Lycoming 8-105 Engine Tick Under Load Only

[Curt Curtiss]

OK, here is a mystery noise I need help figuring out. I have a 1933 Auburn 8-105 with a Lycoming engine and it seems to run great ad idle and low speed flat service driving.

My issue is when I am in 2nd going up a 1 block long hill or driving in 3rd going over 40 MPH for a mile or so I will hear a tick in the engine and it seems to loose a little power, not much though. As soon as I get back on level ground and let off the gas (no load) in about 20 to 30 seconds the tick goes away and I can continue driving on level surfaces or at low speeds with no issue. During the event it has good oil pressure and is running at about 170 degrees.

I just changed the oil and put in fresh 40 weight oil with 1 quart of Marvel to see if that helps. I have only run it for about 10 mins with the new oil and marvel in it.

I am thinking an exhaust valve might be sticking because if it were an intake I would think it might backfire through the carb and it does not.

I may strap my gopro under the hood to try to get a recording of the noise.

[Spinneyhill]

Timing? Pre-ignition?

 

A sticky valve will give rough running.

[Guest]

A temporary vacuum gauge might give you lots of information.  Hang it inside and watch what happens.

[DavidAU]

Could be a spark plug / lead /distributer breaking down under load.  This will cause the lose of power and in some cases can cause engine noise as well.