How much play?

[mcgarrett]

While checking/setting my ignition timing I was turning the crank nut to move the distributor shaft into position and I noticed what seemed to be a LOT of excess play before the distributor rotor actually moved. It seemed like almost 1/4 of a revolution of the crank before the distributor shaft moved. Sure seems like a lot of play to me. How much is acceptable? Is the play due to excess wear on the distributor drive gear or cam gear? What effect does this much play have on timing?

Thanks in advance for your diagnosis.

[Brentwood Bob]

That seems excessive to me. I would pull the distributor and look at the shafts. The joints tongue and mateing slots like to wear.

[Y-Blockhead]

Y'all don't have a Nu-Rex auto advancer hidden away down there do you?

[Patrick L.]

You're turning the crank nut to align the distributor shaft ? Hmm.
When turning the crank nut there will be quite a bit of rotation of the crank nut in either direction when at TDC.

Find TDC with the cam gear dimple.

When setting the timing, rotate the distributor cam to remove all the shaft slack.

[mcgarrett]

Just to be clear, I was turning the crank nut to locate the timing gear dimple with the pin to make sure timing was set right. Still seems like an awful lot of slack (free play) when turning the crank before the shaft in the distributor begins to turn. Don't know what is considered normal. I'm going to pull the distributor and check for worn shafts, gears, etc.

Question: Can the distributor/oil pump drive gear be removed from the engine without a major engine teardown?

[Big hammer]

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Originally Posted by Patrick L.

You're turning the crank nut to align the distributor shaft ? Hmm.
When turning the crank nut there will be quite a bit of rotation of the crank nut in either direction when at TDC.

Find TDC with the cam gear dimple.

When setting the timing, rotate the distributor cam to remove all the shaft slack.

Don’t start taking things apart before doing what Patrick said to do!!!!

[nkaminar]

Try rotating the rotor in the distributor back and forth. If you have a lot of motion there then there is something worn or you have an automatic advance somewhere. If you do not have an advance mechanism and everything is good, the rotor will move a few degrees, maybe 5 degrees at the most.

If the rotor rotates a lot start by taking the distributor out to see if the slot, tab is worn. I had a 30 coupe 50 years ago where these pieces were so worn that the timing would jump 180 degrees causing the engine to backfire and stop.

There are a lot of gears between the crankshaft and the distributor. The cam gear fails often and some have an aluminum hub that can come loose from the fiber gear. If the rotor test above indicates everything is good with the distributor then this is the next place to look. You can take the side cover off the engine to see the cam gear.

The gear that drives the distributor and oil pump can be removed by removing the valve cover. There is a big spring that holds down the gear housing. Pry off the spring and the gear will lift out. The Nu-Rex advance mechanism that Blockhead was talking about is located behind the valve cover.

[mcgarrett]

Thanks for the helpful responses. I'll check things out per the advice of all the seasoned veterans who chimed in!