Effects of incorrectly shimed valves?

[TADracer]

Interesting discussion !

Assuming (I know, I know) that the valve length is approx. 3 1/4" and using the expansion rate of mild steel along with a conservative estimated temperature change of 350 degrees from room temperature to hot operating temperature, the valve stem will expand in length .0006" or .015mm. That is three shim sizes since they are supposed to be in increments of .005mm. And maybe it is overkill but the hot gap is more to consider than just valve stem expansion. You would also need to consider expansion of the cylinder head, which is hard to measure but being aluminum with a higher coefficient of expansion than steel is probably more than negligable. Also, expansion of the cam lobe, while negligable, contributes and then there is the actual remaining oil film between the lobe and the shim. So, if you are very, very tight on clearance at room temp it is easy to see your clearance can be reduced significantly at operating temperature causing a possible host of problems on a street motor.

When we used to race Super Stock we would keep our valve clearances on the tight side but then, operation was only approximately 2 1/2 minutes per run total, including the drive time up through the staging lanes. But then, we were checking our valves gaps often and adjusting valves on a HEMI motor is actually alot easier than our Eleven motors.

So, on a street motor I would stick somewhere in the middle of the range and not have to worry about it until a check at tune-up time.

[crazy steve]

here's a pic of a burnt exhaust valve,



came out of the number 1 cylinder, it occured a few
thousand k's after i lapped the valves.

the thickness of the edge of the valve should be no
smaller than 1mm, its a bit hard to tell from the pic
buts its smaller than that.

That's a reason I missed, but next to too-tight adjustment is probably the leading cause of burned valves. This also gives you an idea of how fast this happens...

Pete, did that kill the seat too, or were you able to save it?

'78E original owner

[firemanstan7]

In an earlier thread, someone mentioned clicking and clacking. I have some loud clicking going on with my engine. It usually gets noisiest at about 4k rpm and up to 5k rpm. It never goes away, just gets louder in that range. It can get loud enough to be heard over my exhaust (4-1) at 80km/h when I tip my head to listen to the engine.

Could this be the valve noise you guys have referred to? The valve clearances have not been checked since I bought the bike (only 300km put on it, short runs of ~20 km max).

One of my buddies mentioned piston slap...is this a possibility also?

[cywelchjr]

In an earlier thread, someone mentioned clicking and clacking. I have some loud clicking going on with my engine. It usually gets noisiest at about 4k rpm and up to 5k rpm. It never goes away, just gets louder in that range. It can get loud enough to be heard over my exhaust (4-1) at 80km/h when I tip my head to listen to the engine.

Could this be the valve noise you guys have referred to? The valve clearances have not been checked since I bought the bike (only 300km put on it, short runs of ~20 km max).

One of my buddies mentioned piston slap...is this a possibility also?

Piston slap is a possibility as is rod knock. I would keep a close ear on it, but if you can hear it over all the other noise and don't have a fairing I would suspect something likely not good. I have what I'm almost sure is minor piston slap, and if I didn't have a fairing I would not be able to hear it above about 35 MPH if even then, but with the fairing I get a megaphone affect that throws it back into my face. It's been pretty much the same in volume and character now for almost 6000 miles, so I'm not overly concerned by it.

Now that said, my original engine had rod knock, which didn't sound much different, but it pretty rapidly got louder, and would have been audible even without the fairing, as it could be heard in the next lane. One difference I have found in the two, is the piston slap tends to get quieter under heavy acceleration where the rod know got louder. That and the rod know was there even without any load, and the piston slap is only there under load, and is loudest under very light load, and almost totally gone under WOT.

And before anybody asks, disconnecting the vacuum advance does not make it go away, although it get a little quieter, just as advancing the timing makes it louder and retarding it makes it quieter, but it's still there without the vacuum advance.

[firemanstan7]

What causes rod knock? The noise seems to be primarily coming from higher up on the engine...in the cylinder head but not at the cam cover.

[cywelchjr]

What causes rod knock? The noise seems to be primarily coming from higher up on the engine...in the cylinder head but not at the cam cover.

Well, you need to be sure where the sound is coming from, but rod knock comes from badly worn rod bearings or a damaged crankshaft (the bearing is by far more likely). If it's a rod knock, you will almost surely find metallic bits in the oil filter, but not for sure. I have found that it's hard to tell if the noise is coming from crank area or the jugs, but if it is high in the engine it could be valve noise, although that tends to quiet with higher RPM's.

In my experience piston slap is not going to be really loud, but rod knock can get really loud, loud enough for riders next to you to hear it at speed.

[firemanstan7]

I've listened to some examples of rod knock on you tube and the noise from my engine is nowhere near as low pitched as those examples. It's a higher pitched noise like the cam chain slap just faster and not in the same location. It seems to be a bit louder on the right side of the engine. I just replaced the cam chain tensioner so I know the noise that makes. I also just changed the oil and filter and found no flakes.

[XS1100_OEM4ME]

Re-shim

Ah, I should have guessed. I suppose I will re-shim based on that.

That would be smart IMHO, you will want to re-syc carbs and color tune as valve shims can change motor settings required for best preformance

[natemoen]

I've listened to some examples of rod knock on you tube and the noise from my engine is nowhere near as low pitched as those examples. It's a higher pitched noise like the cam chain slap just faster and not in the same location. It seems to be a bit louder on the right side of the engine. I just replaced the cam chain tensioner so I know the noise that makes. I also just changed the oil and filter and found no flakes.

Could it be the cam chain slapping

[firemanstan7]

Not the cam chain...I just got rid of that noise. Now I have this new noise. I'm gonna have to do the valve clearances to take it out of the equation I guess. I'm really hoping it's not rod knock or a bad crank bearing. If it is something worse I guess I'll have to rebuild it over the winter! Fun.

[TADracer]

Sometimes it is hard to tell but a rod knock sounds more like dull knock while a loose set valve will sound more like ticking or clacking if it is really on the loose side. Also, the engine speed can help tell. Rod knock and piston slap both happen at crankshaft speed while a valve clacks at only half of the crank speed.

If it is a rod it is only a matter of time before failure. So, if you even suspect a rod knock, get yourself a cheap $10.00 mechanics stethoscope and listen. You will definately hear a rod and the sound will be quite distinctive and easy to pinpoint with a stethoscope.

[firemanstan7]

Where on the engine would I place the stethoscope to hear the rod knock, if it exists? Would it be up in the cylinder head or down in the crank case?

[natemoen]

Where on the engine would I place the stethoscope to hear the rod knock, if it exists? Would it be up in the cylinder head or down in the crank case?

Down on the front side of the crank case or even inbetween the lowest set of fins on the cylinder should work.

[firemanstan7]

Thanks. I'll give that a try.

[petejw]

Hi Steve,
The seat was fine, just had to replace the valve
and relap.


Ive got a rod knock in my engine, i can hear it
mainly coming from the left side timing cover.
syncing the carbs can help.


i was running hotter plugs and a lean float level,
that caused a knocking sound around 4k rpm, correct
plugs and float level fixed that, just somthing else to think about.