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Username Post: SBC 327 Timing        (Topic#366446)
DucatiRod 
Poster
Posts: 85

Loc: Maine
Reg: 12-31-20
09-19-21 05:36 AM - Post#2827362    

How do you figure out timing on a modified engine? I built this with an Isky Z-25, right around 10 to 1 comp. a Vertex mag with 12 degree of mag advance @ 1250 mag rpm & 461X heads. It's running very good with just an hour or two on it, but I'm only seeing about 11 inches on the vac gauge. I ended up with a harmonic balance wheel with the timing mark in the wrong place, I did scribe a mark at TDC. but this makes the whole deal less accurate~



 


wagonman100 
Site Ambassador
Posts: 15360

Loc: Baltimore, MD
Reg: 11-27-04
09-19-21 06:46 AM - Post#2827370    
    In response to DucatiRod

You need to make sure the timing tab is correct for your balancer. You can get a piston stop and find true TDC and see if the timing slot on the balancer lines up with zero on the timing tab. If it does, then you’re all set. If it doesn’t, you need a new timing tab to match the balancer. They sell ones that bolt on with the timing cover bolts and even have ones with an adjustable pointer to make it easier to see when your line on the balancer lines up with your desired timing. If it’s way off, your balancer ring could have spun on the balancer hub. That is not that uncommon. You can remark the balancer, but if it has moved, you are better off getting a new balancer. If it is a new one, it is probably the wrong one. Small blocks changed their position of the TDC line a couple of times over the years. After about 1978 the TDC line was in the 12:00 position.
The low vacuum could be caused by several other things as well, including valve adjustment and/or carb. adjustment. Vacuum is also affected by how much overlap your cam has.

Jay
Friends don’t let friends drive Fords.

1999 Silverado Z71 4X4 extra-cab short bed
1983 Malibu Fauxmad - tubbed
1978 El Camino Kustomized
1972 Monte Carlo
1957 210 handyman wagon
1957 Nomad sport wagon
1957 Cameo Carrier


 
Shepherd 
Frequent Contributor
Posts: 2330

Loc: Lake George, NY
Reg: 11-11-15
09-19-21 07:06 AM - Post#2827371    
    In response to wagonman100

Great advice



Edited by Shepherd on 09-19-21 07:07 AM. Reason for edit: No reason given.

 
DucatiRod 
Poster
Posts: 85

Loc: Maine
Reg: 12-31-20
09-19-21 07:43 AM - Post#2827373    
    In response to Shepherd

I had the whole thing balanced so can't change parts, and the harmonic must be from after '78, it's at 12:00. I was thinking if I make something like a cardboard circle the size of the harmonic balancer and lay it on my degree wheel I could figure how far in inches around the harmonic balancer my desired timing mark should be from TDC. I have marked TDC with a magic marker & scriber. So what would be a good number to shoot for? I've set the valves & checked & reset a couple~



 
Rick_L 
Member #409
Posts: 27913
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
09-19-21 09:45 AM - Post#2827390    
    In response to DucatiRod

As for the balancers, Chevy made 3 different ones.

68 and older, the timing mark on the balancer is lined up with the keyway.

69 and newer, the timing mark on the balancer is 10° CCW from the keyway.

On a few mid 70s and up balancers, the timing mark is 30° CCW from the keyway. This type is fairly uncommon. You must use a long water pump to even see the timing mark, pointing in the gap between the pump and timing cover. These balancers are 8" diameter, but the hub is hollowed out and very light on the backside.

The keyway is at 45° CW from 12 o'clock when the engine is at TDC.



 
bobb 
Super Senior Member
Posts: 5899

Loc: paradise
Reg: 09-05-03
09-19-21 10:05 AM - Post#2827391    
    In response to DucatiRod

dont get stuck on numbers. set it where it runs best and write it down. every vehicle is different so any recommendation will be just that. fine tuning a carbed engine is very time consuming especially if you dont have things like a wideband 02 gauge and road testing area.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
DucatiRod 
Poster
Posts: 85

Loc: Maine
Reg: 12-31-20
09-19-21 10:45 AM - Post#2827399    
    In response to bobb

I got an O2 gauge that's switchable, and bungs for both pipes but being a project in development my plan is to do the bungs when I redo the pipes to get them up a few inches. This was my summer project, but when the Mini blew the freeze-plug from between no 1 cylinder and the timing chain, thereby filling the oil pan with antifreeze, I got a new project. I kind of put the mini on the back burner till I got the truck out of the garage by bringing out the 74 3.0CS BMW, a very clean example. Well, just to keep me crazy, 2 days ago the BMW blew the top off the right rear shock tower



 
pauldian 
Contributor
Posts: 414
pauldian
Loc: seligman,arizona
Reg: 05-14-09
09-19-21 11:29 AM - Post#2827406    
    In response to bobb

  • bobb Said:
dont get stuck on numbers. set it where it runs best and write it down. every vehicle is different so any recommendation will be just that. fine tuning a carbed engine is very time consuming especially if you dont have things like a wideband 02 gauge and road testing area.


