Need advice on engine noise

[Guest goldgooz]

Hi everyone, Need your help! After changing oil and replacing the plugs ( getting the Lemans ready to ride down to Road Atlanta for the last superbike race of the season), I took her out for afternoon ride. About 15 miles from my house I run her up to 7 grand in the top three gears ( 120mph) for about an 1/8 mile. The bike is running perfect. Stop at a stoplight, no problems. As I leave from the light I hear a rattling or light tapping sound coming from ( I think) the top in. I first think that I've got a very loose rocker arm but the bike sounds fine at idle and runs perfect. Got her home and let her cool down and pulled the valve covers and found everything to be in adjustment. This is the first problem I've ever had in 14000 miles. Could it be carbon ? Help ! Thanks, John B 02 Lemans

[Guest ratchethack]

Sounds like detonation (pre-ignition or ping) to me. What gas have you been running? Go for the highest octane gas you can find and see if it persists. If it was a particularly hot day, this would exacerbate the ping. Don't lug it at the RPMs where you hear it or you'll burn the piston crowns. Most every V11 has this to some degree, best stay away from cheap gas and learn to limit it by keeping it under control as much as possible.

[dlaing]

Ditto on it sounding like detonation.

I suppose the cylinders were pretty hot after the run.

If the cylinders are out of balance, it is more prone to detonation, because one cylinder is doing more of the work.

Also, a PCIII can help.

I just enriched mine 10 points where it was pinging, and so far so good.

But the performance felt a little flat so,

I'll have to try bringing it down to 5 points of enrichment and see if it still pings.

I wish I had a laptop so I could do remap on the road side.

Considering you have never had this problem, I can only guess something slipped a little.

Maybe the TPS or throttle bodies are a little off, or the timing chain is stretching.

I don't think mine ever pinged before 10,000 miles.

You checked the valves, so that is eliminated as a LIKELY cause.

I am not sure how to check the timing chain...

[jrt]

John,

What were (are) the valve clearances?

 

Also, the top end of these bikes do make some tapping noises- it's the nature of the beast. Not loud, but some.

 

Question about pre-ignition in general- Is detonation a regular or irregular occurance? That is, if a cylinder is prone to detonation, will it do so on every stroke or just once in a while?

[Guest ratchethack]

Is detonation a regular or irregular occurance?  That is, if a cylinder is prone to detonation, will it do so on every stroke or just once in a while?

Somebody will hopefully answer this better than I can, but by my experience, as far as Guzzi's are concerned, it's caused by a combination of many factors, including ambient temperature, air-fuel ratio, humidity, barometric (ambient) pressure, ignition timing, operating temperature of the engine itself, amount of carbon buildup in the heads, etc., and assuming the timing and compression ratio are constant and you're not replacing pistons to alter the CR, milling the heads, re-shaping the ports or combustion chambers, or otherwise messing with the squish band. For most practical considerations with respect to our Guzzi's, it's mostly determined by the octane rating of the gas.

 

Detonation occurs when the flame front moves across the combustion chamber too quickly - in other words, when the gas burns too rapidly. Higher octane gas burns more slowly and in a more controlled manner. Hemi-head pushrod engines are less efficient at combustion than modern engines due to the shape of the combustion chamber, so they're far more susceptible to fast burn or knock than modern DOHC 4-valve designs, for example. I'm not gonna open another can o' worms here with a discussion of dual-plug heads, but with single-plug heads, we're more or less constantly encroaching on some combination of conditions that result in detonation. It's usually a somewhat irregular occurance, depending on what combination exists on any particular day. Heat's a biggie. Also, loading the engine within certain RPM ranges and throttle openings will bring it on whenever a combination of conditions permit, while not as much in other RPM ranges and throttle settings. Bad gas will generally come in, make Pals with all the other stuff, call himself the gang leader, and then they'll all team up to get you there immediately.

 

Where's Pete?

[Guest Steve_W]

Where's Pete?

He's sitting in a lounge chair at some luxury resort somewhere, IIRC, sipping (Ha!) a drink with an umbrella atop it. He or his wife apparently won this trip in a contest of some sort. Well, that's what he said, anyway.

 

He mentioned it on WildGuzzi last week.

[dlaing]

So, that is why BelfastGuzzi got away with making fun of Pete's helmet!

[Guest goldgooz]

Thanks everyone for your thoughs. A little more info. My Lemans has a Power Commander and I,ve never had much of a problem with pinging. Could the PC be screwing up and going way lean in the 2500 - 3500 rpm zone? This is where the noise is most noticable. Tomarrow I'll disconnect the PC and see if the noise presists.

[Guest ratchethack]

Goldgooz, I'm gonna take another run at this. It's highly unlikely that disconnecting your PC III would be a step in the right direction, or that this would tell you anything of value. PC IIIs screw up right next to never, and when they do, you're generally looking at a dead quacker (or in our case "honker") . PC IIIs and maps don't "go lean". Code is code until it's re-coded. If you either had a custom dyno-tuned PC III map done and it didn't ping for quite awhile afterward, or if you got an "off the shelf" map that was done by someone else for a similar config and it likewise didn't ping for quite awhile after it was installed, there's an extremely high probability that your problem is that you have bad (polluted or otherwise low octane) gas.

 

My strongest recommendation, FWIW, would be to get the gas that's in your tank now out of the equation before you do anything else. Drain it out if you have to and put it in your lawnmower or your car - just get it ALL out. Then per my post above, fill it up with the highest known octane gas you can find and put a couple miles on it (all the old gas will get diluted via the recirc. pump & FI pretty quickly) & see if you get an improvement. (I bet ya do...)

[dlaing]

FWIW my PCIII went out on me, but the symptoms were nothing like pinging.

I sent it the maker, they updated the firmware and it has been fine ever since.

A shift in your TPS output could certainly cause pinging that could be aggravated by the PCIII map.

Of course the problem would be the TPS and not the PCIII, but disconnecting the PCIII could be a a clue.

It is easy enough to disconnect the PCIII, so I say go for it.

If it improves, the first thing to look at is whether or not the PCIII was zeroed.

But yah, Ratchet is correct that it is much more likely to be bad fuel, judging by the presented evidence.