I've got the distributor back in my car after doing some de-bubba work... The car starts quick and runs well. Now, to set the timing just right, what do I look for on the timing index mark on the balancer? I should add that we're working with a 1967 modified L36 (454 block, L36 heads, cam, bore, unknown), MSD 6AL box and coil - MSD is not modified.

What I'm seeing with the timing light are units of 10 on the balancer and units of 4 on the index


From memory it looks like this:



10 <12
20 <8
30 <4
40 <0
50 <4


I figure I'm in the ball park if I can see all these markings can someone help me zero in on this! I'm not sure just how these marks are to line up to give me the propper timing.



steve

 

Your first step should be to set total timing. With vac advance disconnected, rev the engine until the timing stops advancing and set it at about 36º. Ideally, you should have advance all in by 2200-3000 rpm. If yours comes in much higher consider changing springs. Test drive the car and adjust timing if any pinging. Depending upon your cr and fuel, optimum timing could be a little more or less than 36º.

 

Thanks for the guidance. I hate to expose my ignorance once again but dose this mean lining up the 36 on the harmonic balancer with the 0 on the guide under the timing light, at top of advance or around 3,000 rpm?

I just don't want to assume anything, I usually get it wrong when I do.

steve

 

If you have a 36º mark on your balancer, yes, you would align that with the 0º mark on your tab. At what rpm you set it depends on where your particular distributor reaches total advance. Depending on the springs installed, that could be anywhere from 2,000 to over 5,000 rpm. Rev the engine while watching the marks. When it stops advancing and that will be the rpm that you want to set it. If you want it to be at a different rpm you will need to change the springs.

 

Make sure your vacuum advance line to the distributor is disconnected and plugged when doing the above adjustments; at idle, when you re-connect it, the timing at idle should increase by 12 degrees if the vacuum advance is working properly. If your base idle timing is 4* BTDC, it should increase to 16* BTDC when you re-connect the vacuum advance (and idle rpm will increase - reset it to your desired idle speed).

 

Steve,
A very helpful tool for timing of older motors like we have is a dial back timing light. This allows you to set the timing at any RPM to any value.
Using a dial back light...as stated earlier...disconnect and plug vac line to distributor....rev motor until timing does not advance any more with increased RPM....thats all in timing....should be 3,000 RPM or so for performance....if it is not in by 3,000 rpm or if in earlier than that... that is where you change springs in the distributor to correct or modify.
Then set timing light dial to 36 degrees....rev motor until max advance and set mark on balance to 0...0... by moving the distributor and you have 36 degrees because you have that dialed into the timing light.
You can purchase this type of timing light for about 50$.....
Dave62

 

thanks guys, I might be slow, but I'm getting it!

 

The dial back light is the easy way to go, but you can also use a timing tape on the balancer with a conventional light. The light is a little more expensive but a lot more user friendly and versitle.

 

When I set the timing at 36 degrees at 3,000 RPM it idles at about 20 degrees -700rpm. Starts and runs okay but seems like it wants to run at an even higher setting. When I advance the timing up to 45, even 50 degrees, at 3,000 rpm the car sounds like it's running smoother, but I don't have a trained ear for it either. This is with the vacuum line pulled from the dist. and plugged. Should I use a vacuum gage and set the timing based on that, as I have read about here - one inch below max? Or do I need to replace the spring in my MSD distributor to make sure I'm at max advance at 3,000 rpm and go from there? One other thing, there is an index mark at about 44 degrees on the tape on the harmonic ballancer, is this some idication that I should shoot for this number?

I guess these are just the problems you have to work out when you have an engine with some modifications.


Thanks again for the help, steve

 

I prefer to set the timing at idle and then check the total to make sure it's in the right ballpark.

Setting only the total advance (and ignoring the initial timing) doesn't make much sense unless you keep your engine above 3,500 rpm most of the time. Me, I let my engine idle while I'm stopped. And I usually don't leave an intersection like I'm competing in the Winternationals. I think I spend 99% of my driving time at engine speeds below 3,500.

Quite often the rubber bushing on the advance limit pin is missing. If you just set the total advance and blow off checking the idle advance, this would mean you'd have incorrect timing except when you're at full mechanical advance. Be honest with yourself.... just how often is that?

 

Actually, you should map out the whole advance curve to be sure all three components are correct and functioning as advertised.

 

Okay, from what I'm reading in the archives, anything above 10 degrees initial or 38 degrees full advanced would be too much. So I should stay out of that relm even if it seems like the car "wants" to be running at a higher setting. I'll crank it back down to 10 initial and see where it goes as I bring the rpms up.

steve

 

Setting timing with a vacuum guage is only useful if the engine never runs above idle. Because there is no load at idle and the distributor will add advance with rpm, what looks good at idle could be terrible under different conditions. There's no point in changing springs if you don't know where your total is all in now. It might already be all in by then. As already advised, rev the engine while watching the timing marks. At whatever rpm they stop advancing is where you want to set your total. If you want your total to be sooner or later than it currently is, yes, change the springs. Setting total at any point below where the distributor is through advancing is meaningless and a waste of time. Don't fall into the trap of "more's always better". Sometimes too much advance, by increasing low end power, "feels" stronger but is actually hurting power once advance is all in.

