I rebuilt the motor in my '79 Vette. Bored it .30 over and did a relative stock rebuild. I have since been working on getting it ready for the road, but I have been having problems with it overheating. I have checked my water pump, thermostat, and hoses and they are all working properly. The weird thing is that when I first got the motor running I set the timing by ear and it ran fine and did not over heat. It wasn’t until after I set the timing that it started to overheat. It was at 9 degrees when I did it by ear and I lowered it to 6 because that’s what factory settings are. Has anyone ever heard of timing affecting overheating the motor? I wouldn’t think that 3 degrees in timing would do anything and I'm not convinced that it is the true problem. I'm working on having the radiator tested to make sure that it is working as it should. The radiator is only 3 years old so I am having a hard time believing that it is the problem. Air was purged out of cooling system when it was running. It would overheat while it was parked and even with 2 auxiliary fans running on the radiator. Any idea's?

 

Timing can have a huge affect on whether an engine overheats or not. Are we talking stock-like 350 cubic inch SBC here? If so, 6 degrees sounds late. Also, when you set the timing to 6 degrees, was that with the vacuum advance disconnected and plugged? This can make a huge difference. Also, more information would be helpful. Lots of folks on here say their engine "overheats", and then later we find out that the coolant temp is steady at 210, but they think it is overheating because they "want" the coolant to be 180. There is nothing wrong with a 210 degree coolant temperature, especially when idling or sitting in traffic on a hot summer day with the AC on.

 

Its a stock like 355 with a 4 speed. No A/C. According to the sticker under the hood stock setting for timing are 6 degrees at 700 RPM's. When I set the timing I did not disconnect the vacumm advance line and plug it. When I say it is overheating I do mean that the antifreeze is boiling.

 

Go back and reset it by ear.

 

Could timing really be the problem? I understand that the motor is not "stock" anymore, but could 3 degrees in timing truly make the motor overheat?

 

OK, good info. If you are boiling over, you are definitely overheating. You didn't specify a year, but the base timing (at idle) in my limited experience, is always stated without vacuum advance. Because vacuum is high at idle, if you are not using a ported vacuum advance connection, you could be getting 10 degrees of advance out of your vacuum advance can (depending on its specs). If this were the case, you would have your initial timing effectively set at 4 dgrees AFTER top dead center. Timing that is too retarded can cause overheating since the burn will still be happening when the exhaust valve opens and heat that was supposed to be used to push your piston down will go into the head. If it was me, I would re-read the sticker to confirm that the 6 degrees is without vacuum advance, and re-time the engine with the vacuum advance disconnected and plugged.

 

Three degrees, probably not. 10 degrees, yes.

Easy Mike's answer, though probably half-kidding, isn't terrible. I have set the timing on engines by ear before in a pinch, and then put the light on it when I got back to the garage and they have always been within 3-5 degrees of where I wanted them. If you are sure your carb is set up the way you want, you can also set the timing by vacuum if you want. There is tons of good reading on timing here on the site, go to the "technical/performance" section and a bunch of it is in a sticky at the top. I don't think of timing as an "exact science", but the general guidelines laid out there were written by folks with much bigger brains than mine

 

Well. After I get the radiator and cooling system put back together I think I will try that. between the sticker, manuel, and by service manuel I never found anything that pointed to needing to deconnect and plug the vacuum advance. If this is the problem, I am supprised that the motor was even running as well as it did.

 

I had the same trouble when I rebuilt a BB. The problem turned out to be that the distributor sat for 3 months and the weights did not throw out ( light rust ) to advance the timing.
Installed a new distributor and end of problem.

 

Well, again, you didn't specify a year. Later models will probably be running on a ported connection, so you will get no vacuum advance at idle and you shouldn't need to disconnect to set initial timing. However, sooner or later on your new motor, you are going to want to see what your advance curve looks like, and for that you will need to disconnect and plug the vacuum advance line.