How much slack should a timing chain have ?

I am asking this because after I got my car running I realized that it surges while cruising and definitley doesn't have the power it should. What I did was pull the timing cover back off to make sure that I didn't have the cam gear off a tooth. The cam and crank were lined up dot to 0 just like they should be and the way they were when I initially took it apart. So that wasn't the problem. I did notice that I can move one side of the timing chain from side to side about a half inch. Is this normal ?

 

Larry, I have your great write up printed out and have read it. My initial is 10*, it's at 30* just about 2200rpm, It slowly climbs to 36-38 between 2500 and 5000. I just got a spring kit for the distributor.

I wanted to make sure that my timing chain didn't have too much slack before I put it back together. I am also considering a new cam.

 

I think 1/2 inch is ok and withing tolerance. To be sure put a timing light on it. If the chain is too slack it will move back and forth and not hold timing steady. your surge sounds more like low vaccum

 

Over-advanced timing and lean mixture are the principal causes of surging...that said,

I'd think that the chain tension against all those moving parts would provide enough resistance against the chain that the timing wouldn't change all that much under load. Half an inch of deflection isn't all that bad, but if you have it apart, and all the rest is reasonably fresh, replace the thing...and the gears.

When you turn the engine forward and backward, how much does the crank turn before the distributor turns? That will give you a handle on far the cam may be retarded (not a surging issue, btw).

 

http://www.v8buick.com/showthread.php?236050-Surging-low-vacuum-no-power&highlight=surging+aubrey

Not this much is about all I can say. I haven't run it yet because I'm overseas but I'm certain my problems were atributed to a loose chain.

Since you have it apart, can you put a degree wheel on it and see how many degrees cranckshaft rotation you get from the slack in the
chain? So CCW till the cam moves, then reverse CW and measure how many degrees on the degree wheel the crack turns before the cam begins to
move. While there isn't any standard that I know of, I believe this is the best way to measure slack. I was getting just a hair over 10 degrees worth of
slack (measured as crank rotation) through my old timing chain. Replaced with new and it came down to about 2 degrees. This is the standard I
am using from this point forward. Anything over 5 and I'll replace my chain.

 

Aubry, I did read your thread, that's what made me pull my timing cover back off. I thought maybe I had the cam a tooth off. I will measure the slack with the degree wheel after work. Thanks.

 

Techinally ,,, :laugh: any slack in the chain is too much,,,, but like stated when the engine is running the resistance of the cam against the lifters keeps all the slack out.... the slack comes into play when the rpm's go up or down.... and inertia takes hold, and,,, and,,, so on.... the main thing is to keep the assembly as tight as possible for as long as possible....
All that said,,,,I am like Larry and Steeve a lean carb or too much advance is most likely the cause.... have you looked at the bushing that goes on the mechanical advance in the dist???? if that rubber bushing dry rots and crumbles all to pieces it can cause a over advanced condition...big time.... get the dist. spot on and then richen the carb just a little and I would bet that the condition goes away....
But back to the T/C and gears,,, it is a good rule to replace them if you have over 50,000 miles on them and,, and,,, you already have to go into the timing gear cover for any reason....

 

Tim I have a slitely us timing set you can have if you need it.

 

Nothing to add except to echo it being a lean surge or over ignition advancing. I've seen some horribly stretched chains on engines, and haven't seen them exhibit this symptom.





(A friend's big block Chevy's chain was tagging the timing cover between the super stretched chain and original nylon timing gear worn down (and amazingly never broken at 110k!))

 

My theory is that excessive slack in the chain is a problem until the RPMs go up to about 2200. No scientific eveidence, only what I saw while trying to time my engine with a very loose chain. It was a nightmare! Timing was very unsteady and did not become steady until around 2200 RPM. Two diferent timing guns on my part and when i bought the car i was told the shop that looked it over for me before the purchase had a difficult time with the timing.

I disconnected the vacuum advance and installed the heaviest advance springs I had to make sure it wasn't a matter of either coming in too early. Tried two different carbs as well, one of which was rebuilt/ tuned by a very reputable builder spoken highly of on this board. Couldn't find a vacuum leak and disconnected all lines including the one the brake booster and the trans modulator. All this and the car still seemed underpowered and was surging. Put in new gas as well as a last resort.

After all of that, I broke into the engine to check the cam timing and found the lose chain.

My point is that I exhausted everything else that could ahve been the issue before breaking it open and the chain was the only thing I found wrong. I haven't finished getting back together yet but when I return home in June I will and I will know one way or the other.

While this does affect spark timing, it's the cam timing and the way it changes your opening/ closing events that causes the real problem. Spark timing is easy enough to adjust even though it tends to be jumpy with a loose chain. Cam timing however, will constantly change as the the tension on the chain changes. I believe this is why my car had the surging.

Just the way I see it. I'll know for sure come June and will update my thread then.

Hope you can get yours squared away!

 

Saw that once with an oil leak on a 350 SBC, at about the same mileage. The chain was so loose that it wore a hole in the cover. The driver was so gentle on the truck that it didn't actually jump time. One of a kind, for sure, in my many years of fixin'.

 

I actually think the only reason my friend changed it was because he thought the gasket was leaking and it did have a hole in it, lol.

I just looked it up, and I was wrong about it being the big block, it was a small block chevy. Just happened last February.

 

Larry, I put it back together today. Like you suggested, I tried it with the vacuum advance disconnected. At idle I had to bring it up to 12* initial. It didn't want to run at 10*. Also the timing mark and the idle seem to move around a bit at idle. When I bring up the rpm the timing never get to 30 at all. While cruising it seems like the surging is gone but it still doesn't have the power it should.

 

I have a mr. gasket spring kit but it doesn't tell you which prings are what or where the brass bushing goes.

 

1112542

---------- Post added at 07:26 PM ---------- Previous post was at 07:19 PM ----------

Ok, I see where the bushing goes. I also have 1112110 distributor( not currently in use).