Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 04-09-2019, 04:23 PM   #1
smurph
Member
 
smurph's Avatar
 
Join Date: May 2010
Location: Cold Spring Harbor, NY
Posts: 99
Default Engine Knock Diagnostic Help Needed

I need some help from the FordBarn experts.

My 1929 ďAĒ has developed an engine knock.

At idle I can hear a steady tapping of the valves which sound normal.

But, there is also a steady knocking sound at idle, which stops as revs increase to 800-900rpm, and then resumes again as revs increase to 1500ish.
I would estimate the frequency of the knock at idle at 3X per second, and the
frequency increases at higher revs.

At idle, if I short out #2 spark plug the knocking sound gets louder. This does not happen when #ís 1,3, and 4 are shorted out.

Iíve compression tested all cylinders and they all read the same at about 60-62 lbs.

I think the electricals are working OK. I was having carburetor problems which Iím not sure are fixed yet, but I think that is separate from the knock.

So, I would appreciate hearing your thoughts on what the underlying problem may be.

Thanks in advance for your inputs.
smurph is offline   Reply With Quote
Old 04-09-2019, 08:21 PM   #2
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Location: Wisconsin
Posts: 1,215
Default Re: Engine Knock Diagnostic Help Needed

Quote:
Originally Posted by smurph View Post
I need some help from the FordBarn experts.

My 1929 “A” has developed an engine knock.

At idle I can hear a steady tapping of the valves which sound normal.

But, there is also a steady knocking sound at idle, which stops as revs increase to 800-900rpm, and then resumes again as revs increase to 1500ish.
I would estimate the frequency of the knock at idle at 3X per second, and the
frequency increases at higher revs.

At idle, if I short out #2 spark plug the knocking sound gets louder. This does not happen when #’s 1,3, and 4 are shorted out.

I’ve compression tested all cylinders and they all read the same at about 60-62 lbs.

I think the electricals are working OK. I was having carburetor problems which I’m not sure are fixed yet, but I think that is separate from the knock.

So, I would appreciate hearing your thoughts on what the underlying problem may be.

Thanks in advance for your inputs.

If it sounds like it is coming from the lower end of the motor, you may have to drop the oil pan and inspect. I recently had a motor rebuilt due to a motor knock. In my case the motor had a cracked Rod Cap form the bolts holding the cap on were over torqued.. I am sure there are a multitude of other things that can cause a knock, this was wha happened to me.

Last edited by 30 Closed Cab PU; 04-09-2019 at 08:22 PM. Reason: Added info
30 Closed Cab PU is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 04-09-2019, 08:36 PM   #3
LeonardS
Senior Member
 
Join Date: May 2010
Location: Ellston, Iowa
Posts: 389
Default Re: Engine Knock Diagnostic Help Needed

Cam gear knock?
LeonardS is offline   Reply With Quote
Old 04-09-2019, 08:47 PM   #4
eagle
Senior Member
 
eagle's Avatar
 
Join Date: Aug 2011
Location: Eagle Bend, MN
Posts: 1,436
Default Re: Engine Knock Diagnostic Help Needed

You're going to get a ton of wild guesses, maybe a few educated guesses. None really worth much I'm afraid. I'd just pull the oil pan and check it out. If nothing else, it gives you a chance to check bearing cleaarances and clean out any sludge. Could try to take out the timing pin, then insert something in the hole to apply pressure to the cam gear, see if it makes a difference.
__________________
"There are some that can destroy an anvil with a teaspoon and shouldn't be allowed to touch anything resembling a tool."
eagle is offline   Reply With Quote
Old 04-09-2019, 09:53 PM   #5
Chuck Sea/Tac
Senior Member
 
Chuck Sea/Tac's Avatar
 
Join Date: May 2010
Location: Between Seattle & Tacoma
Posts: 1,721
Default Re: Engine Knock Diagnostic Help Needed

