'76 RS pushrod rattle

[jagarra]

When you had the rocker arm assembly off did you check to see if all the needle bearings were there and in good order?

[Seth]

My 77RS has a good rattle from the fuel cap, as SteveD mentioned. Put your hand on it while you hear the rattle. I kept checking my fairing for something loose before I found it.

[Wobbly]

Welcome aboard !

• We assume you are using name brand high octane fuels, such as Chevron, Texaco, or Exxon high test
• We assume you have installed new plugs, NGK BP7ES or equiv
• We assume you have checked the condition of the carb diaphragms against a bright light and found zero holes or tears
• We assume the pilot screws are ~1.5 turns out
• We assume you have balanced the carbs not only at idle with the idle screw, but also at 1500-1700 RPM with the cable adjusters.
• We assume you are running 20W50 oil with a API grade of SF and/or SG.


Things to do, in order...
• Re-torque the heads and adjust the valves. While there, check the rocker arm up-down play once again.
• Cam chain replacement should have included a new spring and new tensioner blade.
• Install new springs in the auto advance unit and lubricate.
• Use a strobe lamp to set the ignition timing at full advance using the "F" mark at 3000 RPM. This is far more accurate than at idle. Especially if you have not rebuilt the auto advance.
• Replace the air filter
• Replace both float needles and check float levels
• Replace the 2.66 needle jets with 2.68 in both carbs
• Replace the needles in both carbs and insure they protrude from the slides the same amount as the old needles, and the same on both sides

That should cure it.

[Shades]

I did not check the rocker bearings but I did check if they moved freely and they did.
Carbs are ultra sonically cleaned and have all new o rings and diaphragms and they are synced with new filter.
It is not the gas cap or camchain I have come to the conclusion that it must be the pushrods on the left side hitting the tubes. I will check and see if they are centered in there holes. Maybe they are bent but is it possible the tubes is not fitted right ? The tube for exhaust side is hitting the frame when installing the cylinder, is that normal ? I can see that the left side has been repaired, maybe the cylinder have been machined/decked and the new geometry is wrong and the rods hits the tubes? Or can the tubes be damaged in a crash and are now bent? The seals are oil tight so they can't be that crooked!

[jagarra]

Sounds like you have a few things to check. When I googled this noise issue I found a thread on the MOA site that was discussing the same noise, different side. The consensus there it had to be rockers/bearings,lifters or bend push rods.
In the past I have heard of some issues with the pushrods, something about the ball end separating or becoming loose. Don't remember the exact years involved, but another item for the list.

[ME 109]

I chased rh side pushrod rattle for some time. Turned out to be a worn ex valve guide.

[hal]

Puff of smoke from the left side is common if the bike has been standing on the side stand.

[Wobbly]

I did not check the rocker bearings but I did check if they moved freely and they did.

This is not the test. With the valves correctly adjusted, the rocker arms should move no more than 0.002", or just enough to see oil move in and out.

Carbs are ultra sonically cleaned and have all new o rings and diaphragms and they are synced with new filter.

One can't sync the carbs without the timing being correct. Timing can't be set without the auto advance being correct. All static adjustments must be in tolerance before any dynamic adjustments can be worthwhile. Carb adjustment then is the very last thing done.

It is not the gas cap or camchain. I have come to the conclusion that it must be the pushrods... Or can the tubes be damaged in a crash and are now bent?

Anything is possible. I thought you wanted to know what was probable.

I sincerely sense your frustration, brother, but wild guessing is not going to get you very far.

[Rob]

Roll those pushrods on a sheet of glass.

Look for a problem with any of the new valve guides.

[Shades]

Thank you for all the replies! The bike is trimmed, both ignition, head nuts torque, valves, rocker end clearance, spark plugs, carb sync, timing chain spring, valves lapped and no excessive play in guides, compression reads 150psi on both cylinders, all oils and filters are new, 95 octane gas and I just pump the tires.
I really do think it's one or both of the pushrods on the left side that is rattling at a certain frequency (equal to 3000rpm). I was hoping I was able to pull the rods out without removing the towers but I am not. I did find that when the adjusters are backed off both rockers the rod on the exhaust side has more metallic sound when pushed up and down than the one on the intake side. The protection tube (as it is called in the Clymer manual) on the exhaust side is seated further out to the opening than the other one. So the base end of the metal part of the rod is able to hit the tube. The rod on the intake side is not. This is with the rockers of the rods I know but would it be completely nuts to open the tube up a bit with a dremel tool ? Only a mm of the tube is all.
Please stop me if I'm wrong before I start drinking beer and getting my courage up, It's not far from 5'o clock in Copenhagen!