Low mileage 1968 500 knocking and pinging

[burvis]

I am a new owner of this low mileage 1968 model 500, 95 HP, powerglide. The car is a true barn find with only 13,000 miles on it. I acquired it from a fellow who had made some mods - stock air box is off and carbs look newish. Unfortunately, he has had a stroke and is incapacitated, so I can't ask him anything.

The car sounds great and pulls strong while warming up. Once the auto choke lets off it starts knocking and pinging under load. I live in Chicago, and I attributed this to the fact that you spend most of your drive time sitting at red lights. I figured it was getting hot, and if I could get it onto a highway, it would be fine. I was, um, wrong. I took it on a 180 mile round trip to Milwaukee and back on a hot day, and it was knocking pretty bad at 70 mph when going up hills. When I got to Milwaukee and started driving at neighborhood speeds, it was knocking like a London cab. I drove it home slowly, feeling guilty the whole way.

With my skill set, I should be able to:
Look and see if the air ducts are open when warm
Set the static timing (best procedure for this?)
Or - buy a timing light and test/set timing that way.
Get some starter fluid and test for vacuum leaks

I don't have a lift, and every video I've watched of removing the shroud involves a complete teardown with the engine out of the car. Is there another way to test for blockage under the shroud? Pointers for blowing it out with the shroud on?

I read through a 'knocking and pinging' thread on here, and I know carb balancing and adjusting the transmission can be possible cures, but that's a little beyond my ability and I'd rather eliminate everything else first.

What else should I try? Anyone know of a Chicago based Corvair mechanic? All help and answers greatly appreciated.

[66vairguy]

That's a nice looking car for the rust belt area. So few 500's exist now it's nice to see one.

First you'll get a lot of advice and the most obvious place to start is the ignition timing. HOWEVER - I've worked with local club members that had 1968-9 cars and they are tough to tune. Why? They were designed to comply with low emissions regulations. Over the years folks tend to make modifications to "Get rid of the SMOG equipment". Sometimes the changes caused more issues than the were suppose to fix.

I suggest you check the car and report if it still has the Air Injection System on it and find the distributor number (on the base casting - hard to see). The engine number is not visible in 69 since the VIN was stamped in it's place. You have to remove the fans shroud on most 69 cars to get the engine configuration number. Not sure about the 68 cars.

Note that premium fuel is advised on the 1968-69 95HP engine. The head chamber was revised to lower emissions making it more prone to detonation (knocking). Either that or retard the timing and loose power.

[burvis]

I should have mentioned, yes, the smog pump has been deleted. But the good news is all the parts came with the car, they are in a box in the trunk. I will spend a little time taking pictures and try to supply more specifics about what engine I have, distributor number, etc. Thanks

[terribleted]

Check timing and condition of ignition first. Timing issues are the primary cause of pinging. Also remove the cover under the alternator (oil cooler inspection cover) and make sure that the cooler is not blocked by leaves which could cause actual overheating. You will need to check and set the point gap (you need a feeler gauge set with .016"-.020" blades) to around .017. You will also need a basic timing light to set the initial timing. Manual says 95HP powerglide should be set to 14 degrees before top dead center, but this may need to be a bit different if the engine was smog and it has been removed(if you do not have factory shop manuals you should really get some you would need the 1965 main book and the 1968 supplement book...Clark's Corvair parts has them in repro). I would start with point gap and timing at 14 and advance or retard the timing some to see what the engine does. Generally more advance is good BUT never so much advance as to induce pinging. Lean conditions or poor fuel can also cause ping. How old is the fuel in the tank? Old fuel loses octane and can ping like crazy. What grade is the fuel in the tank? these car really like octane...I will never run any of mine without 92 octane or better fuel (particularly automatics which are prone to being lugged a little and pinging). If the point gap and timing is right and the fuel is good but the car still pings regardless of lower initial timing setting I would suspect carb issues. How long has the car sat without operating? Carbs may be plugged up some limiting fuel delivery. If the car has sat a lot I would want to rebuild the carbs to clean out any varnish or goo that may have accumulated in them. The fuel tank is also suspect for issues such as internal rust, blocked fuel pickup screen and gum from sitting. Mileage is somewhat irrelevant when fuel systems are involved as sitting around is worse on them than frequent use.

