Daren Don who ever else might know?? Push rod breakage

[ALKYBURNER]

We have two blown alcohol buick headed engines that have aluminum blocks 8-71 ssi super chargers msd 44 amp mags and have had a problem with one of them breaking the lash caps or for a better term shattering them and one time the engine free wheeled only one of the four tires was on the ground and the enigine detonated and poped the burst panel. Getting home we found that the pushrods and lifters for the 6 5 7 2 cylinders were bent and then broke in different places and that 4 of the jesel lifters and come up out of the bores. Also looked like 4 pushrods had come in contact with the sides of there rocker arms and gouged them up. Motor never hit the rev chip of 9800 and valves never touched a piston. This same engine also had a hard time to keep from burning through the head surface or the head studs,never burned the gaskets though this might have been detonation. It had a 113 286/ 290 @ .50 set in at 106 and these numbers were for an .842 lifter but plans changed mid stream and used same cam for the .904 lifters cam grinder said it would only change 1-2 degrees does any one know how much this would actually affect the cam numbers. The problem kind of went away by backing the cam to 109 instead of the 106. Some engine builders thought it was that the intake valve was opening at 35 degrees with the .842 lifter and that it would be around 40 with the .904 lifter but I'm not sure the 40 is correct. Been told that the lifter change was good for 4-5 degrees and thats why the engine would not turn up because of the extra overlap it created.Any help would be great full . This board is great and I personnally have learned a lot from all of you on here. Thanks Alkyburner

[Guest]

I would be looking into 2 possibilities.The lifters coming out and the misfire would be understandable with a pushrod failure.The lash cap shattering is a result of the valve clearance opening up too much from the growth of the alum. heads and block,which would also contribute to the burning into the headbolt hole and such.It could be as easy as allowing for more groth by setting the valve clearance much tighter.Here's where the second avenue comes in.At the rpm's you are turning the blower could be producing so much boost which would generate so much cylinder pressure the head studs simply cannot keep the heads down.The studs will stretch.Try changing the pulleys to tame down the supercharger if the lash does not completely fix it. You may need to heat the eng. up and check the lash to see how much it grows and then deduct a few more for distortion.

[autorace]

What pushrods, diameter and wall thickness, and spring pressures?
What overdrive?
What ign. timing?
What port/hat nozzles, pump and flow rates, and bypasses?

Sounds to me like major detonation, and the cam seems a bit strange for the application and might be adding to the problem. I would think more exhaust duration and cam not so far advanced. I don't think the exhaust can keep up with the intake. You should datalog with a wideband after changing the cam. Has the motors ever made good passes before with that combination? What type of racing 1/8 or 1/4 and what type and weight of car?

[ALKYBURNER]

Both motors are the same except for the cam the blowers are restricted to a 10 percent overdrive limit as for the pump its an enderle 110 brand new was on the high side like 14.2 gals. per minute at 4000 rpm pump speed pushrods are 3/8 .080 wall springs are 385 at 2.100 and 1150 over the nose the first never layed down just stayed upstairs so we tryed more cam in the new motor but I beleive it was to much after changing to the bigger lifter as well just compounded the problem, I think the bigger lifter also changed the seat to seat timming and the over all duartions my guess it changed the timing events 5-6 degrees does any one know the real amount that a .904 jesel with the .785 wheel compared to the crower .842 lifter. As for the nozzels and pill size it was getting about 10.5 gals per minute and using it. It is in a pulling tractor 1850 pounds.

[bill jones]

-I'm not really an expert on this but two things that bother me is the little pogo sticks for pushrods, and I pretty well believe that the intake spring pressures need to be increased to compensate for the blower PSI acting against the square inch area of the intake valve.
-like if you have a 2.200" intake valve there is about 2.100" exposed to the blower boost when the valve is closed.
-That is something like 3.46 square inch area that if it's seeing an easy 20 pounds of boost that's 69 pounds of the original intake valve come closed and/or stay closed.
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-In case you don't believe it just pressure test the intake port and see how air pressure it takes to make the valve pop open.
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-You are using the same spring pressures as common stuff I see for big chief heads and low .800's for valve lift for normally aspirated
-We use the the biggest clubs we can get in there for pushrods which usually are something like 1/2" single tapered to 7/16", sometimes a dual taper and they start at something like .120" wall.
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-Who does the engine assembly?
-why not just measure the tappet duration at various lift points between the two lifter wheel diameters and see what it does to you and then you'll know what's going on.
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-Since my first serious race engine I have always measured the durations in .050" increments and the raceready valve lift in .100" increments so if you went thru those processes you'd start to open up an entire new dimension of the engine.
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-I assume that you haved checked the valve adjustment hot because I see engines that the valve lash loosens up more than they are supposed to be set at, meaning we may set the lash at .002" or so cold and they might end up about .024" to .026" when the engine gets hot.
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-I haven't seen it myself but other guys have told me that they have to adjust valves just to get the engine started and then readjust after the engine is hot.
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-So if you aren't paying attention to what the valve lash ends up being immediately after a run when it's so damn hot you don't want to get in there, maybe you need to get in there and get burned and find out for sure.
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-If you are running Jesel or other rubber timing belts that's an entire other ordeal that you thave to cosy with what the belt stretch does to you.

[ALKYBURNER]

Iwould agree you bill on the valve springs and how blower boost could actually hold the valve open but in this case they are fine and I knew that concept when building these motors. I assemble them and I would also agree about the valve lash except for the fact that it is only one cylinder breaking the lash cap on the number 7 exhuast valve. We run the shaver wesmar gear drives and have very great success with them. I think the springs are more than enough for these motors its the same spring preasure used with most alcohol big chief and kb hemis so I have already thrown that out and for the pushrods they should be allright but may deflect some going to the 7/16 this season but one motor is fine and the one with the bigger cam is the only one act up and have these problems so I would have to think that it is the cam not these others peices that you brought up, I had already thought of most of those and accessed them. I do want to thank all of you for giving me your ideas as to why these problems occurred is there any one on here that builds or runs blown alcohol motors. Thank you all for the information and ideas that come up in all post have learned a great deal already and look forward to learning more on here DARRIN