Erratic running after fitting new timing gear

DennisR

DennisR

Senior Member
Fitted new gear, checked timing with pin. Car starts after juggling choke, throttle etc. then dies with a couple of pops and backfires, can be persuaded to run a bit longer if pumping the accelerator. No settings were changed just fitted new gear, new oil...................
Petrol getting thru, carb floods if choked, must have done something but what ?
Any ideas welcome.
 
Did you make sure that the timing marks on the crank and cam gears matched up?
The timing of the gears in relation to each other determines where the piston travel is in relation to valve opening and closing. The timing pin is for timing the ignition. Matching up the gears is a separate function.
 
Last edited:
I agree.
It sounds like the only thing you touched was the timing gear, so I'd make sure the gear is timed right. Remember, some books have pictured the cam gear timed to the WRONG side of the keyway. As viewed from the front of the engine, the cam gear is timed to the RIGHT side of the keyway.
 

Attachments

  • Timing Gear Marks.jpg
    Timing Gear Marks.jpg
    78 KB · Views: 193
TBH I`m not sure, I lined up the marks and bolted it back together. If I`ve got it wrong would that be the cause of the way it runs ? would it even run at all ?
 
As a matter of interest I checked the distributor, not had cause to look at it since I`ve had the car, been busy with restoring and just started it up now and again, I found the rotor/contacts different to what I`ve been used to, there is quite a large gap between them and the rotor runs lower than the contacts, I`ve not seen that before.
 
Rotors on my Model A have always sat low on the shaft where the tip of the rotor is lower than the contacts so I put a rubber shim up into the rotor which raises the rotor tip level with the contact points. On some distributor bodies I have also had to solder up the contacts and file them flat to keep the rotor tip to contact gap about 35 thousands. I wrote a article for the Restorer Magazine sometime in the late 1980's or early 1990's about this but off hand do not remember which issue it was printed in at this time.
 
If you haven't touched the distributor since replacing the timing gear, then the spark timing should tell you if the crank gear is one tooth off. When the timing pin drops into the cam gear dimple, then the rotor should be positioned exactly as pictured.
 

Attachments

  • Timing Rotor Position.jpg
    Timing Rotor Position.jpg
    66.7 KB · Views: 112
I'm pretty certain it was as your pic Tom but I will double check everything tomorrow and take my own pics.
 
Tom, the camshaft, distributor and pimpled timing mark will all line up the same as before even if the alignment marks between the crankshaft gear and cam gear are off by one or more teeth. The piston position to the spark timing is what is off.
 
AL in NY said:
Tom, the camshaft, distributor and pimpled timing mark will all line up the same as before even if the alignment marks between the crankshaft gear and cam gear are off by one or more teeth. The piston position to the spark timing is what is off.
Click to expand...

How do I correct it ?
 
Al's right. I was thinking of other cars where the timing is on the crankshaft pulley. First you need to determine TDC for the crankshaft, then see where the distributor rotor is positioned. The most accurate way to find TDC is to use a dial indicator with something through the spark plug hole that can touch the top of the piston. Then pick a distance, say .250" BTDC and mark the pulley and adjacent spot on the cam gear cover. Now roll the crankshaft over the other direction and mark the pulley again at .250" BTDC, which would be next to the mark on the cam gear cover. Now measure the distance between those two marks on the pulley and mark the exact center between them. Line that mark up to the mark on the cam gear cover, and you'll be on exact top dead center.

You don't need a dial indicator to do the job. You can use anything that would stop the piston at some distance before top dead center. Say you take a junk spark plug and gut the center of the plug, then bend a heavy rod so it could be inserted in the plug and screwed into the plug hole to block the piston say 1" before it reaches TDC. Do the marking as above, roll the crank over the other direction and do the same as mentioned above.

When I get time, I'll make a tool for doing this. What I just wrote is to get the job done of finding TDC for the crankshaft without having to remove the front cam gear cover.
 
Went to follow up the suggestions, the rotor has some slack, the 2 pics show the amount of play, how much I can move the rotor by hand. Is that acceptable ? or...............................
 

Attachments

  • no1.jpg
    no1.jpg
    63.3 KB · Views: 47
  • no2.jpg
    no2.jpg
    60.4 KB · Views: 50
Your picture looks OK, and the picture on the right is correct for when the pin drops into the dimple.
Now we just need to establish that the piston is TDC when the pin drops into the dimple.
 
Dum question, what is the reason you changed the gear without doing any other work? Could be there was a problem before you took it apart?
 
You must log in or register to reply here.
Back
Top