timing issues.

[j.rigby15r]

So here is my second thread this hour. I'm finally getting around to checking and setting my timing. I've got less than fifty miles on my rebuilt motor. It has a mild cam, edelbrock carb and intake, and gm hei dizzy that has been rebuilt and a mr gasket advance kit. The motor was running like crap but hadn't put a light on her since I was trying to put out other issues first. When I put the light on it was about 12° btdc which is were I wanted it. When I revved it up it wasn't really advancing. So I changed the springs to a lighter set and she started advancing but only to about 25°. I've tried adjusting it and when I get it to break 30° the idol timing is around 20°. It's running better but not quite were it should, I think. Also in another post I was reading about timing and a sluggish motor someone mentioned valve being too tight. How do I know if my valve lash was set to tight?

[morethanstock66]

Turn the engine around until the exhaust valves just begin to open and then measure the intake valves in the engine's firing order. Use a lash feeler gauge to measure the distance between the valve tip and rocker arm. Use your new cam card as a baseline and adjust it for fine tuning. Once you check/adjust the intake valves, utilize the same procedure for the exhaust valves (turn over until the intake valves just begin to open, measure, and adjust if necessary)

[morethanstock66]

I forgot to mention, do this when engine is cold

[Mackie]

Do the mech advance flyweights move freely? I used the MSD kit and the plastic bushings were a tight fit on the posts causing binding and incomplete advancing. I did a light "honing" of the bushings with small rolled up 400 grit sandpaper to fix it.

[j.rigby15r]

As far as I can tell the weights move freely. Prior to installing the dizzy i made rebuilt the dizzy including putting new weights and bushings on. I was talking to a friend of mine who is a old time mechanic and he was telling me about grinding the weights so you can get more mechanical advance. As of right now the truck seems to be running fine. I think once the engine is broken in fully and I get the steering tightened up I will tinker with it more and try and get more advance in the higher RPM range then.

[j.rigby15r]

Originally Posted by morethanstock66

Turn the engine around until the exhaust valves just begin to open and then measure the intake valves in the engine's firing order. Use a lash feeler gauge to measure the distance between the valve tip and rocker arm. Use your new cam card as a baseline and adjust it for fine tuning. Once you check/adjust the intake valves, utilize the same procedure for the exhaust valves (turn over until the intake valves just begin to open, measure, and adjust if necessary)

Does this method work for a flat tappet cam? Ive done this with other cam styles but never a flat tappet. The reason I ask is I dont understan how this works because you would have pressure on both sides of the rocker pushing against the valve head as well as the push rod. The truck seems to be running fine and I am not getting any noise from the engine that would concern me. The main reason I ask is this is the first flat tappet cam engine I have done. I fallowed all the steps to set lash when I first built the engine, I am more just paranid that I have over tightened them and will have pre-mature cam failure. Mostly jumping at shadows.

[fleetsidelarry]

terminology: flat tappet refers to the base of the lifter (tappet), the lifters themselves can be hydraulic or solid. the other type is "roller", they also come in solid or hydraulic

the method quoted is for solid lifters. hydraulics don't have lash to measure.

solids are pretty rare these days.

here's one explanation of the preferred method (EOIC) for hydraulics (you don't have to use this, there are less complicated ways):
http://www.chevytalk.org/fusionbb/sh...?post/2080137/

[j.rigby15r]

I do have hydraulic lifters. And what I was confused about is were I'm supposed to put the feeler gauge.

[fleetsidelarry]

that was my point j.rigby. you don't use a feeler gauge if you have hydraulics. apparently morethanstock66 assumed you had solid lifters. just saying you have flat tappet (your post #6) doesn't tell us whether you have solid or hydraulics.

[fleetsidelarry]

to get back to your question about timing, you said you have a rebuilt GM HEI with a Mr. Gasket weight/spring set that's giving you 30° total with the light springs. BUT that is at 20° initial. As far as you can tell the weights are moving freely.

first thing I'd suggest is getting a better weight/spring kit. I bought a cheap Summit brand kit (which I'd bet is from Mr. Gasket), didn't like the looks of it and bought an MSD kit (cost like $10 more). the MSD weights are heavier and better quality. Lots of guys like the Crane Kit. Back in the dark ages I did what your "old time mechanic" was talking about. but I had access to a distributor machine (bet you've never seen one ). no need to do that nowadays

A little more info would help. You are checking the timing with the vacuum advance unhooked and carb port plugged, yes?

[j.rigby15r]

So let me recap and clarify. Rebuilt hei with Mr gasket weights and the lightest springs I think black. Vacuum advance unplugged and carb capped. Initial timing set about 12°. At about 3k it's maxed out at about 25° of advance. If I go past 3k timing does not increase any further. I have a mild cam with a edelbrock intake and carb.

[geezer#99]

Best thing for you to do is prove your timing marks are correct.
Look here for that.
http://www.crankshaftcoalition.com/w...op_dead_center
Then set your timing. 20 degrees initial isn't out of the question if you've got a bit of a cam and live at your elevation.
What are you using for a timing light?

