Mk2a Exhaust Nut

Hi Mark, 

Big C spanner is best. As to where from, look in the NOC shop (tab at top of page) and search for 063968. Cost £11.75 plus VAT. Other sources are available - RGM, Andover Norton etc.

Regards, George 

Tighten the nuts before you go for a run and take the tools with you, when the engine is hot do it again. Use copper grease on the threads.

Wouldn't that help them undo? Or am I missing something. If they are prone to come loose, perhaps silicone sealant on the threads might be an idea.

Big C spanner , tighten up hard as you can with a tab locking ring in place. Turn over tabs into convenient cylinder fin when nut tightened as hard as it will go. Never had a problem with an exhaust nut loosening , damaging threads. 

Copper grease allows you to undo them later with no damage to the thread, as long as they are tight enough they will not come undone. Tightening them on a running engine also helps as the vibration is like a windy gun,

If they are properly tightened — i.e. re-tightened when engine is at working temperature — the locking tabs are a waste of time and money.

If the roses are not properly tightened the locking tabs are worse than useless: they will hold the roses loosely in place so that they can jiggle around and wear out the thread in the cylinder head.

I bought a pair of stainless ones complete with matching  wrench from Seager Engineering brilliant piece of kit

I believe Commandos are more of a problem than Dommies. The rubber mounts being the issue. My PO lock wired mine on the Dommie but with copper grease and C spanner they've never given me any problems. I don't know if lockwire works on Commandos?

Lockwire works but the Tabs are an accident waiting to happen.

A big C wrench and lockwire has never failed me.  Always  release the silencer fixings before undoing the Ex nuts  as moving the pipes  can help a lot with stuck nuts.

Don't know if they are still available, but I have bronze exhaust roses. Never a problem.

Something not perhaps considered is the different expansion rates of metal when they are exposed to heat. Rose nuts made of aluminium or brass will expand to a greater degree when hot than some Roses made out of 'heavier metals'. This means there is less of a tendency for them to loosen, the other problem I have encountered is that some of the Rose nuts available are up to 25 thou undersize. The RGM 'Naval Brass' nuts are machined the correct size and being made of brass they sufficiently expand when hot and {in my experience} don't loosen.

 I have fitted these nuts to my machine and used the readily available lock tabs where the tangs fit between the fins and also embrace the Rose nut itself, (why are they an accident waiting to happen}? The RGM nut doesn't use the standard 'C' spanner  it requires a three pronged spanner specially made for these nuts. This spanner allows the nut to be sufficiently tightened as it grips the nut in three places. Even though I have fitted the lock tab washers they haven't been necessary so far as the nuts haven't loosened. So I'm with Gordon 100% in recommending nuts made from non ferritic metal.

Be your own judge, but after owning a Commando for 33 years the RGM Naval Brass nuts are the best in my view. As long as the lock tabs are fitted with care you wont have a problem but you might not even need them with Roger Myers Brass 'Nuts'

This is only my personal view and experience, do your own research and then make an informed choice! If you do follow this advice then slightly distort the lock tabs before fitting so that they don't rattle. 

Lockwire works but is ugly looking, you drill holes in the nut fins and the head fins and join the holes with lockwire so the nuts can't untighten. It works but why bother when using Bronze nuts and tightening the nuts properly eg when the engine is hot and running works.

Use brass lock rings, get engine very hot, tighten real tight. Check every few months. You'll have no problems.