I agree with bobb. I set mine with a vacuum gauge to the highest setting and then reduce vacuum by one inch on the gauge. Have done this for many years and it's always worked for me.


Remember,I'm not always right. But I'M never WRONG !


 
japete92 
"7th Year" Silver Supporting Member
Posts: 1783
japete92
Loc: No. Virginia
Reg: 01-18-13
09-20-21 11:02 AM - Post#2827492    
    In response to DucatiRod

would something like this be helpful/useful?

https://www.autozone.com/ignition/timing-tape/ p/ms...

Pete



 
DucatiRod 
Poster
Posts: 85

Loc: Maine
Reg: 12-31-20
09-20-21 11:41 AM - Post#2827495    
    In response to japete92

  • japete92 Said:
would something like this be helpful/useful?

https://www.autozone.com/ignition/timing-tape/ p/ms...

Pete


That is exactly what I was thinking must be out there, but couldn't find, I have turned up the timing a little more and got 14 inches of mercury! Thank you for finding that for me!!!



 
japete92 
"7th Year" Silver Supporting Member
Posts: 1783
japete92
Loc: No. Virginia
Reg: 01-18-13
09-20-21 01:32 PM - Post#2827507    
    In response to DucatiRod

Here's a 'sticky' from a Chevelle site. It may be helpful too.

https://www.chevelles.com/threads/ignition-101.189...

Pete



 
aghaga 
"4th Year" Silver Supporting Member
Posts: 2331
aghaga
Age: 67
Loc: Altavista, Va.
Reg: 07-05-08
09-20-21 05:17 PM - Post#2827525    
    In response to japete92

Years ago I bought a timing degree cover that bolted onto the harmonic balancer behind the pulley. It fit snuggly over the 350 balancer.



 
aghaga 
"4th Year" Silver Supporting Member
Posts: 2331
aghaga
Age: 67
Loc: Altavista, Va.
Reg: 07-05-08
09-20-21 05:29 PM - Post#2827533    
    In response to aghaga

https://www.summitracing.com/search/part-type/harm ...



 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10863
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
09-20-21 06:58 PM - Post#2827560    
    In response to aghaga

Keep advancing until it pings under a load and high gear, then back it off two degrees and reconnect the vacuum advance.
That's my story and I'm sticking to it.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
japete92 
"7th Year" Silver Supporting Member
Posts: 1783
japete92
Loc: No. Virginia
Reg: 01-18-13
09-21-21 01:14 PM - Post#2827620    
    In response to aghaga

  • aghaga Said:


Yup; a variation on the theme of the 'tape'.

The point being: in any circle there are 360 degrees (on a balancer; 360 degrees from TDC, around all the way back to TDC). The diameter of the circle determines the 'space' between the degrees.

Pete




 
blue56 
"18th Year" Silver Supporting Member
Posts: 408
blue56
Loc: LaGrange, KY
Reg: 05-24-03
09-22-21 05:13 AM - Post#2827676    
    In response to pauldian

  • pauldian Said:
  • bobb Said:
dont get stuck on numbers. set it where it runs best and write it down. every vehicle is different so any recommendation will be just that. fine tuning a carbed engine is very time consuming especially if you dont have things like a wideband 02 gauge and road testing area.


I agree with bobb. I set mine with a vacuum gauge to the highest setting and then reduce vacuum by one inch on the gauge. Have done this for many years and it's always worked for me.



I've done the same thing for years too, but didn't know about the -1 inch step. I'm going to try that and see if it helps my hard starting when hot problem.


You can't drink all day...

...if you don't start in the morning.


 
IgnitionMan 
Valued Contributor
Posts: 3909

Reg: 04-15-05
09-23-21 10:14 AM - Post#2827793    
    In response to DucatiRod

I'd post a picture of a balancer that has all the places used for TDC zero line, but, this website doesn't have an easy way to do it, only the most complicated one, and I am not able to do so.

Email me, ask for the balancer picture, and I will send it to you, sir.

info.davessmallbodyheis@gmail.com

Engines should NEVER have timing set by vacuum levels. There are settings parameters that need to be adhered to.



 


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