401 exhaust manifold

[RALPH M]

I noticed the flanged connector to the rear manifold was blowing slightly and upon investigation I see that the threads on the cast manifold itself are worn down and as I tighten the ring clamp, it slips and never quite gets a tight seal. Any suggestions??

[Stefan]

Worth trying a new exhaust ring - it might have enough meat to bite on the tired old thread - and you could clean out the cast iron threads carefully with a file.
I made up my own rings from brass stock on the lathe once. But don't make the same mistake as I did; after a fast run the exhaust blew again and both rings had drooped and distorted, in a surreal, Salvador Dali-esque style. I think the correct material should be bronze or bellmetal, something with a higher melting point. Engineers please advise!

[Stefan]

And dont forget to lock wire up the Bronze flanges so they cannot start to creep round and get undone.
Ideally one of those aviation lockwire pliers and some stainless steel wire. Excellent gadgets.

[Thor]

I have a customer who has consulted a Midlands business called 'Slinden' who claim to do reliable iron welding. www.castironweldingrepairs.co.uk - I have no connection. They might be worth a try ?

[HughMiller]

I think this is the same problem as appeared in this forum in October 2018 as 'Another 403 problem'.
In that thread, Dave Dale said (I hope it's OK to quote you, Dave):
"A few years ago I had the same problem with my 403. As Geoff K correctly observes, the threads in the manifolds were corroded and allowed the bronze nuts ( correctly called 'peg nuts' with reference to the tool that is used to tighten them ) to slip over the threads when an attempt was made to tighten them. Spencer Lane-Jones had supplies of replacement nuts in stainless steel and in three slightly dissimilar sizes of thread, to accommodate varying degrees of manifold thread wear. If one of the three sizes is a close fit, the nut can hopefully be tightened up without too much force or used as a die to cut its own thread into the manifold by reshaping the faulty existing thread, thus obviating the need to subject the manifold to a proper re-thread. At least, that is how I understood it at the time and it worked for me. You could try […] office@spencer-lj.com Telephone: 01985 847133. Hope this helps.
Dave Dale."

[peterg]

I had the same problem last year. The people who refitted my engine managed to put the exhaust pipes into the wrong port of the silencer so the front pipe came up at an angle and never sealed with the results you mentioned.

I got a set of stainless nuts from Geoff Leigh in the Manchester area. I don't have his details but he appears to be well known in the circles.

In my case the stainless nuts didn't do the job and I had to get a second hand manifold from Spencer James. However, they are now very thin on the ground.

[Des]

I've fixed similar on a motorcycle exhaust that had been previously bodged by squashing the nut oval, some thin copper sheet, almost tinfoil thickness from an old radiogram or something used like ptfe tape in plumbing fittings. Not sure there wouldn't be galling between copper and bronze though.

[Geoff Dowdle]

Ralph ,
many years ago I had a large hexagon die nut made to clean/recut the threads before fitting a new brass exhaust rings (see attached photo)

I have found that the problem with most of these faulty exhaust manifolds is that rust builds up between the thread and the exhaust rings .
The die nut recuts/cleans the thread in most cases . It is important the renew the exhaust rings as the original are often damaged or oversize and lubricate the thread with high temperature grease before refitting.

A 400 owner in Australia had a manifold that the thread was completely removed . An engineer built up the thread area with weld and machined a new thread . This required a special gig to hold the manifold in the chuck of a large lathe .(see attached photo)

Geoff

[peterg]

From enquiries with IN Racing, Nottingham last year, rebuilding the manifold threads it a job they would consider but haven't done before, so would do on a hourly cost basis.

[RALPH M]

Many thanks for all the advice/ideas from top class re engineering to bush engineering fix. A spare new “peg nut” came with the car so will compare that to the one fitted and also remove the manifold to have a closer inspection. I have the time as frustratingly cannot really go anywhere, like the rest of us I guess. Stay safe.

Mike from sunny North Devon

[RALPH M]

Just to say I have managed to effect an airtight joint by using Holts sealant but suspect it will not survive any spirited driving so I am looking for a decent spare manifold (rear) with good threads. Just PM me if you have one or know of one.

[RALPH M]

Just to say many thanks to Bill at Pegasus for sorting some decent manifolds for me. At the moment my use of Holts sealant is working well and have yesterday driven my 401 along the beautiful Devon roads for the first time for months.