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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.
If the pistons have valve relief, which they do… would p-v still be an issue? And how much math and finagling is involved if the rockers are non.adjustable and the push rods are suppose to be a standard length. Isn’t the math pretty much done already? Sorry for the questions that may seem elementary, but I am trying to
learn. Would math still be involved due to the cam duration and lobe separation?
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?
Originally Posted by pdxmotorhead
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..
I gave the builder a set of Morel 7717 Drop in , no tie bar, hydraulic lifters.
It is true that stock rockers aren't adjustable. But that doesn't mean you walk away from checking things. Who knows how screwed up the geometry may be with different length valves, different rockers, lifters and pushrods etc. For all we know things can be binding up. If it warrants, the rockers can be shimmed to some degree as needed.
Usually aftermarket pistons have more relief but it HAS to be verified that there is no p/v clearance issues. Just takes a little time. I didn't really do any math when modding my 6.2 out of a 2013 Denali, I put a BTR STG2 cam, LS7 lifters and 7.425 pushrods. Using checking springs P/V clearance was pretty tight - about .080 IIRC and more on the exhaust. Confirmed with the valve springs there was no coil-bind and adequate retainer to seal clearance.
All I'm saying is, the more that things are changed, the more that has to be inspected and adjusted. This is what builders are getting paid to do.
If the pistons have valve relief, which they do… would p-v still be an issue? And how much math and finagling is involved if the rockers are non.adjustable and the push rods are suppose to be a standard length. Isn’t the math pretty much done already? Sorry for the questions that may seem elementary, but I am trying to
learn. Would math still be involved due to the cam duration and lobe separation?
Duration and lift affect P-V so yeah you need to take measurements when working with aftermarket parts, The rocker arms you have are non-adjustable and fixed on the pedestal but you deviated from stock. Stock heads doesn't mean you can install 7.40 "stock length" pushrods in there and expect everything to play together so measurements have to be taken. Changing to different rocker arms, camshaft, lifters, valves, milling the heads and going to thicker or thinner head gaskets can affect the pushrod length so if it were me I'd be verifying pushrod lengths, checking for coil bind, inspecting the rocker arms to see if there is any contact on the back of the rocker to the cylinder heads, verifying the fastener that holds the rocker arm into place is not making contact with the rocker arms and doing a swipe on the valves to see if the valve geometry is correct. You're looking to see the lines across the tops of the valves to be centered or just a little towards the intake manifold from center.
Also if you can feel something hitting when you place your hand on the valve cover you need to verify the rocker isn't making contact there as well. GL
Last edited by 01CamaroSSTx; Dec 8, 2021 at 07:46 AM.
Duration and lift affect P-V so yeah you need to take measurements when working with aftermarket parts, The rocker arms you have are non-adjustable and fixed on the pedestal but you deviated from stock. Stock heads doesn't mean you can install 7.40 "stock length" pushrods in there and expect everything to play together so measurements have to be taken. Changing to different rocker arms, camshaft, lifters, valves, milling the heads and going to thicker or thinner head gaskets can affect the pushrod length so if it were me I'd be verifying pushrod lengths, checking for coil bind, inspecting the rocker arms to see if there is any contact on the back of the rocker to the cylinder heads, verifying the fastener that holds the rocker arm into place is not making contact with the rocker arms and doing a swipe on the valves to see if the valve geometry is correct. You're looking to see the lines across the tops of the valves to be centered or just a little towards the intake manifold from center.
Also if you can feel something hitting when you place your hand on the valve cover you need to verify the rocker isn't making contact there as well. GL
the coil bind for these BTR LS6 springs are set at 1.150”. Do they have to be extracted to test them or can they be tested in placement?
would the guides have either been mishandled upon initial placement or shifted to effect the valve geometry and effect the lobe from making contact on the center of the valve. Could this directly be associated to my loss of power.
It is an exact science more than I thought was involved. I have a new found respect for the knowledgeable. Wow
One step in the right direction,… the builder is coming l, hopefully today to inspect the motor. I have a list of questions to inquire thanks to all that commented. Hopefully I can get her back on the road and continue the build to the rear end and trani
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.
This is why there are people who "assemble" engines and people who "build" them
Friend of mine builds engines, often he doesn't procure any of the parts. he charges roughly
1800 to build a basic engine, including block and head machining, if you are building a boutique
motor its closer to 5K due to the hours to make all those mystery parts work.
I was helping him prep some parts one afternoon when he had a backlog, I noticed he put clay in all 8 chambers assembled the engine and
rockers and rotated the motor all the way round. I asked him why he did that,, he said because he's never had a valve strike and never intends to..
