It's stable @ 600-650 rpm & 8* with VAC connected. That's where it's pulling 14-15". If centrifugal is coming in too soon, my understanding is the springs are too light. Heavier springs would delay centrifugal introduction and would lower additional timing degrees as rpm's increase. Is this correct? Can going from a distributor set-up with the Crane electronic conversion with the old B1, which by the way ran great through all the gears, to the B26 also require heavier spring weights to compensate for the earlier reaction to vacuum of the B26? How else would I slow down the introduction and duration of centrifugal?
I have your tuning seminar and several of your other threads, along with others on this subject but parsing out where I'm at to what I need to do is taking me some time. If I'm at 8* with stable 650 rpms without the VAC and 36*-38* is my WOT target and I'm currently too much too soon, then it follows the springs are my next target. Is this correct?

 

Yes, you need stiffer springs to slow the rate of centrifugal advance. Also it's not clear to me if you have found the maximum centrifugal advance. Your previously only reported total WOT advance at 2100. What about high revs. In order to find the point of max advance you have rev the engine until the timing mark stops advancing.

For your idle behavior 14-15" @ 650 the B26 VAC is ideal.

Remove the cap and rotor, snap a photo of the centrifugal advance mechanism and post.

Duke

 

Picture is before I swapped out the B1 for the B26. And you’re correct. I didn’t take it up to all in since I was working alone on this and running out of hands. I’ll try and conscript someone to run the throttle up to the “all in” advance and report.
I looked online at the Mr. Gasket spring kit mentioned a lot here. All the springs in the kit appear to have more windings than the ones on my distributor. I know wire gauge has a lot to do with spring tension as well but it’s lending more evidence to believe that the current springs are too light by comparison. Anyone agree?

 

I'm going to close this overheating issue thread because I believe that issue has been resolved. Thanks to all who contributed here and to those who've taken the time to compose all the articles and stickies on the matter. I learned a lot from all of you. Due to the relationship of overheating and timing, this thread morphed into something going on with my distributor as the last several posts show. As of today's efforts, changing the weight springs yielded no improvement when mapping out the curve. I'm going to start another thread regarding the distributor issue and on what to do next.
Gentlemen again, thank you.

 

Spike66, so what do you feel was the key to finially improving the cooling at idle/stop and go? I've been following closely since I'm having a very similar problem with my '66 327/300.

 

I read everything I could find on the subject; here and on other sites. There is a wealth of information within the Stickies here and I printed out all that were relevant. I also read other previous threads and printed those out. All of that information is mentioned in the posts on this thread. If you need help finding them, PM me and I can direct you to them. And the generous and knowledgeable, although sometimes snarky, responses by forum members proved extremely valuable. There are several wizards on this forum.
Also I checked all the relevant parts along the coolant path and replaced those that were suspect or flat out fails. In my case, water pump, expansion tank cap, fan clutch and coolant. The radiator is new as are all the hoses. As a matter of course, I replaced the thermostat as well. An IR gun was a great diagnostic tool. It told me, among other things, that the temp sender and dash gauge were inaccurate but within livable limits. It's bloody hot right now in SW FL. I don't drive the car until late October. But I've noticed it can idle in the driveway in the hot sun way longer than it did before before creeping up above 215-220*. So I'm calling it mission accomplished.
With all the parts in the cooling system up to spec, I started in on the timing as, I learned, it is relevant to engine temperature .......and fell down the rabbit hole. I'm trying to find my way out of that on another thread.
Check every part in the cooling chain. Repair or replace those that don't pass muster. If you do all that and you're still overheating, you might need to look at your timing. As a couple guys suggested, there's always the electric fan option if you hit a brick wall. Good luck.

 

Does the bottom radiator hose have the spring in it?

 

It’s a newly rebuilt engine, new high flow water pump, new DeWitts radiator, new hoses/coolant
new 180 thermostat, replaced fan with 7 blade and new fan clutch. Even added the AC radiator seals (upper and lower) …. still in traffic temp increase to 230-230 but drops back to 190 once speed increases.
Should it be very obvious when the fan clutch fully engages? I’m not sure it’s working properly.

 

What fan clutch did you use? Doesn’t sound like you’re getting enough air flow.

