'69 427 "Starter kick back"

[Michael B.]

Had the car for many years and this is the first time this has ever happened. Cold start, it turned over once, and then made a loud 'clunk' noise. Next time I hit the key it did not turn over at all, just dimmed the lights. I became concerned that somehow the engine had seized. However, I was able to turn it over manually at the harmonic balancer bolt. I then proceeded to try to start it again, and it again turned over once and produced the 'clunk' noise. Note, this noise is NOT the grinding starter noise you get when there is no starter to flywheel tooth engagement.

So what has changed recently to potentially cause this condition?

The car was suffering from misfire at 4000 RPM. I checked the dwell, and it was around 27 degrees. I increased it to 31 degrees and then reset the timing to about 10 degrees BTDC (with vacuum advance plugged). It appears, at full advance, to be reaching about 34 degrees. (determined with a dial timing light)

I've done some reading online and found out that excessive initial advance can cause "starter kick back". However, I don't believe 10 degrees to be excessive (although the manual CONSERVATIVELY states 4 degrees as the specified setting).

I've been thinking my next step is to retard the timing some, maybe back towards 4, and see if the condition still exists. I am very concerned about damaging the starter or the flywheel if I don't fix this soon.

Thanks.
Mike

[Mike T.]

Re: '69 427 "Starter kick back"

Mike - Can you clarify a couple things for us like when was the timing reset to 10 degrees, was this right before this starter kickback problem?
And when you reset the timing to 10 degrees, what was it set to right before that reset? Battery condition is good and verified? Maybe not related to your starter kickback but what do you feel is the cause of the 4K rpm misfire?

[Steve G.]

Re: '69 427 "Starter kick back"

This does not at all sound like "starter kick back" resulting from early timing. Advance timing will give a "halting" cranking, but generally continue to crank. It will certainly not prevent it from cranking at all.
But a simple and easy way to confirm this is to pull the coil wire from the cap and ground it out then try cranking it.

Steve

[Michael B.]

Re: '69 427 "Starter kick back"

Thanks for the quick feedback.

I have driven the car once since I reset the dwell and timing (actually two crank starts, out of the garage, and then at the gas station after a fill up). It did not have the condition I described at either crank up. The increased dwell also seemed to cure the 4000 RPM misfire condition, at least based on that one test drive. What I don't know is what the timing was set at before I reset it to 10. I wish I remembered. I can tell you initially, after the dwell set, I put the timing to 4 BTDC and it was a little difficult to get it there based on my spark plug wire routing, it wanted to be more advanced. I then did some reading and found out that was a conservative setting and changed it to 10 BTDC. The battery condition is unknown at this time, but it never seemed to have any issues cranking in the past.

I think I understand the confirmation of the advance affect on cranking by removing the coil wire. You are suggesting this because it will remove the spark system from the equation altogether, correct?

Can excessive dwell cause this condition? 31 is within the 28-32 tolerance, however. Dwell is the amount of rotor angle points remain closed between firings, correct?

[Edward J.]

Re: '69 427 "Starter kick back"

Mike by removing coil wire its taking any timing issues out of the equation. if you have a volt meter check the standing battery voltage a fully charged battery will be 12.66, if good, listen to the starter when trying to start do you hear anything when turning key, like the solenoid clicking? generally speaking when a starter is going forward to start and the engine turns backwards because of when holding the key to start you can break the starter aluminum housing.

incorrect dwell will only effect the engine starting and firing up, should not have any effect on the engine's cranking ability.

[Joe C.]

Re: '69 427 "Starter kick back"

If it's a 3x2 engine pull the plugs and look for gas in the cylinders.

[Patrick B.]

Re: '69 427 "Starter kick back"

If it's a 3x2 engine pull the plugs and look for gas in the cylinders.

Sage advice. Also don't forget to remove the wire from the coil at the distributor cap (and ground it) so you don't ignite the gas exiting the cylinders when you turn the engine over the with the plugs removed. Don't ask me how I know this.


As a quick check for carb leakage, pull the dip stick and check for a high "oil" level and the smell of gas.

[Michael B.]

