrote: I’ve yet to refit as I’m buzzing all the rust off the Lafranconi can for a blow over with heat resistant paint. There doesn’t seem to be much here to stop the castellated nuts from working loose, accepting that the gaskets will crush up and offer some resistance, and that there is maybe some taper involved betwixt nut and header flange. Is this likely to be a problem area? Should I be considering drilling for lock wiring?

Thanks
Evguru will be along in a minute. If the thread in the port is good it shouldn't give trouble so long as you retighten with the engine good and hot. Otherwise custom made clips with tabs that go in between 'teeth' on the nuts. I've found his other suggestion of a jubilee clip round the nut with the screw housing butted up against a head fin works - though with a persuaded to fit 2:1 on a 350 in a 2C frame I also lock wire.
Butch
Posts: 94
Joined: 15 Oct 2016 16:47
Location: Essex
Location: Mid Essex

Re: Nuts (exhaust, castellated. Camel)

Post by Butch »

Oh dear.

So I buzzed all of the rust off the Lafranconi silencer the other week and then blew it over with heat resistant black yesterday. Today on refit I've probably found the source of the original problem. The threads in the rear head exhaust manifold are substantially fubared. I'm currently trying to get the big nut in there without further cross threading, but it is not easy - even without the pipe being offered up at this point.

So what's the story for getting those threads repaired?

Thanks.
User avatar
72degrees
Posts: 1549
Joined: 31 Aug 2007 21:24
Location: West Midlands

Re: Nuts (exhaust, castellated. Camel)

Post by 72degrees »

An every day story of older Morinis unfortunately.
Head off and NLM will should be able to get it done, though the turn around time may not be quick. They have done a 350 one for me in the past. Otherwise you might pick up a spare head - though as you might expect, finding one with good port threads, guides and no crack between the valve seats, at the right price, is becoming hard, particularly for 500s.

<Pats pair of spare good 350 heads acquired from Germany>

Evguru or Harrymuffin may have suggestions for a more novel solution as there have been a few tried over the years.
Butch
Posts: 94
Joined: 15 Oct 2016 16:47
Location: Essex
Location: Mid Essex

Re: Nuts (exhaust, castellated. Camel)

Post by Butch »

An addendum to that …

I could only get that nut to spin in cross threaded. This led to it tightening up before nipping up the crush gasket properly, and so probably led to the previous one burning through. I have spoken to NLM and as mentioned here they will do that as a job – turn around for that will depend on what others they have as they prefer to batch them up to reduce the set up time. Their advice – if it will hold then go with it as is and then maybe send in the head next winter.

I slotted the threads on the nut to encourage them to cut a little and then used some extra leverage on the excellent NLM supplied C spanner. After a decent ride out I then found I could get quite a bit more turn on the nuts front and back. Will it be OK now? We can only see if it fails again under further use (not ideal). That nut does appear to hold well at the moment so it may be I could make up a spacer to go in with the crush gasket to help compress it better – or even double up on the gaskets there I suppose.

Either ways, it feels like a bodge there and I don’t like it so I’ll probably pull the head come the autumn anyway. God knows what else that might reveal, this bike is turning out to be a bit of a lemon.
User avatar
72degrees
Posts: 1549
Joined: 31 Aug 2007 21:24
Location: West Midlands

Re: Nuts (exhaust, castellated. Camel)

Post by 72degrees »

I'll confess to doubling up on gaskets when needing to get a bike usable quickly with a far from perfect port thread. I suppose dodgy threads may suggest that someone has at least had that head off before, which makes you wonder what you might find if you remove it. I've had a head crack between the valve seats (rarer on 350s), but the seats didn't actually shift and I couldn't discern any effect on performance. Then I hadn't noticed any smoke or excessive oil consumption when still running with that head, that NLM said the valve guides were toast on. I only swapped it because the port thread was completely gone and I had a spare available.

All being well, I'm going to get the spare 350 heads I recently acquired up to tip top condition, including a bit of port polishing, with a view to putting them on the hill climb engine for next season. For the moment, that's in "if it works don't fix it" territory.
norbert
Posts: 750
Joined: 15 May 2007 15:15
Location: Lübeck/Germany

Re: Nuts (exhaust, castellated. Camel)

Post by norbert »

Butch,
you should carry thre spanner with you and fasten the nuts everytime you heated up the motor. One day will come the moment that you cannot fasten them anymore. Then it´s ok :wink:

good luck
norbert
Post Reply