You should get a mechanics stethoscope ( I like to replace the metal end with a rubber hose), and try to isolate where it’s coming from. Do you have any clubs nearby or know someone that can help you diagnose before disassembly. It would be a bummer to tear a bunch of things apart to realize it was not necessary to go that far.
Chuck Sea/Tac is offline   Reply With Quote
Old 04-10-2019, 07:42 AM   #6
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Location: Wisconsin
Posts: 1,215
Default Re: Engine Knock Diagnostic Help Needed

Most likely not the issue, take the fan belt off and see if the knock changes. Also if you do not have a stethoscope, use a large long screwdriver, handle against your ear as a stethoscope, old mechanics trick. I've done this to find bad distributor bushings, and a bad generator bearing.
30 Closed Cab PU is offline   Reply With Quote
Old 04-10-2019, 07:15 PM   #7
James Rogers
Senior Member
 
James Rogers's Avatar
 
Join Date: May 2010
Location: Asheville,NC
Posts: 3,095
Default Re: Engine Knock Diagnostic Help Needed

Center main or possibly front main. Best to remove the pan and investigate before you damage something.
James Rogers is offline   Reply With Quote
Old 04-10-2019, 07:25 PM   #8
Joe K
Senior Member
 
Joe K's Avatar
 
Join Date: Jul 2010
Location: Cow Hampshire
Posts: 3,145
Default Re: Engine Knock Diagnostic Help Needed

Vaguely familiar to the knock I developed driving the Model A on the Mid-Cape Highway at 55.

Came home and dropped the pan to find one of the connecting rod nuts had dropped off. The connecting rod cap was held by one side.

Joe K
__________________
Shudda kept the horse.
Joe K is offline   Reply With Quote
Old 04-10-2019, 09:49 PM   #9
J Franklin
Senior Member
 
J Franklin's Avatar
 
Join Date: May 2010
Location: oregon
Posts: 3,723
Default Re: Engine Knock Diagnostic Help Needed

Quote:
Originally Posted by Joe K View Post
Vaguely familiar to the knock I developed driving the Model A on the Mid-Cape Highway at 55.

Came home and dropped the pan to find one of the connecting rod nuts had dropped off. The connecting rod cap was held by one side.

Joe K
That is why I use locktite on every nut everywhere along with lock washers or cotter pins.
J Franklin is offline   Reply With Quote
Old 04-11-2019, 06:59 AM   #10
Joe K
Senior Member
 
Joe K's Avatar
 
Join Date: Jul 2010
Location: Cow Hampshire
Posts: 3,145
Default Re: Engine Knock Diagnostic Help Needed

Quote:
Originally Posted by J Franklin View Post
That is why I use locktite on every nut everywhere along with lock washers or cotter pins.
These were cotter pinned - but admittedly this motor was so worn if you carefully set the nuts "tight", the shaved bearing caps would "bind" on the egg shaped rods. So one backs off a flat and inserts the cotter.

Thus the vibration of the engine was transferred to the cotter and eventually wore through it. In the bottom of the engine pan besides the nut I found the THREE pieces of cotter pin.

BUT - the end of the story is pleasant as I finally had motivation to replace that engine with a newly rebuilt.

This one uses nylock nuts which the rebuilder recommended over cotter pins and their possibility of wear. (They do move with the engine he explained - which technically makes sense.)

Joe K
__________________
Shudda kept the horse.
Joe K is offline   Reply With Quote
Old 04-11-2019, 08:43 AM   #11
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 4,957
Default Re: Engine Knock Diagnostic Help Needed

You have done the right thing by trying to isolate the noise. I'd recommend a little more like has been said by trying to isolate it a bit more with a stethoscope.

It does seem like there is a problem with #2, but, a little more looking might be worth while before dropping the pan or side cover.
Patrick L. is offline   Reply With Quote
Old 04-11-2019, 09:48 AM   #12
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Location: Wisconsin
Posts: 1,215
Default Re: Engine Knock Diagnostic Help Needed

Have not experienced it, but have read that if the screw that holds the distributor in the block is over torqued/tightened a knock can occur.
30 Closed Cab PU is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 01:09 PM.