[Mackie]

Originally Posted by j.rigby15r

So let me recap and clarify. Rebuilt hei with Mr gasket weights and the lightest springs I think black. Vacuum advance unplugged and carb capped. Initial timing set about 12°. At about 3k it's maxed out at about 25° of advance. If I go past 3k timing does not increase any further. I have a mild cam with a edelbrock intake and carb.

Your mach. advance should be maxing out more like 35* and should be all in by 3k or so, but first verify the timing marks as Geezer suggested. And connect vacuum advance to full manifold.

[j.rigby15r]

Originally Posted by Mackie

Your mach. advance should be maxing out more like 35* and should be all in by 3k or so, but first verify the timing marks as Geezer suggested. And connect vacuum advance to full manifold.

I thought you set your total advance without the vacuum advance hooked up? Or are you suggesting that you set your advance and then hook up the vacuum after it is set? I think I am going to take it to one of my machine shop friends who builds race motors and have him check and make sure I am doing it right.

[67 Burb]

This is a good read.

http://www.73-87.com/7387garage/drivetrain/hei.htm

This also.

http://67-72chevytrucks.com/vboard/s...d.php?t=290498

[Mackie]

Originally Posted by j.rigby15r

I thought you set your total advance without the vacuum advance hooked up? Or are you suggesting that you set your advance and then hook up the vacuum after it is set? I think I am going to take it to one of my machine shop friends who builds race motors and have him check and make sure I am doing it right.

Yes, set timing then hook up vacuum line, which will increase the initial but not effect the high RPM as vacuum diminishes with opening the throttle. I'll stress again to confirm the timing marks on your dampener first. The outer ring has been known to slip which makes the numbers useless.

Oh and the way I found my flyweights were binding was when I turned the rotor by hand to watch their movement, they did not snap back when released, which would make them sluggish to fly out also.

[HemiChallenger71]

I lock the timing on my HEI's. But typically its a more of performance application.

I've done that weight and spring advance game. Wont ever do it again.

[fleetsidelarry]

Originally Posted by Mackie

"...then hook up vacuum line, which will increase the initial but not effect the high RPM as vacuum diminishes with opening the throttle...."

true enough, just want to add a clarification, not a correction. once you've reached cruise speed and not accelerating or otherwise loading the engine, the vacuum advance does add to the total, whatever the RPM. which is why one is supposed to limit the vacuum can to 10 or 12° when more centrifugal advance is put in. need to do both centrifugal AND vacuum can mods as a package deal

[Mackie]

Yes, good point Larry. I did the vacuum can limiter mod on my HEI and I guess you can use one of the adjustable cans too.

[crazy longhorn]

Go to the boneyard, & try to pick a good set of weights/center plate, off a 3/4 or 1 ton truck....then opt for the Crane advance kit. You want tween 32-36 total, all in @ 3000 rpms heavy (2800-3200). If you figure that you have 20 degrees advance, in the mechanical...12 initial will get you 32, 14 will get you 34. I tend to shoot for 34 total (heavy/street) . Add 10 degrees to the vac advance, hooked to manifold source @ the carb. Limit the Crane can from the front side, not the back as they suggest? just tack weld , or drill/tap, and screw the pc down. You know that the vac can on the crane pulls 22 degrees (crankshaft).....measure the pull, do the math, & cut it where you want it Best of fun, Longhorn

[67 Burb]

Originally Posted by crazy longhorn

You know that the vac can on the crane pulls 22 degrees (crankshaft).....measure the pull, do the math, & cut it where you want it Best of fun, Longhorn

I set up a couple of known vac cans in my vise and measured the pull with a dial gauge. Then tested my calculations with the vac can in the Burb. It works out that .127" of pull = 10 degrees (crank).

Without using a dial gauge, 1/8" would get you 9.8 degrees, close enough to 10.

[j.rigby15r]

You guys are so awesome. Teaching me all kinds of new tricks and information. This is why this is the best forum.

[crazy longhorn]

Thanks for the pic burb & cut right! Just a thought, depending on the can, & the vac numbers on ea different can (from different manufacture), the numbers can be a tad different? The last Crane can I cut , had 8 degrees (crankshaft) when done, IIRC, it was .086 on the pull. The engine was 10-1 on the ratio, & had a fairly aggressive curve? As said, just measure the pull, do the math & go from there. If you have a can stamped with 11, it will pull 22 degrees (crankshaft) on the vaccumn. Once again, thanks Burb, for the pic....this old man is a little computer "illiterate" Longhorn

[67 Burb]

I'm still trying to get this all straight in me old head. I have a can stamped 30. I would have thought this would be 30 crank degrees. ???

[crazy longhorn]

I don't have all the answer to the question either Burb....you might check the pull on that one? Is it a bunch longer, than some you have played with? Longhorn