The Ford Barn

Planojc · 11-04-2011, 04:50 PM

I have a 24 stud that has a slight knock when under a load at low rpm's. It almost sounds like pre ignition knock. I removed each plug wire one at a time and the knock did not go away. I also used a long screwdriver to listen with, but could not hear anything abnormal. Any idea what could cause this? The distributor was rebuilt by one of the vendors listed on this site. Thanks

flatjack9 · 11-04-2011, 05:33 PM

If it has a vacuum brake, try increasing the tension a small amount. Test drive and adjust until it is gone (if it is spark knock). If it is a later distributor, back off the initial advance.

don's 37 · 11-04-2011, 05:37 PM

Exactly, how does a vacuum break work and how do you know when it needs to be adjusted? On my '37 Ford it seems to run well but maybe it could do better adjusting the break.

flatjack9 · 11-04-2011, 05:42 PM

The vacuum brake slows the advance when accelerating(low vacuum). There is a piston that is held back by manifold vacuum. When you accelerate, there is spring that forces the piston against the advance plate, slowing it's movement. Back the screw out until you get pinging when accelerating. Tighten a little and you have it

Marv · 11-04-2011, 07:38 PM

If it is not in the ignition, then is probably a rear main bearing. Marv

G.M. · 11-05-2011, 08:05 AM

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If the cylinder or the piston wears in the distributor the vacume go's past the piston and won't pick up the leather brake, it just sits there jiggling up and down. I doubt this has anything to do with the knock. How about the fuel pump if it's a slight dull "knock". G.M.

Planojc · 11-05-2011, 10:30 AM

I did remove the fuel pump rod to compare the length with a nos rod I have, but did not change the fuel pump. My next step will be to change out the distributor and fuel pump and see what happens. The engine was rebuilt several years ago but only has about 500 miles on it, so should I drive it and see of the knock gets louder before I pull it?

11-04-2011, 04:50 PM	#1
Planojc Senior Member Join Date: May 2010 Location: Plano, Texas Posts: 844	engine knock I have a 24 stud that has a slight knock when under a load at low rpm's. It almost sounds like pre ignition knock. I removed each plug wire one at a time and the knock did not go away. I also used a long screwdriver to listen with, but could not hear anything abnormal. Any idea what could cause this? The distributor was rebuilt by one of the vendors listed on this site. Thanks

11-04-2011, 05:33 PM	#2
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,526	Re: engine knock If it has a vacuum brake, try increasing the tension a small amount. Test drive and adjust until it is gone (if it is spark knock). If it is a later distributor, back off the initial advance. Last edited by flatjack9; 11-04-2011 at 09:21 PM.

11-04-2011, 05:37 PM	#3
don's 37 Senior Member Join Date: May 2010 Location: Palmyra, NY Posts: 195	Re: engine knock Exactly, how does a vacuum break work and how do you know when it needs to be adjusted? On my '37 Ford it seems to run well but maybe it could do better adjusting the break.

11-04-2011, 05:42 PM	#4
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,526	Re: engine knock The vacuum brake slows the advance when accelerating(low vacuum). There is a piston that is held back by manifold vacuum. When you accelerate, there is spring that forces the piston against the advance plate, slowing it's movement. Back the screw out until you get pinging when accelerating. Tighten a little and you have it Last edited by flatjack9; 11-04-2011 at 09:20 PM.

11-04-2011, 07:38 PM	#5
Marv Senior Member Join Date: May 2010 Posts: 875	Re: engine knock If it is not in the ignition, then is probably a rear main bearing. Marv

11-05-2011, 08:05 AM	#6
G.M. Senior Member Join Date: May 2010 Location: Florida and Penna. Posts: 4,471	Re: engine knock Sponsored Links (Register now to hide all advertisements) If the cylinder or the piston wears in the distributor the vacume go's past the piston and won't pick up the leather brake, it just sits there jiggling up and down. I doubt this has anything to do with the knock. How about the fuel pump if it's a slight dull "knock". G.M. __________________ www.fordcollector.com

11-05-2011, 10:30 AM	#7
Planojc Senior Member Join Date: May 2010 Location: Plano, Texas Posts: 844	Re: engine knock I did remove the fuel pump rod to compare the length with a nos rod I have, but did not change the fuel pump. My next step will be to change out the distributor and fuel pump and see what happens. The engine was rebuilt several years ago but only has about 500 miles on it, so should I drive it and see of the knock gets louder before I pull it?