Packard Forum Index » Post-War (1946-54)

Hi

Recently had a backfire that broke the starter motor front - that has now been specialist welded and is back on the car and working - however once rolling I'm now experiencing a vibration at about 25mph and a distinct lack of power.

The engine's timing was we thought correct before the backfire - could it be that the backfire upset the timing ?
or is it the case that the timing was NOT set-up correctly and so caused the backfire ?

I also understand that improper or damaged ignition wiring and/or spark plugs can cause a backfire but all those components are new.

I understand that low fuel pressure can also cause backfiring but again the fuel pump seems to be giving the correct pressure but how can I test that ?

Any help greatly appreciated (as usual !!)

Best regards Michael

Backfire could have damaged something in the motor itself. (aka Piston, Rod, etc)

Don't know your mechanical skills, but you can easily check whether the timing chain has jumped.

Also, I had an experience with a badly running engine. I found that part of the primary lead insulator inside the distributor was cracked. This caused me all kinds of problems (missing, backfiring, loss of power). The insulator was replaced, and now the engine starts and runs smoothly with plenty of power.

(o[]o)

Dear mearch:

Any backfire that can break a starter housing indicates a serious problem.

You need to go through all the systems, firing order, timing, valve timing, and check everything.

The best scenario is advanced ignition timing. But I'm not sure if there is a way to foul up the spark plug wires to cause your problem.

Even a bad primary connection could cause that thing to open prematurely half way up on compression. So check everything.

Hope this helps.

Thanks Guys for prompt responce.


I'm on the case and will try my best to remember to report back on progress.


First step is to wake up my restorer to your comments - that'l take some doing !!


Best regards and if anyone else has had the same experience report here please - all and any comments VERY welcome


Michael

I have had a number of causes for such a problem in my long car experience. Here is a list of what I would check in order:
1. Ignition timing slipped (common problem)
2. Spark plug wires hooked up wrong (common problem after working on the car and easy to check)
3. Broken crankshaft (yes the engine can sometimes still "run")
4. Timing chain jumped a tooth (not very likely)

Best of luck. let us know what you find.

Thanks Fred

If you could expand your comments it would be a great help.

Best regards Michael

I suggest you check the items I listed in order listed.

The ignition timing requires finding the mark on the crank damper and clearly marking it with white paint, chalk, or something with contrast. If you have a timing light you can start the engine and see if the timing is in the ballpark at idle. Check your owners manual or shop manual for specs. It should be a few degrees before top dead center (TDC) If you do not have a timing light just turn the engine with a wrench on the crank damper bolt and with the ignition on and the distributor cap off see when the points break. Look at the timing mark and see if it is close to spec for static timing.

The spark plug wires are easy to check. Note which way the distributor rotor turns when you crank engine. Find the plug wire on the distributor connected to spark plug number one. Then write down the order that the plugs fire at the rotor turns around. Check your owners manual or shop manual for the firing order and see if the car matches that. If not rearrange the plug wires. Usually there are only two wires interchanged because the car would not start if many of them are wrong.

A broken crank or jumped timing chain are a lot less likely than the two ignition issues, so don't worry about that right now.

Thanks Fred

Much appreciated.

Best regards

Michael