Silencer problem.

[Mark]

Hello all.
Trying to fit new silencers to my 1982 K1 and couldn't get the left side to slide fully on.
I've found that the left side pipe is 25mm longer than the right side (measured back from the balance pipe). This didn't affect the old Sitos that are coming off, but it does affect the fitting of the new black chrome items I have sourced in Italy.
Chopping the last 25mm off the left side pipe will solve the problem, but I'd be grateful if someone out there can confirm that the difference in lengths is just manufacturing sloppyness and I'm not doing something I shouldn't?

I wonder if this may have had something to do with the left side pipe being in much worse condition than the right on dissassembly, but that's another issue.

Cheers.

[3potjohn]

I also have a K with Black sito pipes that will need replacing soon. I have had the left hand one off recently and the exhaust pipe goes into it about 6-8 inches with a slightly smaller bore. I have no experience of what the effect of not having this is; I assume it has something to do with exhaust pulses or pressure waves but some other pipes I have seen do not have this extended piece. I am interested to know about sourcing some black chrome replacements as well. I am keen to retain the look of the bike if possible. I do not fancy the barbecue paint idea, that should be used for barbecues, nor the expense of ceramic coatings. If I have to go dowwn the stainless route then i will look at Keihan silencers as the ones on BMWs last for ever.

[Mark]

Hi John.
The problem with these new silencers is that they are shorter than the Sito's by about 4" so the pipe is going further inside the silencer, causing the pipe to hit the baffles about an inch before the silencer mounting bracket is correctly lined up.
They are nice looking pipes so if they work well when fitted I'll be sure to let you know as my brother lives in Italy and sourced them for me. About £180 the pair if I remember correctly.
Cheers.

[corsaro chris]

It's a long time since I dealt with silencers on a Sport or Strada, but from memory the rear pot exhaust (l/h side) had an extension within the silencer to equal up the length of gas flows from the valve. Lambertini was always fastidious over exhaust design - it was (and is) an essential part of overal tuning. Talk to NLM and listen to their reccomendations - they retune even when they fit stainless pipes, let alone repacement silencers - of whatever pattern!

Good riding,

CC

[72degrees]

It's a long time since I dealt with silencers on a Sport or Strada, but from memory the rear pot exhaust (l/h side) had an extension within the silencer to equal up the length of gas flows from the valve. Lambertini was always fastidious over exhaust design - it was (and is) an essential part of overal tuning. Talk to NLM and listen to their reccomendations - they retune even when they fit stainless pipes, let alone repacement silencers - of whatever pattern!

Good riding,

CC

Indeed so. I could point you to a very lengthy thread about the arcane art of tuned exhaust lengths in another place. Morini 2:1 systems have suitable contortions to achieve this before the Y piece. Although you might think the end of the silencer dictates the tuned length it's affected by diameter changes. That's why modern competion 4T singles have stepped pipes and even a 'bomb' between head and silencer to get resonance and extraction effect at more than one rev range. To be fair it's possibly not that big a deal if not after ultimate performance, but it should run more sweetly with equal header pipe lengths, even with a linking balance pipe. 25mm shouldn't make too drastic an effect though if cosmetic appearance is the prime consideration.

[Mark]

Hi.
It wasn't cosmetic, the pipe was hitting the baffles inside and the mounting bracket wouldn't line up until I shortened the offending pipe by an inch.
Seems to run fine tho, appears to breathe a bit more freely than with the Sito's.

Can someone please explain to me the meaning of "tuned lengths"?
I believe it's about keeping the pipes the same length for more even back pressure, gas flow etc.
I can see the logic in that, even as a layman, but if that's what it's about, why is there (roughly) a 17 inch difference in lengths between the 2 pipes on my standard 3.5 sport?

[72degrees]

The tuned length is of the header pipe not the overall length including silencer. So the OEM setup has a pipe that extends quite a long way in to the silencer. The outlet acts as the end for resonance purposes to create negative pressure waves at the exhaust valve as it closes. Only effective at a certain RPM range. I guess max power RPM in the case of a wee-vee. More modern machines have stepped pipes to get the same effect at different RPM.