He does a lot of Sprint/midget builds, 100% methanol ,, 15:1+ compression, PTV clearance is TIGHT..
Takes only the smallest error and kerblooie! (Technical term)
Here are the rocker photos OP uploaded to the sister truck forum (since he can't post yet here)
Are those specs of aluminum on the rocker pictured far right in the first photo? Looks like the center rocker may have a witness mark from the valve cover too
If the rocker has marks so should the valve cover ,,
That top end sure looks DRY, Like its not oiling. May just be the pics. OR those rockers don't move oil very well?
I would not expect to see that much contact marking on the rollers yet.
[QUOTE=pdxmotorhead;20397655]This is why there are people who "assemble" engines and people who "build" them
Friend of mine builds engines, often he doesn't procure any of the parts. he charges roughly
1800 to build a basic engine, including block and head machining, if you are building a boutique
motor its closer to 5K due to the hours to make all those mystery parts work.
I was helping him prep some parts one afternoon when he had a backlog, I noticed he put clay in all 8 chambers assembled the engine and
rockers and rotated the motor all the way round. I asked him why he did that,, he said because he's never had a valve strike and never intends to..
He does a lot of Sprint/midget builds, 100% methanol ,, 15:1+ compression, PTV clearance is TIGHT..
Takes only the smallest error and kerblooie! (Technical term)
The Death truly is in the details.[/QUOTE
was the clay placed in the valve relief trenches to imprint the valves for PTV?
Here are the rocker photos OP uploaded to the sister truck forum (since he can't post yet here)
Are those specs of aluminum on the rocker pictured far right in the first photo? Looks like the center rocker may have a witness mark from the valve cover too
The Death truly is in the details.[/QUOTE
was the clay placed in the valve relief trenches to imprint the valves for PTV?
Yes, and a few small beads on other parts of the head/chamber area, The sprint heads get the head to piston clearance very thin. So he's looking at that as well.
Its quite intriguing to watch him assemble and engine ,, lot of small checks that I would not have ever thought of.
If the rocker has marks so should the valve cover ,,
That top end sure looks DRY, Like its not oiling. May just be the pics. OR those rockers don't move oil very well?
I would not expect to see that much contact marking on the rollers yet.
there was oil on top of rockers and in the bolt divot. I may have inadvertently wiped it to check for play. The springs were covered in oil. But again not as knowledgeable as I should maybe not enough oil as mentioned.
Yes, and a few small beads on other parts of the head/chamber area, The sprint heads get the head to piston clearance very thin. So he's looking at that as well.
Its quite intriguing to watch him assemble and engine ,, lot of small checks that I would not have ever thought of.
If the rocker has marks so should the valve cover ,,
That top end sure looks DRY, Like its not oiling. May just be the pics. OR those rockers don't move oil very well?
I would not expect to see that much contact marking on the rollers yet.
they could be used and passed on as new. As I mentioned I wanted to go with a needless trunnion kit, but was moved to augment the original plan due to a possible issue with trunnion. Sorry just thinking out loud.
1) look like GM LS6 springs, I believe good to .550 lift? Your cam if I'm looking at the right one is .553. If they went in any tighter than spec - you have a problem.
2) the small wheel on the rocker looks like its digging into the side of the rocker on some of them.
3) is there adequate clearance from the back of the rocker to the head? Hard to tell from the picture angle.
4) looks like white alum dust/shavings on the rockers?
1) look like GM LS6 springs, I believe good to .550 lift? Your cam if I'm looking at the right one is .553. If they went in any tighter than spec - you have a problem.
2) the small wheel on the rocker looks like its digging into the side of the rocker on some of them.
3) is there adequate clearance from the back of the rocker to the head? Hard to tell from the picture angle.
4) looks like white alum dust/shavings on the rockers?
is the dust presumably from the rockers or the head? And why not the driver side as well?
How far in motor would that dust travel?
can the motor operate to optimum performance after this?
ok that is an oversight that should have been picked up immediately. The builder should have put flags up and advised me, shouldn’t he? Options should have have been presented.
The BTR cam was accompanied by the LS6 springs in a kit sold together. And it is .550 lift.
Should it have been dual springs or just single springs with higher lift value?
Well it's not Pixie dust! Those rockers are making contact with the valve cover and the back of the rocker arms look close to the side wall of the cylinder head and could probably use some more clearance. Hate to say it but you might as well pull the other side too while your at it.
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