Noise diagnosis

[NevNZ]

After a total refurb of my 77 850 LM a couple of years ago it was making a seriously upsetting rattle and I was looking at stripping the motor again but needed to narrow down the cause of the noise to give me a clue as to what I'd done wrong and now needed to fix.  Long story short, it turned out to be the new standard breather box I had installed to replace the old one which had rust flaking from inside, and followed the Guzziology recommendation I had busted out the flapper valve but the bits stayed inside the air box.  When it sat in the 'normal' position it rattled like a bastard and when I tilted it backwards the rattle stopped.  You can imagine my relief at finding that the noise was not the 'new' engine about to grenade!

[2gooses]

  My 99 bassa had an annoying rattle around 3k rpm.Took me a while to hunt down.Turned out rattle was inside fuel tank.Tightend electric petcock half turn no more rattle. (Low fuel sensor?) Good luck!

[czakky82]

You guys are absolutely making me feel better.

@Nev, I too did the re-pop breather box surgery. Only because after a mildly spirited ride my Sport was marking its territory through the breather pipe. Checked oil, was down .5 qt. Since then it hasn’t puked at all. Still rattles though.

If I get ambitious this winter I might try real hard to track this down with some authority.

I just can’t find any symptoms that align with my own. Therefore I have to assume it’s in my head.

[czakky82]

After around 400 miles with new breather valve, I went for a ride yesterday. Started puking oil again, checked compression R 150, L 165 three squirts of 2t oil in each cylinder: R165, L 185psi.
Fresh pistons, rings, cylinders.

I didn’t think these were horrible numbers. I’ll do a pressure test this week.

Am I pressurizing the case that extremely with those numbers?

[czakky82]

Roughly a 6% loss at 100psi, mostly through the exhaust valve…
 
Went for a 20 mile spirited ride. No oil dripping…

[John A]

It’s best to flog it without overheating it. It’s the fun part.

[czakky82]

I still seem to be pressurizing the crankcase. I’m still suspicious of the small end.

Are telescoping dial gauges a good way to measure wrist pin bush (22mm)?

[czakky82]

I’m diving back in. She’s coughing up oil through the breather and going through oil pretty good.
I see some specks on top of the pistons, these don’t look like pistons with 1500 miles on them, eh?

[Thunderbutt]

Hi Bill,  I am definitely not an expert engine guy but those pistons look more like they have 15,000 miles on them.
The brown around the top of the piston looks suspicious and the scuffing on the skirts reminds me of my race bikes when they were due for a rebore.  What is the skirt to cylinder wall clearance?  If it's to great that would allow the piston to "wobble" as it goes thru its stroke and cause a slapping or knocking noise.
I know this is a fresh rebuild and I am thinking the new rings are sealing well enough for the good compression but those pistons look suspicious.

[pressureangle]

My gut reaction;

Your rings aren't well-sealed, supported by the dry/wet leakdown numbers. If you're using synthetic oil, drain it and get some cheap lawn-mower grade 30w. Run that for a tank of gas, run it a gear lower than you normally would; keep the RPM up but the throttle opening lower. When the rings don't seat, you get oil coming up past them, and you get combustion pressure blowing the oil off the cylinder walls and piston scuffing. Higher RPM will keep the walls well oiled, low throttle will keep the blow-by reduced. I don't mean to say don't load it at all, you need to get some pressure against the walls with the rings but not overheat. The cheap oil will help as you actually need a little more friction to get the job done. I put new Total Seal rings in my LeMans, asking them how to break them in- they said "Run it like you stole it". Back in 883 Racing days, iron cylinders of course, I used WD40 for assembly lube and on first start held it up to about 2500RPM until the cylinders were pretty warm to the touch. That got the rings broke in before the synthetic could keep them from it.

[Huzo]

more rhythmic and not as fast as what I’d imagine a crank knock to be. It seems in rhythm to cam more than crank… if that makes sense.

If it’s not every power stroke, then I cannot see how it can be in the engine internals.
Each power pulse is under identical conditions to the previous one.
Are you certain it is not rearward of the gearbox input shaft ? This is why I suggest riding it in the regime where it rattles and immediately change gear. If the noise stops, it’s in the engine.
If it doesn’t, it could be gearbox output shaft, UJ, or bevelbox.
How good is your camchain tensioner ? My Norge suddenly developed a non rhythmic type rattle and it turned out to be the pathetic spring had broken on the Valtek tensioner, hence the gears.

[czakky82]

@thunder, I’ll have clearances measured tomorrow. Stay tuned…

@pressure, that is uslful info. I’d never heard using straight weight before. I’m going to re-measure ring end gap, plus I have fresh rings. Total seal? Mine are Cabre(?).

@huzo, I’m fighting this thing on two fronts. Well many fronts actually for a few years now. This noise started with these pistons, cylinders. Which are new aftermarket pistons and re-plated nikasil.

Stay tuned ya’ll

[Moparnut72]

were the pistons matched to the cylinders or vice versa. When I worked in the radial engine aircraft shop we had to have replated cylinders ground to fit the pistons as new ones weren't available. Pistons had to be FAA  approved, nobody would get them approved as the cost couldn't be recovered with so few in demand. We would recondition pistons and have the re-chromer grind the cylinders to size.   Check your clearances, even feeler gauges will give you a pretty good indication of what you have.
kk

[czakky82]

@ mopar, yes the pistons were sent along with cylinders to millennium for re-plating.

I finally got around measuring piston to bore. I have .002” with the pistons I was running(“C” kit, GPM brand). The original OEM pistons (“B” kit) were about .0002” smaller. The cylinder is showing no wear. Next will be ring end gap and wrist pin bush just for piece of mind.

.002” clearance seems a little much for a 82.5mm bore.

[czakky82]

Ring end gap was good on the compression rings.


There is a good amount of carbon behind the top ring on both pistons. Is this a clue to anything?

[Moparnut72]

Sounds like there is too much clearance between the rings and the ring lands for carbon to build up there. I haven't re-read the thread but I don't think this condition would lead to any noise issues.
kk

[czakky82]

So ring lands to ring clearance is impossibly tight….

[czakky82]

So a pile of rings on my bench after being removed with a ring removal tool. I look and see a piece of about 1/2” piece of ring….
Pretty sure this is the source of noise, oil consumption and atleast some of the extra bonding I’ve been doing with this bike

[Chuck in Indiana]

  Well, at least you found it.