Valve(?) noise only around 20mph (1 Viewer)

[OverLubed]

May 1971 3 speed.


I can usually find the answers I need here, but this problem has me baffled and I can’t find a similar problem in another post. At approximately 20 mph, give or take 2 mph, I hear a sound like valve clatter/clicking. No noise before or after. No noise when running up rpms while stopped. I cut the engine while the noise was occurring, and it ceased. So it seems to be engine related. I use Delo 400 15w-40 and it’s nice and clean. If it is sticky valves (only at 20?) it’s not from neglected maintenance. I have adjusted the valves twice, but I’m going to do it again and be absolutely sure that’s not the problem. I have moved the timing all over the place (say from 7BTDC to around 20BTDC; fyi, I’m at 3500 ft) no meaningful change. I have disassembled the (retard) distributor and cleaned and lubed the mechanical advance weights, thinking they might be hanging up around 20mph causing a retarded timing issue. No change. I’ve disconnected the speedometer cable at the cluster, thinking that might be the problem. No change. I’m out of my depth as far as other possible causes. Any input will be appreciated.

 

[OverLubed]

What else could be causing what I am calling a "valve clatter" sound at a specific mph? I have been focusing on timing issues, and lean that way only because I don't know where else to look.

Today I am wondering if the breaker plate is moving as it should. Would a plate that 'hangs' at a certain point momentarily prevent the timing from advancing and hence cause a pinging/clicking noise? How freely should the plate move? The vacuum retard mechanism isn't hooked up to a vacuum source, could the arm from the mechanism that is attached to the breaker plate interfere with the plate's proper movement?

Would a too lean mixture cause noise only at a specific rpm? I'm flailing here...

I think the last thing I worked on before this started was a drum brake adjustment. In trying to narrow the problem down I did apply light pressure to the brake pedal while the sound was occurring: no change.

 

[thebigredrocker]

Are you checking valve lash with the engine running? Go-No Go feelers are handy for that.

My first thought was the noise could be U-Joint related, but that’s a ways from the engine. Are you running stock shackles?

 

[OverLubed]

Thanks for the input. Stock shackles with ancient bushings (number 742 on to-do list). My other set of ears (wife) thinks the sound is more toward the driver's footwell. I don't know what could be clicking or clattering there--voltage regulator?

I usually check the lash with the engine hot and off, should I check with it running?

 

[OverLubed]

Flasher unit on the right, what is the circled item? I think it's what's clicking.

 

[OverLubed]

I guess it is a "speed marker"(?) in the wiring diagram it looks like its a relay connected to the "speed detector;" where the heck is that and do I need it?

 

[65swb45]

did you try disconnecting it?

 

[OverLubed]

Not yet. If disconnecting is an option, I guess that means its not needed? If so, I'll unplug it tonight.

 

[OverLubed]

As far as I can tell, on my vintage 40 (71) the speed marker's function is to send a signal to activate the VSV. Since I no longer have anything connected to the VSV, I have disconnected the speed marker and .... no more clicking/clattering. Diagnosis would have been easier if my ears were better, I could have located the offending sound more accurately. But, all's well that ends well.