[66vairguy]

Ted made a good point about old gasoline.

It sounds like the previous owner did some work on the car. So-- how long did it sit after he got it running and you bought it?

Gasoline goes bad after a couple of months of sitting unless a preservative like Sta-Bil is used and then six months is the limit.

Oh - check the PCV orifice to make sure it is not blocked with crud. I recall the manual says to check it every 12,000 miles - Ted can correct that if incorrect. Note the old rubber hose may be too stiff to re-use after you pull it off the orifice input on the balance tube on the back of the engine (between carburetor pads). Only use fuel or emissions rated hose to replace.

BTW - Brakes system hydraulics are suspect if a car sat for more than a year. If in doubt the brake fluid should be replaced and if the old fluid comes out rusty or opaque then the master and wheel cylinders, plus the lines are suspect.

A nice find and good luck with the car.

[bbodie52]

You stated that the car seems to run well when cold and the automatic choke system is active with the choke butterfly valves at least partially closed. But when the engine reaches normal operating temperature and the choke butterfly valves are wide open, it starts knocking and pinging under load. This is a sign of detonation, which can be caused by a very lean fuel/air mixture. The application of the automatic choke is intended to enrichen the fuel/air mixture by partially closing the air intakes on both carburetors, restricting airflow while pulling more fuel from the float bowls. With the chokes off, the fuel/air mixture should be normal, unless there is a vacuum leak somewhere that is permitting excessive air into the intake manifold(s).

Carefully examine your system and look for loose or cracked/split, missing, or disconnected vacuum hoses. The diagram below should help you to know where to look...

[skipvair]

Ted made a good point about old gasoline.

It sounds like the previous owner did some work on the car. So-- how long did it sit after he got it running and you bought it?

Gasoline goes bad after a couple of months of sitting unless a preservative like Sta-Bil is used and then six months is the limit.

Oh - check the PCV orifice to make sure it is not blocked with crud. I recall the manual says to check it every 12,000 miles - Ted can correct that if incorrect. Note the old rubber hose may be too stiff to re-use after you pull it off the orifice input on the balance tube on the back of the engine (between carburetor pads). Only use fuel or emissions rated hose to replace.

BTW - Brakes system hydraulics are suspect if a car sat for more than a year. If in doubt the brake fluid should be replaced and if the old fluid comes out rusty or opaque then the master and wheel cylinders, plus the lines are suspect.

A nice find and good luck with the car.

What is the carb jetting like in That year? I suspect it was leaned down some from previous years.


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[skipvair]

Ted, correct me if you disagree, but on my 1st 140, it would carbon up increasing the compression ratio and creating hot spots in the combustion chambers. About once a year when it did it, my Dad, an old time mechanic, taught me a decarbonization trick that worked. When the engine was hot, I would run it to about 2000 rpm and very slowly drizzle about 8 ounces of water through each carb. It would usually be apparent that it helped. Meanwhile, today’s premium is probably lower octane than regular was
Back then. But if engine has never been apart, I would suspect crud in the cooling fins.


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[terribleted]

Ted, correct me if you disagree, but on my 1st 140, it would carbon up increasing the compression ratio and creating hot spots in the combustion chambers. About once a year when it did it, my Dad, an old time mechanic, taught me a decarbonization trick that worked. When the engine was hot, I would run it to about 2000 rpm and very slowly drizzle about 8 ounces of water through each carb. It would usually be apparent that it helped. Meanwhile, today’s premium is probably lower octane than regular was
Back then. But if engine has never been apart, I would suspect crud in the cooling fins.


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We used to call this an Italian tune up:) The water explodes into steam and can knock carbon deposits off the heads and pistons. Can also hydrolock the engine and bend a rod if you are not careful. 13k Engine likely not carboned up (but it is possible), but, very likely to have crudded up fuel system, old gas, varnish in carbs, bad points etc.

