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 06-23-2019, 05:02 PM   #1
SteveR.
Member
 
Join Date: Nov 2017
Location: Aledo, TX
Posts: 63
Default Engine problem - maybe broken cam

Just got back from a shortened drive. At idle, the engine made a sudden loud "clack", followed by severe knocking/banging. The sound eased up pretty quick, and the engine kept running. I shorted the front two plugs and it doesn't seem to make a difference. Shorting the rear two plugs causes a noticeable drop in RPM. Seems like the front two cylinders aren't firing. Is camshaft breakage common?

I'll do some more troubleshooting and pull the head soon.
SteveR. is offline   Reply With Quote
Old 06-23-2019, 05:12 PM   #2
Y-Blockhead
Senior Member
 
Y-Blockhead's Avatar
 
Join Date: Jul 2011
Location: Redondo Beach, CA
Posts: 5,817
Default Re: Engine problem - maybe broken cam

Quote:
Originally Posted by SteveR. View Post
Just got back from a shortened drive. At idle, the engine made a sudden loud "clack", followed by severe knocking/banging. The sound eased up pretty quick, and the engine kept running. I shorted the front two plugs and it doesn't seem to make a difference. Shorting the rear two plugs causes a noticeable drop in RPM. Seems like the front two cylinders aren't firing. Is camshaft breakage common?

I'll do some more troubleshooting and pull the head soon.
Steve if the cam broke the front two would still be running and the back two would not. Also your distributor is turned by the cam. This is because the the cam is turned by the front of the cam. It also would be pretty hard to break a cam. So you can rule that out. Keep us posted to what you find.
Y-Blockhead is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 06-23-2019, 05:29 PM   #3
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Largo Florida
Posts: 7,225
Default Re: Engine problem - maybe broken cam

What Y-blockhead said.

Cam breakage is very rare. Before pulling the head I'd recommend looking inside the valve cover and doing a compression test. You may end up removing the side timing cover and looking at the cam gear. I check everything I can before pulling a head.
Patrick L. is offline   Reply With Quote
Old 06-23-2019, 05:53 PM   #4
Dick Steinkamp
Senior Member
 
Dick Steinkamp's Avatar
 
Join Date: Apr 2016
Location: Bellingham, WA
Posts: 1,163
Default Re: Engine problem - maybe broken cam

Is the engine idling now the same as it did before the "bang"?

Are you shorting out both front plugs at the same time, then both rear plugs at the same time or one at a time?

I can't see any reason to pull the head now. What are you expecting to find if you do?
__________________
All steel from pedal to wheel
Dick Steinkamp is offline   Reply With Quote
Old 06-23-2019, 06:18 PM   #5
Jacksonlll
Senior Member
 
Jacksonlll's Avatar
 
Join Date: Jul 2012
Location: Michigan-- Member of Oakleaf of MARC
Posts: 1,686
Send a message via ICQ to Jacksonlll
Default Re: Engine problem - maybe broken cam

Take out the plugs and make sure there is compression in each cyl. You may find one or two with no compression. If so, drop the pan and look for broken pieces. Good luck.
Jacksonlll is offline   Reply With Quote
Old 06-23-2019, 06:24 PM   #6
CWPASADENA
Senior Member
 
CWPASADENA's Avatar
 
Join Date: May 2010
Location: PASADENA, CA
Posts: 1,881
Default Re: Engine problem - maybe broken cam

Sponsored Links (Register now to hide all advertisements)
I agree with doing a compression test first.


This may give you a direction to go.


I also agree, not a broken cam.


My opinion,


Chris W.
CWPASADENA is offline   Reply With Quote
Old 06-23-2019, 06:35 PM   #7
Purdy Swoft
Senior Member
 
Purdy Swoft's Avatar
 
Join Date: May 2010
Location: Alabama
Posts: 8,099
Default Re: Engine problem - maybe broken cam

The model A&B cam shafts are forged steel not cast iron like most later cams. Its not likely that a forged cam could or would break .
Purdy Swoft is offline   Reply With Quote
Old 06-23-2019, 08:01 PM   #8
johnneilson
Senior Member
 
Join Date: Jun 2010
Location: 34.22 N 118.36 W
Posts: 1,043
Default Re: Engine problem - maybe broken cam

Sounds possibly like a broken rod.
Pull the first two plugs and make sure the pistons are moving up and down.
If not, drop the pan, go from there.

