Broke a BB Valve Spring Today

[Peter M.]

Took the 66 427/425 for a ride today - 15 miles from home #1 cylinder exhaust valve spring broke. I limped home keeping RPM under 2 grand and seemed to make it with no problem. Can I drive another 20 miles to my mechanic or should I flatbed it? I certainly do not want to put the valve into the piston

[William C.]

Re: Broke a BB Valve Spring Today

If it were mine, I'd pay for the flatbed.

[Mike McKown]

Re: Broke a BB Valve Spring Today

You're playing with fire if you drive it.

[Mike M.]

Re: Broke a BB Valve Spring Today

remove intake and head and do it yourseld. its not that difficult. mike

[David D.]

Re: Broke a BB Valve Spring Today

Peter, A question for you. If one valve spring broke, what makes you think that the other 15 will not do the same? I would replace ALL THE VALVE SPRINGS. The head DOES NOT have to be removed, IF the valve still SEALS and IS NOT BENT. The whole job can be done with a hand spring compressor tool with just the valve cover and spark plug removed. Dave

[Joe L.]

Re: Broke a BB Valve Spring Today

Peter and Dave----

First of all, I wouldn't recommend driving the car with a broken valve spring, particularly if you have the original engine. The chances are that you'll have no problem but there is a risk that's not really worth taking.

Big blocks of the 60s early 70s period have a propensity for breaking valve springs. They did this even when the cars were new with relatively low mileage on them. My 1968 Chevelle with L-78 broke several of them during the 18 months and 20,000 miles that I put on the car from new. My 1966 Chevelle with L-34 broke several, too. I still have one of the L-78s broken springs.

So, at this point, I too would recommend replacing all of the springs. I wouldn't use stock GM springs, either. I'd go with the highest quality aftermarket springs that I could find with a similar spring rating to the stock ones.

All you need to replace the springs is a compressor, spark plug hole adapter fitting and a lever-type spring removal tool. The latter 2 items are easily and inexpensively purchased from automotive tool sources. No need, at all, to remove the heads. Just removing the valve covers is all that's necessary.

[Dan Pepper]

Had 2 broken exhaust springs for months...

and didn't know it. The car ('66 L36, 53k original miles) developed a noticable miss and lifter clatter on a drive to a regional meet a couple years ago. After popping off the valve cover, the nut on #1 was loose. Felt like I had a bad lifter and/or rocker nut. I readjusted the valve with a new rocker nut and the sound went away. After about 100 miles, I noticed a slight miss that just kept getting more pronounced. I figured it was an ignition system problem since I'd had lots of problems with lectric limited plug wires, and also figured my distributor needed to be rebuilt.

Finally, after going through/rebuilding the ignition system completely to no avial, I took a CLOSE look at the valve springs and found #1 and #4 exhaust springs broken. I probably drove 400 miles on them trying to narrow down the problem. Guess I was just lucky I didn't swallow a valve.

I'd suggest replacing all the springs and seals while you're at it. Took me about 8 hours. You'll need an air compressor to pressurize the cyls. to keep the valves up as you compress the old/new springs and set them in place. The valve spring compressor tool is about $12 at most any auto parts stor. Overall, it's a pretty simple operation. The car runs smooth as silk now

[John L.]

Re: Broke a BB Valve Spring Today

Peter

Sorry to hear about the valve spring. I would also suggest doing it yourself if the valve is not bent. As I remember from past conversations, you are pretty careful about driving this car. I am really curious -- when did it break -- just going down the road etc ?

[Clem Z.]

i had one break driving my new 396 home

from a st louis factory pick up back in 65. i would replace them all with GM 3970627 or the kit of 16 GM# 12371061. i have bought this kit and sometimes it comes with the correct retainers and valves seals and sometimes you have to order 16 GM# 3964264. i would also replace all the valve spring retainer keys with 32 GM# 3947880 as these are heat treated keys and the orignals were not. the heat treated keys are purple in color so all you BBC corvette owner check the color of the valve spring retainer keys in your engine and if they are not purple i would change them. the orignal keys,copper color if i remember correctly, were "soft" and these lead to a lot of "dropped" valves

[G B.]

Hand grenade engines

Back in the sixties, my friends all considered factory 396 engines to have a 50,000 mile life, tops. And we knew the end would not be pretty.

[Michael H.]

Re: i had one break driving my new 396 home

Peter,

I agre 100% with Clem. The original design valve springs for 65-66 were dangerous and I remember a LOT of these breaking on almost new cars at that time. Often, the valve drops down into the cylinder at a time that it shouldn't be there and if the piston happens to come in contact with it, the valve head usually breaks off and that generally leaves nothing but the intake manifold and sometimes one good cylinder head. The rest winds up completely scrap. I wouldn't even start that engine again until all the springs are replaced.

Also, as Clem recommended, the newer GM springs are excellent and will last for many years without problem. I replaced the entire set in my 66 car over 20 years ago and have had zero problems.

Michael

[Verne Frantz]

Re: Broke a BB Valve Spring Today

Peter,
Just my 2 cents of advice from experience. Using the air-pressure-in-the-cylinder method, Make sure you only do one spring at a time, not both valves on one cylinder. Most times, the retainers are stuck to the keepers and require a little tapping with a small hammer to break them loose. If you remove the spring from one valve, then pull on the compressor tool on the other, you will very likely overcome the air pressure and open the valve. Now all the air pressure is gone that's holding up the other valve and it drops into the cylinder.
That's when you have to remove the head!
Verne

[Peter M.]

Re: When It Broke

John
Reference your question "I am really curious -- when did it break -- just going down the road etc?"

Answer - I had just come off the parkway cruising at 60MPH. My normal shift point is around 3500. (I do bring it up to 5500 on occasion) Anyway - it broke at idle! I was waiting for a light to change and all of a sudden I heard a metallic clicking sound - like a loose rocker and the left sidepipe sounded different. I pulled over - pulled the drivers side valve cover and expected a loose rocker but found the broken spring. It did not break in pieces - just a broken coil on the outside spring

[Peter M.]

Thanks All - I Will Not Drive It ! *NM*

[Joe L.]

Re: Broke a BB Valve Spring Today

Verne-----

When replacing the valve springs with the heads on the engine and using air pressure to hold up the valves, it's always best to rotate the piston on the cylinder you're working on to the "TDC" position. Among other things, this prevents the valve from dropping into the cylinder if air pressure is lost for any reason. It's a little more trouble, but it's worth it for the "insurance". You only have to rotate the engine 4 times since there are 2 cylinders at "TDC" for each 90 degrees of crankshaft rotation. Simply mark the balancer at 90 degrees, 180 degrees, and 270 degrees relative to the timing groove and use these as the points to set the engine to work on each pair of cylinders.