I have a 72 340 with a unilite 37 mechanical distributor. Supposed to have 20 degrees built in but seems to be 25 when engine is hot. Initial is set at 15 and reads dead on 35 when warm but after a drive and engine is at full temp reads 40 at about 3000 rpm. Pulled it and set it to only have 18 degrees advance built in. Set initial to 17 and was at 35 all in at 2500 rpm and stayed there up to 3500 rpm. Took it for a drive and rechecked it. Still reads 17 degrees initial and 35 degrees up to 3000 rpm then back to 40 degrees over 3000 rpm. Haven't pulled the distributor back out to check the settings again but will when it cools down. Any ideas on why it is changing? Do I need to worry, is 40 too high?
Too much timing???
- Thread starter dgibby
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tekslk
Well-Known Member
Do you have vacume line plugged when your checking this?
yellow rose
Overnight Sensation
Verify the number with a different timing light. I have had the same timing light since 1980 so I know it is correct.
Did you actually verify that the dizzy was set for 20 at the factory? That 37 should use a tapered key to set mechanical advance. I would use no more than 10 (which is 20 at the crank) because that only gives you 15 initial.
Did you actually verify that the dizzy was set for 20 at the factory? That 37 should use a tapered key to set mechanical advance. I would use no more than 10 (which is 20 at the crank) because that only gives you 15 initial.
yellow rose
Overnight Sensation
Then you should probably look at the advance mechanism itself and make sure it isn't rusted or have other issues that cause it to move when warm.
I'll have to find my catalog and see exactly what advance mech is in the 37. If it's the typical one they are pretty much bullet proof.
On a 340 that is stock or close to stock, I think 34-degrees is plenty of total advance for best performance... 40 is definitely going to slow you down.
Just my 2-cents... :coffee2:
My 68 340 with a .484/284 MP cam liked 17° initial and 36° total... You're very close to that...
yellow rose
Overnight Sensation
I found the Mallory drawing of that advance mech and there are several areas that can have issues.
My drawing shows bushings in the advance weights but I have never seen one that had them. If yours has bushings they could be dirty or worn out.
It is possible the screws that hold the fingers onto the plate are loose, or worse yet, they have been wobbled out, you could have an issue there.
It appears to be something simple I believe.
EDIT: once upon a time, a customer assembled his own engine. The thing would not repeat at the track. The timing would move, but not on the first pass. It would move almost the same every time. First pass was the quickest, second pass slower, the third pass was slowest. Then it would come back to about the second pass was for the rest of the day.
He parked the car. A few weeks later he called and asked me if I lock tight the cam bolts. I said heck freaking yes I do. He did not. So the bolts came loose, the cam would move in and out and change ignition timing, not to meant ion cam timing.
Just throwing this out there because things happen.
nm9stheham
Well-Known Member
Just a long shot: With this being heat sensitive, it could well be electrical. Do you have the correct ballast and coil? Or is this triggering a different ignition module? If so, what?
Here are the instructions: make sure it is wired this way....an inverted trigger line (green and brown reversed) to another ignition module will make the timing erratic or move around.
[ame]http://documents.holley.com/mallory_instructions_unilite_distributor_37_38_45_47.pdf[/ame]
BTW, do you have a voltmeter in the car? If so, what is the reading cold versus hot, and idle versus 3500 RPM?
Here are the instructions: make sure it is wired this way....an inverted trigger line (green and brown reversed) to another ignition module will make the timing erratic or move around.
[ame]http://documents.holley.com/mallory_instructions_unilite_distributor_37_38_45_47.pdf[/ame]
BTW, do you have a voltmeter in the car? If so, what is the reading cold versus hot, and idle versus 3500 RPM?
yellow rose
Overnight Sensation
I never think to look where people live. If he is down on compression at that altitude he may very well be able to go as high as 40 total. Just have to keep on to of the tune up so if somehow he gets to mineshaft air it don't eat itself to death.
That's good advice, I trhink. I didn't notice the altitude where he lives, but, looked it up and it's nearly 5,000 feet. I gave advice based on a sea-level operation, and, I agree, he needs more... probably, lots more....
Forty would be a good place to start, I think.
Sorry for the bad advice...
ops:
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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I have no clue; but like the cam-walk idea. Or even the oil-pump drive walking up and down.Or the cam-chain doing a little dance.
That shouldn't be hard to prove tho.
With a cold engine you could index the rotor(or reluctor) to the dist. body,with #6 at TDC-compression. Then check for rotor-shift after the engine is up to temp. I know 4* is gonna be hard to see, so accuracy would be paramount.Why #6? Cuz it's closer to the fender and easier to eyeball, and maybe you don't have to get up on the fender..
'Course this assumes the balancer mark is staying put.
If you do find rotor-shift, you still have to figure out where the source is; cam, chain, or
drive.
That shouldn't be hard to prove tho.
