Advice on header connections.

[utopia]

A while back I bought a slightly battered Sil Motor 2-1 exhaust system off ebay.
It has been badly grounded underneath such that the front header is scraped, dented and somewhat flattened, and there are other scrape marks on the 2-1 collector, but its the only system like it that I have ever seen for sale .. and as a bonus it was fairly cheap.
I have always considered that the second can is just unnecessary weight and complexity.
I also rather like the unbalanced look of a single can exhaust.
This system was designed originally for a 900, so I will have to shorten the headers and generally tweek the pipework to fit my 750 .. and in so doing I will also cut out and replace the damaged sections.
It sounds like a rigmarole but the design of the exhaust fits my vision for the bike far better than anything else I have ever seen.
One "problem" though is that it is a big bore system.
I wouldn't particularly have chosen big bore headers on performance grounds (I'm more keen to improve torque and low speed grunt than top end performance) but I'm prepared to suck it and see. I can always consider replacing the header sections with smaller bore tube at a later date, once the general fitting has been established (and if that happens, I would be looking at titanium rather than stainless .. but that's for the future).
Anyway for now, I am looking to just reduce the headers down to std diameter at the exhaust port connections, leaving the full length of big bore header pipe in place for now.
The connections at the cylinder head on the Sil Motor system are not bolted via ring clamps and half-rings as per std but are held in with a pair of springs attached to dummy clamps on the exhaust studs .. as I have casually observed on other systems over the years.
I am unsure whether to stick with this method of attachment or instead to weld in short stubs cut from std headers in order to reduce the dia down to std at the heads, and retain the std, bolted up fixing.
The latter might be favourable as it makes the process of adaptation to 750 dimensions a little easier.
It also blends the exhaust port to pipe diameter step favourably, in my judgement.
But, I was just wondering how those folk that have used systems with spring retaining attachment to the heads have found them to work in practice.
Do they seal adequately/properly ?
Do they use the same gaskets (which are presumably asbestos-filled copper rings) ?
Also, it appears that there is no end flange on the Sil Motor headers .. they just end in plain pipe. Is this how such systems seal against the exhaust port gaskets or am I missing some bits from my system ?
I can see that a thin pipe would give greater pressure on the gaskets and may therefore seal adequately ... but it just looks a bit dodgy to me.
Would I perhaps need different (softer ?) gaskets in such a system ?
Like I said, I probably favour converting to the std, bolted up arrangement anyway, particularly for a road bike where a reliable connection in the long term will outweigh the ease with which the spring-retained headers can be quickly detached for maintenance etc. That system seems more appropriate to a race bike than a roadster.
But before taking the plunge, I thought it sensible to canvass opinion from those with experience of the springy type.
Thanks in anticipation.

ps. I've weighed both systems and it looks like the new system will save around 4kg against my current one, which is std headers with link pipes to a pair of hi-level titanium termis.
With the new system, the total weight of the bike will then be on the cusp of dropping into the 150kg bracket (ie it may just scrape in at 159.9 kg).
Ok, the numerical barrier is only a psychological goal but I fancy breaking it nevertheless.

Right, I'm off to machine some temporary adaptor pieces out of an extremely rusty length of old scaffold tube that I dragged out of the bottom of a local hedgerow.
"Overground, underground, wombling free"

[Nickj]

All of my pukka competition bikes (2T enduro's) has this kind of fitting for the headers and most didn't leak gas or even seep oil. It was also a just a bit easier to get the pipes off for the very frequent ring changes.
I don't see that it should be a problem.

[Mr Gazza]

Mate! You seem to be fighting a head wind!
I'm sure that the 750 Paso used a 2-1 system that would bolt straight on yours, maybe with just a bit of jiggery pokery to get a silencer mated.
I saw a second hand one advertised somewhere fairly recently for not a lot of gold. I'll have a bit of a look for it.
Or come to think of it a bespoke collector for that RoadRacing system that was for sale on here would do the trick?

[utopia]

Hmm .. yes I thought I remembered seeing the springy system used to retain expansion chamber exhausts on racing 2 strokes.
Although it does seem to me that relying on the springs (which can stretch/weaken etc) to provide an even sealing pressure around the joint , is a little haphazard.
I'm fine with spring connections where two pipe sections join but I'm less than convinced that it is ideal at the exhaust ports.
On the other hand, if the spring connections do work adequately it would save a bit of modding work and would also mean that I could fire her up with the new system on in the very near future, to see how it sounds.
Thanks for the reply, Nick.

ps. Did your bikes use the std, fairly rigid gaskets ?

[utopia]

Yes, I do tend to fight headwinds.

