Gas tight exhaust connection

[SUPERGRUMPS]

On fitting the exhaust front pipe to the cylinder head of my C15, I was surprised there is no gasket or sealant to make it a gas tight seal, or am I missing something. any comments please,

[AdrianS]

That's how the pipe fits! Just push home and the support brackets keep it in place. I have seen people put exhaust sealer around the pipe -but I never have personally.

[OVERTHEHILL]

I used a little exhaust sealer on mine I think it helped to slide the pipe in, but I have done it without and it seals ok.

[chaz]

the expansion of the pipe and head should be enough to seal, I had a Enfield bullet 500 that had red sealer around, did the job but looked a mess and a bu99er to get out when the head had to come off. main problem is ill fiitting pipes rattling making the head bores oval. you could try modern compression rings that we use on modern bikes, available in many diameters and either asbestos style or copper crush

[cdsdorset]

Use RTV silicon flexible and stays put.

[hoogerbooger]

I've not taken the exhaust off before, but am intending to a) to rule out lack of adequate seal as a possible cause of my tick over flutter and b) as the silencer doesn't silence much, so I may try a replacement .....and at least want to have a good look inside the current silencer it to see if internal corrosion may be part of that issue ( Am I correct to think there should be some sort of perforated tube/baffle internally....wot may have corroded away after 25 years of sitting in a garage doing #ugger all ?)

So with the push fit at the head, should I be cleaning up both head and pipe and using grease or something to aid fit. Advice appreciated.

Also should I be getting a sealant for the joint at the silencer?  If so any particular type ?

[cdsdorset]

Clean up the cylinder head and exhaust pipe. Fit using RTV.
Same with the silencer fitting.

[hoogerbooger]

RTV: On the mating faces or just around join after  after mating.

Am novice...so forgive me as needed.

At head I presume I don't want to be forcing silicone inwards.

[Spaceman]

On one of my non-BSA bikes, I assemble the joints in the exhaust system with Halfords Firegum paste that dries hard and seals effectively. However, on this particular bike, the downpipe is held firmly against the inside of the engine exhaust port with a copper gasket used to seal it as tends to be the case with most more modern bikes.

The BSA C15 was derived from the Triumph Tiger Cub and, as is the case with most Triumphs of that period, the downpipe on the Cub was clamped over an exhaust stub that screwed into the cylinder head to provide a gas tight seal. Unfortunately, Edward Turner did not copy this feature over to the C15 after he took over BSA. What you are left with is a hit and miss way of sealing the exhaust port that most times works ok but sometimes leaks badly.

If it was me, I would consider buying a copper gasket (circular in cross-section), if necessary, from another bike and then fitting it inside the exhaust port such that the downpipe ends up being pressed against it. I've never seen RTV used in this way but have seen people using Firegum but that tends to be a bit of a messy solution.

[cdsdorset]

Clean the pipe and port smear RTV on the pipe and in the port. Push the pipe into the port , you cant do any harm with it. RTV is flexible and woll allow some flex/movement without leaking.

[Spaceman]

If you are going to use RTV, it must be Red RTV although this is designed to withstand temperatures of only up to 343 deg C in general.

[cdsdorset]

If you are going to use RTV, it must be Red RTV although this is designed to withstand temperatures of only up to 343 deg C in general.

Really?
Ive been using clear RTV for years on customer bikes and my own.  Have on more than one occasion removed RTV that i used years before.

[JulianS]

I used one of the Loctite copper coloured silicones, cant remember if 5990 or 5920. Worked fine on my A10 but hard work to get it off.

Information on ther Henkel website

https://www.henkel-adhesives.com/uk/en/product/gasketing-sealants/loctite_si_5990.html

Fortunately a replacement exhaust fitted without needing sealant.

[Spaceman]

Never used RTV silicon for this purpose and can only go by the data sheets which specify temperatures of up to at most 350 deg C which I would have thought is at the lower limit of the temperature at which the upper part of a downpipe reaches. For comparison, an exhaust that has turned blue will have reached a temperature of at least 650 deg C.

Nevertheless, the proof is always in the pudding and it seems that an essentially rubber gasket is able to survive the exhaust temperature of the average BSA motorbike. However, my preference would still be the use of a copper gasket if BSA's push fit exhaust was leaking badly!

[cdsdorset]

A copper gasket wont seal around the outside of the pipe. A copper gasket is fine if the headers are bolted in with a retaining ring but most british bikes rely on push fit. Most pipes will leak through the gap between the pipe and port due to years of movement wearing the port oval.