 

Confused now...

when I set the initail timing to 10 degrees, the car would barely idle, any lower than that and timing was impossable to read. Can rotate the distributor from 10 degrees through 50+ with a subsequent increase in rpm. Is my timing tape off or am I? Maybe this is normal, but I thought if one set the idle timing at the position that gives the highest rpm, he would be close, I'm not even in hte ball park.

 

The "initial" timing is simply a reference that can be used if you don't have a dial back light. It ASSUMES that the mechanical advance is stock and properly operating. On these old cars, it is an almost meaningless number until the complete advance curve has been mapped. The numbers you are looking for are around 36* total of mechanical and initial. This will all be in hopefully before 3000 RPM, preferably somewhat less. At idle, you are looking for around 25* total of initial and vacuum, with probably a little mechanical thrown in for good measure. If you have old copies of Corvette Enthusiast, John Hinkley wrote a real good article in timing within the last year.

 

That settles it! I'm going to go get a dial back timing light. My fiancee refuses to sit in the car for me anymore (unheated garage with door half open.) And I'm about to pull my hair out with all these timing terms and numbers! The 1967 CSM calls for 4* BTDC on this engine and I can't even get close to that (if I'm doing it right). I'll go get the light and try this again in the morning.

Thanks
steve

 

You should start by confirming that the mark on your harmonic balancer actually indicates true Top Dead Center for the #1 cylinder according to the timing tab on your engine. You do that with a tool called a piston stop. It's basically an adjustable bolt with a rounded tip that inserts through the spark plug hole. In fact, you can make one out of a bolt and an old spark plug.

You don't need a dial back light. You just need to use the timing tape you've already installed on your balancer as God intended. Surely you can rev the carb linkage with your right hand while you hold the timing light with left hand.

Personally, I don't consider the initial timing setting to be meaningless on my own cars. I also don't like mechanical advance to kick in below idle speed. I really like a stable 800 rpm idle speed. I also prefer full time vacuum advance, and using a vacuum canister that requires less vacuum (for full advance) than I expect my engine to have at idle. And, worst of all, I actually run stock spec cams. You guys with 1.5" of valve lift and 360 degrees of overlap simply amaze me.

I admit I'm an old man and I drive like it most of the time. I realize that most posters prefer to drive around town with their foot on the floor all the time, even when stopped at traffic lights. So I guess I'm saying: "Your results may vary."

By the way, I have a large collection of Mr. Gasket advance weights and springs that I removed from FI distributors so they would run correctly. You can have these zoom parts for free if you promise not to put them on any injected car. I don't ever want to encounter them again.

 

Jerry, the reason I stated that the initial figure was almost meaningless is that on so many of these old cars, the stock parts have been replaced with so many "mystery" parts or combinations of unknow origin, that the initial setting in the service manual may not be even close to what's actually required. I too, believe the mechanical advance shouldn't be a factor at idle, but with unknown weight/spring combos, it may very well be. And yes, if a timing tape is already installed a dial back light is redundant. The timing tape is probably more accurate if the tab has been properly aligned with TDC.

 

Ed, I came by my "stock is good enough" opinion the hard way. I've made so many mistakes working on cars over the years that I rarely challenge factory engineering much anymore.

I completely screwed up my '65 GTO by 1968. I started out with a single 4-barrel 389 with a mild hydraulic cam that would do an honest 125 mph and grab 4th gear rubber at 90. I ended up with solid lifter dog that wouldn't idle below 1,000 and ran out of steam at 115. And forget fourth gear rubber.

I was so smart back then. I read every Car Craft and Hot Rod article and thoroughly understood about 20% of the half-baked ideas in them. I then applied my newfound "knowledge" to ruin a perfectly good GTO. I first installed a radical solid lifter cam that only made power between 4,000 and 6,500 rpm. Then I disconnected the vacuum advance and cranked in 14 degrees of initial advance without changing the limit slot controlling the total mechanical advance. I also shaved the heads .030" to up the already high compression. All the time I was running full stock exhaust, a 3.08 rear, and those crappy bias ply tires we all thought were better than "European" radials. I never touched the carburetor because I was scared of it.

Now I'm real proud when I can make an old Corvette run like it did when it was new. I don't even try to top that. Those guys who can make them run better than new? Well, I know they're just a whole lot smarter than I am.

Sometime I'll tell you about the first 2818 Holley I ruined by trying to "improve" it in 1970. And yes, it was running perfect before I took it apart to add mechanical secondaries, a different power valve, and larger jets. In the end all I could salvage were the float bowls. Really. I'm so ashamed.

 

Jerry, I think we are pretty much on the same page. It's just that when you get your hands on one of these cars that has had most of its parts replaced out of the Summit racing catalog and everything is of an unknown quantity, ya gotta have some place to start. The factory spec may be right on or way off. I agree that it's hard to top the factory specs on the HP engines without making some sort of major compromise.

Now, the L48 in my 75 is a different story altogether. Its screaming 165 hp has been significantly improved by undoing all of the atrocities commited by the factory engineers under government duress. But, I know, you don't fool with those "new" cars. If you get close to B'ham, I still owe you a beer. You can tell me all about the 2818 Holley.