Antz81

Hi, I was checking my chain earlier, and found that I can rotate the crankshaft by about 7* before any any movement can the seen at the distributor rotor (or valves). I assume this is too much and the chain should be replaced (correct me if I am wrong). Anything else I should replace at the same time? I replaced the balancer not long ago so that should be fine.

Could this also cause a lower than normal manifold vacuum? I'm getting a stable 15-16"

Kirk H

Antz-
I am no expert, but I think this play would be normal because of all the spacing between gears and the chain and sprocket itself. Once the motor is in motion, however, it is not bouncing around because of the forward angular momentum of the engine, kind of like rotating pedals on a bicycle... as long as you keep pushing on the pedals in the direction of rotation, you will have constant contact as needed. However, your chain should not be sloppy, due to stretch. If it has over 100,000 miles on the chain, I would replace it as long as you're in there- they are not that much.
Kirk

leadfoot4

If you go with a Cloyes "True Roller" timing set, there should be VERY little slack in the assembly, therefore very little movement in the crank gear, before the distributor starts to rotate.

FWIW, a number of years ago, I replaced the OE timing set on a 1993, 50,000 mile, 350 cu.in. small block Chevy, with a Cloyes TR set. After doing the job, I put a timing light on the engine, and the timing had changed by 3*. So, yes, I think you'd see a difference with a new timing set, but I don't know if it would affect your vacuum.

gkull

Any c3 motor with a stock timing chain needs to be replaced after 50K miles or any signs of slop no it is not like a bicycle in the above post

When the chain becomes longer it is retarding the valve events and timing

Replace with quality double roller timing chains

USAFVeteran

This is the only fix

Antz81

I've got it all open now. The chain appears loose just looking at it. Not sure but may be the original chain. It certainly was the original water pump. I'm going to go with a cloyes double roller. I'll also replace the pump since it's off.

CanadaGrant

One other thing besides the loose timing chain is distributor shaft end play. Because of the helical gears on the cam and distributor, shaft end play can cause large variations in timing like you describe. I don't doubt your chain is worn but correct shimming of the distributor shaft will also cut down on large timing "movement" under acceleration and deceleration. For roughly every .013" of end play it's one degree of timing slack or movement and .050" shaft end play or more on some of this old stuff is not uncommon.

leadfoot4

Antz81

Just one more small thing to look into.

Antz81

Slowly getting things back together. New timing chain is on, and is alot tighter than the old one. New water pump fitted. I just need to get a 14mm hex bit to tighten the bung on top. I had play with the old fan clutch and decided I didn't like the way the bearing felt so I should have a new one arrive tomorrow.

I checked the distributor end play. I will need to address this (I got 0.066"). No one locally sells the shim kit, so I will have a look at making a shim or shims at work later this week. (I would use 316 Stainless or maybe 4140 steel, not mild steel) But I may end up ordering some.

leadfoot4

Your avatar says you're in NZ, so that may limit your availability to parts, but does anyone in your area stock the 'Mr.Gasket' line of parts? I know that they sell, or used to sell, a package that had 5-6 shims of varying thicknesses, specifically for distributors.

c3_dk

I replaced chain setup last week, on a 71
I needed it a "bit"

Antz81

From what I can tell they no longer sell the shims. I did a Google search for them, found summit and Amazon still have them on their sites, but not available.

CanadaGrant

Glad you checked for end play. At .066" play that's 5 degrees of timing slack right there. I think Moroso also makes a shim kit but not sure of the size selection in the kit. There are some listed on fleabay under "distributor gear shim kit" I think Corvette Central also sells them. Between that and the loose chain, looks like your timing problem will be cured.

USAFVeteran

If I can help you get parts, and ship them to you, let me know. I know you can ship them from vendors with no issues, but if you run into something, let me know. I've lived in other countries and trying to get parts can be a tough one. If I can help, let me know!!!

leadfoot4

Moroso part number 26140


Jegs stock number 710-26140

Antz81

thanks for the offer. Most places will ship straight to NZ but I also have a US shipping address that I can use for larger items or items that the vendor won't ship to nz. (It just takes a bit of time as they come via ship)

Antz81

All back together and running. Timing moves around a bit less when setting it, not that it ever moved a lot. I will still get some proper shims for the distributor.

Found a good tip for installing the distributor, move the engine to TDC on #1 compression, then fit the distributor with the rotor roughly at #1. if to doesn't line up the the oil pump turn the engine over by hand and the distributor will drop down when it does line up, but will stay in time with the engine. This made the job so easy.

After all this no change to the vacuum readings. (but at least I know this was not the problem) Any ideas what could be the cause for this? I have done a thorough check for vacuum leaks and found nothing. Timing is set at 6*BTDC. Idles is 700RPM in Neutral. I'm not 100% sure but I believe it is still the factory cam. I know ignition modules normally just fail completely, but can they fail so that they don't advance the timing correctly? I'm sure mine is still the factory module (With the yellow dot on it) and do have a spare module anyway.

Rescue Rogers

thats amazing how did it run before and after the replacement

c3_dk

Most of the time ok, but sometimes shooting out of the exhaust.

The chain hit the cover almost to a point where a hole was made.