 

Has your car puked coolant yet? If not, you're really not overheating and your dash gauge could be in error.
From what I've Iearned, a quick test for the fan clutch is before you start the car, spin the fan blade and note resistance and rotation. It should spin fairly easy and offer little resistance. Start the engine and let it come up to temperature. If you have a IR gun, this is a good time to check temperatures along the coolant path. Scan your water outlet fitting at the thermostat and/or the sending unit and note that temperature. You'll be able to tell when the stat opens up +/-. Compare that with your dash gauge. Do this several times while running the engine, allowing it to "overheat" into the yellow range on the dash gauge or until you start getting temps higher than you're comfortable on your IR gun. With the driver's window down, reach in and shut it down and watch the fan. If it stops nearly immediately, that's a good sign it's ok. Try to spin it as before. If you meet with greater resistance and less travel than you did when the engine was cold, your fan clutch is ok.
You didn't mention replacing the expansion tank cap. If you can have yours tested that would tell you if it's holding @ 15#. If not, get a new one. Beyond that, it sounds like you've done everything you can in the cooling department and you may need to check your timing data.
Re-read this thread from the beginning. There are excellent posts by guys far more experienced than me on this. I'm only reiterating what they've posted. Good luck.

 

Any time you park a car with a fan clutch installed the silicone in the fan clutch settles to the bottom. When it cools off it is thick and will engage the fan clutch on start up. IF you grab a cool fan clutch it will resist you turning it for about a full turn or a turn and a half and then it will almost free spin. That is normal. If you park the car hot with the fan clutch engaged fully and go turn the blades by hand it will be hard for just a moment while turning and then spin free. As you turn the blade by hand it pumps the silicone back into the reservoir until the spring turns on the front and opens the valve letting the silicone back into the clutch body. Odd but this is how they work. Silicone is thin when hot and thick when cold. When you shut down some always settles to the bottom. This is why it is normal to start your car on a cold morning and listen to the fan clutch roar for the first 30 seconds as you drive away. I think they claim 30-45 seconds roar is normal. Longer would be a problem.
Most fan clutches are designed to work on cars with a vertical radiator set up. The springs are set to work with this vertical radiator. The Corvette has an angled radiator and the temps end up being lower at the fan clutch so you need a spring with a lower temp to engage properly. These are hard to find. Some of the older fan clutches allowed you to re clock the spring for lower temps but most do not today.

 

It’s a Hayden spring style thermal fan clutch

 

And yes, when I shut it down if temp gauge in the yellow zone, it does puke some coolant from the expansion tank over flow hose.

 

I don't know if Hayden offers a lower temp spring but worth a phone call to find out, if they don't you might be able to weaken the spring you have so it comes on at a lower temp. Springs lose tension when exposed to heat but it would be a hit an miss project to somehow get the spring to open that valve at lower temps. If you can get a feel for how much tension the spring has and how soon it starts to unwind to engage your clutch you might get an idea how much the spring needs to be adjusted to change your engagement temperature. The fan clutch pictured is a thermal design but a very light duty clutch. Note zero fins to cool it on the face plate, just stamped steel. The aluminum covers which have fins all over them cool the clutch much better and keep it working when you need it. Take a look at this Hayden page, it shows the clutch you have can engage your blade up to 65% of engine speed, a Heavy Duty clutch will spin the fan close to 90% of engine speed so much more cooling potential. The severe duty would be overkill and is designed for much larger fan blades in trucks. Fan Clutch Info

 

I found this youtube video that shows an adjustable fan clutch, this one is used in Diesel applications but the video shows how minor movements of the spring makes a 10* difference in the engagement temp. Looking at this video I was thinking you may be able to make a new spring slot in your Hayden clutch and see if it works better with your car. Since it does not work as is there is little to lose. Maybe just open the slot the spring rests in now about 1/16" wider, from the video it sounds like this movement would make a 10 or 15* engagement change for the better. If you go too far the clutch will be engaged all the time so start slow and see where you like it. It is trial and error and might involve pulling the fan clutch off a couple times increasing your slot size each time but you could sure save many owners time in the future if you solve this issue. I will go back and edit my previous post so no one starts with a 1/2 turn attempt, I think that would be too much but I bet you will know when you remove the spring and see how much resistance it has when you clock it and how much movement is needed to slightly reduce the pressure on the clutch valve.
I have not seen any automotive fan clutch with adjustment slots like this diesel application but it might lead us to a better fan clutch solution for our C2 cars.

 

gonna try a different fan clutch.....let ya know if it helps. thanks for the help!

 

Leif,
Did you need to remove the radiator to install the lower and side support seals?
Thanks

 

Mine was in place from the factory. You shouldn't have to remove the radiator to add the lower extension...possibly have to remove the shroud to attach the extension which would require removing the fan. I've never had to add an extension after the fact. Hopefully, someone who has done this will chime in.

 

I installed the extension on my '66. I did remove the shroud to install it. I think it would be difficult to do a nice job of installing with the shroud still in the car.

Ted