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Silencer tailpipe

I have just finished making a new silencer box to Bill Sheehan’s instructions Re earlier contributions on the subject. I have tried to scale up the tailpipe from a 1927 List of spare parts using the width of the tailpipe as a datum, but find that this only gives a box dimension of about 15 inches long! Clearly not drawn to scale with the tailpipe. Bill can you help with the length and bend angles of your original tail pipe (the short version) I use a separate tail pipe fixed with a clip, was this the case on the original or was it welded to the box like the 29/30 long pipe versions I have seen? I think I made my previous one detachable as I could not get it between the cross members with a fixed pipe.

Re: Silencer tailpipe

Ian, the tailpipe on original pattern silencers was integral with the silencer box. As far as I can remember (box with A7 books not unpacked yet!) the tailpipe was 7" long.

David

Re: Re: Silencer tailpipe

Thanks David,That is about what I expected,looking at the 'Chassis lubrication' plan view of the chassis the pipe appears to finish about an inch past the centre of the shock arm bolt

Re: Re: Re: Silencer tailpipe

The New silencer is now finished and fitted to the car; I thought it might be of interest to give my observations on the comparisons with the ‘straight through’ silencer I have used for many years. At first I was disappointed that it did not seem very much quieter on tic over, but on the road at speed it is quieter than the old one, in fact I can now hear a ‘hum’ in the rear axle that I didn’t know I had! Down hill on a closed throttle occasional ‘popping back’ has been eliminated. As you may recall from earlier posts to the forum, the main reason for making a new silencer was that I always suspected that my problem of not having a clean pickup from rest no matter how many adjustments to the carb I made, was in some way due to the silencer not having any baffles. Well I am pleased to say that I no longer have any problem with a clean pick up from rest. It appears from this that a slight backpressure is desirable on a standard engine. So all in all a good result and well worth the work, and in true Austin 7 fashion it didn’t cost me a penny! Thanks to all who have helped with original details on construction to make this possible. “The Forum at its Best”

Re: Re: Re: Re: Silencer tailpipe

Congratulations Ian, a good outcome in the true sense of the word!

So, what did you use for the 3" casing? How far in from the edge (or how far off centre if you prefer) did you drill the baffle holes? 1" diameter? Each baffle offset 180 degrees? What gauge material did you use, and did you "cup" the baffles to a snug fit? Any alowance for moisture drainage? I will be having a go myself, so am interested in your construction details. I have a surplus 75mm diameter drive-shaft that looks useful for casing material (at the right price).

Cheers,
DG

Re: Re: Re: Re: Re: Silencer tailpipe

There you go Ian, good to see it worked out OK - remember the old Irish adage "now that it works in practice, let's see if it works in theory". In my past submissions on the subject I didn't mention that for late-'29, early-'30, models there were considerable changes from that described. The body itself remained the same, but instead of the (early)pipe from the manifold having a kink to enable the muffler's entry pipe to be horizontal, the pipe continued on it's same angle, therefore the entry pipe on the muffler body was angled up to suit. On these models, there was no mounting bracket on front and the rear bracket was stepped (but different shape)as per the stepped front bracket on the earlier mufflers. Whilst the early type had a kink in the exit pipe (it comes out near the rear tyre but I don't think this is shown on some lubrication charts), the later versions had a longer exit pipe with a distinct "S" bend to them. In either case I didn't describe the original clamp with internal half-pipe and external spacers through which the clamp was bolted, all fitted over the "Join" where you've slipped the engine pipe inside the muffler inlet pipe. The appropiate Parts List shows these items clearly. The different muffler construction including it's pipes is of no interest to Ian or Dennis, but may be of use to anyone making their own muffler to suit the later model. Cheers, Bill

Re: Re: Re: Re: Re: Re: Silencer tailpipe

Hello Dennis, Sorry for the late reply but have been busy. I have made the main body out of 3 inch “Bristol” bus exhaust pipe (the same as all the others I have made in the past) they are good quality steel and of a thick gauge. As for the 3 internal baffles, I used the round galvanised lids that are fitted to industrial electrical conduit junction boxes (not sure if you will have these down under) these are about 18 gauge and only needed a couple of rubs with a file to fit inside the pipe. I chain drilled and filed out the 1 inch holes keeping them ¼” in from the outside edge, these were arranged so that the middle hole was to the top and the other two to the bottom, I didn’t worry to much about water retention as if its there its there, being divided into four chambers instead of one will not make a lot of difference. I noticed in the original Spare parts lists that 3 rivets are shown along the side of the box. So I riveted two small angle brackets to each of the baffles and slide them inside the pipe and fixed them through the sides just like the original drawing. The ends were made from 16 gauge steel, chain drilled and filed to a ‘hammer fit’ over the end pipes and also a tight hammer fit into the box itself. The end plates were knocked down to be ¼” below the end of the box. The whole lot was silver soldered together (perfectly done by my eldest son). A new front and rear bracket to resemble the ones in the parts list was made from 1/8” plate. The whole thing painted with two coats of heat resistant aluminium paint (that is starting to burn off already!!!) Total cost a nice round ‘zero’ as I had everything in stock.

Re: Re: Re: Re: Re: Re: Re: Silencer tailpipe

Fan 'effing tastic Ian! That is the sort of detailed info that this list excells at. Great to hear that it worked out so well. Thanks also to Uncle Bill for the dimensional details. The information library is slowly filling.

Cheers,
DG