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Username Post: TIMMING QUESTION        (Topic#347460)
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-02-17 09:32 AM - Post#2709495    

I notice that the timming mark on my '67/'68 350SS jumps around about 2 - 4 degrees when the light is on it at idle. Is this a chain/gear issue? Also noticed that my rotor has some rotational movement (slop). How much is acceptable,if any Could this be the cause of the moving mark? Thanks for your input

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 




farm rat 
Contributor
Posts: 106

Reg: 09-13-16
10-02-17 11:18 AM - Post#2709503    
    In response to Lead sled

Did you remember to unhook the vacuum advance and plug the line from the carb?



 
Junkyardwarrior 
Contributor
Posts: 262

Loc: Yuma AZ
Reg: 02-25-15
10-02-17 12:05 PM - Post#2709507    
    In response to farm rat

How much cam are you running? I know on my motor I have a very light bit of cam surge at idle (the idle speed actually bounces a bit between 850-925) which caused the timing reading to be off when I had too light of a spring on the mechanical side. Also there will be vacuum surge too so if you didn't take the vac advance off and plug the hole it will bounce as well.



 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-02-17 04:56 PM - Post#2709554    
    In response to farm rat

OH yeah, vacuum advance unhooked,and pluged off.The man I bought it from 10years ago,said it did the same thing to him?????

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-02-17 05:11 PM - Post#2709556    
    In response to Junkyardwarrior

JUNKYARD...... As far as I know it's a stock cam for a 1967SS Camaro 350,that was put in my 52 Belair some 35yrs ago. I also noticed that the vacuum gauge has an erratic "bounce"/shake at idle too. Jumps around 17 - 20 @ an elevation of 1,300ft. Other than the timing mark moving, it runs pretty good for what it is. I did put a lighter set of springs for the mech advance a few yrs ago,but the "jumping" was there before that....no change Still need help. Oh ya,I know the cylinders have been rebored,or honed before I bought it (still saw hatch marks in them.) NOOOO telling how many miles on the rest of it

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
Junkyardwarrior 
Contributor
Posts: 262

Loc: Yuma AZ
Reg: 02-25-15
10-03-17 06:35 AM - Post#2709618    
    In response to Lead sled

With the vacuum moving around that much it sounds like it either has a leak or it has a bit of a cam in it. I guess it could have a flat spot on the cam where a lobe is worn causing the fluctuation in the reading... Do you have a tach on the car? Does the idle speed move around a bit as well?



 
models916 
Valued Contributor
Posts: 4700

Age: 66
Loc: Addison, IL
Reg: 05-28-10
10-03-17 06:37 AM - Post#2709620    
    In response to Lead sled

Could be play in the distributor gear to housing. They sell shims for this. Or set total timing and forget about it.



 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-03-17 08:39 AM - Post#2709631    
    In response to Junkyardwarrior

Yes it's got a tach,but that stays steady as a rock....Total timming is at 34/36 deg.
I don't know,maybe I'll just leave it alone. Thanks a lot guys

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
Junkyardwarrior 
Contributor
Posts: 262

Loc: Yuma AZ
Reg: 02-25-15
10-03-17 11:11 AM - Post#2709645    
    In response to Lead sled

That's odd. Every time I've had a fluctuation like that there has usually been some kind of idle speed movement. Even now mine bounced about 20-50 rpm occasionally, but I'm pretty certain that's all cam overlap making the engine do that. I think he may have called it on the distributor play. Could either be a worn cam gear or even that shaft shim situation he was talking about. The timing fluctuation could theoretically explain the jumpy vacuum reading as well. It'd be a lot easier if you knew the cam specs too.



 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-04-17 10:45 AM - Post#2709755    
    In response to Junkyardwarrior

Junkyard, my tach isn't that accurate(100rpm).As for the cam specs,I wish I knew what it is

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
Junkyardwarrior 
Contributor
Posts: 262

Loc: Yuma AZ
Reg: 02-25-15
10-04-17 12:10 PM - Post#2709762    
    In response to Lead sled

The only other thing I can thing for you to check would be to watch the cam and turn the motor by hand to see if the cam is moving independently of the crankshaft. If the chain is as tight as it should be then the cam motion should be instant with the turning of the crank. If the chain is worn moving the crank will let the cam sit independent for a small fraction of the turn. The chain bouncing could cause the timing bounce if it's too lose. I'm not 100% certain what the acceptable slack from the cam gear to the dizzy is, but I'm sure it's all over the googles. If that gear is worn on either the cam or the dizzy it could also cause that...



