Yes, I did that step very early on.



After I finished last night, the next step in my game plan was to pull the rocker cover and check the rockers. I did not ignore your advice. It's very good advice, which I plan on following this morning. I merely wanted to defer this step as long as possible...you see, to do this I have to pull the upper rear intake manifold-mounted A6 compressor bracket off, and move the compressor out of the way to gain access and clearance to remove the cover...not overly hard, but a step I was hoping I could eliminate if I found I was able to get this issue fixed by locating TDC on the balancer and resetting the timing.

Honestly, I have a hard time believing that this engine can even run at about 90º BTDC. I'd also like to mention that I'm using an ancient timing light that I've had for decades...is there an issue there? I don't know...but I think I'm going to also invest in a new dial back timing light. This way I'll know my test equipment is good.

On the topic of the heat issue (or more appropriately overheat)...one thing I noticed is that the upper radiator hose is always about room temp at the upper inlet to the radiator...like there's no coolant flow. Is the engine heating so fast that the thermostat doesn't have a chance to open to allow flow, or is it as simple as a stuck thermostat?? I'm also going to yank the thermostat to answer that question.

I'm going to get all of this mess sorted out yet.

 

It's a timing issue, so you may have to verify everything involved. Back to the setting of the timing sprocket alignment. I have seen in the past a mark on the reverse side of a cam sprocket that looks a lot like the correct mark

 

What intake is on the engine? I had a problem with my 69. The intake was not machined correctly and it was sucking air in to two cylinders causing rough idle and overheating (too lean). I initially thought that it was a timing issue and scratched my bald head for days until I finally figured it out. Not saying this is your problem but it was mine.

I really think that you should remove the timing cover and check the timing setup.

When installing the distributor, I use an old cap where I cut out the side of it below the number 1 post so it is a quick check to see if it lined up or I need to move it back or forward a tooth so it is positioned correctly to allow for adjustment.

 

I have a feeling this is definitely headed in that direction.


The intake is the stock GM cast iron intake.

I'm going to spend a little more time on rechecking everything I can without tearing this thing down to the block and starting from scratch...but I have this sinking feeling that's the road I'm headed down.

 

So far.......you and I are having nearly identical problems! 1970 350 stock engine/rebuilt by previous owner.

My NEW $12 thermostat was stuck closed causing overheating on highway----I am running without a thermostat now to eliminate the overheating after 5-6 minutes of idling.

The distributor cap center contact disintergrated-I replaced all defective parts.....now have good spark.

Checked timing----it was at 11 o'clock position on passenger's side (amazing coincidence)---I removed valve cover.....rotated engine to TDC on #1 cylinder until both valves were closed.....I reclocked distributor to the #1 cylinder and reset timing again to 10*BTDC.

The engine cranked over about 15 seconds before starting and running PERFECTLY.

I let it idle 20 minutes with NO overheating at 170*F at 70*F ambient air temperature......idled great/revved great!!!!!

I turned off the ignition..... Now it WON'T start---it just tries to run for a second or two but will not run continuously.....fuel/spark/timing all are good.

I have given up for the night/will try again tomorrow and will check in on your thread.

 

Its FIXED!

I went through the carb/cleaned/adjusted it.....

I went through the distributor/cap was damaged--center carbon contact was shattered/ignition module under advance plate was shorted out.

 

For anyone who may be interested: Problem(s) resolved.

To recap from an excerpt of post 1:

** One thing I forgot to mention in that original post is that when I was able to get it to start with the timing way retarded, at idle it sounded like it had a cam other than stock installed...way other than stock.

When I removed the rocker covers and looked at the valves (both sides), the rockers did not move the way I expected to see them move on a stock built engine.

THE FIXES:

• TIMING: I tore down the engine and found the "builder" had installed what appeared to be a high lift-short duration cam. As I could not identify the cam and did not have the spec sheet for it, I had no idea if it was installed per mfg. specs, and should have been installed with the timing advanced or retarded, or for that fact if it was even a good match for a stock motor with 882 heads, stock manifold, carb, etc... so to remove all of the unknowns, I ordered and installed a new cam/lifter kit with stock lift/duration. Before installing the new cam, I compared the two side by side on the bench and they didn't look anywhere even close to one another. Installed and degreed the "stock" cam, and all of my timing and start/run issues are now a thing of the past.
  
• TEMP: Replaced the T-stat. The new 195º thermostat was defective. Tested it in a pan of boiling water and it barely cracked open. Compared it to a new one I had on hand that under the same conditions which opened fully.

My lesson learned here is NEVER trust a "fresh build" that you get without the ability to obtain the specs from the actual builder, or one that you do not have all of the paperwork for, including the all important cam spec sheet.

 

ANNNNNND..........

as I found out also.......

NEVER trust a brand new brand-name thermostat.....test it first!

It's good to hear it wasn't a really serious problem with your engine.