Please confirm my conclusion about overheating

[Doug L.]

Finished the restoration. Took it for setup of timing and FI (1964 L-84). Had to leave the shop during setup which was completed when I returned.

They told me they plugged the vacumm hose because "I didn't need the vacuum advance". The next day I took it out for its first drive. Once I had stopped for a couple of traffic lights, parked and restarted twice, the temperature rose to near the highest mark. Driving it for a mile or two without stopping brought the temp down but never to the 180 deg mark. At one traffic light it loaded up and almost stalled.

The FI unit is freshly restored by one of our experts with his 180 deg thermostat installed. The same for the distributor. The water pump is freshly rebuilt. The fan clutch is a fresh rebuild. The radiator and overflow are new from DeWitt with shroud in place. Hoses and fan belt are new. No water leaks detected. The radiator cap is new at 13# and it has not boiled over but the rough running at lights is enough to convince me that something needs to be fixed. The only thing I can think of is the vacuum advance being disconnected and causing a too rich mixture at idle.

Am I on the right track or missing something?

Thanks in advance.
Doug

[Joe R.]

Re: Please confirm my conclusion about overheating

Doug,

Congrats on your fresh restoration!

I'm with you. I would try connecting the vacuum advance first.

Good luck and may the force be with you!
Joe

[Dan H.]

Re: Please confirm my conclusion about overheating

Doug, you must have the vacuum advance hooked up to have the timing map work. My 64 is bone stock, runs 160 (gasp) thermostat, never even gets to 180 on the gage. They probably have the timing so far advanced it is a cooker at slow speeds. Had my vacuum canister fail once, ran hot, no idle etc. You'll like it if you set it up as original.
Dan

[Duke W.]

Re: Please confirm my conclusion about overheating

Your better fire those guys and find a mechanic who understands how engines work, or just do it yourself. A sixteen year old with a shop manual can do it.

Your high overlap cam engine needs about 28-32 degrees total idle spark advance to idle efficiently. Without the 16 degree contribution from the VAC, EGT will go up several hundred degrees and heat up the coolant.

Don't believe me. Reconnect the VAC, and go through the idle speed/mixture adjustment procedure. Get an IR gun and measure the exhaust manifold temperature after coming back from a drive after a few minutes of idling. Then disconnect and plug the VAC line and reset the idle speed to normal. Check the exhaust manifold temperature for the next few minutes and tell us what you find.

If you still have a 30-30 cam I recommend you target an idle speed of no less than 1000, and 1100-1200 may be better.

The other thing you need to know - I'm sure your mechanic hasn't got a clue - is that if no one has messed with the OE centrifugal advance, it starts at 700 so unless you set the initial at less than 700, which is difficult to do, the engine won't have enough advance.

The best way to set the timing on these engines is to use a dial-back light. With the VAC disconnected, rev the engine to 2500-3000 and verify that it no longer advances. (The OE max centrifugal is 24 deg. @ 2350) Use the dial back to set the timing at 38 degrees. Then blip the engine up to at least 6000 and verify that is doesn't advanve beyond this. Now reconnedc the VAC and go through the idle speed/mixture adjustment procedure in the '64 Shop Manual Supplement. Just follow the instructions. It's easy.

The next thing is a detonation check - full throttle fourth gear acceleration from 1200 to at least 2500. If it doesn't detonate you're done. If it does detonate, back off the total WOT timing from 38 degrees in two degree increments until it doesn't detonate.

My bet is it won't detonate at 38.

Duke

[Tony S.]

Re: Please confirm my conclusion about overheating

How's your fan clutch?

[Doug L.]

Re: Please confirm my conclusion about overheating

Thanks guys. Duke, I believe you. What I need to do is find someone in South Florida that knows about Corvettes. Any suggestions?

I can unplug the vacuum hose but I now wonder if the primary and centrifugal advances are set up correctly. I don't have a timing light or IR gun, so would like to take it to someone knowledgeable.

[Doug L.]

Re: Please confirm my conclusion about overheating

How's your fan clutch?

Fresh rebuild as mentioned in the original post. Stuff like the clutch, FI, distributor I sent out for restoration.

[Duke W.]

