new noise - panic or not?

I have now done about 100 miles on my re-built Mk3. Running in as per the article from INOA site - 20 minute runs accelerating and decelerating in 2nd and 3rd - full cool down in between, gradually build up revs over 4 or five runs, etc, etc.
Last run was the 2nd time I had used top gear - up to about 5 grand.
On the way home I noticed a metallic knocking/clicking under load.
I know it is hard to describe and/or evaluate noises without hearing them. I have had a couple of old BMs and this noise sounds just like bad BM tappet noise!
I checked the tappets - OK. Can't help thinking it is little ends but can't really pick it up enough at standstill. I know some of you guys have/had BM's so maybe know what I mean. Any diagnosis suggestions?
Thanks

You sure as heck don't want a bike that makes a noise like my BMs...

(sorry, couldn't resist)

Go for the simple one first, pinking, try retarding the ignition a couple of degs see if it improves.

Cash

Is it possibly pinking under load? The standard ignition timing indicators in the primary cover are notoriously innacurate and you may be too far advanced. It is best to establish TDC and other marks with a degree wheel.

Timing (CHECK WITH STROBE), too high octane fuel, even valve adjustment, and/or a combination of these can all be factors.

DO NOT USE EXXON fuel. Try Shell, Velero, or Chevron.

Does sound like pinging - shows up when hot, under load in top gear?

Two easy checks - (i) does higher octane gas prevent/minimize it? (ii) when it starts, will downshifting and increasing revs make it go away?

If either, you've got a prima facie case for pinging.

If it's pinging, retarding timing a few degrees is the way to go. Colder plugs may help in the meantime/in addition.

Wouldn't let it go too long....

Thanks for the help guys. Retarded the ign about 4 deg's and it certainly decreased heaps. Still seems to be a bit there but I will play with the timing today. For some reason Pazon recommends 31 degrees instead of 28. Maybe I should start at 28 for now. I am going off the std marks and haven't checked them with a wheel so I guess its a bit of a lottery anyway. As against too far advanced is there any danger in too retarded?I did put in hotter plugs before that last run as well!
Sounds like I need to do "ignition theory 101"
Anyone recommend a class?
Thanks again

Interesting title to this thread. You ride a Norton so whilst you shouldn't panic at the appearance of a new noise, you should be moderately alarmed and seek to identify it immediately. Most of us ride with one ear cocked listening for changes !

Retarded ignition will result in loss of power and overheating. The Pazon is set for higher advance at higher rpm. The standard bob-weights are fully advanced sooner.

You really need to check everything with a degree disc or all the rest is guesswork. If the problem has just appeared, are the new plugs too hot or have you taken sub-standard fuel on board ? It can happen. Mine used to pre-ignite on B.P. fuel to the extent that I stopped using it if at all possible.

One other thing;

Use the best strobe you can get your hands on better still one that the manufacturer states will hold the timing beyond 5000rpm.
Most strobes are accurate enough upto 1500 rpm, after that due to the accumulation of error the flash is signifcantly delayed. This delay in flash makes the ignition look retarded and of course the operator unknowingly over advances it.

Been there got the bloody scars my new super-duper strobe was faulty .

Cash

so, i just started my commando up after rebuilding the engine. it was my dads, and i have no idea about these bikes (well after building one, i guess i have some idea, but i'm pretty green all in all), i have no idea what pinging is, but at idle, my bike is making a similar noise to the one discribed. i haven't even taken it out. it sounds like it's coming from the engine head, so i checked the valves and rockers twice and then checked them again (clearances and so forth) and nothing seems amiss there. is that where a "pinging" noise would come from? could somebody please explain "pinging" to a newbie?

johnny 750 said:

could somebody please explain "pinging" to a newbie?

Click to expand...

Info: http://www.answers.com/topic/engine-knocking

But if you are hearing a noise at idle after starting then I doubt that's the cause of the noise?

its a pretty glaring, higher pitched noise, almost like somethings rattling around in the engine head. i know i haven't lost any parts, or dropped anything in there. my uncle said it sounded like piston slap, but it seemed to get better the longer it idled, and behaved the same through the lower rpms, just reving it a little. also, the pistons were professionally bored and honed, so i don't think it would be that. to be honest, i have not strobed it yet (don't know how), but i set the timing acording to the meter in the chain case (which someone said earlier could be not entirely accurate). could bad timing be the cause of that noise even just at idle?

Unfortunately it is rather difficult trying to identify a noise that we can't hear, and it could be one of a number of things, from piston slap (incorrect ignition timing could make that sound worse possibly?) or it could be cam/cam-follower noise, or a pushrod with a loose end cap, worn rocker/rocker spindle, or worn small end bearings?

haha. yeah, the joy of motorcycle rebuilding. well, i'll start with the strobe for timing, and mabye take a mic to it to see if i can isolate the sound. i appreciate all the help/suggestions. this is a really great website.

Johnny,
A slightly slack timing chain can make strange noises.
I have found;
As the cam lobe goes over centre the valve spring forces it forward taking up the slack in the chain, the up coming lobe hits the follower with a click. I'm sure the click comes from the chain. If you turn the motor over slowly you might hear the click.

A long shot.

Cash

This is a good piece to read. It has a trick about listening for engine noises. It will separate the knock and the rattle and teach you a bit about how nasty things can get and how quick. http://www.contactmagazine.com/Issue54/ ... asics.html

Noise and timing

Do this first:

Remove spark plugs, kick through 3-4 cycles. Do you hear it? If so you probably have a push rod not on the tappet correctly - wedged sorta Moves the valve (look for more threads on each adjuster - if way more on one - you have pushrod problem) and can bend the pushrod. the noise you would be hearing is the pushrod catching and releasing the valve after the cam closing ramp has past. Can bend valve, but usually just pushrod. If its not that, go find the wristpin clip you left out before you start it again. This is assuming its not a slack camchain etc.

A note on timing from an fast ole fart. Well...I use to wuz.
With plugs out rotate engine through compression stroke (just after intake closes) to top dead center (TDC). Get a piece of brass rod about 8" or so. Stick in plug hole touching top of piston. Find a reference point on the head and mark the rod at that point . Use a old pair of wire dykes and mark all the way around. Measure 3/8" UP from your reference mark and make a mark the same way. Stick back in hole touching piston and in fifth gear turn BACKWARDS until your reference mark on the head matches the 3/8" mark. I think that will degree at 28deg. That's were idle wants to be. Full advance is a different puppy. I basically advance the timing on everything I owned until it detonates going uphill under load I back off just till it quits. It of course will change with time of year (air density and ambient heat) and octane rating.