Re: '69 427 "Starter kick back"

It is a 3x2 (400 HP).

Well, when I pulled the plugs I found the problem. Number 1 had a significant amount of fuel on it and number 7 was full of fuel, full enough to dump gas on the floor when the plug came out. Thanks Joe and Patrick.

Any idea which carb would be to blame? Probably not a bad idea to rebuild them all considering the last time they were rebuilt was 1996.

What is the likelihood that the engine is damaged internally from this? It does turn over by hand still. Any way to check without pulling the heads or the pan?

Thanks,
Mike

[Patrick B.]

Re: '69 427 "Starter kick back"

Drain the oil. If there is only about an extra quart of gasoline and the oil still feels normal, it is probably OK. In my case, there was enough gas in the cylinder to bend the connecting rod on start-up. It took surpising little bend to cause the bottom of the piston to contact the crankshaft counterweight and cause a hellish clunking sound within the engine. Even with this, the only damage was the rod and piston which I replaced without removing the engine. Since your engine is not clanking (this is not a subtle sound-you can hear it a block away), the rod should not be a problem.

If the oil looks dangerously dilluted, remove the oil pan and check the bearings. Removing the oil pan is easier on a Corvette than any other classic Chevy because there is no need to raise the engine off its mounts. The bearings will still probably be OK even with heavily diluted oil.

[Steve G.]

Re: '69 427 "Starter kick back"

The most common form of damage from hydraulic locking is a bent rod. If the engine hadn't fired prior to bringing up the locked cyl and was just rotating on the starter when the lockup occurred there's a reasonable chance of no damage. If it locked with force of combustion from other cyls already having fired, there's a pretty good chance you bent a rod.

The piston hitting the crank is a sign of a very big bend. It may not seem like it took much to contact the crank, but usually the bend in the rod can only be detected by putting it in a checking fixture. Smaller bends where the piston is not hitting will run fine and make no noise, but that bearing will prematurely fail. Forensic examination will show the wear pattern across the bearing to be heavier on one side than the other.
Sometimes they make it all the way to the next overhaul interval without causing a problem and is only noticed when the shells are examined. Sometimes they wear sufficiently over time to cause a knock or even spin in the rod.

There is no way to confirm a bent rod without checking it in a fixture. You could run it for a while then pull the pan and examine that rod bearing to get an indication of uneven wear, but that is a lot of guess work. Did it run long enough to show a tell-tale wear pattern?

I'm not sure what I would do, and I do this stuff for a living. I think if the engine was fairly fresh I would pull the pan and that head and check those two rods. If the engine was already getting a little long in the tooth I might drive it a while with the plans for a full teardown in the nearer future than I might otherwise have done.

Steve

[Domenic T.]

Re: '69 427 "Starter kick back"

Wow,
Followed this thread, what good diagnostics. I've seen my share of cylinders that had hydraulic locking from the coolant, but without a electric fuel pump would never have guessed that there was enough fuel in one of the carbs to cause a hydraulic situation.
All good advice. Wonder if more than one carb drained? In the past, with a hydraulic situation we ran the engine long enough to see if it started making noise. Some did and some didn't. As Steve said, as long as it didn't fire on the cylinder, chances are much better that there may not be damage.
I have 3 carbs on my big block and will remember this thread.

Dom

[Michael B.]

Re: '69 427 "Starter kick back"

I drained the oil and there was very little gas in it. It measured out to be really no more than 6 quarts.

I've already pulled the carbs to rebuild them. When I pulled the center one it appeared to be soaked in gas under the gasket. I'll be ordering the rebuild kits from Paragon tomorrow. Any hints on the rebuild?

What is it about the 3x2 that makes it prone to this issue? Is there anything I can do to prevent it from happening again?

Thanks again.
Mike

[Steve G.]

Re: '69 427 "Starter kick back"

In my experience the amount of gas in the oil is not indicative of whether a rod bent or not. You worry about fuel diluting the oil and the damage done to bearings if the engine actually ran with the diluted lubricant. That doesn't appear to be the case here. The question is how hard did it run up against the non compressible fuel above the piston.

