5.0 stockers/ distributors

[7423]

Throw a socket on the crank bolt and rock the motor back and forth. Any movement is the chain slop. It would have to be super loose and ready to break to retard 15 degess.

[Mike Taylor 3601]

Sounds more like cam walk but should'nt have that issue on windsor due to them having thrust plate between cam and gear,unless it's loose or something else,as cam moves moves back or forth ign.timing changes just like you are twisting the dist,usaully changes with RPM.
I think you mentioned slack between dist/cam gear could be there.
If you are using ford style ign. module may try that,I've seen modules go bad and timing would move around.
It's computer controled may have computer problem?
I don't know if that is any help but might give you ideal.
Mike Taylor3601

[pmrphil]

The only time I've seen cam walk in a windsor style is when a billet cam gear was used, without the required hardened thrust plate.

[Tim Ellis]

I'm gonna try a different MSD box tomorrow if I can. Also starting to wonder about the fact that I'm using a dial back timing light, I've heard you shouldn't use those with MSD, but I have for YEARS. However I didn't usually check at higher rpms, usually just timing at idle...Hmmmm

[Mike Taylor 3601]

Use light w/o advance , advance timing lights will do weird stuff on msd when you rev,but I don't think they will actually change timing,just give wacky readings.
You said in post you could hear engine change sound like timing is moving,the only way light could do that is if it caused some kind of interference.

You have'nt changed anything on car that could created this?
If it has alternator be sure it's OK diode can go bad send (slight) AC current and make computer do weird stuff.
Check MSD box wires just to be sure in parts changing some thing has'nt got crossed,is battery full charged?I checked time on my car once batt.was a little low,starter was slightly draggy timing was jumping all over,was'nt that low but was enough to mess up stuff. Try wiggle and pull on wiring while it running listen for change you could have broke wire or connection that would show up.

I had pull truck worked on timing was going haywire mag pickup was bad,I know you changed dist. does your car use any kind of crank/cam/hall effect sensor or trigger.
Just kinda throwing out there any ideal that pops in my head.

Boy it be nice if you could run off ign seperate from computer to narrow it down
Mike Taylor 3601

[Tim Ellis]

Update, I pulled the cam out to take a look. I believe the dowel pin was a real tight, possibly damaged, fit. I think the cam sprocket wasn't snugged tight to the cam, and that allowed the cam to walk backwards. I didn't check cam end play last time {silly me} . This time I will. BTW I did check timing with a regular timing light, no difference. Thanks for the brain trust.

[HawkBrosMav]

I may be naive here, but can someone explain the idea of the cam walking back and forth changing timing? It seems to me the the timing would be in the same place the only thing changing would be where the lifter contacted the lobes? even if the timing gear was loose if the pin was in the locating hole I don't see how the timing could change but maybe 2 or 3 degrees just depending on the angle the gear got cocked, but no way does it change 15 unless it was falling off the locating pin....

Just looking for an honest explanation, not trying to be a smart *** or anything.

Thanks
Brad

[ALMACK]

Originally Posted by HawkBrosMav

I may be naive here, but can someone explain the idea of the cam walking back and forth changing timing? It seems to me the the timing would be in the same place the only thing changing would be where the lifter contacted the lobes? even if the timing gear was loose if the pin was in the locating hole I don't see how the timing could change but maybe 2 or 3 degrees just depending on the angle the gear got cocked, but no way does it change 15 unless it was falling off the locating pin....

Just looking for an honest explanation, not trying to be a smart *** or anything.

Thanks
Brad

Brad:
The way I understand it is when the cam on a SBF moves forward in the block (walking) it will spin the dizzy shaft more in the counterclockwise direction (as viewed from above).
This effectively advances the ignition timing on a SBF.

[buzzinhalfdozen]

Personally I would throw out the cam walk as your issue. Though it appears you found an issue with the cam gear install, the cam simply cannot walk enough in the block to change the timing 15 degrees. The thrust plate prevents it's forward movement, and eventually the lifters will stop it's rearward movement. You mentioned you were going to try another MSD box, did you? Is the dist. wiring near any other high power devices...coil, electric water pump, electric fan? It's not unusual to see a bit of timing flucuation triggering off a dist. 1-3 degrees would be considered normal. Joe

[Mike Taylor 3601]

Cam walk on small/big block chevy happens on roller when timing cover flexes or cam button has to much clearance or if belt drive is'nt shimmed correct,cam moves forward and timing retards because cam gear comes forward does same thing as if you twisted dist.,and if it's severe enough lobes will start hitting sides of other lobes. I saw one idle @ 40 degrees and retard to 0 when revved,you could see timng cover bowed out.

If ford came forward it would advance timing

I have never seen any cam walk issues on ford,but cam walk acts like his description,but I also Tim's problem is more of interference like Buzzin half dozen said,I threw him out alot of things to check as always good to cover basics first.

In case anyone does'nt know and are wondering, flat tappets without thrust plate or method to keep cam from moving,the lobes are on taper so as cam turns the taper pulls cam rearward to keep time gear against block and located
Mike Taylor 3601