The Stovebolt Site Forums The Shop Area Engine Shop Problem with timing gears

Hi all. I have a 54 235 that could be in deep doo-doo if I don't get this right.

After replacing the rear seal (engine in truck) I was getting ready to start putting the front timing cover back on. It was then that I noticed the dots I painted on the crank and cam gears were not lined up anymore. I swear that crank didn't drop enough to jump teeth. I did rotate the crank a bit during the seal installation, but the two dots do not seem to be the same number of teeth away. So, although I don't see how it could have happened, I have a strong suspicion that the timing is now messed up.

The engine seemed to run fine before, so I'm assuming it was correct before I started this seal job. Ok, so here are my questions:

1) I see a small circular mark on the cam gear right near a tooth valley. I'm assuming this is the "valve timing mark" referred to in the shop manual. On the crank gear, all I see is two little divots (like someone hit it with a punch) that line up on a tooth peak. It isn't the same kind of mark as the cam, but it is the only marks I can see. Is this also the "valve timing mark"? I'd just like someone to confirm these marks before I use them.

2) I've read an old thread here about how to get the gears lined up correctly without marks. I could of course just try to get my dots lined back up, but this is an opportunity for me to learn something, and I don't want to assume anything. So, if I were to rotate the crank, would you all agree that the "valve timing marks" should come together in either the first or second rotation of the crank (and then ever other rotation thereafter)? Put another way, does the cam gear have exactly twice the number of teeth as the crank gear?

3) If I am able to drop the crank in front enough to re-align my white dots, then I'm thinking I can prove it is timed properly if the "valve timing marks" line up every 2 crank rotations. Is that correct?


Please advise!

BTW, I'm glad a put the dots on the gears before I started this job. Someone on the board made this suggestion, so thanks to whomever that was.

Unless you dropped the crankshaft WAY down, it's pretty unlikely the gears have skipped any teeth. Not impossible, but I've never seen it happen. There should be factory marks to time the cam to the crank, and they will align every two turns of the crankshaft. The cam runs at exactly half crank speed, so there are twice as many teeth on the cam gear. When the marks align, there should either be a dot on each gear that will match up, or possibly there will be a dot on the crankshaft gear, for instance, and a dot or other mark on two cam gear teeth that will align on each side of the crank gear mark. I've seen timing gears set up both ways.

If the marks are indistinct, or missing, there's a way to check for proper cam timing. Remove the valve cover, and watch the motion of the valves on either #1 or #6 cylinder. Remove the spark plugs so the engine is easier to turn, have a helper turn the fan, and probe into #1 or #6 cylinder with a piece of soft wire (NOT a screwdriver, or anything else that's hard and unyeilding!) Turn the crankshaft until you can feel the piston come to the top of its stroke. One of the cylinders, either #1 or #6, will have both valves closed, with clearance evident at the rocker arms if you have a solid-lifter engine. The other cylinder's valves will will be "rocking", with the exhaust valve closing and the intake valve opening. Each valve will be approximately halfway of its travel. The relationship of the rocker arms and the piston position will be way off if the cam is out of time even one tooth. By simply turning the engine in the normal direction of rotation (clockwise when viewed from the front) and watching the valve action, it's pretty simple to check cam timing, even without timing marks.
Jerry

Thanks for your reply Jerry. I agree with what you say about the crank needing to drop WAY down. If the crank had dropped "way" down the rear seal installation would have been a heck of a lot easier! I just can't reconcile how my dots don't align.

I think what I'm going to do is pull the plugs and rotate the crank a number of times and see how the timing marks line up (both mine and the ones stamped on the gears). If they never line up, then I'll loosen the bearing caps again and see if the front drops down enough to disengage the teeth. I'll need to do this anyway to get the teeth lined up .

Thanks for the info about the 2:1 difference in the gears. This will help alot I think. Worst case scenario (which doesn't seem so bad) is to do what you say with the soft wire, valves, etc.

Thanks.

Do you have the harmonic balancer and timing cover removed? If so, I guess it would be possible to get the gears out of time. Otherwise, there's no way to drop the crank far enough to disengage the teeth. That seems like a lot of unnecessary work just to change a rear seal, however!
Jerry

Jerry-

Yeah, I have the balancer and timing cover removed. My engine was leaking from the front too, and the front engine mount was rubberized goo. So I needed it all off, and I can only assume that the front part of the crank did indeed drop enough to disengage the gears. I'm frankly surprised, but it is what it is. I'm hoping I'll get this issue resolved with 100% assurance using the method you describe, the marks on the gears, and common sense.

Forgive me if this is way off base, but you said there is a different # of teeth on the gears from your original mark, and HRL said one gear turns at half the revolutions as the other. Is it possible that the teeth difference on one is twice the other. It seems that should be the case. Good luck.
Jeff

Jeff- I'm no math expert, but since the gear ratio is 2:1, I would expect my mark to align from the beginning, then after revolution #1, the mark on the crank gear should be at its original location (meshed with the cam gear) and the mark on the cam gear would be 180 degrees away. Then the marks would align again after rotation #2.

So the marks will not "fade away" from each other in terms of # of teeth. Of course the marks will be moving at different rotational speeds (again, the 2:1), but the marks should always line up or be out of phase by 1 rotation.

When the teeth are a few away from where they come together, it is easy to think that they don't match. I would be rotating it to the factory marks to make sure.

Exactly!

Well, this is the plan, and I hope it all lines up without extra effort. But I did count pretty carefully, so I'm either going to learn that the teeth disengaged or that I'm a horrible counter! Thanks for all your replies.

gjberche,
Did you ever solve this?