The problem with these kinds of situations is that while the probabilities of a damaged rod are very small, the subsequent damages from an undetected bent rod can be very large. In the best of circumstances, the undetected damage could result only in an unevenly worn bearing detected at the next time the engine is overhauled. The worst case scenario, albeit it very unlikely, is putting a window in the side of a very valuable, perhaps irreplaceable, engine block.

Personally, the amount of fuel in the oil would give me no comfort. Not trying to scare anyone, but the best decisions are made with the most information.

As to the carbs, this should actually never happen. This is a leak between the metering block and the body of the carb. The gasket between the two, on it's own , won't fail out of the blue like this. There's no moving parts and gaskets in a static situation between two similar metals at the same temps seldom fail for no apparent reason.

The most likely cause of this situation is a warped metering block. The blocks warp for a couple of reasons. The bowl screws were over tightened on assembly, the block screws under tightened, or the bowls were removed and reinstalled over the service life of the carbs without replacing all the gaskets and tightening to spec.
Steve

[Joe L.]

Re: '69 427 "Starter kick back"

In my experience the amount of gas in the oil is not indicative of whether a rod bent or not. You worry about fuel diluting the oil and the damage done to bearings if the engine actually ran with the diluted lubricant. That doesn't appear to be the case here. The question is how hard did it run up against the non compressible fuel above the piston.

The problem with these kinds of situations is that while the probabilities of a damaged rod are very small, the subsequent damages from an undetected bent rod can be very large. In the best of circumstances, the undetected damage could result only in an unevenly worn bearing detected at the next time the engine is overhauled. The worst case scenario, albeit it very unlikely, is putting a window in the side of a very valuable, perhaps irreplaceable, engine block.

Personally, the amount of fuel in the oil would give me no comfort. Not trying to scare anyone, but the best decisions are made with the most information.

As to the carbs, this should actually never happen. This is a leak between the metering block and the body of the carb. The gasket between the two, on it's own , won't fail out of the blue like this. There's no moving parts and gaskets in a static situation between two similar metals at the same temps seldom fail for no apparent reason.

The most likely cause of this situation is a warped metering block. The blocks warp for a couple of reasons. The bowl screws were over tightened on assembly, the block screws under tightened, or the bowls were removed and reinstalled over the service life of the carbs without replacing all the gaskets and tightening to spec.
Steve

Steve-----


Warped metering blocks are not unusual on these Holley carbs. Just another "foible" of Holley carbs. It's bad enough having one on an engine let alone three. It's another reason that Rochester Q-Jets are a MUCH better choice for street operation.

For example, the only difference between an L-36 and L-68 is the induction system and, reportedly, 10 horsepower. All the 3X2 set-up provides is a bit of "cachet". It's definitely not worth the problems.

[Steve G.]

Re: '69 427 "Starter kick back"

Steve-----


Warped metering blocks are not unusual on these Holley carbs. Just another "foible" of Holley carbs. It's bad enough having one on an engine let alone three. It's another reason that Rochester Q-Jets are a MUCH better choice for street operation.

For example, the only difference between an L-36 and L-68 is the induction system and, reportedly, 10 horsepower. All the 3X2 set-up provides is a bit of "cachet". It's definitely not worth the problems.

Joe,
I agree fully. In fact I'll go one further. All this hype about what carb performs better is just that, hype. All that really matters is how much air it flows. You can adjust any one of them to mix the desired amount of fuel into the air, the limiting factor is how much air.

Yes, the warped blocks is not uncommon to the Holley's. My belief is that is because they made it too easy for the weekend warrior to take the bowls off and fiddle with things. I remember it from back in the day when everyone sported a 3310. Every Sat afternoon they pulled the bowls off and tried another set of jets. Or just took it off to have a look see. Even if they didn't over tighten the bowl screws and used a new bowl gasket )almost never), they never replaced the block to body gaskets. In short order the perimeter of the block gasket is compressed and the inside portion is unchanged. So the block warps.

If you had a straight block, installed (torqued) it properly and left it alone this wouldn't happen. And if you had to remove the bowl, remove the block, replace all the gaskets, you would have a reliable carb.

And if maintaining the originality is important, that's what I would do.

Steve