750 Breva Engine noise |
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NevilleG
Falcone Joined: 07 Nov 2018 Location: Nairn Scotland Status: Offline Points: 72 |
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In my previous post, I mentioned that the engine seemed very tight to turn over, but at that time I had the clutch lever pulled in and tied back to the handlebar, but I have now carried out a few more checks, with the lever both pulled in and released and with the engine both hot and cold.
Below are the torque readings required to turn the engine over with the plugs removed as well as the alternator's stator, as the magnetic pull from the rotor is remarkably significant. ENGINE COLD, clutch released = 8nm. ENGINE COLD, clutch pulled in = 18nm ENGINE HOT, clutch released = 8nm ENGINE HOT, clutch pulled in = 22nm You can see that the readings with the clutch released are the same (8nm) regardless of the engine temperature, so the piston expansion when hot has no effect. However, as soon as the clutch lever is pulled in, applying a load to the end of the crankshaft, the effort required is more than doubled and, not only that, but the effort needed is slightly more when the engine is hot. On each side of the rear main bearing is a thrust washer to locate the crankshaft laterally and control end-float, and each thrust washer appears to be made up of two semi-circular halves. When the clutch lever is pulled and pressure is applied to the end of the crankshaft, it is pushed onto these thrust washers, so I assume it must be that friction which is causing the increase in the torque readings. Is it possible that as the engine warms up and the crankshaft expands laterally, the clearance between it and these thrust washers becomes too small, decreasing the amount of oil getting in and making them bind ?? Would it be the binding that is making the knocking noise, or could the two halves be moving about ? The crankshaft is always relatively free and perfectly smooth to turn, although there is a tight spot near Top Dead Centre where I took the torque readings, but I am assuming that this is because that's where the con-rods are in their worst position for leverage. Any comments on this theory by any experts out there would be very welcome !! Nev. |
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V7II Stone
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rapheal
Senior Member Joined: 13 Nov 2014 Location: west country Status: Offline Points: 573 |
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I think you are worrying too much
swap it for a Honda mine makes all sorts of awful noises, 15 years later its still running I just dont listen any more, as long as the bloody thing keeps moving I am fine with it |
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NevilleG
Falcone Joined: 07 Nov 2018 Location: Nairn Scotland Status: Offline Points: 72 |
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We all have our different approaches to how we treat our bikes and mine is obviously different to yours. Being an Ex-RAF aircraft maintenance technician, mine is based on the principle of dealing with potential problems early, before they become major failures and expensive repairs. Having maintained and repaired car and bike engines all my life, my experience tells me that this noise is not normal and it's unlikely that Guzzi would have designed it like that. When I started this thread, I was asking for anyone out there to let me know if their bikes do the same, to try and establish if it WAS just a trait of the 750 engine, but so far, among all the replies, only one person has responded that theirs does. That being the case, I am assuming it must be unusual. It may not be detrimental at all, but on the other hand it could be the beginnings of something far more serious. The other Breva that I had, initially made the same noise, only louder, which was later accompanied by a harsh metallic screech and carried away in a van by the chap I bought it from ! Living and riding in the remoteness of the Scottish Highlands, reliability is of paramount importance to me. Nev. |
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V7II Stone
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Dave P.
Senior Member Joined: 12 Jan 2015 Location: Northants Status: Offline Points: 5572 |
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Just a thought. Is there any mileage in contacting the vendor of your previous bike and asking him whether he found the source of the knocking and screeching? And if he did, what was it?
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TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.
1971 V7 Special. 1972 850GT. 1970 T120 Bonnie. 2009 500 Bullet. |
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V7Chris
Senior Member Joined: 13 May 2017 Location: Powys Status: Offline Points: 1881 |
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They certainly make a racket hot or cold, clutch in or out compared with many modern liquid cooled ohc engines. I have stopped listening to mine after three years ownership like Raphael.
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Brian UK
Moderator Group Joined: 13 May 2014 Location: Surrey Status: Offline Points: 17637 |
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I admit I am surprised by the extra resistance you found whith the clutch pulled in or out. I would have expected the opposite, indeed Guzzi often suggest pulling in the clutch lever when starting to reduce the load (of the gearbox primary) when starting. |
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Brian.
