The proper way to figure out what length pushrod yoou need would be to purchase a pushrod length checker (Basically an adjustable length pushrod) from one of the major cam companys. A quick check on summitracing.com shows one from Tric Flow (TFS-9000) for $11.95 that ranges from 6.125" to 7.500". the same unit from Comp Cams (also from Summit, CCA-7905-1) is $16.99. You will, however, need a a fairly accurate dial caliper to accutarely measure the length of the pushrod checker once you figure out the idea pushrod length.

 

Thanks,

I'm thinkingy ou should check pushrod lenght.

 

Blownfuel1 and/or Alvin - How do I find the correct pushrod length using one of those checkers?

I was also thinking of buying this kit so I can degree the cam and then use it for my 396 build.

Thanks again,

Dave

 

I'd like to take credit for this photo but I just Googled for it and added to it. The guy has a great idea for looking at your tip relationship.

Set up one of your valves on the base circle of the cam with zero lash and zero pre load and see if it looks like this picture. You could pre load it just a bit to simulate real world.

I can almost guarantee yours (roller) will be more towards the exhaust side of your tip.

To move the roller more centered on the tip you have to get a shorter pushrod. It almost seems like backwards thinking but it isn't, believe me.

Ideally you want it to start at zero lash more towards the intake side of the valve tip. Error more on that side if you have to.

It may be so far near the exhaust side of the tip it rode over at full lift high RPM and hung the rocker for an instant and that's where things went really wrong.

We're not there to see what's going on so you have to be our eyes. We can only speculate at things.

I know you asked Alvin or Blown but I've been through this a zillion times. Paint your valve tip, I just use a Sharpie, this guy used a small piece of the sticky portion of a Post It. Get the adjustable pushrod and make your tip look like this (picture) with it by lengthening it or shortening it. Lock it down, turn the motor over several time and look at the pattern on the tip of the valve stem. The pattern should be centered, if not make adjustments to your adjustable pushrod until it is centered.

When you're happy with it you can take that rod to a machine shop and have it measured for the correct length. You'll probably find 7.150 or 6.950 is what you want. 6.950 might not work with the short slot on the LT4 rockers so your limited to the 7.150 rods.

BTW, you can get a real close measurment yourself with a simple tape measure. 1/16=.0625, 1/8=.125, 1/4=.250 and so on.

Once you get the pushrod length right you can ask around about adjusting the lash, I'm not going there again.

 

Will the intake valve be on the base circle of the cam when the exhaust valve starts to open and then the exhaust when the intake valve just closes?

I will take pictures of something I noticed yesterday. One of the arms on the valve lifter guide retainer is bent up slightly. This is on the cylinder that the pushrods broke on. It allows the valve lifter guide to move up and down a little but not out or off of the lifters. Could this have done something to the cam?

Looking at the intake valve, it looks straight. I will pull of the header and inspect the exhasut valve.

Thanks again,

Dave

 

I have the Comp Cams R Lifters. They have been working fine but some have stated they have seen and had lots failures with them. Most everyone has said good things about the GMPP LT-4 lifters. If I were you thats what I would go with, along with hardened pushrods of course.

 

VR'92 - I plan on buying the GMPP Kit and the CC hardened pushrods. I just ordered a Cam Degree Kit and a Pushrod Length Checker today to see what's going on and then I'll order the other stuff.

Dave

 

Yes.

This probably happened after the fact. With no pushrod or valve spring holding the lifter down it was allowed to fling up trying to escape the lifter bore. Thereby bending the retainer up a bit. Pull those lifters and look down their bores at the cam lobe with a flashlight and see how they look. Just bend that retainer back down with a good "eyeball" to the others.

OOPS, I didn't just say "eyeball" again did I??? On second thought you'll probably have to find a way to count threads somewhere, do some math, triangulate, multiply by pie, then kill yourself. Just kidding!

 

I finally got some time to work on the car. So far i have pulled the plugs which are gapped correctly and appear to be in good shape. I've only pulled a few pushrods off but they have all been straight. The roller rockers on the 2 pushrods that broke have slight imprints from the oiling holes on the ***** of the pushrods.

I will now check for the proper length of the pushrods as well as pull off the rest of the roller rockers, pushrods and then the lifters. I will also take pictures so you gusy can see.

Dave

 

ALLT4 - You were right on the money with the shorter pusrods. The stock length ones make the roller sit more towards the exhaust side. With the adjustable pushrod set to 7.150" it is almost perfect.

On a side note, all of the remaining pusrods were straight. All of the lifters also looked good. Only 2 roller rockers, the ones where the pushrods broke, have marks on them from the oiling holes on the pushrods. I will have pictures tomorrow morning as the batteries on my camera died. I looked into the lifter holes and from what I can see the cam looked okay.

So I guess I can now order the lifter kit and the shorter, hardened pushrods.

So any idea on why this happened in the first place? Was it a fluke or what?

Thanks again,

Dave

 

while you are at it, better check the install height of the valve springs to make double sure your not seeing coil bind.

my guess is you had some pistons hit the valves.. this same thing happened to me using the GMPP lt4 hot cam springs.. I replaced the bent pushrod checked everything over real well and 2 months later i lost my timing set and destroyed the motor.. after inspection, ALL my pistons were notched not only the ones that hung open.. come to find out the springs were not enough to keep the valves out of the way of the pistons on the exhaust stroke and after a few times touching the pistons at higher revs the weakest link let go. unfortunately I used chromoly pushrods that were NOT the weakest link.. the GM timing set was. live and learn, had it happen once before.. no fun either way.. my recommendation is to bite the bullet hwile you are torn down this far and put some high quality comp springs in there and double check the install height and be sure you have plenty of room at max lift.. most like to see a minimum of .050". good luck with it!