Re: Please confirm my conclusion about overheating

I live in California. I've been to Florida once - back in the seventies.

How about someone in your local chapter. Verifying and setting up the spark advance map makes for a good chapter meeting tech session.

Once thing you should be able to do is check the number on the VAC. Assuming you have any SB mechanical lifter cam, it should be "236-16" or B28 if it's been replaced in the last 20 years. One should also use a Mity-Vac to verify that is functions to spec. The specs are in your '64 Shop Manual Supplement of the info package you can download from the GM Heritage Web site.

If you just reconnect the VAC that should signifantly mitigate the overheating. This will increase idle speed, so just adjust it to about 1000-1100. You can figure out the rest later.

[Michael J.]

Re: Please confirm my conclusion about overheating

"They told me they plugged the vacumm hose because "I didn't need the vacuum advance". I can't believe there are people out there working on high dollar cars that say things like this.

[Joe C.]

Re: Please confirm my conclusion about overheating

The following is from the 1965 Supplement to the 1963 Shop Manual, and are the same as those from 1964. You'll need a timing light, so have a knowledgeable person with a light verify that your distributor is delivering spark advance per the "375" or "375 TI" columns pictured below. Start off by disconnecting and plugging the vacuum hose to your vacuum advance can and tying the advance weights in place. At an idle of about 850 RPM, set your initial spark advance to 12* BTDC. Your vacuum advance canister should be a "236" if it's a reproduction part, otherwise, the proper match for the original is a Eichlin VC1810 or Delco B28. You MUST use any of these three part numbers. Untie the weights, connect the canister to a manifold vacuum source and verify operation per the chart.

[Doug L.]

Re: Please confirm my conclusion about overheating

Thanks Joe, Duke. I'm starting over on it.

[John D.]

Re: Please confirm my conclusion about overheating

Hi Doug, I agree with Duke's initial comment on your issue. It's very disturbing to read your complaint. Your distributor was restored by one of the best fuel injection distributor guys this world has ever seen.I am sure it was tested to the nth degree. Then some bubba comes along and disconnects your big buck 236 16 and thinks it's OK to run the car like that forever and a day. Plugs the rubber hose up with silicone or something to that effect.
In the old days when I played with Model A Fords all the time my friends used to idle their 4 bangars so you could count the piston strokes. For some reason lots of FI owners like to idle their cars like that also. Dukes answer about setting your idle at 1000 to maybe 11 or 1200 is the way to go. Especially with a 30-30 cam.
Keep us informed please. JD

[Doug L.]

Re: Please confirm my conclusion about overheating

Hi John,
Thanks for your comments. I called the guy in Ft. Lauderdale after you and I talked this afternoon. He can't get me in until the end of the month and I'm traveling through July 3rd so I plan to take it to him on July 9th. I've already corrected the vacuum line. I'll start it tomorrow and see if I can get the idle set so I can drive it to Lauderdale for the tune up.

To Duke: yes, I have the 236-16 can, a repro unit installed by Don Baker when he restored the distributor for me last year. I'm also running a Crane copy of the 30-30 cam. FI unit by JD.

I'll let you know what happens but it won't be until July.

Doug

[George J.]

Re: Please confirm my conclusion about overheating

Doug,
I have a '65, with one of Don's distributor rebuilds. All of what Duke and John said, I agree with. Also, don't trust your tach on the dash to be correct at the low rpm scale. It will be fine for setting it to get you to a shop, but have them verify it when setting the timing. I have witnessed +/- 200rpms on almost every tach I've tested. I actually roamed around a shop for an hour testing the different cars with the owner. I don't think one was spot on. Let us know how it turns out.

George

[John H.]

Re: Please confirm my conclusion about overheating

I've already corrected the vacuum line. I'll start it tomorrow and see if I can get the idle set so I can drive it to Lauderdale for the tune up.

Doug

Doug -

Your guy who thinks you "don't need vacuum advance" desperately needs to read the article at the link below, especially if he's the guy who's going to be working on your car next. It's amazing how many "mechanics" haven't a clue how engines and ignition advance systems work.


http://www.lbfun.com/warehouse/tech_...101Article.pdf