Timing dimple always right?

C

Commander Toasty

Member
I have read that you cannot rely on the timing dimple because they were not always correctly machined even from the factory, and certainly questionable once an engine has been rebuilt.

Mine is way off. It is a very pronounced dimple, and no mistaking when I hit it, but it doesn't correlate to anything in terms of the engine timing, such as #1 TDC or rotor position.

OK fine - so this is well known although I would like to hear how common it is from you. But the real thing (on my engine) is this ... TDC doesn't seem to exist.

No kidding. If I put a dowel in #1 and cycle the engine it barely moves up and down. Maybe half an inch. So I pulled all the plugs and put dowels in all the calendars and gee - the other three move up and down a lot. But not number one. I have thought maybe it was resting on a valve head but I moved it plenty of times to avoid that.

Now to make it more weird. The dowel in #1 and #4 do not move the same. Not just in amount of travel, but when they are rising or falling.

Oh - engine runs great! Low miles on a rebuild, lots of power.

Thoughts?
 
Well, to a certain extent, that statement is valid however it generally speaks of the cheapo reproduction timing gears that Specialized imported back in the 60s. It would not surprise me if Ricks in Ks or JC Whitney (or a few others) did not retail some of those too, ...HOWEVER other things can interfere with the timing such as the front cover but I think your porblem may be the manner in which you are looking for TDC.

With regard to TDC, I promise that TDC does in fact exist on all four pistons. Just make sure your wooden dowel is indeed resting on the top of the piston, ...and not a valve. I would also be willing to wager that if the engine is indeed running smoothly, that all four pistons are traveling within .100" the same as each other.

.
 
You may have a Model "B" timing cover. The pin position is different. Do you have an "A" or a "B" dizzy?
 
you are right about the time marks are not always correct, after 1000's of engines being built on the same tooling things wear and specs change, the timing marks will be close enough to start the engine but most likely not correct ,always verify tdc , you can do it on any engine by just marking the pulley and putting a mark some where on the timing cover, just make sure they line up at tdc, do that when you are over hauling the engine, ive seen timing marks off as much as 30 degrees
 
I once had a Model A that had the timing dimple 180 degrees off. The book says that the two pins are offset so that the timing gear cannot be installed backwards.... it should say the two pins are offset so you really have to force the timing gear to get it on backwards. The guy that rebuilt that engine sure figured out how to install the gear backwards.
 
MCHinson said:
I once had a Model A that had the timing dimple 180 degrees off. The book says that the two pins are offset so that the timing gear cannot be installed backwards.... it should say the two pins are offset so you really have to force the timing gear to get it on backwards. The guy that rebuilt that engine sure figured out how to install the gear backwards.
Click to expand...

The cam gear can't be 180* off since the crank gear comes around twice for each turn of the cam gear, and the crank is what determins TDC. Hopefully the cam gear is timed correctly to the cam gear.

A couple of places (books) don't have a correct picture of the crank to cam gear timing marks.
 
Tom,

The timing gear on that car was off 180 degrees. It had been forced on that way and had run fine until the head gasket blew and I was trying to set the timing using the dimple in the timing gear after replacing the headgasket. An old friend showed me how to find TDC and set the timing without using the timing pin and had the car running in about 5 minutes.
 
Good luck with the hurricane!

How did you find TDC?

MCHinson said:
Tom,

The timing gear on that car was off 180 degrees. It had been forced on that way and had run fine until the head gasket blew and I was trying to set the timing using the dimple in the timing gear after replacing the headgasket. An old friend showed me how to find TDC and set the timing without using the timing pin and had the car running in about 5 minutes.
Click to expand...
 
Thanks, we should just get some Tropical Storm winds and rain here, but further North it might get ugly.

This was years ago with my 2nd Model A. I had spent a couple of days retiming it according to the book and scratching my head. I called a friend and asked him if he could help me with it, because I could not figure it out. The old friend was a Ford Mechanic when Model A's were new (who unfortunately is dead now).

When he came over to help, I started to pull the timing pin out and he said, "Don't bother with that, you can't never trust those things!" He grabbed a wrench, pulled the number one plug. He had me slowly crank the engine over with the hand crank and he put his thumb over the spark plug hole to determine if it was on the compression stroke. He took a long skinny screwdriver and felt inside to see when the piston was at top dead center. I turned the crank slowly as directed and stopped when he told me to stop. He then adjusted the timer, popped the cap back on it and told me to "Start 'er up!" About 10 minutes after he arrived, it was running and he was adjusting the carburetor.
 
Interesting story, but "why" do you think that the old Model A mechanic said that you can never trust the timing dimple ?


Marc
 
I can only guess that he had seen engines put together by idiots like the guy who put that engine together before. I know that I spent days trying to time that engine "by the book" and I know that if I ever have another one that someone else put together that will not run, I will be sure to double check where TDC is instead of trusting the dimple in the timing gear.
 
Ok, maybe this is a dumb question. But if the dimple on the cam gear is not correct and 180-degrees off; how did the camshaft get timed to the crankshaft correctly?

I am not understanding something here, and that is no one's fault but my own. I am trying to see the connection between the camshaft timing to the crankshaft, and the ignition timing to the TDC of piston #1. To me, if one is correct, then both have to be correct.

Am I over-analizing this?
Thanks,
 
Ron/IA,

If you are talking about my experience, the Timing Gear was forced onto the two alignment pins backwards, so the dimple was 180 degrees off. When they originally assembled the engine, they probably simply did not use the timing pin and timed it by placing the #1 cylinder's piston at TDC during assembly (before installing the head). The engine does not care where the dimple on the timing gear is. It will run fine as long as it is timed correctly. The dimple on the timing gear is there to make it easy to find TDC... which it does as long as it is installed correctly. In that case, the guy who rebuilt that engine failed to note the instructions that are on page 1-51 or 1-138 of the Model A Mechanic's Handbook.
 
You must log in or register to reply here.
Back
Top