My relatively stock 354 is giving me grief. I got a little problem with #2 intake valve. Not once, but twice the valve has sheared at the keeper. Both times at idle. (So my luck isn't all bad) ! The last time, let's call it yesterday, the top of the stem broke but the keeper stayed put. Not so much the valve. It buried itself in the top of the piston. Engine was assembled by reputable builder, as was the repaired head. Before strike 3, am I missing something?? Any systemic problem? Any tips, tricks suggestions happily considered!
Jesus! Have you been lucky!Check your spring travel! If your actual spring travel from installed height to coil bind is not at least actual valve lift +.060" (and better .080-.100") you are going to break valve train parts.I have seen this sort of thing happen with rebuilds when for instance seats are replaced and the mechanic did not check for stem protrusion,or when an oversize head valve is installed and no one checked stem protrusion ,or when 1 spring or retainer or pair of keepers was not the right one etc.Check installed spring height-The distance from the top of the lower spring seat(where the spring sits on the head)to the bottom of the upper spring retainer.Use a "try spring" for this(light spring that will hold the valve up).If for example your installed height is ,say 1.500" and your spring coil binds at 1.00" your spring travel is .500" and your minimum working height is about .440".That means a . 500" lift cam wont wont work!! To establish coil bind height put the spring(s) inner,outer etc- in your bench vise,put a piece of note paper in the coils,close the vice until the paper cannot be pulled out and measure the spring height with a dial caliper.That is your coil bind height.Since you have had the same failure twice I would be looking real hard at the installed height,spring travel,valve stem protrusion,valve head size,keeper and upper retainer etc on that valve.If this doesnt make sense say so and I will post pictures to walk you through the process.
Certainly that.Since you said "profile" are you thinking of rate of lift rather than distance?I suspect that since there is a problem twice with the same valve it was due to an oversight on the mechanics part ,but you would be much more familiar with this engine than I am.I was just working on the idea that until you have established spring travel and valve travel you aint got nowhere to stand so you can jump
no, distance, as you discuss, and then pondering some of the possibilities...lots of random thoughts go through my brain.... As with the issues you mention, I wonder about what cam has been stuffed into that "relatively stock 354" and then that circles back to the spring install, etc......just random thoughts....nothing specific until more is known. .
That is the whole problem with long distance diagnostic attempts. gbgh we REALLY need to know whose cam you are using and we need some pictures of both the broken and unbroken parts.and good close ups of the top of the cylinder head(valve side).
Might be worth checking the valve timing on just that lobe. I know on my engine I only have about six thousands of an inch clearance between the inlet valve and the piston. I'm interested in the fact that both times it went at idle it might be that at low rpm with lower oil pressure in the rod / main bearings and perhaps a little timing chain flutter you get valve to piston contact. I would have thought that coil bind on the spring would have bent / broken a rocker rather than broken the valve. Another thought. As the spring broke at the top is the rocker setup somehow generating an excessive side load on the valve? P
I have seen that type of failure occur for a number of reasons.the upper retainer hit the top of the valve guide,the spring coil bound,the stem protrusion was so excessive that the rocker arm was actually hitting the edge of the upper retainer just before it started to open the valve,the wrong valve keepers were installed,IME those are the common ones.Why at idle? see the second sentence in my first post in this thread.A lot of them do NOT fail at idle and that is pretty high on the list of the worst things that can ever go wrong in an engine ! I just wish the OP would post some pics.In most engines you want to have about .060"-.080" minimum piston to valve clearance intake\exh and .080"-.100" is safer.As to why it didnt bend the pushrod,I dont know,sometimes it does.
Should have posted these with my original question. Notes are a bit redundant. The Head of the Valve stem is still in place. Guide didn't do so well, Broken valve head punctured the piston, but did not damage the cylinder wall. The OEM non adjustable pushrod was NOT bent, nor did the rocker arm appear to be damaged. I'm inclined to come down on the side of Valve spring travel, or similar. One reason is, we originally assumed it was a valve defect (Fresh Motor and all that). , and while we replaced ONLY the broken unit, used the same springs. I am embarrassed to say, i do not know the cam specs. [long story] but I'm gonna find out Luckily there was Zero damage to the connecting Rod and cylinder Bore. Thanks for your help
Could the guide be causing a problem, being too tight? Looks like part of it stuck to the valve on your arrow with exclamation marks.
If you need to know your actual valve lift and dont have the cam info try this-Rotate the engine until the lifter for the problem cylinder is as far down in the bore as it will go,rig your dial indicator so that it registers on the lifter and preload it slightly,set dial to zero,rotate the engine and measure how far the lifter comes up in the bore.That is cam lift,now add in your rocker arm ratio and that is your valve lift.IE-lift at cam =.200" rocker arm ratio = 1.5 to one-actual valve lift=.300". I do not know the RA ratio on your engine,but I am sure 73RR does.
And there lies another problem, let us suppose that the RA ratio is not stock (I am not sure that you can buy altered ratio rockers but let us suppose) Now the geometry is screwed up. Putting things in a bind, or maybe a bent pushrod is not letting the valve close and the piston smacks the valve or the wrong pushrod, too long, too short, too big around (about as likely as an altered ration rocker). Or perhaps the wrong spring got installed and is being installed in the same place when repairs are made, it would not be the first time that a mechanic/machinist picked up the wrong spring by accident. All of this is just food for thought and not to discount in anyway something that has already been posted.
All of the EarlyHemi rockers are 1.5...well they are supposed to be. We have found some very minor variation over the years but it is safe to assume 1.5. Looking at the photos I see part of a guide and I see double springs... Is the guide firmly stuck on the stem? Some folks set up an EarlyHemi as if it were a brand-x engine thinking that there is massive amounts of oil flying around. Bad assumption. It is actually easy to seize a valve with too little stem clearance because there is too little lubricant. Double springs. They should be tested to see what they are. It could be that if the spring is some monster and there was a flaw in the valve stem then the tip separated. Add in any additional problems like the retainer contacting the under side of the rocker arm and disaster follows. .
Valve comes apart at the keeper groove?? And always in the same cylinder. Thats a rather odd failure...How much other damage was there the first time? It seems like thats the initial failure that starts the bad stuff happening? Thats an odd one.
Yeah, there's a some sense to this. The machinist did a straight swap, good possiblity the original problem wasn't addressed!
Yeah, there's a some sense to this. The machinist did a straight swap, good possiblity the original problem wasn't addressed!
How well do the keepers fit the grooves in the valves? Do they fit tight, or is there any room for them to move up and down in the groove? Do the keepers fit the retainers properly? Still, its very odd to see a failure like this at idle speeds, VERY odd. Had the engine been run at higher speeds prior to the failures, or was this occurring on first fire-up? Beautiful car by the way, i bought that issue of Canadian Rodder just to see it.
No, it ran fine on startup, has never been run hard. Re: Double Valve springs, they were in the motor when I bought it. A 500 hr Industrial motor that (to my knowledge) had never been opened up until the rebuild. Thanks, by the way, overall it turned out pretty good!
I guess if the retainer hit the top of the guide, the valve could shear at the bottom of the keeper groove?? I dont think spring stack-up would cause it, more likely bend the pushrod or break the rocker...puzzling.
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