Hello, all. I was referred to this forum via Performancetrucks.net. I posted a few questions but was advised to seek some direction here. I recently attempted to upgrade an L33 in a 2006 silverado. Sought out a notable builder in the area. BTR stage 2 truck cam, stock crank, pro LS forged pistons and rods, ARP head studs, 799 heads worked over full competition port and polish, Beehive springs. Inconel exhaust valves, hardened push rods, NNBS intake, 90MM TB, CAI, LTH, X-pipe, true duals on magnaflows,,….. originally procured a set of needle-less Straub technology trunnion kit but the builder informed me that he previously had a bad experience with trunnion kits and opted to go with a scorpion roller rockers instead.
Got it tuned by DSM lights (awesome guy Edgar) set my rev limiter to 6500. Went through the 2500 miles break in oil period, changing as directed. Changed to synthetic penzoil platinum, I’m 1500 hundred miles in. Now I’m experiencing sputtering on acceleration and hearing a knock from the passenger side valve cover. Also sluggish at highway speeds. I have not had it WOT yet. I kept it under 5000 rpm but only hit the gas a few times. Was trying to bring in it gradually. Before this it was running beautifully. The knocking is slightly audible but more tangible, i can put my hand on the ignition coils and the oil spout-and the whole valve cover for that matter and feel the consistent tapping,
Popped the passenger side valve cover off. A buddy that turns wrenches for a living said that i may have Clarence issue with the Rockers. I initially thought it was hitting the valve cover. But it may be hitting the back side of the head.
Would this concern contribute to the sputtering on acceleration, and loss of power? Or perhaps the tapping? Or would it be something else like a dropped valve?I checked the springs and they look good. I will post some pics of the rockers.

 

Possible stuck lifter, roller rocker trunion/bushing fail, broken valve spring, stuck valve.
I would also pull the plugs and use a cheap amazon bore scope to check pistons. < than 100 bucks plugs in to a phone.
Stop running it.. It wont get better if its got a mechanical knock. I would tow it to the builder.. At < 2K miles, It should still be his problem.

 

Ever since i notice the tapping i stopped running it. Would a rocker rubbing the back of the head cause issues like what i described?

 

If the rocker is rubbing the back side of the head there is a problem, Without looking it over myself the first thing that comes to mind is the pushrod could possibly be to long or there could be an issue with the rocker arm itself. Either way they aren't supposed to come into contact with anything as it travels.

 

Have you changed the oil and looked for or any signs of metal? Nothing wrong with factory style bushed rocker arms and it was Comp Cams trunnions that was having failures.



Can you tell us more about these Scorpion rocker arms? I've heard some horror stories about running cheap aluminum rocker arms and If it was me I'd be pulling the valve cover and inspecting it and everything else looking for signs of metal shavings and damage from metal to metal contact. I'd pull every rocker arm and pushrod to inspect them for signs of wear and damage and I'd also thumb check the valve springs to see if I have any excessive guide wear as those should be stiff and hardly move at all when you apply pressure. Verifying PR length would be on the list and hopefully you caught it in time before you done any significant damage.

 

Scorpion Roller Rockers SBC 1098
1.7 Ratio, 8MM bolt, non adjustable, use standard length PR. Cathedral port, 1.6” fulcrum width, clear 1.625 valve springs, needle bearings fulcrum and roller top, and it is aluminum.

 

I tried to post a pick of them seemingly a little to close to the backside of the head but I was moderated on the image.

 

What did the builder say when you asked him about the noise? Honestly unless its was a sideline cash build,, you should be covered for street use..

 

he said to open the valve cover and investigate. I’ve already sent him the photos of this weekend. I will see tomorrow about what he says. Hopefully it will work out. He is a reputable builder. I’ve had really good experience with him. Builds power plants on the international boat racing scene. Miami

 

I was hoping that it was just Rocker clearance hitting the valve cover. But now based on experienced eyes from this forum and performancetruck forum, as well as a buddy of Milne that I called and told him… he said awww man!!!! You dropped a valve or bent a pushrod, I didn’t believe him but. Like Frank Sinatra said the Best is yet to come. Minimal,…. Push rod bent,…. I hope it is not total destruction in the bottom end. The buddy I have is a beast, but he is currently building 2 hellcat engines at the moment and has no time. So I really appreciate the help all you are giving.

