Ok, bad day! Went for a drive and was heading home when I noticed a mis in the engine. I was less than a mile away and limped home. No smoke, no oil consumption issues, just a miss. The idle was choppy and sounded "wrong" on the drivers side. So I pull it into the garage and start checking things. I pulled the plugs to see if any looked suspicious, they looked fine and normal. I ran a compression check, and all were close save for #1 with only 75psi The rest were between 155-165. I remove the power steering bracket and pulled the drivers side valve cover, and after close inspection, I have a broken valve spring on the exhaust valve in the #1 cylinder. I scoped the piston, and it looks fine best I can tell. It broke near the bottom of the spring. The engine has never been apart (as far as I know) and original with just over 40K miles on it. The springs look like they have a gold paint mark on them, I assume that's to identify the spring rates? I'm a decent mechanic but not very experienced with the valve train and would like to hear some opinions on how to attack tis if you've had a similar issue.

Can I replace the spring and move on? Where do I get one, or a set? I read you can compress the cylinder with air or possibly stuff it with cotton role and hand crank the piston up to hold it? I don't have a spring compressor so I'd need to get one.

Note - I see no oil in the antifreeze (or visa versa). It was about 70d here today and the car was running cool. I don't beat on it but had given her a good rip in first and second gear not long before the mis started.

Please help!

 

Use rope to hold the valves up. I have done the compressed air method, it obviously works, but working around the air hose is a added hassle. Not to mention the possibility of a broken air line, power outage, etc.

You could probably get away with replacing one spring, but they are all old and equally worn. Do you want to roll the dice on replacing one and having to open up the engine again to replace another?

 

Consider replacing only the broken spring first and checking the compression on that cylinder, if it is good replace the rest. If it isn't good put air in the cylinder and figure out where the leak is at valves, and/or rings.

Good luck!!!

 

M,
Your machine shop should be able to get you a spring. Unless you are ABSOLUTELY certain that the springs are original what I would do is take a good one off first and let your machine shop measure it to make sure you get the same replacement. Its a simple procedure. I would just replace the one for now. Its not all that uncommon to just have one break and all of the others last forever.

 

Thanks to everyone for the ideas, Sugar Bear, that's a really good point. No point in moving on if I don't get good compression after replacing the single spring.

I should have said also, "at some point" I was going to pull the motor and go through it, just for ages sake. I'm going to try just the one, once I figure out what to get, and recheck the compression. I do still have 75 psi and I can see the spring is broken just up off the first coil.

 

Lots of good advice !!!! I am of the belief that you should replace all the valve springs. While no more might break, they could be fatigued and weak. Replace them and reduce the chance of valve float if you want to hammer it in 1st and 2nd.
Changing valve springs without pulling the heads will be cumbersome and time consuming. But you won't create a problem with possible leaks and sealing.
.......Just my two cents worth.

 

I overhauled my 350 shortly after getting my 71 in 1997 or so. I had the heads done at a local machine shop, reusing original valves and springs, etc. I guess it was about 2015 and maybe 40,000 miles later, we drove car about 150 miles away on a cruise and it started missing like you noticed. I had no idea what it was, but drove car back home. I was super lucky as a valve spring had broken and wrapped around it self allowing valve to just bounce around. I shouldn't have drove it like that for 150 miles! But I was lucky. If keeper had let loose then valve would have fallen into cylinder destroying piston and maybe head and maybe even block, connecting rod, crank, Coulda been a huge catastrophe! So I pulled heads and had them redone and made sure it had all new springs that time. I would recommend you do the same. You and I both dodged a bullet but keep in mind how old those springs are and what a problem you could have if a valve kisses the piston!!