Hitchcocks Forum

Hi all, perhaps you can help with a very curious incident. On my 2015 B5 bullet I replaced the existing log with our hosts 91130 exhaust system (compatible with existing ECU). A lovely thing, works wonders though did take a bit of fettling to get it to fit properly. Now, it comes supplied with two exhaust gaskets to cover different depths of the exhaust port. I found I needed both for a good tight fit. I carefully attach said exhaust, check for leaks, none, so off I ride. All works well, but I start to get the occasional pop on the overrun. Bit loose I think, so I tighten the exhaust a little. Starts to pop a little again, so I tighten again, though no evidence of any escaping exhaust around the junction between pipe and head. All ok, then it starts to pop again, so I tighten. This is getting silly thinks I, these nuts are loose, I know everything shakes loose on a bullet, but this is just too silly. So I strip down the exhaust intending to silicon-seal the gasket to pipe junction and thread-lock the nuts, and find NO GASKETS. Just a trace of grey dust. Where have they gone? Do they burn? Have they been abducted? Did I forget to put them in? Two new ones are or order, but I know I shall stay awake at night wondering what happened to the last ones.

Probably burnt out if they were made without asbestos, check if the replacements contain asbestos, although these days I doubt that they would. I don`t know what is used in its place.

Exhaust pipe seal 510804 is what I call a cement biscuit, perfectly useless, it crumbles and gets blown out of the exhaust. H provided me with copper seal 582638 (do check number with H on phone). There are a lot of small parts not shown online and not in the printed catalogue. You may need two of these, you may need spares if you adjust the fit again. I found it important to get the down pipe square into the seal and the flange nipped up before fitting the silencer - if it goes in at an angle it crosses over the seal. Your new pipe has a taper at the end to aim inside the seal(?) Absolutely no silicone bath gunk is needed with the copper gasket. This should fit all Bullets with bolt-on exhausts

Thanks Jefrs, I suspect that may have been what happened. The old 'log' came with a copper gasket, though it was so mangled that it took a lot of effort to extract the thing from the exhaust port. I have a couple of the cement biscuits arriving tomorrow, I'll put them on and see how it goes for a bit, but i think new copper washers may be the order of the day...

DOH!!!!! Now I really must get some better lighting in the garage. My gaskets were not missing, oh no, there were still there, all intact and everything. It turns out that they were so perfectly squished and of exactly the same colouration as the inside of the exhaust port that I assumed they were just the exhaust port! It was only when I went to fit the new ones that I ran my finger around the inside of the port to clear any particles that one popped out onto my ring finger. It was like my Enfield was marrying me. Quite a tender moment really. Mystery solved. Well, one of them. There are always mysteries with Enfields.

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I guess that you accepted?

Delighted to report that with two new gaskets and a small smear of silicone gasket sealant that the popping on the over-run has gone. Must have been a very small leak on the head-exhaust junction.

All this reminds me that I really should reseal our Bullet pipe/ ex. port. Been popping & banging on over run for months now, never really bothered me and it did keep the tailgaters off my rear end