Fevre

My timing is bouncing a little and would like some input on what to check. I recently switched plug wires from Summit 8mm to Accel 8mm custom fit. Weird thing is that with the Accel I can't get a timing reading unless I am close to the plug. Have done a few other things but it was stable when I originally timed it after engine installation.

Thanks

BTW it is bouncing from 10 down to about 5 or 6 at idle every so often, not constantely.

verskel

Sounds more like a 'vacuum' problem to me..... :eek:

The only things that I'm aware of that affect timing on a normally aspirated engine are 'advance' & 'vacuum'.... :yesnod:

Fevre

Thought the same thing vacuum is rock solid at 17 degrees.

But it is worth checking again.

Like I said, the timing was steady when I original timed it but I guess it could have developed a problem since. Just seems funny it started after the plug wire switch. It idles nice bu does seem to skip about the same time of the fluctuation. Lifter adjustment maybe? Another thing I did since original timing was adjust the valves lash.

Thanks verskel

Sigforty

My erratic timing issue turned out to be 5 broken teeth on the cam timing gear.

Mark B.

Fevre

Hope I didn't break steel teeth. It's a GM OE single row steel timing chain and gear set, came in the engine.

verskel

Yup - this would do it also,.... and it's very 'rare' for a chain to 'stretch' but I've heard about specific cases of this also. It probably wouldn't hurt to check the rockers again - but make sure that 'everything' else has been checked 2-3 times first (unless you like pulling the valve covers off :jester:)
....Make sure you're distributer is 'tightened' down, too ;)

Fevre

lucky I got nothing covering my valve covers so it's a breeze. I have seen pictures of some other member's engine bays and would not want to deal with all that crap. Someday I will get high tech and post some pic's of the clunker.

PatsLs1vette

timing chain stretch will do it and also cam walk will do it too,thats why i use cam buttons on everything now timing stays rock steady.

Fevre

I probably should have went to a double roller but the engine isn't going to stay in more than a year or two so the only thing I did was upgrade the cam. It runs pretty good except for the exhaust smell being a little richer than I think it should be. I guess I can live with that until I get stroked again.

Vetterodder

What is your normal idle speed? If it's high enough for there be to distributor advance, vacuum or centrifugal, a miss or loading up that reduces rpm momentarilly will also reducing timing at the same time. First thing I'd check is the connections on the new wires and also that they're not cross firing.

thebruce

My timing 'bounce' was exactly like yours. I fixed it by attaching the inductive pickup to the spark plug wire up near the distributor, not down near the header. I had my spark plug wires routed underneath, and the pickup actually was reading the spark from the wire next to the number one wire every now and then. If your pickup doesn't work up near the distributor, I'd suggest trying to move the wire from the next cylinder as far as possible away from the pickup.

Good luck.

Fevre

Idle speed is set about 800 to 900 rpm's. It is just funny that the timing read fine with no variance before the plug wire switch. I also made sure all the wires are not touching which I didn't with my old set. Reason I switched is I burnt 2 of the boots during cam break in.

I will try some of the suggestions given and see if I can figure out what happening.

Thanks all

Fevre

Found that the connections for my MSD noice suppressor had come loose, or more likely, I had left loose from the last time I fiddled with it. After tightening them up the erratic timing went away. Go figure.

Thanks for the help.