The original cams are tough, we have welded on them and back ground the base circle way down into the cam, nothing broken even up near 7k revs.

J
__________________
As Carroll Smith wrote; All Failures are Human in Origin.
johnneilson is offline   Reply With Quote
Old 06-23-2019, 08:27 PM   #9
Dick Steinkamp
Senior Member
 
Dick Steinkamp's Avatar
 
Join Date: Apr 2016
Location: Bellingham, WA
Posts: 1,163
Default Re: Engine problem - maybe broken cam

Quote:
Originally Posted by johnneilson View Post
Sounds possibly like a broken rod.
Wouldn't a broken rod continue to make noise as the engine was run?
__________________
All steel from pedal to wheel
Dick Steinkamp is offline   Reply With Quote
Old 06-24-2019, 12:40 AM   #10
40 Deluxe
Senior Member
 
Join Date: May 2010
Location: now Kuna, Idaho
Posts: 3,774
Question Re: Engine problem - maybe broken cam

Quote:
Originally Posted by SteveR. View Post
Just got back from a shortened drive. At idle, the engine made a sudden loud "clack", followed by severe knocking/banging. The sound eased up pretty quick, and the engine kept running. I shorted the front two plugs and it doesn't seem to make a difference. Shorting the rear two plugs causes a noticeable drop in RPM. Seems like the front two cylinders aren't firing. Is camshaft breakage common?

I'll do some more troubleshooting and pull the head soon.
If a broken cam caused the front 2 cylinders to quit firing, what is operating the valves on the back 2 cylinders?!
40 Deluxe is offline   Reply With Quote
Old 06-24-2019, 08:22 AM   #11
johnneilson
Senior Member
 
Join Date: Jun 2010
Location: 34.22 N 118.36 W
Posts: 1,043
Default Re: Engine problem - maybe broken cam

Quote:
Originally Posted by Dick Steinkamp View Post
Wouldn't a broken rod continue to make noise as the engine was run?
Once the interfering parts are pounded up and away from the rotating crank there will be no more noise. It depends on where the break occurs. Typically the piston is shoved up into the top of the cylinder.

I sure hope this is not the case, but OP description of "the engine made a sudden loud "clack", followed by severe knocking/banging. The sound eased up pretty quick, and the engine kept running" describes a typical rod separation.

Could be flywheel or clutch but that wouldn't explain the front cylinders not responding. Flathead motors can't drop a valve into the piston either, so that is out unless this is a OHV motor, OP didn't mention that.

I wish the best of luck to the OP here, take the time to properly diagnose and let us know what happened.

John
__________________
As Carroll Smith wrote; All Failures are Human in Origin.
johnneilson is offline   Reply With Quote
Old 06-24-2019, 10:12 AM   #12
Purdy Swoft
Senior Member
 
Purdy Swoft's Avatar
 
Join Date: May 2010
Location: Alabama
Posts: 8,099
Default Re: Engine problem - maybe broken cam

More than likely the problem is a broken piston skirt . The original pistons had a split skirt , all the way from the oil ring to the bottom of the skirt . I've seen a few model A engines drop a piece of piston skirt into the dipper tray . When this happens , the rods hit the broken piece, make a hell of a knocking sound and then sort of settle down . The engines would still run but skipped on the broken piston cylinder . It could be something else but I can't see a forged model A camshaft breaking or a connecting rod . Model A engines unless highly modified are low compression low RPM engines .

Last edited by Purdy Swoft; 06-24-2019 at 03:01 PM.
Purdy Swoft is offline   Reply With Quote
Old 06-24-2019, 10:36 PM   #13
SteveR.
Member
 
Join Date: Nov 2017
Location: Aledo, TX
Posts: 63
Default Re: Engine problem - maybe broken cam

Time to drop the pan...pulled the valve cover and all seems normal there. Piston skirt or rod sounds likely...it was a lot of bad noise, not something small.
SteveR. 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 04:13 AM.