I've never measured a standard setup but I suspect the primary pipe lengths ignoring the silencer are the same?

[Mark]

No, the difference is from the castellated nut end to the end of the pipe itself, not including the silencer. Wherever you measure the two pipes, end to end or just head to balance pipe, they are nowhere near equal.
They are standard Morini pipes, just the same as seen on any other 3.5, so I don't think I have some sort of dodgy set up, just that if tuned lengths are important, either Morini didn't think so or I'm still missing the point somehow!

[72degrees]

So the rear one does not extend in to the silencer, that is beyond the balance pipe, at all?

[EVguru]

I think noise considerations and/or cost were more of a factor in later exhaust systems. I've never ridden a K series bike that's as crisp and free revving as my 77 Sport

[MarkB]

Looking at the illustrated parts list, (Sport and Strada up to 1979), both downpipes extend the same length aft of the balance pipe. I've just checked this on my 76 Sport, which is still wearing a pair of original Lafranconis, although the downpipes may have been replaced at some stage, and it's 2.5 inches on each side, with the silencers slipping over this for 2 inches. And as Paul mentioned about his Sport, mine's got a delightful well-balanced engine.

[72degrees]

It's a long time since I saw a standard 2:2 system, but I distinctly remember the extended header pipe in to the left hand silencer that Chris mentioned. The bike I was most likely to have noticed that on would be the early Strada I turned in to a hill climber (76 I think), or it could have been my first 75 Strada, or even the 250 that quickly became the 2C/375. I'm quite prepared to concede that my memory is playing tricks though. I suppose it's more important on a 2:1. When I built the "Bitza Trio" which included the 250 motor in a 350 frame "Wombat" (winner of best drum brake award at the AGM in 83?) I fabricated a crude 2:1 with distinctly unequal header and definitely not tuned lengths. It never ran particularly well - but the brazed on Megaton 'silencer' may not have helped

[George 350]

Hi All,
Wonderful thing memory playing tricks etc.
My memory recalls that the header pipe was one of the differences between Strada and Sport, along with cam, compression and the obvious cosmetics - even the silencer brackets were listed as different for Strada and Sport at one time...).
My owned from new Sport (bought in 1978), came with the extra 6-8" of inner diameter pipe on the left/rear exhaust downpipe, and whilst no longer on the original pipes now (now on it's 3rd set) I have always used the ones with the 'extension' like the original. (Apart from a short time with a 2:1 system while I got the originals re chromed again that is, but that is another story.)
My recently restored Strada is on it's original downpipes, and it came without any extension on the left/rear pipe, which seems to support my original recollections.
Over the years there have been many claims and counter claims as to the effectiveness of this primary pipe tuning by various members, some of whom had cut off the extension and not found any difference to performance, others welding it back on again. With the balance pipe being located at wildly differing distances from the exhaust ports, any pulse tuning from the extra length would be compromised anyway.
Me? I'm keeping it the way it was designed as it works.
Mark. I agree with you on the rot. For me the left silencer has always rotted first, and always close to the clamp.
happy tinkering,
George.

[72degrees]

Ah, perhaps I had the LH silencer off the '79 Sport then

Memory did return better re. the first hillclimber. Before I got an RMS system for competition use I briefly put the bike on the road on a 'daytime MoT'. Silencers were in short supply (well in my garage at least) so I rigged up a 2:1 by blanking off the LH pipe with a U2 battery (google it you youngsters) clamped in the header beyond the balance pipe. So yes George the extension may only have been specified for the Sport.

How did it go you ask? Well it ran well enough to confirm the handling was pretty good and experiment with gearing, but as it was a temporary fix I wasn't that bothered.

[corsaro chris]

Summing up then - did earlier Morini Stradas have a different pipe from later models? My original Morini (still extant in 2000 in Somerset / Devon) was registered in 1977 and went to France (with me riding it) on holiday in 1978.

I swapped it for a 500 in 1980 - Happy days!

CC