750SF2 - Strange ?engine? noise when under load

Oil pump will have no bearing on this noise. If there's something blocking oil putting a bigger oil pump on is going to do bugger all. You can shine a light through a tappet cover and examine the cam lobes anyway.

Don't think clutch rubbers make that sorta noise under load - usually more prominent at idle or on a neutral load. Even when they're rock hard and old I doubt they'd be the root cause.

If nothing else can be found, you might have to pull the motor - you just don't know ... could even be a small end, although I've never seen one worn. Be a bummer to pull the motor and find nothing sinister, but if all else fails .... at least you get to see the condition inside, which is the eternal mystery when you buy a bike with an unknown history.
 
If you feel the noise is solely from the motor use a boroscope to see condition of the barrels and then tilt the engine forward enough to remove the rocker cover to examine the cams and followers. Or warm up the motor and remove the oil to inspect for any extreme metal shavings. Have you inspected the cam chain tensioner and is it properly set? These are mechanically noisy motors but persistent noises need to be investigated.
 
I'm with ChrisK, failed camchain tensioner plastic wheel. Or possibly the rockers loose on the spindle I suppose, but I've not experienced that noise myself so don't know exactly.
Or, more dramatic, the description sounds similar the noise made by TTW's Jota when the main bearings were failing. Made a little knock, only under load IIRC. I mentioned it to him and he scoffed as it was a one owner bike with moderate km. Sure enough a few months later we were pulling the crank out. Other than the ball bearing 79 triples it an unusual failure even on a triple - even more so on a twin - but I guess it's possible if you've exhausted all other possibilities.
Bear in mind also that these old engines make a bit of a racket, I once thought my RGA had some weird noise in the primary drive area. Turned out I'd bought a new helmet and everything sounded different.
 
As already mentioned, pulling the cam chain tensioner off is about 3 minutes work (you won't even need as new gasket if you're careful). Pulling off a couple of tappet covers about the same - a torch, a camera, whatever ... just have a look - before you pull the whole bloody thing apart!

Any chance you could record the nasty noise?
 
breganzane said:
I'm with ChrisK, failed camchain tensioner plastic wheel. Or possibly the rockers loose on the spindle I suppose, but I've not experienced that noise myself so don't know exactly.
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My clatter wasn’t there at all, until, over 4,000 rpm under load. The clatter was like a big predetonation, under 4,000 rpm nothing

The cam chain tensioner roller had a flat spot, and presumably at a certain rev range the roller decided to turn, rather than acting as a triple tensioner blade.

The question remains, was the clatter coming from the carrier arm bouncing back and forth, or just a result of the chain slapping 🤷‍♂️

A new roller, and a little relieving of the tensioners bump stop rubber stop fixed it,
 
My SF3 has had a rattle under load since I got it 10 years ago. Nothing to worry about. I remember reading a thread where someone had the same noise and cured it by replacing the camshaft bearings, despite no play in the old bearings.
 
natm said:
I remember reading a thread where someone had the same noise and cured it by replacing the camshaft bearings, despite no play in the old bearings.
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Doesn't make sense on paper but maybe there was damage in the ball races. Or maybe in the process of fitting new camshaft bearings - for no apparent reason - they also inadvertently resolved the actual cause? Could be something as simple as not using the appropriate technique when adjusting cam chain tension (eg, simply undoing the plunger lock bolt without regard for where the slack in the cam chain is).
 
After rereading your original post it sounds like the noise is coming from the top end so doing a leak down test will give you an idea about the valve condition. The clanging could be worn followers or tappets.
 
Leak down test won't tell you anything about pitting on valve tips. And my first rebore was done when my bores had a huge wear ridge, top rings in about 5 pieces and the need to go straight to jail ... 2nd oversize. At 110,000km there was no discernible wear in the valve guides. The motor wasn't making any bad noises - it just didn't have much power.

But any test and investigative work is of benefit when you've bought a bike with an unknown history, so no harm in performing a leakdown.
 