Did I mention that the Sil Motor is a hi-level system ?
I began by considering fitting the low-level single can system from the 600SS but then I discovered that their header/collector pipes were plain steel, not stainless .. and most rotted away years ago.
Somebody on a Ducati stand once told me that stainless aftermarket systems used to be available for the 600SS, but I've never found one .. and they're low level too.
Dunno about the Paso but again, I suspect only low-level systems were available (and probably would require more mods needed to fit a monster than my Sil system might need).

It will be a headwind though ... I didn't mention how battered (and crudely shortened) the carbon can is, did I ? Only the end-caps will be useable, I reckon.
But the whole system is sitting on the bike now (albeit with the front header sawn in half) and it just looks the dog's.
I even have a bit of a fetish going about the little "Sil Motor" engraving on the silencer end-cap.
I think its going to have to be a labour of love .. in a headwind.

[Jez900ie]

I have a Sil Moto stainless 2 into 1 on my bike, though it bolts on and has a low level can. Like you you I think the unbalanced look is great, and it certainly sounds the part.

My Suzuki 185 Blue stroke exhaust is held in place with a spring and regular looking exhaust gaskets. It doesn't leak at all.

[Mr Gazza]

Paso would definitely only be low level with all that bodywork on the tail.
Sorry I can't help! Good luck... Hope the wind eases..

[Dukedesmo]

Both my M900 and 916 have spring connected exhausts throughout.

The M900 as it is an aftermarket setup and 916 are like that from the factory. The benefits IMO are that there is room for movement/expansion.

As an example my old Guzzi has fixed into the heads exhausts and the left side was made slightly out of alignment - it fits but is under tension when fitted. The combination of heat & vibrations have caused the flange to split off twice; the first time I thought it was just bad luck/poor manufacture so I welded it back properly (only had minimal welding originally) but it pulled off again.

I then realised the alignment wasn't quite right (the curve of the pipe is not quite enough) so welded a new (thicker) flange on at a slight angle to compensate and whilst its' still not perfectly aligned (if it breaks again I'll look at bending it more) it is better and has lasted thus far.

My point being that spring fittings would allow for alignment/expansion/vibration and would never have broken in the first instance.

Also the Guzzi exhaust is mild steel whereas the Ducatis are stainless and I'm pretty sure stainless generally expands more with heat and is less flexible/more brittle so potentially the movement could be more of a problem?

Neither of my Ducatis have any leaking/sealing issues at the joints (at least not once warmed up) so I'd say the sealing is fine, on that I'd go with springs and flexibility given the choice.

[utopia]

Originally Posted by Mr Gazza

... Hope the wind eases..

Parp !

My preference for a hi-level system is partly because it makes the rear wheel more accessible for, eg brake, chain, tyre maintenance.
Apart from liking the looks, the other reason that I think I favour a longer pipe is because when I originally fitted the hi-level termi system, I thought it felt like it had improved low down engine response .. which I think also ties in with accepted theory.

Also, now that it is semi-fitted, I must admit that some of the scrapes look kinda cool.
They don't really matter functionally, as the pipe is stainless and corrosion isn't an issue.
I might not bother cutting out all the damaged sections .. just the badly dinged bit underneath .. and simply polish around the scrapes.
Patina, ain't it ?

[utopia]

Originally Posted by Dukedesmo

Both my M900 and 916 have spring connected exhausts throughout.

The M900 as it is an aftermarket setup and 916 are like that from the factory. The benefits IMO are that there is room for movement/expansion.

Yes, I thought I remembered seeing it on at least one of your bikes.
Do they both use the same (relatively hard) copper/asbestos gaskets as the clamped-up system ?
And do the pipes have a flange at the end or is the joint at the heads made using just the square-cut pipe ends ?
Tbh, the ends of the Sil headers didn't look to be cut entirely square, against my engineer's set-square.

Not quite sure on the movement/expansion thing.
I see what you're saying but I'm not sure whether flexibility .. at the heads .. is the way to go.
I think I might prefer to focus on flexibility in the rearmost sections of the pipe, rather than the front.
Also, having seen the deteriorated state of the used springs which came with the system (which had stretched and bent their hooks) I'm not sure that I would rate springs as a reliable way of providing consistent "clamping force" at the head gasket.

Thanks for the reply .. all very useful stuff and definitely food for thought.

