Timing and Knocking (getting worse)

M

modelmodela

New member
Thank you for reading my post.
My '29 Model A has a habit of falling out of time. I feel minor lateral movement in the distributor shaft and understand that this may be the problem. This is no my primary issue with the distributor, though. When I manage to find the sweet-spot in timing the vehicle runs excellent and for long duration. Sometimes when I time too advanced I hear knocking and my heat gauge will slowly creep over 140F. I am normally able to correct that with a re-time.

Recently, I am unable to correctly time the ignition. No matter what I do with the distributor cam, placement of TDC, etc., I hear pronounced knock and experience overheating. Knock is heard at idle, lessens slightly at full retard while driving, and is very loud at any spark advancement while driving and idle. There is also engine vibration at 40 MPH +, which feels like the engine is topped-out and stressing.

I read an earlier post "Loud Hammering Noise" which indicated the possibility of a center main bearing issue. However, my knock is dependent on moving the spark advance and, most notably, causes overheating (knock begins before overheating but overheating is allegedly caused by timing).

I replaced the condenser, points, rotor, distributor plates, and coil wires. I also checked spark adjustment lever and linkage. Carburetor and cooling system also appear to be functioning properly. I am out of ideas and, again, believe that timing is the culprit due to heating and knock dependency on spark advance. I am not ruling out bearing issues, though. I welcome any comments that may be provided with this regard. Thank you for your help! Jim
 
Think you better check the fibre timming gear, sounds like a loose centre, Take the cover off & inspect , Tell us the results .
Or is the cam not locking on the top dissy shaft , allowing it to slip.
 
Hi Jim,

1. To save lots of time, money, & find peace of mind, "sounds" like you may need some help with differentiating various "sounds".

2. Like try calling upon "any" senior professional mechanic, who repairs "any "make of vehicle who can tell the difference between ignition knocks, timing gear knocks, & or bearing knocks after listening "in person."

3. Why guess & tear "everything" apart?

4. Knocks are very detrimental, will get worse, & usually cause lots of expensive damage.

5. We all started from scratch -- humbly asking for somebody to "listen" may be a very intelligent move.

6. Also, finding the "sweet spot" ....... by ear? .....again, "sounds".

7. Are you familiar with timing a Model A with the timing pin?

8. Could it be you are confusing the hearing of the "sweet spot" as hearing less bearing knock as the spark is retarded ..... then the spark is so retarded the engine overheats?

9. Just asking .... difficult for us to diagnose without being able to "hear" what you have from miles away.
 
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Seems to be a good post with good answers. What have you done to really locate the source of the 'knock' ? Can you make it 'knock' while standing beside it with the hood open ?
If the noise comes from the front cover, then hold the timing pin against the gear and see if it goes away. If it does, change the gear.
If the noise comes from the bottom of the motor then its time to adjust some bearings.
 
Timing and retiming seems to be done way too often. Once the timing is CORRECTLY set it should not have to be touched again, unless the distributor cam is loosened for some reason. Make sure the cam screw holds the distributor cam from turning.

An accumulation of rust and junk in the cooling system can cause a hot spot, which will make the engine ping. This was the problem with a used engine I installed to use while I rebuilt my original engine. This junk settles near the rear of the block by #3 and #4 cyclinders and will cause a hot spot which will make the engine ping under the slightest accelleration. I used vinegar for 30 days then a sump pump to flush out the system, and now the pinging is gone.

As mentioned, you need to find the source of the noise, as you might have a main or rod bearing out. The center main usually goes first. Adding counterweights to the crankshaft, or buying a new counterweighted crank will help a lot to prolong the life of the babbit.
 
If it pings under load, it could be timeing. If it knocks (clunk,clunk) under load, it could be mains. If it knocks (click, click) when backing off the throttle, it could be rods. Ron W
 
get a knowledgeable member from your local club over there to give a listen and hands-on. The resources of the local clubs are often over looked
 
I wonder if he might have a Model B timing cover or something that is causing him to find TDC using the timing pin that is way too far advanced?

Either that, or if his timing keeps "slipping", could it be a really worn gear mesh on the cam or the distributor shaft allowing it to slip a tooth here and there?
 
:rolleyes:Thank you for your responses. Since my post, I changed the distributor cam, added new points, and added high-quality fuel. I also visually observed the #1 piston at TDC when feeling the timing gear dimple with the timing pin. The knocking sound is 70% better, but still pronounced. It's hard to explain the sounds. The knocking is deep and does not at all sound like a ping, such as that I hear in my modern vehicle when climbing a hill (I live at 6,200' elevation with common 15% highway/road grades). It sounds like a bad rod bearing, but again is dependent on timing. When revving the engine by hand, I hear the knock coming from the front area of the engine. Again, the sounds is very dependent on the position of the spark advance: more retarded=less knock; more advanced=more knock. As I stated in my post, my distributor shaft has significant play, and I understand that may be contributing to the issue, and is the likely culprit causing the cam to move no matter how tight the screw. Accordingly, I don't think I can diagnose said symptoms until I press in new distributor shaft bushings and get that issue resolved. I will do that next and will be happy to give you all an update on the situation. Also, joining our local "A" club is an excellent idea. Thank you again for your suggestions. J
 
Have you pulled the side cover off the timing gear, so you can check to see if you have the cam gear with the aluminum center, which works loose from the fiber outer part? This is a common cause of noise and a good reason to NOT buy the two piece gear.
 
Your timing problem and the associated knock is quite possibly coming from a broken spring inside of the camshaft thrust plunger. This allows the camshaft to "walk" back and forth which alters the timing and which also causes the knock when the front camshaft flange bounces off of the front bearing with changes in torque, such as "when revving the engine by hand". I chased this problem around for weeks before discovering the cause after I pulled off the front cover.
 
One change at a time. did you have a thin special lock washer under the screw that holds the distributor cam in place? fix the distributor. Retime the motor correctly. some get the point when the points should open wrong. Marco's website has the timing explained to eliminate slop in the distributor.
then restart the car and see if that eliminates the problem, If not then check the timing gear.
Start the above by joining the local club and asking for help.
I personally have found that most hobbists are not going to embarrass you. They honestly would like to get you on the road, and into their club. And it won't hurt.
This is supposed to be fun.
Bob
 
With the timing in a position for the pronounced "knock", use a screwdriver and short out one cylinder at a time, pausing a couple of seconds to listen for a change in the knocking sound. This will identify or confirm or eliminate the "rods" from the candidate list!
 
don't rule out a head gasket. i've had a head gasket burnt out between #3 & #4 knock loud and go away when retarted. Might try a compression test to see what you have without taking anything apart. good luck
 
After reading the orignal post again...40mph,viberating and stressing? Sounds like the motor is running very Lean,this will cause a higer Temp,and if its too Lean it's only gonna run so fast.....and it's gonna Knock. Could be trash reducing the gas flow at the tank shut off valve.
Also Lefty makes a good point.
 
Without hearing the noise, I agree with George, and the center main was my first thought. I suggested the two piece cam gear because the noise was said to be from the front of the engine. Anyway both of these possibilities have often been the cause of such a noise. Nosie can travel and make it difficult to locate the true source.
 
A sloppy distributor shaft, will/can cause ruff running, because the point gap is changing. However I don't see how it would cause retard/advance problems, or knocking.
 
I'm wiht James G. His is the easy way to eliminate a rod as the source. It sounds like a rod to me. Do the easy things first.
 
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