Timing is everything

[Joe S.]

Hi Folks:
I have posted before about my 61 270 HP Vette. When I first started driving it I was having cooling problems. After a discussion with the Paragon technical folks, I started to turn the timing ahead a little at a time. It eventually cooled much better and runs better. It will still get 5-10 degrees warm on a hot day. While making these adjustments, I had left the timing scale behind and under the timing light the mark on the balancer was up under the water pump. I figured the rebuilt balancer was off so I got a TDC finder to check. As it turned out the mark was off about ten degrees. At TDC the balancer mark is at 10 degrees advance. I also got some timing tape and applied it to the balancer aligning the 0 mark on the tape with the 0 mark on the scale. I used the tape specified for to the balancer diameter, or as close as possible. Then I put the light on it and it is reading 45 degrees advance. I also readjusted the valves at the new TDC, they were a little loose. The car runs reasonably well, although I think I need to drop the timing back a few degrees in that it struggles against the starter sometimes. It has never pinged even though I have tried to get it to. What are the chances that I have the timing chain on a tooth off? I know how to align them, this was by no means the first timing set I have installed including a few belts. I never screwed one up before, but that is no guarantee. Naturally I would not look forward to taking the timing chain cover off to check the chain. Any thoughts?

[Joseph L.]

Re: Timing is everything

Hi Joe

It appears you are trying to point to a timing issue. You did have one with the balancer being off and appeared to have corrected that.

What does your timing curve look like? Specifically, what is the advance in BTDC deg. you are getting at maximum centrifugal advance? It should be an 891 distributor with no vacuum.

What is the actual compression ratio you have? It is a function of a lot of things. I run an 0.016 shim head gasket, know the combustion chamber volume and have a calculated ratio of about 9:7. With a 0.050 gasket I will have below 8:0. Where are you at?

The timing gear issue that you are asking about would make it run different than an 097 cam engine. You did not mention that.

Joe

[Frank D.]

Re: Timing is everything

I want to know how you're reading 45* advance...make SURE your timing light inductive pickup is on the #1 spark plug wire.

Also not sure how a rebuilt balancer is 1o* off.

I ran the same motor in my 61 for over a decade in Orlando stop and go traffic in the summer.
The biggest temp excursion I ever saw was 195* after a long stoplight in August and once moving again the temp dropped to 185* again.
I assume you confirmed your temp gauge is correct - they are notorious for reading too high.
There are several non-factory changes you can make to enhance cooling that are easily reversible, cheap and help greatly.

I ran the car at 12* initial timing at around 800 RPM with no issues.
35* with the centrigugal "all in" at 2500 RPM.

[Joe S.]

Re: Timing is everything

Thanks Joe.

It is a 891 distributor that I bought years ago at Carlisle. (my car had no engine when I bought it) It has a petronix electronic ignition under the cap. As for the timing curve, I am not sure. I do know that you can watch the timing mark move forward as rpms increase so the centrifugal advance works. I can not swear that the weights are correct. Until I had the timing tape in place I had no way of measuring the exact number of degrees the advance provided nor do I know what that number should be.

As for compression, I only know that the heads have the correct markings for the 270HP engine. Supposedly 9.5 to 1. They were machined just enough to make sure they were straight and a standard head gasket was used. They have hardened seats and valves with new springs, rockers, and nuts; all as close to stock as possible. The pistons were again as close to stock as possible but .0020 over to accommodate a clean up bore. It has Howard's version of the 097 cam and of course solid lifters. The machine shop that did the engine work went under during Covid so I can't get back to them.

I have to admit that I am not sure what you mean by not running like an 097 engine. I have never driven another 097 car so I nothing to compare it to. I will say that it is not as quick as I expected. I also recently found that I had no access to the front carb. At full gas pedal the linkage between the two carbs (a quarter inch bolt) could not be adjusted short enough to engage the front carb. Another great repro part! I took the bolt that runs between the two off and threaded it further back and then cut some off. Now I at least can get the primaries of the front carb to come in. You can notice the difference that made.

[Joe S.]

Re: Timing is everything

My timing light is not an inductive pickup! Yes it is that old; a chrome plated Craftsman from the early 70's. I have traced the wire twice hoping that the wrong wire was the problem. It wasn't. The number one wire is also is in the correct position on the cap per the drawings in the AIM and service manuals. The balancer was a rebuilt that came from a supplier in CA.. The two sections were pressed apart, new rubber installed between them and reassembled. If the outer ring is not pressed on in the correct position in relation to the inner, the timing mark will be off. That was why I used the TDC finder to check it. Once the real TDC was found, I applied timing tape to the balancer that has a scale that goes to 70 degrees advance and I was able to read that much advance on the new scale. I also set the timing at 800 rpm. Although I know the centrifugal advance works as I can watch it advance the timing as rpms increase, I can't swear that the weights are correct. It is a 891 distributor with a petronix electronic ignition under the cap. I did use some of your earlier tips to help with cooling, but the thing that made the biggest difference was advancing the timing. As I did I also had to turn the idle back a couple of times to keep it at about 800. It also ran better and used less gas so I had to conclude that it helped.

As for the temp gauge, it is an original sending unit and a heat gun at the thermostat housing read pretty close to the gauge. On a cool day it runs under 180. As I said the cooling is not the problem it was before the timing adjustment.

[Frank D.]

Re: Timing is everything

We all love our old tools but you would be much better off with a modern dial back timing light.
The Actron CP 7529 is an affordabe choice and will help you "dial in" a responsive timing curve with accuracy.
Short of a SUN distributor machine its the best thing going. At any rate, it sounds like you are getting close to a decent tune.
Anytime I've mistakenly seen 45* initial timing I had the light on the wrong wire or my distributor install was off.
I'm just sayin'

A nicely tuned 097 Duntov car will have that old Singer treadle sewing machine sound at an idle and produce a snappy response and pull hard to the redline with no issues.

Even horsing around doing mild sprints they are a visceral hoot: https://youtu.be/j0BdovAFjkQ

You will never get the full "punch" until you get your dual quads squsred away though.

[Joseph L.]

Re: Timing is everything

Carburetor adjustment is covered in many shop manuals. The correct linkage is available from part suppliers.
The accelerator lever (attached to the firewall) connects the rear throttle rod to the rear carburetor throttle lever. Always use the upper hole in the rear carburetor throttle lever.
With the front carburetor throttle rod disconnected and the return springs disconnected, The rear carburetor should be adjusted to wide open when the accelerator pedal is on the floor.
Now connect the front carburetor throttle rod (long 1/4" bolt) to the lower hole in the front carburetor throttle lever. You will see the front carburetor does not begin to open until the rear carburetor is about half open.
With the accelerator pedal on the floor, the rear carburetor will be wide open. Adjust the long 1/4" bolt until the front carburetor is also wide open. The two carburetors should arrive at wide open at the same time.

If you cut the long 1/4" bolt, a new one may be needed. The carburetors can also be set up with the front carburetor rod in the upper hole in the front carburetor throttle lever. The motor will run rich and get lower fuel economy.

Joe

[Frank D.]

Re: Timing is everything

The above is correct and describes a "progressive" linkage setup - best for street; there is nothing mysterious about it and the repro linkage should work just fine;