 

If your experiencing a loss of power, to me that indicates much deeper issues. I would pull the rocker covers, do a good visual inspection, and then crank the motor over and make sure the rockers are all moving equally. I would pull all the plugs out for this so the engine rotates smoothly. Maybe disconnect the injectors/harness and coil packs.

Next thing I would do is a compression and leak-down test. These are critical and will tell immediately is something is amiss, and if something is wrong you can speak to the builder armed with undeniable info vs. him telling you some nonsense like "its fine" or "put some more miles on it".

And cut your oil filter open while your at it.

 

Good idea,….. I also got my hands on an endoscope as advised. The rockers are coming off for sure. Check the push rods. And see if a valve has been dropped. And if any damage to the pistons. Check the oil filter for metal with a magnet. Anything else?

 

don’t need a magnet for a filter inspection. Just cleanly cut it open (there special filter cutters, got mine from summit) pull the paper element out and stretch it open and look for debris. You’ll see it easily if it’s there.

Did you notice any oil pressure loss?

 

no oil pressure loss at all. No check engine light. But then again it’s been tuned. The loss of power is Lilke 25% at most. The sputtering is intermittent. If I was to accelerate slowly up the Rpm ranges it would not sputter or hesitate. (Besides the audible and tangible tap).

 

Every single component was new or has been machined. Does this happen frequently ? with mods and performance builds not to imply by any means, that mine is a performance build. And not say I’m not enthused about the craft either. I really enjoy the learning, the sound, and potential of any worked over power plant. More so LS family though. This will not be my last build.

 

this happens a lot more than it should. To correctly build an engine, it takes an exhausting amount of hours to mock things up, measure, break/down and adjust, re-mock up, measure etc. All this time just dilutes the builders profit margins and I believe some just go with the “it’s good enough” mentality. I don’t think most builders even u/s rocker geometry, proper piston/valve checking etc.

But continue with your tests. 25% reduction in power means something is very wrong. Hopefully just a clogged injector or fuel pump. But if a new noise is involved, it be very concerned.

 

Geometry of a stock rocker arm that is fixed due to it being mounted on a pedestal with a predetermined height and pushrod? I can see the "It's good enough" in building an engine with stock parts that have been proven to work without checking P-V clearance. It's when you change something is when required like wanting to build more compression and knowing how much you can mill the cylinder heads.

 

Even the best builders can miss something, I had a set of 4 engines a few years back, little Nissan 4 cyl, we put a Nismo cams & Pistons in them,,
Got some basic head work etc.. Ran first one and it blew up on track. Rebuilt and no issues, built another and it blew up on track,,,
After about 3 rounds we finally found a subtle difference in the heads, turns out a couple of the motors originally had dished pistons and some didn't.
The engines that came dished has a small bump in the combustion chamber that at high rpm would kiss the piston.
Since these were student cars, they occasionally got wound up a little higher than we would have liked.. because of the shape
of the bump and it was hitting right on the edge of the piston "just barely" it was really tough to spot. Resulted in broken ring lands,
We thought we had a tuning problem that was causing detonation.. If you just ran it easy ,, no problems..

I would find it hard to believe the scorpion rockers don't need custom pushrods..
I cant recall having seen roller rockers go in without needing to adjust the push rod length, or high end lifters..

 

trust me, I am concerned, this was actually my first oversight on a build as far as selection and procurement of the components required right down to the Cometic .040 gaskets. With the exception of the rockers….. I have been an observer on this sight for a few years now. And kinda did a copy and paste technique for a budget friendly build.
Try To soak in the physics of the do’s and don’t’s, via
trials and errors of others. It is enjoyable though. Hopefully soon, the countless tedious hours required of a builder to manipulate the math for a high output, durable power plant, I maybe afforded the time and opportunity to do a lot of it myself and just allow the builder to machine the required parts. Mainly I wanted to understand cause and effect hence my my inquiry on this sight that I have been watching from a distance. My next build I definitely will asking more questions. S0 much to learn. In the mean time I will keep peeling the onion. Would love to share a triumph or 2.

 

So that brings the question to mind,… donor engine or something like a RHS or Dart LS Based block to start with? As budget friendly as a donor would be, do the possible issues and potential cost down the line out way an aftermarket casting? And what about big name internals and valve train components?