Breaking Valve Springs
 

This same gripe came up 2-and-a-half years ago:
'68 L6 292 -- Burnt Valve, Brkn Rings?
http://www.67-72chevytrucks.com/vboa...d.php?t=636925

Same truck, same signs and symptoms, different cylinder.
Subject is a 292 L6 in a '68 C/10 Stepside, rebuilt in 2005, under 40,000 SMOH. Engine is original to the truck, but rebuilt after being stored 25 years.

Last time after some diagnosis, we found a broken exhaust spring on Cyl #4. This time the Vacuum gauge is reading about the same [9.5" Hg w/slight bounce] where 17"Hg Steady would be the nominal indication at operating temp. RPMs also dropped. Basically, it's a 5 cylinder.

I ran a Dry Compression Check:
1] 0
2] 136
3] 135
4] 145
5] 128
6] 130

I did not run a Wet check since I found the source in Cylinder #1. Cylinder #4 only looks good since that was the one replaced in July 2014.

One broken spring is a fluke. More broken springs is an alarming trend. This time I will replace all the valve springs and set valves again.

Plug from #1 was smudgy, all others had normal ash.

New springs are on order. Also need to get valvespring compression tool = modified wonderbar. And fresh rubber umbrella seals.

Question is What causes valvesprings to break? This never used to happen in my other Chevy engines, either L6 or V8.
:chevy:

Re: Breaking Valve Springs
 

Was there a mix and match of internal engine parts in this rebuild?? Harmonics of a poor balance job will cause valve springs to fail. Bought a 350 in a Blazer years ago that 'just had a rebuild' Was fresh but the moron decided a 305 crank was a fit replacement for a 350 (+.040) engine. Was VERU noticable vibration at 2800rpm (cruising speed) and the Z-28 valve springs on the 441 heads would pop about 2 a year RANDOMLY. When I pulled it apart and found the 305 cast crank did some research. Some crank casting #'s are used in both the 05 and 350 BUT The same number and same stroke is all they have in common! The two have just over 100 grams difference in bob- weight in the balance.

I bring that up just in case someone made serious swaps in internals during this rebuild and didnt have the assembly balaced,, it WILL cause harmonics and all sorts of random engine problems.

Re: Breaking Valve Springs
 

Thanks, Marv.
I thought my machinist was meticulous about balance and parts quality. It was about 14-15 years ago.
When the first spring broke, I brought it back to him and he found a like-sized replacement 'good, used' at no charge. We thought it was a fluke at the time. He asked if it was a Z-28 type. I didn't think so only stock. But now reading in Leo Santucci's "Chevy 6 Cylinder Power Manual'' he says ''Z-28 Chevy V8 springs with stock retainers, keepers, and stock length valves can be used on hot street cams up to .480" lift with flat tappet or hydraulic lifters.'' I would have remembered if I had Z-28 springs and even bragged about it if I knew.

Build was a '68 292 block, bored .030 over, with Badger pistons [cast], OEM rods, ARP fasteners, Intake valves are 1.84'' [stock for a V8 307, where 1.6'' is stock fr a 292], Exhaust valves are the stock 1.5". New valve springs [I thought]. Stock 12-lobed '68 292 crank. Crane 260H cam. Rhoads variable lift lifters. Mellling hi-volume oil pump. Centerforce II clutch. He rebalanced the pressure plate. '68 292 11" flywheel. Offy intake, Edelbrock 500 CFM 1404 carb. Clifford headers. Cross-over dual exhaust. Now has HEI. SM465 4 speed, to an Eaton Posi in a 12-Bolt Corp rear.

Talking to one of my local [non-chain] parts guys, he said if one spring goes, they should all get replaced. That's what we'll do once all the parts get in.

Re: Breaking Valve Springs
 

How much lift on the cam? Stock valve springs are only good for .450. After that you have to go a step up. Z/28's are good for .500 and tend to create a little to much open pressure. Those that have used them haven't complained of flat cams that I'm aware of.

Re: Breaking Valve Springs
 

Crane 260H.
From the Cam card -- Lift
Intake at valve=.498"
Exhaust at valve = .530"

Now I'm wondering if I have the wrong value springs on order? I just specified stock 2.1090" free height.

Re: Breaking Valve Springs
 

The Z/28 springs are the same height if I remember right. And never mind, I just looked back at my power manual and it says the z/28 springs are good to .600 lift.

Re: Breaking Valve Springs
 

I'll have to take my broken valve spring into Don's Hot Rod Shop, and ask if it's a Z-28 type.
Didn't think so.

Re: Breaking Valve Springs
 

I doubt it, unless you have something worse going on...I think it's a case of to much lift on stock springs.

