SF1 Under engine balance pipe

[RJS]

I'm having trouble getting my exhaust system with the big under engine balance pipe to fit properly. I have the exhaust pipes and collector box that came with the bike and a set of nos Conti silencers from Wolfgang. The bike was in pieces when I got it so I don't know how well things fit originally, or if something may have gotten bent in 35 years of storage. I have managed to get everything bolted together and the exhaust system looks right but on the right side the collector box/balance pipe is just slightly more than a millimetre from the frame cross piece just behind the gearbox, and on the left side the exhaust pipe is .5 mm from the head of one of the primary cover bolts. Surely there should be more clearance on both sides. How much clearance should there be ion bikes with under engine balance pipes?
If I can't figure anything else, I may take off the balance pipe, heat it up and bash more relief on the right side. Anybody got better suggestions? I know I could eliminate the balance pipe but I don't want to do that if I don't have to. I don't know if the photos will show what I tried to explain.

 

[sfcpiet]

Do you have the silencer (the balance pipe is a preliminary silencer of sorts) support bracket that fits to the lower rear engine mounts? This will position the silencer properly and afford necessary clearance to both frame and cases, as long as your headers have the correct bend (many aftermarket headers do not and their fit can be pretty lousy). The whole caboodle shoud be loosely fitted, first the silencer and bracket tightend, then headers at the head, header to balancer clamps and finally balancer to silencer clamps, lining it all up as you go.

piet

 

[TeddyG]

I want a mid pipe for my 750 that came w/ a Malcolm Cox exhaust system w/o any mid pipe. There are varying opinions on the benefits, but Wolfgang swears by them. This is the mid pipe he offers but it doesn't appear the fabricator is still making them. Is yours like this or different? A few more pics showing the problem will help others to advise you better.

 

[piranha-bro2]

The original is completely different from yours, Teddy. It's a large bulbous affair and is far more complex than a simple joining pipe. That looks more like a Ducati SS item. I rebuilt the motor for a bike that came with one of those (source unknown - maybe Staintune?) but I on-sold it, as it was an awful fit and dragged on the road far too easily; the issue may have been non-std headers, but I can't say for sure.

If replacing the underbox with a straight thru more cornering clearance can be gained by bending the headers to raise them at the point that will hit the ground when cornering. IMHO it's actually easier and neater to have new headers made that eliminate the need to the join and can be custom bent to give excellent cornering clearance.

I'd love to know what the science behind the supposed 'benefit' of that crossover is. Personally, i don't buy it.

 

[sfcpiet]

The original is completely different from yours, Teddy. It's a large bulbous affair and is far more complex than a simple joining pipe. That looks more like a Ducati SS item. I rebuilt the motor for a bike that came with one of those (source unknown - maybe Staintune?) but I on-sold it, as it was an awful fit and dragged on the road far too easily; the issue may have been non-std headers, but I can't say for sure.

If replacing the underbox with a straight thru more cornering clearance can be gained by bending the headers to raise them at the point that will hit the ground when cornering. IMHO it's actually easier and neater to have new headers made that eliminate the need to the join and can be custom bent to give excellent cornering clearance.

I'd love to know what the science behind the supposed 'benefit' of that crossover is. Personally, i don't buy it.

First and foremost Quentin, it brings the noise level down to the legal limit of the time. The original Conti straight-through silencers can't really live up to their name. Maybe not so important in Oz, UK or US, where obnoxiously loud exhausts seem to be the order of the day and vehicle inspections seem to be extremely lax or simply non-existant. The wide-open spaces of Oz or the US cannot really be compared with heavily congested central Europe either! In much of noise-conscious Europe, it's pretty difficult to get away with an over-noisy bike for very long. Even modern-day Italian traffic has become strangely quiet... mainly ancient petrol-heads like us still making anti-social rackets, along with a few kids on scooters tuned to within a millimetre of their exitus.