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17109
grumpyvette
Age: 69
Loc: FLORIDA USA
Reg: 03-16-01
10-05-17 11:59 AM - Post#2709847    
    In response to Junkyardwarrior

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

if your seeing the timing change a few degrees, back and forth,
slack in a worn timing chain, worn distributor gear or not having the proper shim clearance on the distributor center shaft will provide slop that allows timing to vary several degrees


IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


Edited by grumpyvette on 10-06-17 04:07 AM. Reason for edit: No reason given.

 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-10-17 10:12 AM - Post#2710410    
    In response to grumpyvette

Thanks for the info guys.I'm leaning to a wore out chain/gearset. Who knows what was done to that engine 30+ yrs ago.The man I bought the car from(engine already instaled) did have the heads off(double humps) to get valve seats hardened,and the guides reworked. He said,he could still see the cross hatch marks in the cyls. BUT...It could have been put back together with the old distributor,and timing set??????? It's probably got 35,000 miles since the "SO CALLED REBUILD" I'll check out the shim issue in the dist. Easiest place to start at. Thanks again, Lead

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-10-17 11:20 AM - Post#2710414    
    In response to Lead sled

Well, I just came in from the garage,took cap off,and to the best I could measure the up/down play of the rotor with dist still in engine, it lifted approx 1mm if that? But the rotational movement of the rotor going clockwise is about 1/2" to 3/4"

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
IgnitionMan 
Valued Contributor
Posts: 3219

Reg: 04-15-05
10-10-17 12:16 PM - Post#2710419    
    In response to Lead sled

Yes, a distributor with a mechanical advance WILL have movement of the mechanical curve into and back out of the advance.

How much did the actual distributor shaft, the one in the middle of the distributor, move in its circle, not the rotor????

How I would measure that is to pull the cap off the distributor, and then, BY HAND, WITH A BREAKER BAR AND SOCKET, rotate the engine backwards until the rotor turns backwards, then, stop.

Now, mark the balancer with a line at TDC, then, slowly rotate the crankshaft forward, until the rotor starts to turn the correct direction. Stop.

Make another mark on the balancer at TDC. HOW MUCH DISTANCE BETWEEN THE TWO LINES?????

It should not be a large amount of open balancer between the two marks.



 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-10-17 05:29 PM - Post#2710452    
    In response to IgnitionMan

I did notice that while turning the rotor,that the cam that opens/closes the points, moved from a flat,over one high point,to the next flat point. Make any sense to you,or is this explanation clear as MUD? I will try the crank turning,and check the dist movement when I can get a helper to watch it. Thank you very much.

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-10-17 05:58 PM - Post#2710453    
    In response to IgnitionMan

IgnitionMan you said this...rotate the engine backwards until the rotor turns backwards, then, stop.

Now, mark the balancer with a line at TDC, then, slowly rotate the crankshaft forward, until the rotor starts to turn the correct direction. Stop.

Make another mark on the balancer at TDC. HOW MUCH DISTANCE BETWEEN THE TWO LINES?????

Now, you are saying I got to find tdc before checking this? or just make a mark on the balancer where ever it's at,and when rotor moves back/forth,then measure the differance?

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
IgnitionMan 
Valued Contributor
Posts: 3219

Reg: 04-15-05
10-10-17 07:23 PM - Post#2710456    
    In response to Lead sled

OK, let me clarify.

When you stop turning backwards, chalk line a line onto the dampener, at the TDC mark on the timing scale.

Then, do the same when the rotor starts to move when you turn the engine forward.

Don't touch the rotor during these tests, we want the cam to move the distributor, and the crank to move the cam, so we can see all the slack in the cam chain, which is the lack of rotor movement between the backwards stop and the point the rotor turns forward.

An example: we have turned the engine backwards, and marked the damper with a chalk line at the timing scale TDC line. We now turn the crank forward, and the rotor doesn't turn until about an inch of dampener movement forward.

We have just proven we have a cam chain with one heck of a lot of slack, as the rotor should have turned forward immediately, or very soon after turning the crank forward.

Of course, "showin' is a lot better than tellin'", but all we have here is the latter. Slow down, read it a couple of times, then, go try it.

Now, why does the rotor turn a bit forward, and "snap back" when we let go of it, with the engine stopped? That is the movement the mechanical advance gives to vary the timing, and it is completely normal. That movement is done by centrifugal force, increasing as the engine RPM's increase, decreasing as the engine slows back down, all ty itself.



 
Lead sled 
Frequent Contributor
Posts: 1875
Lead sled
Age: 57
Loc: Walton,NY.
Reg: 11-04-09
10-11-17 09:48 AM - Post#2710531    
    In response to IgnitionMan

Ok IgnitionMan,that's what I thought you meant. The TIMING POINTER @0 deg. Make marks on balancer foward/backward movement to find any slop. Thanks for clarifying I'll let you know the outcome,when I get a helper Thanks again.

Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 




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