Re: Breaking Valve Springs
 

Maybe I should get Z-28 springs then?

Re: Breaking Valve Springs
 

Wouldn't hurt to try, I'd wait for some of the other folks here to chime in and see what they think. I may be over looking something. :chevy:

Re: Breaking Valve Springs
 

I thought I had a weather window Thursday to work on my engine outside. Doesn't look like there's gonna be much good weather until next week.
We'll be getting what just clobbered your area.
I'll have to work an 11 day week starting Saturday, so this project will have some time to collect parts and knowledge yet.

Re: Breaking Valve Springs
 

Yeah, we're getting slammed with rain as I type this. Glad I have my 66's cab under a small car cover and the chassis in the garage.

Re: Breaking Valve Springs
 

Re: Breaking Valve Springs
 

Are you going with Lump Ports?
Well I don't have Mr Lowe's number, but I could post this same query on www.inliners.org I guess.
Larry Page was my mentor on the build-up, back in 2002-05. I should ask him.

Re: Breaking Valve Springs
 

Here's Tom's number 1-319-310-6920.....this is not his business number. His business number is on his sight. Just tell him Thomas Mccauley gave you this number. He may remember me, I talked with him many times and bought a number of parts from him for my 292 as well. We talked so often that he gave me his personal cell. haha He tends to answer that more often....I should give him a call again. Been quite awhile. He does use both numbers for business though.

You could also PM Larry aka Twisted6 on this forum for info. :chevy:

Re: Breaking Valve Springs
 

Thanks, TJ. I picked up a dozen Sealed Power stock springs today. Jay at Don's Hot Rods [our local hi-perf 'candy store'] said the Crane double coil springs specified on my cam card would require machining into the head to fit. No way.
Waiting for parts to arrive timed out my maintenance schedule today.

Re: Breaking Valve Springs
 

Yes its getting ported, the full head deal, started out with .040 over sealed power pistons to rebuild stock and changed my mind so Ive ended up with some internal parts I wont use, learning curve on a six.

Re: Breaking Valve Springs
 

Take the head to a qualified machine shop and get it set up for the cam in the engine. Just shoving a set of springs in it is not going to get you a good setup. Need the installed height checked on the springs and the amount of lift before coil bind. The pressures need checked and the installed height needs to be checked on the head and the head cut or springs shimmed to get it all correct.
Jimmy

Re: Breaking Valve Springs
 

Would I get the same indications from a collapsed lifter? Even Zero compression in #1 cylinder?

PG-- I'm trying to stay out of the machine shop for the present. This isn't a new build, it's been running good for 12 years, now. [Except for breaking a spring in July of 2014]. All that was done when it was first set up. The replacement springs I got are the same kind as the others. The discussion drifted into the possibility of upgrading to Z/28 springs or the double-coil types spec'd on the mfr's cam card. Those would require machining into the head to use. I will have to check installed height.
I think it's early for a rebuild at 40,000 on a 292. My last one ran for 250,000.

Re: Breaking Valve Springs
 

^^ that x100. This is especially important when working with worn valve seats & valves. Think of distances. More to setting up head/s than many consider. A lot to be said for having all 12 springs working at the same pressures. Not only at the valve, the lifter and cam too.

Re: Breaking Valve Springs
 

Fixed.
New valve springs and umbrella shields.
Runs good.

Re: Breaking Valve Springs
 

What springs did you end up going with?

Re: Breaking Valve Springs
 

Sealed Power from the local hot rod shop. Four Bucks apiece [ X 12]. Could'a been cheaper at rockauto, but I like to support my local candy store venders.
Can't access the p/n right now, as the whole rig is at the tire shop as I have an unknwn hardware fastener/s in my Drivers' Side front tire. Also getting rotated.

New springs are kinda crispy. Like an apple. Lots more direct horsepower applied. Some hickups when cold, mostly singular. A fine-tuning will be in order later. Right now, it's tires time. Then brakes.
Wait was so long on an early Monday afternoon, that I walked home. Waiting for a call back from mgr.

OK-- There it is.
Gotta go.

Re: Breaking Valve Springs
 

Sealed Power p/n: SP VS 521 [x 12].
Excellent fit and exact duplicate of other springs. Hopefully not from a brittle batch. Running like a top.

Re: Breaking Valve Springs
 

Sealed Power are good springs. Have rebuilt hundreds with them. Exact same as most other brands just in a different box.

Point to ponder .... how many cycles between open & closed pressures has a set of springs seen? Quite literally millions if the engine has a decent amount of miles. Not saying this is your case. A shame how often they are re-used in rebuilds.