[66vairguy]

skipvair - Per Bob Helt's carburetor book, the 68 base engine PG cars had a 49 main jet. Over the history of the Corvair the primary main jets ranged from 48 to 54 (note 54 was only used for part of the year on the 60's). Burvis mentioned the carburetors looked "newish" so perhaps the previous owner changed or revised them. This is a problem I mentioned - folks tend to make changes to SMOG engines so assumptions based on originality cannot be made.

The 68 should not have a carbon problem, IF the original carburetors are in place.

In the air-cooled world there has always been a tendency to run rich with a bigger jet size to keep head temperatures down and reduce detonation. The down side is I've pulled apart engines with a big jet in the carburetors and the heads are loaded with carbon and the top piston rings were jammed full and stuck.

My personal choice is a 51, or smaller, jet for most engines and I have not had detonation issues in the HOT Southwest. Just me.

[64powerglide]

Buy a timing light!!!!!!!!!!!!!!!!!!!! A good one!!!!!!!

[burvis]

Thanks for all the help, really appreciate it. To address a few things that have been brought up. The previous owner did a lot more than I realized, as you will see in the pics below. It looks like the engine has gotten a lot of love. The valve cover, sump pan, exhaust and rear shocks look new. The wife of the PO who sold me the car said they started it every couple of weeks at minimum, kept it on a trickle charge, etc. Seems unlikely the problems stem from sitting up, it seems to have been a pretty active project until recently.

As for 87 octane gas, guilty as charged. When I first got the car, I topped it off with premium, thinking I would spoil it. It still pinged a little. But before that Milwaukee trip, I gassed it up with Citgo regular. Bet that is a big contributor. It also has a full tank of regular now. I bought a little bottle of octane booster and dumped it in, hopefully that helps a little. Ralph gets a steady diet of 93 octane from now on.

I am just back from the garage where I took some pics and started looking for possible causes. The carbs are very clean Rochesters, no sign of lacquer looking down the throats. I have gone around the vacuum lines, and some came off pretty easily, so they are all on as snug as I can get them now. But here’s maybe the biggest thing I found - the vent actuator on the left side feels totally different from the one on the right. Sitting cold, the one on the right is tightly closed, and you can open it against what feels like smooth tension against a spring. The one on the left is kind of hanging there limply, and won’t really move in either direction. I took off the rear vented body panel (hope I don’t have to do that too many more times) and popped of the vent door. Sure enough, the actuator is frozen almost all the way against the bump stop, but the door is barely open. There’s a fresh puddle of oil under that left cylinder bank, leaking from the valve cover. I think that side was really hot when I parked after that bad trip to Milwaukee.

Anyway, I’m heading back over - I bought a timing light, and an oil pressure gauge. I will see what I can figure out and post the results.

[steve57]

Yep, failed thermostat on left side. You need to fix that heater hose rubbing on drive shaft also. That’s not good. From the look of those underside pics I would question that low miles claim, imho.

[bbodie52]

Carburetor 7028005 is a 1968-69 Rochester H carburetor.

The SMOG pump air injector exhaust manifolds and plumbing are still in-place.


Is there a harmonic balancer on the crankshaft, or a solid cast pulley? a solid cast pulley is an indicator of a 95 hp engine with an 8.0:1 compression ratio. The 110 hp engine has a different set of heads, a harmonic balancer, and a 9.0:1 compression ratio. The 95 hp engine with SMOG heads and flat-top (non-domed) pistons would have an 8.0:1 CR and should be happy with low-octane fuel. My 140 hp engine also has the same camshaft as a 110 hp engine, and a 9.0:1 compression ratio. It also tolerates REGULAR low octane fuel with a light load, level roads, and moderate to cold ambient temperatures without pinging. A heavily loaded 9.0:1 CR Corvair climbing hills and with a moderate to heavy load in the trunk and passenger compartment needs Premium fuel.