[350TSS]

My experience with spring retained exhausts is all with 2 strokes, 350 TSS Bultaco and TD3 250cc and TZ350 Yamsels. If I can remember correctly the expansion chamber fitted over about a 30/40mm long stub either cast into the barrel or, bolted onto a flange.
On the Bultaco when you revved it you could watch the header/expansion chamber pushing out about 10mm from the barrel against the retention springs. No gasket was used and it never seemed to leak exhaust gas. The one piece expansion chamber /header pipe was a good sliding fit to the barrel stub but I suspect the exhaust was really located/held in place by the Mini exhaust isolation mount under the foot rest.
On the TD/TZs similarly no gaskets used and again no issues with leakage. Longevity was not a concern as the maintenance schedule if you wanted the bike to stay competitive was:
150 miles change piston rings
300 miles change pistons, rings and small end bearings
450 miles change piston rings
600 miles change barrels, pistons rings and small end bearings
Repeat sequence every 150 miles until
1200 miles change crankshaft.
On my Monster I have a fabricated (MADASL) SS exhaust retained by springs into the exhaust ports in the head, the exhaust flange is about 8mm SS and is a snug but sliding fit over the 1mm wall SS tubular header. I think it is much more likely to leak exhaust gas because the pipe does not fit over a stub if the retention spring is deflected there will be a gap between the aluminium port and the SS header pipe. Mark Lumb (MADASL) did not recommend that gaskets should be used but I, like you, worry a bit about the end of the header pipe over time fretting the step, cast or machined (?) into the head.
If you want /need to make up your own can try these people
http://www.pjengineering.co.uk/categories.php?cat=9

[utopia]

Now that you mention it, I think I must have seen the "twangy" 2-stroke exhaust stubs in action .. possibly in a paddock somewhere, in the 70s, or maybe at a trials event.

And .. funny how you forget the most obvious stuff sometimes .. I once had occasion to test the performance of "washer-form" gaskets made out of alternate, concentric wraps of thin stainless foil and an asbestos-like material. The foil had a wibble in it too, which gave the gasket springiness.
They might be a tad softer.
As I type, I'm trying to summon a trade name. I do remember their works being in Heckmondwike .. well you would, wouldn't you.

Yes, I thought the MADASL systems used the spring method. Dukedesmo's is one of theirs, I believe.
And from your description, my Sil Motor system is exactly the same.

The Sil headers measure up at about 42.5mm bore, 44.5mm OD, so the wall thickness is only 1mm.

Twiddling with the Sil system, a realised that I didn't much rate the fact that there are only two springs at the header joints.
Even clamping pressure all round would seem to need the three legged stool principle to be considered .. ie a third spring.
But that would be too messy.
And then again, there are only two studs anyway .. but nevertheless I feel that either clamps or a third spring would seem adequate whereas just the two springs seems intuitively borderline.
On top of that, the springs on the front header of the Sil system both go to the same side of the anchor ring thingy .. which seems unnecessarily lop-sided.

350 Yamsel, eh ?
That makes the pulse quicken.

ps.
Maybe the ooomph in a 2-stroke exhaust is not so powerful .. and maybe the pressure at the stubs is lower than you might expect due to the "suck" from the spannies ....?
... so to speak.

[Yorkie]

I have a MADASL exhaust on my Monster and have a custom single side one being made for my SS Cafe Racer.

The fittings work really well and I have had no issues with leaking:

photo_44_zpsff54c6f8

They are lovely bits of kit.

Yorkie

[Dukedesmo]

Originally Posted by utopia

Yes, I thought I remembered seeing it on at least one of your bikes.
Do they both use the same (relatively hard) copper/asbestos gaskets as the clamped-up system ?
And do the pipes have a flange at the end or is the joint at the heads made using just the square-cut pipe ends ?

My Monster setup utilises a short pipe inside the head, held on by the plate. This pipe seats against the existing surface so I use a conventional Monster gasket, this pipe has an ID to suit the OD of the exhaust (45mm) into it and has a small internal seating flange for the pipe to butt up against and the springs pull the pipe up to it.

916 uses a different manifold design (like an intake manifold) and has a flat metallic gasket between head and manifold, the pipe then sits onto the manifold pipe using springs, as per the joins on the Monster pipework.

Mine on the Monster is from Madasl so as per the pic in Yorkies post but if you want any pics of anything I can take them it is currently all off the bike because I've got the cylinders/heads off at the moment for bore replating.

[utopia]

Originally Posted by Dukedesmo

Mine on the Monster is from Madasl so as per the pic in Yorkies post but if you want any pics of anything I can take them it is currently all off the bike because I've got the cylinders/heads off at the moment for bore replating.

Yes please, that would be spot on.
I think I can visualise the stubs and how they're clamped from your description but a pic or two would definitely be helpful.

I'm beginning to think that some sort of clamped up stubs with spring attachments might be the best way to go.
Possibly with tapered bores to smooth the transition twixt port and pipe.
The stubs would also eliminate the aforementioned tendency for uneven clamping via the springs .. they would now just be retaining a slip-joint, which sounds much more sensible.

I'm also starting to wonder whether my Sil system should have such stubs anyway, but I didn't receive them.
That might account for the minimal shortening that seems to be necessary to make the 900 system fit my 750.

Much food for thought though.
Its starting to make more sense now.
Thanks everybody.