Thanks for all the suggestions and comments, and an update.

I check for cracked or loose anything – nope. I removed the cam chain tensioner – no flat spots on the wheel and it measures round – looks newish. I think i set it right. I gerry-rigged gas (see pic, I had a fire extinguisher in my back pack) and rode it without the tank and air filter pods (which touch the frame) and still get the noise, even when pressing and holding various bits re vibration. Attached is a short mp3 of the noise while riding – it doesn’t reveal it well, but you can hear it when I blip the gas on, a harsh rattling noise.

To my helmeted ear it still sounds upper/head, maybe to the right. I just doesn’t sound light, like tappets/valve stems. I don’t feel the noise so assume its not bottom end. I can’t see why anything in the head would be under more force on acceleration under load (ie, when ridden vs when parked), except maybe the breather ball re crankcase pressure. I would have thought little end problems would not fit this pattern (but hey, I’m an office worker).

I think the next sensible step is to pull the head off and have a look, maybe barrels too since I’ll be almost there. Will post back when something is revealed (or when I get stuck!)

Cheers
 

Attachments

mikeb said:
some medium scrapes in the tensioner blade, and very slight wobble of chainwheel (I assume that’s normal).
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Grooves in the rubber surface of the primary chain tensioner are normal. But a wobble in a primary drive sprocket is not normal. Sometimes the clutch drum will appear slightly wonky because its outside surface is a cast, rather than machined finish, but the sprockets should run pretty true. At least with no obviously visible runout. That could be a potential candidate for the noise. It's not beyond the realms of possibility that a little runout in a sprocket would be enough to disturb the smooth running of the chain and cause some kind of harmonic vibration somewhere.

Disclaimer: As previously stated, my familiarity (I hesitate to call it expertise) is with the triple engines, but the 750 twin has an almost identical primary drive arrangement.

A technique I've found helpful in identifying the source of noises is to get an estimation of its frequency in relation to engine revs. If you figure out what part of the engine or gearbox rotates at that frequency it can give a good clue as to the source of the noise. For example, a noise at half engine speed could be in the valve gear, or possibly the clutch (primary drive reduction is approximately 2:1). It's not that difficult to do. An online tone generator can be a handy tool for frequency comparison. Something like this one https://www.szynalski.com/tone-generator/

Select a saw-tooth wave profile. That'll give you one click per Hz of frequency that you can hear right down to 1Hz or less. (A square wave gives two clicks per Hz. A triangular wave gives one but is way less audible than sawtooth. A sine wave just gives a tone). Your noise will be down around the low end (1000 RPM is only 17 Hz).
 
hooksey: yes there is oil getting to the head. and i checked/tightened/added goo to the header pipes, as well as braced with my foot when riding, so i dont think its that rattling.
Dellortoman: by chainwheel maybe i mean clutch basket - other south end of the triplex primary chain, securted with a circlip so I assume some movement is normal. not the crank sprocket - that's tight. here a wobbly vid of what i mean:
my take on the frequency is its with engine speed, not reduced/transmisison. tho i get your point re head noise being half crankspeed.... hmm... it may be difficult to match as it only occurs under riding acceleration...
 
Has another 750 owner ridden your bike to see if the noise is really a problem? Laverda 750's are a 1960's design and noisy compared to a modern bike even when new.

Anyway if it is a bad noise, I am betting cam key or cam bearings. I have seen a few 750's where the cam bearing have rust from sitting. My 750GT had rusty cam bearings as it had sat for 25 years.
 
natm said:
Sounds normal for an SF750.
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Don't agree. Hard to say based on a recording but I've been riding 750s since 1974 and they don't make that kind of racket. I think I can hear the noise that's troubling you and I agree, it isn't healthy. Like a clatter under acceleration. If you feel as though you've exhausted all possible loose items, I agree it might be time to pull the top off. Peace of mind if nothing else.
 
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