Better 5 minutes late in this world than years early in the next. |
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NevilleG
Falcone Joined: 07 Nov 2018 Location: Nairn Scotland Status: Offline Points: 72 |
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I did Dave and he initially came back to me saying that it was a bearing on the gearbox input shaft, which made no sense at all. I asked him for some more information, but got no further reply. He also owed me a refund on the Road Tax, but despite firstly offering to repay it, he hasn't answered any more of my text or emails since. Nev. |
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V7II Stone
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NevilleG
Falcone Joined: 07 Nov 2018 Location: Nairn Scotland Status: Offline Points: 72 |
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The three Guzzi's I have owned have all had exceptionally mechanically quiet engines, especially the California with its hydraulic tappets and this Breva 750 is as well, but the gearboxes make a bit of a clatter, just like old BMW's, pulling the clutch in stops that and you only hear the engine noises. When this engine is cold, it's very quiet, it's only when it's hot that it makes this noise. I put a paint mark on the alternator's rotor and, using a timing light, found the noise coincides with the engine reaching Top Dead Centre, where the tight spot is. Nev. |
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V7II Stone
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Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8731 |
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Have you examined the engine oil for signs of metal particles? 'Cause if something is rubbing on something, it'd make swarf? |
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"Chicken nuggets don't dance on a Tuesday."
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NevilleG
Falcone Joined: 07 Nov 2018 Location: Nairn Scotland Status: Offline Points: 72 |
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Hi Mike. Yes I have, but there is nothing visible in the oil or on the magnetic drain plug. If it was those Thrust Washers,they are probably made of steel, with a non-ferrous bearing material face, like bronze or white metal, at least ones I have come across in the past have. As you probably know, if main bearings or big-ends fail, the bits all finish up lying in the sump and it's only ball or roller bearing bits that you find stuck on the drain plug. As this noise is only associated with the clutch being pulled in, I think it's just the extra end loading on the crankshaft that triggers some movement somewhere. God knows what ! Anyway, I will keep an eye on it, but I'm not going to start pulling the engine apart until I see if it develops any more. It might even get less as I put more miles on it. Who knows ! Nev. |
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V7II Stone
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Dave P.
Senior Member Joined: 12 Jan 2015 Location: Northants Status: Offline Points: 5572 |
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Keep us informed please Nev. Otherwise, we have a play minus the last act.
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TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.
1971 V7 Special. 1972 850GT. 1970 T120 Bonnie. 2009 500 Bullet. |
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Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8731 |
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"Chicken nuggets don't dance on a Tuesday."
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Cylvabirch
Senior Member Joined: 02 Jun 2014 Location: Whitehill Status: Offline Points: 274 |
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For peace of mind I would take the sump off and have a good look round for debris and get someone to turn the engine over while you have a poke round levering things with a long screwdriver and a good torch to see if there is something doing something it shouldn’t.
Put some fresh oil in and a new filter. It could still not be properly run in if previous owners have pussy-footed around on it and used extremely good synthetic oil. My wife’s Citroen car years ago was as tight as a tick at 10,000 miles because her careful husband insisted on using only Mobil 1 and changing it at twice the frequency in the book (because I am an aerospace trained engineer originally). She was a cautious driver back then. Ride it like you stole it for a few hundred miles, it may well improve things. If not; it’s “sh1t or bust” and you will get to the answer!
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NevilleG
Falcone Joined: 07 Nov 2018 Location: Nairn Scotland Status: Offline Points: 72 |
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Your advice Cylvabirch ( We've got a nice lot of those up here in Scotland !!) is very sound and I'm planning to drop the sump off in the Spring to have a look, but whether or not it reveals anything remains to be seen.
With the Scottish winter and the forthcoming holiday period commitments looming, it will have to wait until then, but I'm determined to get to the bottom of it so watch this space. It would have been nice to have got a bit more feedback from other Small Block owners, especially any Guzzi technicians or mechanics with any other ideas, and it seems strange that both the bikes that I've had, both being 2007 models, made the same noise, yet nobody else's do. Mike says that "Theoneandonly" is a Guzzi mechanic and I have sent him a PM to try and start up a dialogue about it, but, as yet, I haven't heard anything from him. Nev. |
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V7II Stone
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Brian UK
Moderator Group Joined: 13 May 2014 Location: Surrey Status: Offline Points: 17637 |
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Baldrick is probably one of the best sources of practical information we have here, but he doesn't check in every day. Probably some sort of excuse like having a living to make.
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Brian.
Better 5 minutes late in this world than years early in the next. |
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