I find that stock Laverda twins benefit greatly from the additional cross-over. Even the later SFCs had a conjoined 2-2 system. It offers greater expansion room for each cylinders' exhaust gases, providing for less back-pressure (that would be the scientific part!). This improves low-down torque, making riding in traffic a lot more pleasant. Case in point; a mate rode his SF2 for several years with the cross-over deleted. Once he got sick of renewing headers and/or header gaskets every couple of months, he reverted to the cross over. He immediately remarked how much smoother the engine pulled, making the ride overall more pleasant. It also made following him more enjoyable...

Of course, if constant hooning with a high-strung engine spinning at more than 5000rpm is your thing, all this hardly applies.

piet

 

[TeddyG]

SFCPIET- do you think this type of mid pipe I showed (if I can find one) would work as well as the OEM? And does it matter where the mid pipe is located, since I've seen other ones that are joined at the headers near the cylinder. I would like to try one just to see if there's any mid range improvement-

 

[arancia]

Count me in as a believer in the value of the OEM underslung intermediate muffler in making the mounting solid and the later bikes more pleasant to ride. Yes, they've hit the road a few times and got scratched but if the rear spring pre-load is set appropriately then under normal road riding conditions (not talking about track use) I think there's adequate ground clearance.
When the clamping of that box broke then the vibration increased significantly till I got it secured again.

 

[arancia]

silencer ....... support bracket that fits to the lower rear engine mounts?

piet

RJS, since you say your bike came as boxes of parts, the piece you need looks like this, though this one is damaged.
Even when in place the clearances around the headers and the under-box are tight so, as Piet says, assemble it and space carefully then tighten from front to back. My experience is that the clamping band around the underslung box is essential, when not tight the bike vibrates excessively and becomes unpleasant to ride. I have used four 4" worm drive hose clips as temporary fixings as getting the OEM clamp band replaced is not trivial.



Piet, this appears directional, never really thought about that before, perhaps its orientation is important, unlikely that I have one that hasn't been disturbed on any of my bikes as a model, any thoughts on which way the longer side should face?

 

[RJS]

I do have the factory support bracket and the headers are original equipment and look like their shape hasn't been disturbed in the 35 years they were off the bike. Your suggested tightening sequence isn't the one I used (my guidance came from the "green book") so I'll try your way next and see if there's any improvement of the fit. It looks to me that if I can rotate the balancer forward in the clamp that fixes it to the support bracket, I may be able to get more clearance, How much space do you have between the balance pipe and the frame on the right and between the exhaust pipe and the primary bolt that's closest to the pipe on the left? Thanks.

Rick

RJS, since you say your bike came as boxes of parts, the piece you need looks like this, though this one is damaged.
Even when in place the clearances around the headers and the under-box are tight so, as Piet says, assemble it and space carefully then tighten from front to back. My experience is that the clamping band around the underslung box is essential, when not tight the bike vibrates excessively and becomes unpleasant to ride. I have used four 4" worm drive hose clips as temporary fixings as getting the OEM clamp band replaced is not trivial.

View attachment 93275

Piet, this appears directional, never really thought about that before, perhaps its orientation is important, unlikely that I have one that hasn't been disturbed on any of my bikes as a model, any thoughts on which way the longer side should face?

i have the support bracket and there are marks on the crossover box that show what the orientation was originally. Clearance is really tight - about 1.5 mm total on both sides combined. I think I need more. I’ll keep on adjusting to see if I can get more.

 

[piranha-bro2]

First and foremost Quentin, it brings the noise level down to the legal limit of the time.

piet

I'm happy to be proven wrong on this. Don't know if it's the type of riding I used to do or my individual bike setup - or maybe i just wasn't that in tune with it all enough to notice a diff in mids or vibration when i went to straight through. I certainly never felt like the extra noise was a factor, never got pulled over for it. Irrelevant anyway, once I went to an SFC 2/1 (with baffling) and my current custom 2-1-2.

i do love the sound of the original SF1/2/3 with the junction box in place.

 

[TeddyG]

I think the definitive test regarding the mid pipe would be a dyno test. If I can find one reasonably priced I'll try it.

