'31 with "B" engine knock

B

BobinDallas

Junior Member
I have a '31 SW Town Sedan with a low mile engine (I now know why) with the worst knock I have ever heard.

Specs: "B" Block, "C" Crank, Full pressure oil system with inserted mains and rods. Original Riley 2 Port, V8 water pump, Mallory Electronic (Unilite) Distributor, Zepher Intake, cast iron header and Stromberg 97 carb. Timing set at 7 Deg BTDC at slow idle, Mech advance, maximum of 25 Deg BTDC.

Runs strong, idles perfect after fixing several items which were done wrong by "professional" shop. Good oil pressure and low water temp.

Knock is at a slow idle, loud klunk, goes away under load, resumes at speed when load is removed from engine in a coast mode. Sounds like coming from the area of the block right in line with the oil pump.

I once heard something like this on my pure stock '29 at high speed. Slowed down, it went away and did not come back.

I have read all of the post about "Knocks" and it seems to point to cam/oil pump gear.

All suggestions on how to isolate the source greatly appreciated.
 
It sounds like your camshaft is walking back and fourth. I had the same problem, fixed it with a new spring and plunger.
 
Might be the cam plunger is missing...that's a common oversight with new engines. Pull the side timing gear cover and take a look to see if the plunger is seated against the cam face or if there is end play in the cam or gear. Or maybe they left out the distributor drive gear spring, pull the valve cover for a look there. If that all checks out, pull the pan and check the bearings. If you can produce the knock by hand cranking it with the plugs out, have someone crank it while you look at the insides with the covers and pan off.
 
BobinDallas said:
I have a '31 SW Town Sedan with a low mile engine (I now know why) with the worst knock I have ever heard.

Specs: "B" Block, "C" Crank, Full pressure oil system with inserted mains and rods. Original Riley 2 Port, V8 water pump, Mallory Electronic (Unilite) Distributor, Zepher Intake, cast iron header and Stromberg 97 carb. Timing set at 7 Deg BTDC at slow idle, Mech advance, maximum of 25 Deg BTDC.

Runs strong, idles perfect after fixing several items which were done wrong by "professional" shop. Good oil pressure and low water temp.

Knock is at a slow idle, loud klunk, goes away under load, resumes at speed when load is removed from engine in a coast mode. Sounds like coming from the area of the block right in line with the oil pump.

I once heard something like this on my pure stock '29 at high speed. Slowed down, it went away and did not come back.

I have read all of the post about "Knocks" and it seems to point to cam/oil pump gear.

All suggestions on how to isolate the source greatly appreciated.
Click to expand...

Your high speed advance should be 28*. I have a centrifugally advanced distributor too, and at idle it's at -10*. Of course your timing is not off enough to cause this knock, just thought i would share this with you. I know of the car you're talking about. I've driven the car before, and i'm pretty sure this knock was not there when i drove the car.
 
Update on troubleshooting. By taking the timing pin and pushing in the hole with the engine running I can check the cam position. When the engine is speeded up, the cam moves forward about 3/16". Since this is a new rebuild with few miles, I think I may have a oil pump gear problem like others on the forum. First will check cam positioner in timing cover, then keep following cam movement until I find cause.
 
We had the same problem with our 28 fire truck see postings by Bob Campbell WE were able to see timing gear move out with timing gear side cover off and hand cranking gear would move in and out changed our new distributor drive gear used older orginal now runs like a firetruck should hope to get to a fire on time Goon luck Glenn allen
 
You must log in or register to reply here.
Back
Top