kdgreen

My New Engine Just started missing like crazy. (350 .030 over) I checked all wires/distributor/carb/etc. Did a compression check and number 5 was down. Pulled valve cover and found broke spring, bent puchrod, bent valve. Pulled head and piston is cracked where valve smacked it. The head was new, timing was dead on, everything adjusted and she was running great-till this. What happened?

kdgreen

Pic 2-Parts

RB83L69

Stock springs?

Did you save money by re-using them?

atc3434

iTrader: (4)

OUchy! Looks like you can probably blame that valve spring.

kdgreen

No I did not use stock valve springs. I purchased the cam kit.
Comp kit.

RB83L69

What cam kit? What was the installed height of the springs?

There's nothing there that looks like it would have caused the spring to fail, unless it's being used with 1.6 rockers and that lift was too much for the spring, or if that one's spring pocket isn't as dep as the rest, or something like that, that would have overstressed the spring.

Is that a Comp intake valve?

KC10Chief

I'd say that from the looks of it, your valve spring broke first, didn't let the valve close all the way, and the piston slammed the hell out of it on the up stroke. You can see where it hit the valve in your first photo. That really sucks. Probably made the rocker arm loose and it bent the pushrod that way too. I've never seen that before. If you had your valves adjusted right and that's a new spring, I'd be pissed! Did it do any damage to your head? At any rate, I'd say you have a piston change in your future if not having to buy a new head as well. Matt

kdgreen

My machine shop said the head was ok. They just called. I am going to pull the motor, replace the piston and rod for safety sake, and put it back together. I had the valves adjusted 2 times just to be sure so I know it was right. I think project camaro Just became project put together and sell. I spent $3000 on this motor not to count the car so this really has been a pocket depening learning experience.

:rockon:

KC10Chief

Don't sell it! It was just a freak thing. I'm not sure if you need to pull the motor to replace your piston. You definately need to do that though. You don't want to drive with a cracked piston. On some cars, you can replace a piston and rod without pulling the engine, but if you're proficent at pulling the engine, it would be a lot easier. Matt

kdgreen

Yeah I guess your right. I am very good at pulling this thing now. I pulled the factory 305 (269000 and still running in my brothers truck) and put this one in. I should probably pull it anyways because I have a small oil drip around the rear seal and should just fix that and this all at the same time. I just ordered new piston,rod. She should be running by first of next week.

dimented24x7

iTrader: (2)

Is that one of those comp cams k kit that your refering to? I was thinking of getting one myself but now im not so sure.

kdgreen

Yep- It was Comp Cams K12-246-3
1800 to 6000 rpm xe274h
Duration-Advertised 274in/286ex @.050 230in/236ex
Valve Lift with 1.5 rocker- .487in/.490ex
Lobe separation angle -110 degrees

Description- Hydrauli Very Strong Mid Range, Torque,throttle response, 2200+ stall.

I don't know what happened. I hope it was the spring honestly. At least that is what I want to believe.

RB83L69

I've used that cam, in a 400.... ran like a bat out of hell.... I rather liked it. People who heard the motor described it as sounding "angry", like it wanted to jump up out of there and kill something. It was mean. I'd use it again in a heartbeat, in the right build-up.

What rockers? Those are 981 springs then, right? Do you know the actual, as-assembled, installed height?

With the cam already that close to the hairy edge of the springs' ratings anyway, even the slightest error or tolerance in the heads's setup will tip them over.... you should give serious consideration to machining the heads for 986 springs (1.45" outer dia) which are good to near .550" lift. That way, if a gnat's hair gets between the head casting and the bottom of the spring, you're not into the spring destruction range of lift.

kdgreen

I don't know the installed height, but we did check to see if they were bottoming out and they were not. They weren't even close as far as my eye(the one that didn't see the crack in the piston untill I blew up the picture I might add) could tell. I am using the stock vortec rockers.

RB83L69

Are these Vortec heads? Have the guides been cut down? Any other machine been done on them?

The way springs work, they can be in serious distress well before they reach coil bind... their force is linear only up to a point, after which it begins to rise rapidly; and as the restore force rises, so does the spring's temperature; and that's what really kills them. Try bending a coat hanger back and forth until it bends, then immediatey touch the ends, and when you get through cursing the day I was born for burning the snot out of yourself, you will understand better what it's like to be a valve spring.

I would suspect that you have one spring pocket that's slightly shallower than the others. Factory machine work on that part of the head isn't particularly precise. Less than .030" of error, not visibele to the naked eye particularly, could have meant the difference between survival and rapid demise; if the shop checked some other spring, or even several others, and then set them all up the same, rather than checking every single spring individually (not common practice for a street build by any means) it could easily have been overlooked.

You should check the nose of that cam lobe, and that lifter, very carefully, for pitting or other damage. Also check the top of the valve guide and the bottom of the retainer, make sure there was no interference there. That's about the only other commonly observed problem of that sort with those heads that I know of.

I doubt that there's anything wrong with it that upgrading the valve springs wouldn't take care of, as long as the retainers aren't smashing into the guides (which they should be at that much lift, if in fact those are stock Vortec heads).