What are the cylinder head casting numbers?

Cylinder heads have a casting number on the end of the head, as shown in the example below...




If your engine has only a low CR and the timing is set properly, it should do fine on REGULAR. If it is pinging with a light cargo load and on level ground your fuel/air mixture may be lean, indicating a vacuum leak.

The pictures below show a couple of SMOG pump configurations. The last three images show that additional hoses were connected to the intake manifolds at the rear side of the carburetor mount castings. Corvairs normally have a tube on each side of the intake manifold casting to connect to the vacuum balance tube. But your engine may have had two additional connector tubes on the rear, to connect to the the air cleaner assembly. It that system was removed, the extra tubes on the intake manifolds should have been plugged. You should check for these extra connection points at the base of each carburetor and, if they exist, ensure they are sealed. Also ensure that the balance tube is tightly connected.

[terribleted]

Gummy carbs you will not see much from the outside. Carb fuel issues from sitting are in the inside. The carbs must come apart to see and clean if needed. Low HP Low compression engine tuned properly may run 87 octane ok. I just pamper mine with 92 and run the timing higher for better performance as the fuel allows. The fuel tank unless it has been replaced or cleaned out is also very likely to have gummy deposits or rust inside it. I do not care how much someone has recently fiddled with the car unless the tank has been serviced any car with only 13k miles in 50 years has had bad , old fuel in it for most of its life. Certainly drain the tank, remove the sending unit and inspect the inside of the tank. I recommend if it is not beautiful to simply replace it. While you are lookin g at the fuel tank also look at the rubber hoses that connect to the fuel filler neck. They could easily be dry rotted if they have not been replaced recently (certainly if they are 50+ years old). It pays to make sure the fuel system is up tight since issues in the tank and lines can come back and bite you over and over and over again with a myriad of different annoying carb issues from blockages causing bad idle or lean conditions to sticking floats causing gas flooded engines to etc. etc. Take the time and effort to see for yourself and fix as needed and save trouble down the road. These carbs are very simple. the GM shop manual gives a step by step adjustment procedure and has good breakdown diagrams. Take apart one at a time to help in reassembly if needed:)

In your photos I can see evidence of fuel spillage by the left carb in the past (the brown stain under that carb in the left side engine pic)...maybe all fixed but maybe not. Look then you will know.

[66vairguy]

I'm in total agreement with Ted on gas tanks. I run into problems on Corvairs with old cruddy and rusty gas tanks plugging up carburetors (fuel stone in carb is not meant to filter fine particulate). First install a generic 5/16" METAL (not plastic) fuel filter on the fuel hose out of the tank. I do this on new tanks also. # Fram:G2, Hasting: GF10, Purolator: F20011, Wix: 33012. NOTE you will find both plastic and metal canisters at these numbers - open and check the box - metal only under a car. This is a disposable filter, change at least once a year.

Use ethanol safe fuel hose - believe it or not some auto parts stores still sell cheap fuel hose that ethanol will dissolve!!

I like the Gates "Barricade" fuel hose that is rated for just about anything that is liquid fuel.

The carburetors have the emissions idle circuit control. Folks will say they are junk, but knowledgeable Bob Helt said they work fine IF in good working order. Get Bob's Helt's Rochester book to learn. Bob's book says your carb. tag number 7028005 was for 68 and 69 carburetors

Yes one thermostat is bad letting the thermostat door hang open. That's a safety design to prevent overheating if the thermostat fails. While I think Clark's is a great outfit with mostly good products, the new thermostats I've gotten from them have a 50% failure rate within a year (that's with low mileage). They have replaced them, but it's aggravating to keep changing them. At this point I try to find good used original GM thermostats and use them. Some just leave the doors off. It's not advised living in cooler climates. - Just me.

Finally - before getting too far along, check the timing and report back. I suspect the previous owner set the timing more advanced than spec. and used premium fuel for more performance. Finally - find the distributor number to see if that was changed.

Good Luck.