 

[sfcpiet]

RJS, since you say your bike came as boxes of parts, the piece you need looks like this, though this one is damaged.
Even when in place the clearances around the headers and the under-box are tight so, as Piet says, assemble it and space carefully then tighten from front to back. My experience is that the clamping band around the underslung box is essential, when not tight the bike vibrates excessively and becomes unpleasant to ride. I have used four 4" worm drive hose clips as temporary fixings as getting the OEM clamp band replaced is not trivial.

View attachment 93275

Piet, this appears directional, never really thought about that before, perhaps its orientation is important, unlikely that I have one that hasn't been disturbed on any of my bikes as a model, any thoughts on which way the longer side should face?

From memory, the longer part should be to the rear. I'd have to crawl under my bike to confirm...

piet

 

[sfcpiet]

SFCPIET- do you think this type of mid pipe I showed (if I can find one) would work as well as the OEM? And does it matter where the mid pipe is located, since I've seen other ones that are joined at the headers near the cylinder. I would like to try one just to see if there's any mid range improvement-

Dunno.

From a flow POV, it's pretty crappy, it is much like that used on Tonti Guzzis and bevel Ducatis. Can't comment on how well they actually worked.

The stock Laverda item has internal tubes directing the gases from each header towards the middle of the box where they can expand and continue on into both exits. This also breaks the noise waves, contributing to the silencing effect. Aftermarket items are most often simply empty boxes, offering only a bit of expansion room, not really convinced on their silencing properties.

piet

 

[Vince]

My Pantah has a large balance pipe under the engine as well, including a complicated internal baffle, at some point, someone attacked it with drill bits and chisels smashing big internal sections out of it. Not an easy job getting in it.

 

[markQLD]

How much space do you have between the balance pipe and the frame on the right and between the exhaust pipe and the primary bolt that's closest to the pipe on the left? Thanks.
Rick

Rick, as they say in the local vernacular, there is two fifths of bugger all clearance on either side.
Well, that's my experience, and today I took some photos of my SF2 that may help for some other reference.
As you have found, the left-side is very close to the primary cover bolt heads and the right-side is very close with the end of the frame cross-tube.
Also realised today, that I have no clearance left anymore on the right-side. The witness mark left near the right-side header clamp suggests the last couple of times that the banana bulge took a bashing into the road surface it was knocked back a bit from the header pipe.
So, I'll loosen it all up again and tap it about some more. If I can get 1mm or 2mm clearance on both sides I'll be happy enough and deserve a beer.
In the photos, the green strip of plastic is 0.5mm thick. It's a chopped up lid off the top of a used butter tub that make good flexible feeler gauges for this kind of work. HTH.
Cheers, Mark

 

[RJS]

Rick, as they say in the local vernacular, there is two fifths of bugger all clearance on either side.
Well, that's my experience, and today I took some photos of my SF2 that may help for some other reference.
As you have found, the left-side is very close to the primary cover bolt heads and the right-side is very close with the end of the frame cross-tube.
Also realised today, that I have no clearance left anymore on the right-side. The witness mark left near the right-side header clamp suggests the last couple of times that the banana bulge took a bashing into the road surface it was knocked back a bit from the header pipe.
So, I'll loosen it all up again and tap it about some more. If I can get 1mm or 2mm clearance on both sides I'll be happy enough and deserve a beer.
In the photos, the green strip of plastic is 0.5mm thick. It's a chopped up lid off the top of a used butter tub that make good flexible feeler gauges for this kind of work. HTH.
Cheers, Mark

Mark
Thanks for the photos. I don’t feel so bad about my limited clearances. I now have over 1mm clearance on both sides of the bike. There is a witness mark on the crease in the balance pipe where it kissed the frame before the bike was taken apart. I guess I’ll live with what I have. I was thinking of taking everything off and grinding a bit off the end of the day frame tube to gain some clearance but I don’t want to face tearing everything apart again.
Rick