With a cold engine you could index the rotor(or reluctor) to the dist. body,with #6 at TDC-compression. Then check for rotor-shift after the engine is up to temp. I know 4* is gonna be hard to see, so accuracy would be paramount.Why #6? Cuz it's closer to the fender and easier to eyeball, and maybe you don't have to get up on the fender..
'Course this assumes the balancer mark is staying put.
If you do find rotor-shift, you still have to figure out where the source is; cam, chain, or
drive.
dgibby.
I set mine at 14 initial with almost 40 total. (I have vacuum advance so it probably won't help you much). I tried setting mine to 16 initial once and it pinged like crazy at around 5500+ rpm's.
The altitude here is 4500 @ Clearfield UT.
I set mine at 14 initial with almost 40 total. (I have vacuum advance so it probably won't help you much). I tried setting mine to 16 initial once and it pinged like crazy at around 5500+ rpm's.
The altitude here is 4500 @ Clearfield UT.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
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Do I understand this correctly; in both cases, after it got hot, the timing went to 40*, from 35* at over 3000?Even tho you changed the base timing?So really, all your work accomplished was to pull up the initial.
I have to ask; are you reving it high enough to set the initial, or stopping around 2500.
To me this almost sounds like the dizzy has a 2-stage spring kit in it: the first all in at 2500, but the second not all in, until further up the rev range.
What do you suppose might happen with the timing set cold, at the current 17/35, if you rev it to say 4500? What Ima thinkin, is that it stops at 35* @2500, but pulls in another 5* between 2500 and 4500;even cold!. Do you think that is possible?
The reason I ask, is cuz I have a curve similar to that in my 367. I have 28* by 2800, and then another 6* or so coming in later, by 3600IIRC. This allows me to bring in a ton of Vacuum advance(22*), like a total of 48/50 at 2800 for part throttle cruising. Smooths her right out, gives plenty of PT torque, and no pinging on 87e10.It's a great curve for a hi-compression street engine.
yellow rose
Overnight Sensation
I never thought of this either, because I have never found a use for two stage springs.
The question I have is why would the OP check it one way when cold and another way hot? Stranger things have happened.
yellow rose
Overnight Sensation
Is that 40 on the vacuum can or 40 total plus the vacuum? The shape of the curve makes a YYUUUUUUGGE difference in how the same total will respond differently. Most engines will take a butt load of timing when the load on the engine is RELATIVELY low. An example of this would be in 1st gear with zero road speed. You can hit it with timing to get it moving because with all the gear and almost no load it won't ping. That same timing curve, now be rolling along at say, 10 MPH and put it in 4th gear.,mash on it and it will rattle your teeth out. That is too much load for that timing. Curve is everything.
I remember when all the rage was timing boxes started coming with adjustable retards on them. Guys would pull timing at the hit (which is great if you want to kill tire spin or reduce HP at the launch but that wasn't the purpose at that time...they were looking to drop the 60 foot times) and wonder why the car slowed down. In most cases, I add 5-6 degrees MORE total timing in low gear that what my best 60 foot time was. Then, no more than 1 second or so, pull it back out. Cars were quicker in 60 by 5-6 hundredths just by that.
Now, you can have multiple retards so you can add more at the hit and pull it out slower. Really cool.
And for the guys who hate themselves and want to find it all, you can get boxes and systems that allow you to ADD timing back in high gear, effectively changing the slope of the curve.
Great stuff really if you can isolate track segments and you like to test.
Tantibus....love the car and love the fact you are using a Mallory ignition. Great stuff, very underrated.
Are you picking the RPM to observe total or are you revving it up until it stops advancing?
I'd try another distributor in the car to see if it has the same "adding timing" issue.
I use drill bit shanks of appropriate sizing to set mallory style advance distributors. I noticed that the stepped keys aren't always accurate.
I'd try another distributor in the car to see if it has the same "adding timing" issue.
I use drill bit shanks of appropriate sizing to set mallory style advance distributors. I noticed that the stepped keys aren't always accurate.
It seems more like it wants to add 4 or 5 degrees over 3k. When it was at 35 to went to 40 when it was at 34 it went to 38. I'd bet if it was at 30 it would be 34/35 and 38 would be 42/43. I have taken it past 3k in the past and it never jump up like it is now. Cold and hot is subjective... I let it get a little temp (120ish) before giving it a rev tune and checking it (that's what I'm calling cold) Take it for a drive, gets up to 180ish and recheck it and that's when it jumps the extra 4 degrees. It runs great, no pinging or anything. I get the two stage spring idea but if it its locked with 18 degrees would that limit the max on it? Here is a picture of how to adjust it.
yellow rose
Overnight Sensation
Whis I had that picture you just posted because it's better than my exploded drawing.
You need to look at the slot that the weight rides in. And check to make sure nothing is binding in the advance mech. I have seen the tabs get bent that the advance spring s slip over and it will change the curve.
Probably should pull the dizzy and look at it.
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