mega spark knock under load and "dieseling"- '66 2

[john tate]

OK, first timer- this site is great- I didn't know these great resources were available for six-shooters.

If anyone can add their 2 cents I would appreciate it. My '66 Sprint 200 has run great for 21 years, and now it spark knocks under load and I can't seem to stop it.

Problems started when I replaced my vac advance unit. Spark knock then started under load. I tried fiddling with return springs to help the situation but was advised to get a freshly rebuilt distributor since mine was pretty crusty.

Rebuilt distributor from NPD and problem continues. I have an auto/no Thermactor, and for years have run 12-14 degrees w/no knocking at all. Now I have knocking under load even at about 3 degrees BTDC!

I used Sea Foam to try and remove carbon deposits. Nothing much came out, but the car does smoke slightly when cranked and may be burning a little oil. However, 20 years ago when it burned tons of oil (before the last rebuild) it never knocked...

Radiator was recently rebuilt, t-stat seems OK, but the car does get hot when stuck in traffic, then cools back down on the road. I'm going to buy a 6 blade fan.

It doesn't seem to be lacking for fuel, and when I disconnect the vac advance entirely the knock goes away and can be driven except it stumbles a bit under load (expected).
With it connected it knocks under load even when cold. When I give it WOT the knock actually goes away some.

Do I have a vac leak, PCV problem, or plugged passages in the carb?

Another issue is it sometimes still diesels when I turn it off. This is all with premium fuel.

Any advice would be appreciated. Sorry for the mega post but figured I'd put it all out there....

 

[Anonymous]

I would check to see if the outer ring of the harmonic balancer has slipped. If it has slipped, when you time it, it may actually be way advanced. Check to see that the #1 cylinder is at top dead center when the balancer and pointer indicate that it is at TDC.
The timing may be way off and causing high temps at idle which are contributing to the dieseling problem you describe.
Doug

 

[ludwig]

Check your fuel/air mix with a vaccuum guage. Turn it in (lean) then back it out until you get the best vaccuum number you can and then check your timing again.
I was gonna say, use a higher grade of fuel, but that would be race fuel so never mind.

Maybe you need to re-stab your distributor to get more or less advance. If you are using a timing light, the outer ring on your damper might have slipped on the rubber membrane and you actually are getting no advance when the mark says it is advanced.
If this is the case, you need to find true TDC and mark it on the damper with a white pen. But that is an issue for another string, which you can find in the copious archives of this fair site.

 

[ludwig]

Heeey 66 Fastback 200!!! You slipped in under my elbow while I was typing.

 

[LEROY POLL]

HEY JOHN


.....DOUG IS RIGHT ON ABOUT THE TIMING. I THOUGHT THAT I WOULD ADD A QUICK HELP TIME SAVER.

.....IF YOU CAN'T TELL FOR SURE ABOUT THE SLIPPED RING THEN TRY THIS. UNHOOK THE VACCUM FIRST...THEN...

.....TAKE THE DIST. AND RETARD IT SLOWLY UNTIL IT START TO CHUG SLOWLY. MARK THIS WITH T/LIGHT. THEN AGAIN VERY SLOWLY UNTIL IT STOPS. YOU ARE AROUND -5* OR -6* AFTER TOP DEAD CENTER. THESE MOTORS DON'T RUN MUCH AFTER ATD. YOU DO THIS FAST AND IT WILL NOT BE CLOSE. THIS WILL NOT WORK IF YOU HAVE IMPROVED THE SPARK. BUT IT WILL BE CLOSE.

.....IF WHEN YOU FIRST MARKED YOU FOUND YOU WERE NOT ABOVE 0* YOU HAVE SLIPPED. AGAIN THIS IS NOT REAL ACCUTATE BUT IS CLOSE. I'VE CHECK THIS ON A GOOD MOTOR AND THE FIRST CHUG COMES AT 0* TO 2*+. THIS IS JUST ANOTHER WAY OF CHECKING QUICKLY.

.....ALSO CHECK TO SEE HOW MUCH YOU CAN CLOSE THE CARB DOWN AT IDLE. THIS WILL HELP ON SOME OF THIS PROBLEM.

.....WE ARE ALL HERE TO HELP SO KEEP TRYING.

LIVE IN GRACE

LEROY POLL

 

[john tate]

Thanks for the great help.

I stabbed the distributor just like the old one so I doubt that's it, but the harmonic balancer might do the trick. I'll read those details in other posts.

Is the best way to check for TDC by using a straw or something in the cyl? comp gauges give you an idea but it's hard to tell exactly when it's at TDC.

Would advanced or retarded timing run hotter at idle? It does seem to be running hotter than it used to and that doesn't compute w/a fresh rad.

I will do some checking and get back to you.

 

[cfmustang]

Some people have made a TDC gauge using an old spark plug. I think they removed the center so that just the metal part that screws into the head remains. Then, they tap/thread that hold to accept a machine bolt and voila.

Or, if you are lazy like me, you can pick one up from Summit (I think it is made by Crane). If I remember right it was around $10.

 

[Anonymous]

Is the best way to check for TDC by using a straw or something in the cyl? comp gauges give you an idea but it's hard to tell exactly when it's at TDC.

This works quite well--make sure you are on comp. stroke
remove spark plug(s) if you remove all 6 an engine is real easy to turn with fan
drop a drinking straw or a broom straw on top of the piston. rotating the fan and watching the straw (or whatever) it is real easy to determine TDC. A helper to hold the straw makes it real easy. When you get to where the straw moves down when you turn in either direction you are there. mark pulley to match 0 on pointer.
If pinging persists check for sloppy dizzy or timing chain. Also make sure you didn't route vac lines wrong when you replaced adv. mechinism.
66 200 SCV???-? Manifold vac isn't compatible???

 

[john tate]

OK folks, STILL knocks only under load. New harmonic balancer (the onld one looked shot anyway), rebuilt radiator, went from 192 to new 180 thermostat, 6 blade fan, and rebuilt Load-O-matic from NPD w/new vac advance.

Car now runs cooler and I reshot the timing at 12 degrees. Idles well, runs well, but still knocks as before where it's worse when under light accel than heavy.

Could I have a plugged vac port in the carb? It's a Motorcraft 1940 and I haven't rebuilt it since the 80s so it's time anyway. If not that, what could be left? Head gasket problems? vac leak? So far it hasn't dieseled on me so that's one good thing.

HEEELP! I'm running out of ideas.