Alex.Sciortino
Active Member
I think you may be the winner. I just pulled the valve covers and I punched through the number 3 exhaust rocker.
Help with Backfire
- Thread starter Alex.Sciortino
- Start date
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diymirage
HP@idle > hondaHP@redline
betcha your excited to find something so little be the problem
im sure someone will have one in the mail to you before the night is over
Inertia
Well-Known Member
Nope, this time you won. I'm experienced, lol, used to carry a coupla spare rockers in the glove box, right beside the spare ballast resistor. cheers.
Alex.Sciortino
Active Member
Well, now I've got a new problem. I got a new set of rockers at the junkyard, pull the old ones off, and the exhaust valve right next to it is broken off. half the stem is still in the retainer, and the other is in the head. I tried moving it and it is real right. The machine shop just went through these, so I'm not sure what the issue is, but there has to be something. I
Inertia
Well-Known Member
Well mine never did that ! If a machine shop did the heads, I suggest you call them, explain the situation, and ask what they would like you to do. I have my opinion of what should happen, I hope they have the same.
nm9stheham
Well-Known Member
If it gets any fresh charge in, it can still fire back up into the intake. It does not need compression to fire.... like fuel out of the exhaust firing off and ignition timing being wildly off and back-firing up the carb while the intake is still trying closing.
But it seems like the OP found it...on the exhaust side so someone gets a prize! That is good.
nm9stheham
Well-Known Member
New, heavier valve springs perhaps? That would stress any old parts in the system... valves, rockers, pushrods.
Valve broke, dropped into cylinder, hit piston, bent and jammed in guide is what comes to mind. If the valve is tight, then the head needs to come off.
Time to pull all the pushrods and roll them on a flat surface to check for straightness.
How much were the heads milled?
Inertia
Well-Known Member
I'm not sure that would explain the pushrod thru the rocker ? Perhaps tight guide caused valve to stick.? just musing here.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Well then you better check your lifter preload, and pushrod length.
tight tolerance guide and not enough timing on break in probably caused the valve to stick.
Inertia
Well-Known Member
Alex, is there any damage, or "witness" marks on the top of the valve guide boss? Any indication that the piece of valve inside of the spring was banging on the top of the guide? That might push a pushrod thru a rocker.
Hopefully the valve did not stick open for any length of time and make contact with a piston. Still though, the head will have to come off so there's that.
Also, IMHO, I would not "just remove" one head. If their "opinion" of guide clearance was tight on one guide, you have 15 more. I would make them redo both heads. Hopefully the rest of the engine is OK.
Also, IMHO, I would not "just remove" one head. If their "opinion" of guide clearance was tight on one guide, you have 15 more. I would make them redo both heads. Hopefully the rest of the engine is OK.
I have never had this happen. What is the root cause of this?
nm9stheham
Well-Known Member
Anything that can put more stress on the pocket in the rocker:
- Stiff springs and high lifts
- Stuck valves (for a wide variety of reasons; I had some old bad gas at start up of an engine and an intake valve stuck due the gum in the old gas and did in a rocker)
- Over revving and valve float (lifters pump out; valetrain overextended)
- Old worn rocker pockets
- Defective rockers
- Stiff springs and high lifts
- Stuck valves (for a wide variety of reasons; I had some old bad gas at start up of an engine and an intake valve stuck due the gum in the old gas and did in a rocker)
- Over revving and valve float (lifters pump out; valetrain overextended)
- Old worn rocker pockets
- Defective rockers
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
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Add
coilbind, and
insufficient retainer to guide clearance,and
Too long pushrods with insufficient spring pressure.
coilbind, and
insufficient retainer to guide clearance,and
Too long pushrods with insufficient spring pressure.
Stock rocker failure at the pushrod cup is a very common occurrence on Mopars as spring pressure goes up. Mopar Performance (RIP) used to make a set of HP stock replacement rockers for both big and small blocks that were a lot thicker and beefier. Used to.
moparownr
Well-Known Member
Had this happen to a 318 that my friend and I just built. Once you have your heads back, strongly recommend push rod length tool to verify push rod length needed, as there are more than one length offered....
Alex.Sciortino
Active Member
None that I can see. Although the one with the broken rocker, and the broken valve are two different valves.
Alex.Sciortino
Active Member
I'm gonna pull both heads on Sunday hopefully.
Alex.Sciortino
Active Member
.020 were milled off the heads. I did install new valve springs.
nm9stheham
Well-Known Member
OK, I'd guess you used the Hughes 1110 springs. That pushing close to 2 times the open valve spring pressure with that cam's lift. And the peak valve lift is high enough to push the retainers into or very close to the stock valve guide tops. You have enough spring pressure and valve lift now that you can't be causal about this and take anything for granted.
The milling will drop the rocker cups down towards the lifter and take away some of the range of adjustment of the lifter's piston. (Depends on the head gasket too.) And with valve work, the valves may be set deeper in the heads and that will also rotate the pushrod cups towards the lifters and take away more of the range of adjustment in the lifter (if the builder did not 'tip' the valves to shorten them). Eventually, you can run out of adjustment range in the lifter; then the valve cannot close. That by itself would not push the pushrod through the cup and since you engine ran OK initially, that does not seem to be the issue. But all that possible stack-up of things shortening the pushrod area ought to be checked out, as has been said.
You may just have had 2 issues:
- A weak pocket broke out with the heavier springs, and/or hitting the ratainer on the guide.
- A valve seized in the guide, or a weak valve stem gave way with the higher spring pressures
Inertia
Well-Known Member
Oh, I missed that, thnx
Alex.Sciortino
Active Member
I got the engine out and apart today. I have 7 bent exhaust pushrods, and 1 bent intake. The valve that broke hit a piston. Attached is a picture. Can I get away with running this piston?
From what I can see from this vantage point, I would say yes, you can run it. Why the bent pushrods?
Alex.Sciortino
Active Member
That's a great question, I just got off the phone with Hughes and their tech guy said the only thing he could think of is the retainers were too thick. I just don't see how that would tie into the broken valve. I suppose they could be two isolated issues as well.
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