348 valve spring symtom

[59fins]

The other day I was driving my 59, it has the 348 250hp, I all of a sudden noticed the shifter handle shaking, and the car was not running smooth, the l exhaust bank is a making a missing noise, I noticed that a plug wire had come off, so I re attached it and really did not notice a big differance.
I am not sure why, but 8-9 years ago I had a vave spring break, and seems to me this was the symtom, (I surrer from CRS... Can't Remember Sh*t)
I am not much of a motor mechanic, body is my thing, I had the motor rebuilt 2 years ago, put it in my self along with the rebuilding of the rest of the car, I have approx 250 miles on the car and motor, asking for guidance, I know if it is a spring it can be done in the car, but what else should I look for or do outside of checking plug wires connection?, I do have pertronix, and everything is new or rebuilt.

 

[bobs409]

I would start by pullling the plugs to see that they are clean and look like they are firing.

Also, make sure your choke is opening all the way.

 

[JimKwiatkowski]

If all the plugs check out and choke pull your valve covers and ck your valve adjustment and check for broken or worn rocker arms.

 

[Ed51]

You might want to do a compression test,then you can narrow it down to which cylinder has the problem.

 

[63z11]

valve spring on-car

59 fins, the other gentlemen made some nice suggestions on other things to check. It is possible to change a spring(s) in the car if necessary. You will need a few special tools however. With the rocker arms removed, you use an adaptor to hook a air hose to the spark plug hole. The compressed air will hold the valves in place while you remove the valve springs. I believe K-D tools makes both the plug hole adaptor and a lever type valve spring compressor that works on-car.
good luck Eric

 

[59elcooldsuv]

I'm still trying to figure out how a broken valve spring can cause the plug wire to come off.

Didn't he say that replacing the pug wire fixed the rough running? If that's so, why assume that a valve spring is broken?

Worse case; a few feet of nylon rope can be fed into the sparken-pluggen hole and the crank rotated so the piston pushes the rope up against the valves. I've never tried the compressed air trick, but have always wondered why the air didn't just escape around the rings.

BTW: got my freeze plugs installed this weekend, finished fabricating an adaptor plate to install a Holley on the 348's manifold & cleaned an old alum sign & made it into a heat shield.
Put the short block on it's "crate" engine stand http://www.geocities.com/rscott77070/enginestand.html
and put the ironglide on the store-bought engine stand so I could roll it over, measure exactly where it's mount pad is realtive to the bellhousing and tailshaft, and draw a representation into my autocad layout of a T-Bucket frame/chassis.
After spending all day Sat in the garage I rested my legs on Sunday by sitting in front of the computer & making autocad solid models of the parts for a torsion bar suspension to fit a T-Bucket. All in all, somewhat productive for a weekend with no money to spend.

 

[Ed51]

I like the nylon rope trick better than the compressed air because if for some strange reason the air supply gets cut off (for whatever reason) your valves could drop into the cylinder,especially if you don't have it at the top of the stroke.

 

[59fins]

I said that the putting the plug wire back on did not sem to help much, the rocking of the engine or, vibration of the engine IMHO shook the wire off, I am going by long ago past experience (I think : )

What is the deal with the rope?, never heard that one, I think I will pull the left valve cover off (hopefully tonight) of course the kickdown linkage and power brakes and generator are on this side, if I find the problem, I will let you know, If I do not find the problem I will ask for further assistance.

motor mechanical work again is not my thing

 

[59elcooldsuv]

What is the deal with the rope?, never heard that one,

Pull the S-plug from the cylinder that you need to work on. Use nylon rope so it won't shed fibers in your cylinder. Turn the engine over by hand until the piston's somewhere down in the cylinder. Stuff the end of the rope into the spark plug hole until it won't go anymore or you have a foot or two hanging out to pull it out by.

Turn the engine by hand so the piston comes up the cylinder and compresses the rope. It will hold the valves up onto their seats while you remove the valve keepers, cap & spring.

Of course, that's assuming you have a valve spring compressor that works on the outside. If you have the C-clamp style, you can't do it this way. You need the one that pivots on the rocker stud.

 

[59fins]

well I found the culprit, the very front outer spring on #1 cylinder is broken, just like 9 years ago or so, ( except this time it is a diff cyl )
question now is, I assume this is an exhaust valve, will any spring from a 250 hp head work or is the exhaust valve and the intake valve springs different?
I have a few of these heads lying around so it should be an easy fix, spoke with a friend tonite, he has the proper tool for changing the spring in the car, hope this does not happen again soon.

 

[dq409]

I`d say it`s time to buy a new set of springs ! Old used springs can be weak and tired. Why take the risk of doing it again?,,,,dq

 

[Ed51]

DQ is right,change all 16 springs,I just did this on a 350 a couple of days ago and all the springs were 41 bucks at NAPA. It's CHEAP insurance.

 

[59elcooldsuv]

Any truth to the rumor that plain, ordinary Chevy small block springs are the right one's?

I was pleasantly surprised to learn that I could get a brand new oil pump for only $15 - thanks to interchangability and the proliferation of aftermarket CSB parts.