Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Tightening Manifold Nuts on M3W

I have tried to tighten the manifold nuts on a number of occasions on my M3W (currently in over winter storage in the south of France) and using various sockets and ring spanners, succeeded to the limited extent of the tooling I have at my French house. I was going to buy a curved shank, thin ring, manifold nut spanner to take out to France with me at the beginning of June. Can someone please remind me of the size of the exhaust manifold retaining nuts on the S&S engine. Mine is 2012 vintage. I seem to remember that they are AF not Metric, which given the US origins of the engine is no surprise. If anyone can suggest a better tool, I would be happy to buy that. My M3W parts book lists the exhaust studs as 5/16" UNF x 1.7", but does not list the size of the nuts. 5/16" thread would normally suggest a 1/2" AF nut but I have a slight feeling that the nuts may have been 9/16", which common for a 5/16" thread, if softer non-corroding material exhaust manifold nuts are used (monel metal or brass), with thicker walls.

Wilson

The standard exhaust nuts are 7/16 A/F spanner size, 5/16 UNF thread size. These are a tight fit for all but the thinest of spanners. A good alternative is to use aircraft high temp Kaynar type nuts, sometimes known as "Jet nuts", usually with a silver anti seize coating. These nuts come with with a 3/8 A/F spanner size that gives a very useful bit of extra clearance for fitting. A Military Standard part number for these is MS21043.

I will check but I should have some 5/6" UNF Jet/K nuts, as all the nuts in the Judd engine in my Ralt single seater hill climb car were UNF Jet/K nuts or 12 point nuts. I use to have a large chest full of jet and bi-hex nuts and grade 8 aircraft bolts in all different sizes but various friends have raided it over the 25 years+ since I was forced to give up speed hill climbing, when old cervical spine injuries caught up with me trying to take corners at 3 to 4G loadings. I will go down to the garage and check. Many thanks for the info. I have a feeling that someone has put 1/2" AF nuts on my exhaust manifolds which may explain both why they are very difficult to keep tight and to get a tool on to them. If I take new 5/6" K nuts down with me, I may have to cut the old ones partially off with a carbide disc in my Dremel tool and then split with a cold chisel.

Wilson

Lots of chat about M3W exhaust studs and nuts in this THREAD.

I started the original thread six years ago. All of the aircraft grade bolts have held without fail. Helicoils as well. I'm sometimes amazed when things go right and I can just let it go!

Does anyone remember the part number for the ARP studs. I contacted them and got a very prompt response with a query. "Do they have a guide nose or bullet nose on the end?". However I don't know the answer to this. I am sure I saw a photo of someone's ARP exhaust studs but of course cannot find it now. I do have 5/16" UNF K/Jet nuts in my garage but they are titanium and that tends to gall, so unsuitable for exhaust stud nuts. I will order 4 of the silver plated ones from LAS.

Wilson

PS Could not order 4 nuts as at £1.22 each, below the minimum order, so ordered 8 nuts to have a spare set, which means they will never ever be needed (reverse Murphy's law). W.

According to the old thread I linked to in my post above, they are ARP3101625.

ARP say that is no longer a valid part number. I found the photo I had been looking for of an ARP stud and sent that along with the original Morgan specs to ARP. I will post the new part number when I get an invoice from ARP.

Wilson

Wilson - the exhaust header nuts on your m3w should be Jetnuts as per Planenut's reply above - 3/8th socket - 1/4 drive sockets fit nicely on a long extension.
That is unless your local garage has been fiddling.
They never come loose.

Steve,

I have to admit I have not looked at the nuts since it came back from you. I presume you replaced the nuts that were previously there, which from memory were 1/2" AF cadmium plated nuts, which when I changed the exhaust to a G56, were a nightmare to undo and do up. It was just one of the things I thought I should look at, when I get it out of storage, as there is an exhaust rattle and I was going to do an end to end on the "pipes" but it is probably the heat shields. The metallastic bobbins could also probably do with replacing but I have spares of those. I think in AF sockets I only have 1/2" and 3/8" drive in France, so I will take a deep 3/8AF 1/4" drive socket out with me. I do have a large 1/4" drive metric set with various extensions and both powered and unpowered ratchets.

Wilson