First Time Owner 250 CSR-exhaust query

[Wal1]

Been promising myself a brit bike for years and am thoroughly enjoying restoring my 250 CSR with my dad, just about to put barrel and head back together and the exhaust on the head is just a push fit from what I gather, is there a sealant that you would recommend to use or do most people just go with a dry push fit. Cheers in advance for your help

[Janet]

I use flexible high temperature resisting gasket goo.

[Rob Harknett]

Never was a sealant used when new or few years old. Never used a sealant on any of my bikes. Perhaps over the years some have got worn or damaged. Damaged???? maybe damaged by scraping off sealant each time the engine is dismantled. Same way head joints get damaged by removing sealant, But they can be refaced, Exhaust ports just get enlarged making sealant needed.

[clanger9]

Mine's just a push fit. It seems fine, no leaks or anything.

[Janet]

OK Rob, I accept your reprimand. Good for you, never using sealant. Now tell me how I get the exhaust pipe to seal when it didn't seal properly at the time I acquired my G2, seven years ago, resulting in backfires and flames from the exhaust pipe when I shut off the throttle? Is is better to keep the backfires? Of course you are right. Everything fitted perfectly when the bikes were new but over the years parts get worn or damaged and, in some cases non-standard remedies are required or the bikes go for scrap. Imagine if we held the same view when bits of ourselves wear out.

For other people's information, non-setting flexible gasket goo doesn't need any rough scraping off, it can be rolled off with fingers. It comes off even easier with a smear of oil on the surfaces first. It's only a gap filler, not glue. I'm not suggesting anyone uses it, just saying that I do.

[SPRIDDLER]

I agree Janet; in an ideal world the bits would fit.............but often they don't.

The manuals will advise swageing out the end of the front pipe by hammering a carrot shaped tapered hardwood mandrel into the end. I tried it, once, years ago, before I nearly lost the will to live, but the theory is more successful than the practise. For one thing, holding the pipe without damaging it whilst one hammers the taper into the end is not easy. More difficult is reducing the end if it is inadvertently swaged too much. Even then I just couldn't get a perfect seal between the pipe and the port in the head. The smallest of gap will produce an air leak and provoke backfiring on the overrun

I don't know if Lightweights have the short bracket at the bend of the downpipe but if they do it's important that it is shaped so that when fitted it 'preloads' the pipe, pushing it into the head rather than holding it away. The port in the head must be completely free of any historic carbon build-up.

Silicone is ideal and invisible if applied with care. I wrap some masking tape around the pipe where it enters the head then remove it when the silicone has been applied so that the silicone doesn't smear down the chrome of the pipe.

Life's too short to swage downpipes.

[Rob Harknett]

I actually got a lot of backfiring and flames coming out the silencer of my 55 G3/LS in 1961. Old boy across the road caught me one night, you wanna fix that exhaust Robert. He called me over at the week end. Hit the bend of my exhaust, which in turn gave a sound of the pipe hitting up in the port. Though so he said. He undid the pipe fitting and silencer clip. Shook the pipe loose, rammed it in the port, tightened the exhaust pipe fitting. The tightened the silencer clip, gave the pipe another knock to check it was fully home. No more back firing. I still make sure I follow that procedure fitting the exhaust system. This seems to suggest, it may not all be down to wear, perhaps down to repro pipes not going fully home. eg the bend perhaps preventing this. If the end of the pipe is not up against the head all round, there's a gap. This does suggest the pipes did not need to be sealed gas tight when new, they did need to fit tight against the head. Today we may have wear and pipes that do not fit good. So need to use a sealant. This is also more likely to be needed on a nice clean SAND BLASTED head. Prewar pipes fit OK as they fit on a spigot. The pipes even have a cut, so they can be opened a bit to ease them on the spigot, The clamped on, almost gas tight. Unfortunately, spigots on the old iron heads were thin, brittle and got broken. Push in pipes solved that problem, but gave the air leak problems.

[ajscomboman]

Normal builders low modulus silicone is more than adequate for sealing the exhaust pipe and has the benefit of allowing the pipe to be easily removed at a later date if need be.

[cbranni]

Where about in Swansea are you, I'm in Southgate.

Colin

PS I use cheap silicone ...............does it for me

[ajscomboman]

Works every time Colin and has done for 30yrs so I see no need to use anything else.