Chris

 

Sometimes things just fail, anything man made is susceptible to failure. Could have just been bad lifters and that's the cylinder that gave up the goat first.

I'd still take a look at those springs on the cylinder where the stuff failed. If nothing else use a solid lifter again and take a flashlight and try to look through the spring at max lift or near max lift, at .040 it might be tough, might need a mirror again.

If you can't see what going on under there and you're confident enough to install a checking spring I'd do it. It would suck to find out again later the guide is too high up or something else is impeding the travel of the valve stem to your full lift.

I had my guides cut down a bit even though I'm also only using the Hot Cam, cheap insurance.

edit; I see lc got in before me, similar response, coil bind, retainer to stem bind or valve float. I was concerned about valve float and went with the Crane 99846 tool steel spring. A lot of guys are running the hot cam springs though so I don't know why your valves would contact the piston.

 

Okay,

I checked all of the springs and they all have a install height of over 1.75". I have also taken some pictures so you guys have visuals of my descriptions.








Well there they are, I have the Magnum 7.150" pushrods on order from Jegs because they only had one set and Summit won't have them untill 7/27. Now I just need to order up the lifter kit.

Let me know what you guys think,

Dave

 

TTT - Anyone?

 

I just went out and did an actual measurement of an LT4 spring in a vise.

Your installed height. 1.750
Coil bound completely. -1.1875
Gross max lift. .5625
Your lift. .525
Margin. .0375 (little thin there)

This is what I don't understand about the Hot Cam cam springs, they run them well below the .060 accepted safety margin.

No way you're coil binding the spring then. Unless without light weight retainers inertia is sending them into coil bind. I doubt it, I had to struggle to squeeze that spring down in the vise.

Even if the rocker and push rod somehow got bent around to coil bind the spring, that's still only .562 max lift those springs can go with your installed height. From what I hear folks are running bigger lift numbers than that. Now I don't know what kind of pistons they have, maybe a deeper pocket, who knows. I still think @ .565 that's far away from the piston.

I really think a lifter or rod just failed. Slap it back together and give 'er hell.

 

Sounds more likely that all the other pistons got knicked in that short time following the timing chain failure as the motor spun down.

 

The photos of the rockers tell me you had too much slop in every way possible. The rockers were out of adjustment, and the guideplates aren't doing their job.

The pushrod tip came out of the rocker pocket and stabbed the aluminum body. You instantly had .2" more lift which caused coil bind and broke the pushrod. The rocker may have hit the valve offcenter during this, or at another time, also from too much lash or a dead lifter, and nothing locating the pushrod.

Obviously, with a selfaligning rocker you don't want guideplates. But this all assumes the rockers stay in adjustment.

 

I don't know what else could be said anymore. Other than make sure those two valves seem to operate correctly and put everything back together with the new stuff to the best of your ability.

 

Thanks for all your time and help guys. This all now makes sense to me. I have the CC 7.150" shorter hardened pushrods and GMPP lifter kit in the mail and it will be going back together Wednesday night.

I thought the rockers may not have been set right and that's what caused this. The thing that makes me second guess this is the fact that the motor was together and untouched for over a year and has seen revlimiter (6500rpm) plenty of times. The lifter going idea makes more sense in this respect. I really wish there was a cookie-cutter way to find zero lash and then to set the preload.

Thanks again,

Dave

 

Dave,

Don't worry about fixing the bent spider, SLT94LT1 posted that you'll get a new one in your GMPP kit. A compression test on this cylinder (I forgot which one it is) will tell you if you've got a bent valve without having to pull the header, it doesn't take much to unseal the valves.

Well, since you have the intake off, there is. When you start to re-assemble the engine, you'll be able to see the lifters plunger as you tighten down the poly lock. As soon as the plunger starts to move, your at zero lash, then just tighten down to your preferred preload. This is a much easier way to do it on new hyd. lifters, since they won't have oil in them to take up the plungers travel space when their new. I usually submerge them in a container of oil, then use an old pushrod to depress & release the plunger a few times to make sure all the air is out of them. I agree with ALLT4 that your spring's are ok, but under the recommended coil bind clearance of .060. If it were mine, I'd change the springs too, just to be safe(err...safer). I'm kinda liking the new Comp Cams Beehive spring's (and I don't particularily like anything that says Comp Cams on it, too many failures with their stuff over the years. I much prefer Crane or Crower (it's so nice having a couple of major cam companies in town!), but thats not a recommendation, cause I haven't had to build anything since they came out, so I can't speak from personal experience, but I WILL use them on my next build up!

Lastly, there are acouple of REAL good book's on the subject by David Vizard that you should get. One is " How to Build and Modify Chevrolet Small-Block V-8 Camshafts and Valves (Motorbooks Workshop) (Paperback)" and the other is "How to Build and Modify Chevrolet Small-Block V-8 Cylinder Heads (Motorbooks Workshop) (Paperback)". Both are available from Amazon.com for around $13.00 each, just do a search on his name and they'll all come up. He's one of the best performance writers I've ever come across, both because he's an ex chevy engineer who worked on the Can AM cars amongst others, and because he verifies everything he does on the dyno and he's not in anybodies pocket. If your product sucks, this isn't the guy you want to sentd it too, cause he"ll d#mn well say so in his next book!