? intake mounting may affect crank bore alignment ?

[rebelyell]

Following is a verbatim quote from a GM Powertrain manual for an rpo L31 (vin code R) Vortec 350 / 5.7L sbc (iron block & heads)

Proper lower intake manifold fastener tightening sequence and torque is critical.
Always follow the tightening sequence, and torque the intake manifold bolts using the 3 step method.
Failing to do so may distort the crankshaft bearing bore alignment and cause damage to the crankshaft bearings.

I've never noticed the reference to intake mounting affecting crank bore alignment; but it makes some sense.

Others' thoughts / experience.

[turbo camino]

Breaking News: There are lots of copy errors in GM, and other, service manuals. That reads like a bit of text that got pasted into somewhere it didn't belong.

For example, according to the ECM connector pinout in the GM manual a '06 GTO only has seven ignition coils.

[rebelrouser]

This is part of a real GM service bulletin. When they changed the bolts on the intake from angled to vertical, is when the issue started. I remember this bulletin first being published for V-6 engines. I remember because I used this bulletin in a power point presentation for my students to scare them into using a torque wrench.

[BillK]

I doubt that it is a misprint. I have seen that in documentation for quite a few late model engines. I did not realize the Vortec engine was one of them. New engines are being made with very lightweight castings and more and more structural members such as oil pans, front covers etc. Proper torque specs and sequences are a must.

[BOOT]

This is part of a real GM service bulletin. When they changed the bolts on the intake from angled to vertical, is when the issue started. I remember this bulletin first being published for V-6 engines. I remember because I used this bulletin in a power point presentation for my students to scare them into using a torque wrench.

Like the sbc TBI center straight bolt change and then how the vortec doesn't have center bolts?

[modok]

it surely DOES distort the main housings....some amount.
Most V8, you might notice there is not that much metal holding the two sides together, and most of that is at the front and back ends.
enough to cause a problem? probbly no.

If you tightened the bolts in the worst possible way it might be significant but....
I assume most of us grasped the general idea of a torque sequence, going up in steps, ect.... pretty early on.

[turbo camino]

I realize everything is flexible if you have the right measuring instruments, but seriously, how much can you twist a SBC block using only eight little 5/16" intake bolts? I mean, how much do the main bearing bores move around when you drive over a speedbump and chassis flex is transmitted through the motor mounts, which are much closer to the plane of the main bores? Maybe it would be safer if engines were left disassembled and stored in a climate controlled laboratory, otherwise there could be misalignment somewhere!

[rebelrouser]

When Ford released the Modular V-8's they soon released a training video on how to use a torque wrench, and how torque to yield bolts functioned. I used this training video in my classes for many years. On the Ford if you do not follow the torque sequence exactly when installing the main caps and jack screws, it will lock the engine, had my students do it several times. The GM intake bolt torque bulletin was in response to warranty claims, technicians were using air tools to tighten intake bolts and causing issues. Engineers monitor warranty claims and look for pattern failures, if they pop up they investigate to change product design or service procedures or what ever the root cause seems to be. I taught automotive classes for 26 years, it made me a better technician and engine builder, because students did things no experienced technician would do and screwed up things I had never seen before in the industry working in a shop. I lost count of how many broken bolts I helped them drill out in 26 years. I even had a power point and demonstration on how to remove broken bolts, heli coils, extractors etc. that went right along with the bolt torque presentation.
When I worked at a dealership, we got notices all the time to save certain parts and then sent them back to GM so engineers could analyze them to see what was up.

[dannobee]

They reference the 3 step method. I can see some hack zapping down one side first, then going to the other side and doing the same. That would likely be the worst case scenario for distorting the block. Most of us just take for granted what we know about assembling something mechanical. Pretty sure that the vast majority of us all grew up taking apart our bikes and lawnmowers or dirt bikes. It seems that what we learned doing that stuff isn't as common today and it becomes glaringly obvious when you work next to someone who doesn't have that knowledge.

What is the doc ID on the '06 GTO diagram that you mention? I see coil controls on C2 connector pins 53, 54, 57, 58, 59, 61, 65, 66. I can forward it to one of my contacts, but this late in the game it's likely that they'll just ignore it.

[GRTfast]

I realize everything is flexible if you have the right measuring instruments, but seriously, how much can you twist a SBC block using only eight little 5/16" intake bolts? I mean, how much do the main bearing bores move around when you drive over a speedbump and chassis flex is transmitted through the motor mounts, which are much closer to the plane of the main bores? Maybe it would be safer if engines were left disassembled and stored in a climate controlled laboratory, otherwise there could be misalignment somewhere!

Have you ever calculated the tensile force of a 5/16 bolt at proper torque? Depending on the alloy, it can be greater than 3000 lbf.

How many intake bolts are there?

Everything is a spring. You put multiple point loads of 2000+ lbf on an engine block and it is going to distort. Probably not much, but when you are talking about bearing clearances, a thousandth matters.

[turbo camino]

I really do realize that things can move in unexpected ways. I am having a hard time seeing this one though. The OEM lower intake is long and wide and relatively thin and flat - maybe 4" at the thickest? - and would seem to be able to pretty easily make a corner-to-corner twist. The block is, yes, a series of boxes made up of thick main bulkheads tied together by thinner water jacket walls and the lifter valley. But the block is stiffened against twist to some degree when cylinder heads are installed. I can certainly see that a worst-case lower intake install could move the block enough to be measurable at the main bores, but measurable and significant are two very different things. With an electronic indicator set to the right scale I can measure deflection in my 4" thick granite plate from just pushing on the corner of the granite with one finger...

dannobee: I have an older, likely 'unauthorized', offline version of eSI. Sounds like it's been corrected in the live versions. Mine shows C2 #54 as Evap Vent Solenoid Control in the ECM connector end view table. In the wiring diagram, it's shown correct (C2 #54 to IC1 Control).

[turbo camino]

And... I'm not advocating ignoring the tightening instructions. If they'd said "Due to the failure-prone gasket design, following the installation instructions is critical", I'd have no argument at all with that.

Has anyone ever found a L31 with burned up bearings because one or two of the intake bolts came loose and the block twisted into a pretzel? (damage from water ingestion after the plastic gasket fails doesn't count, LOL)

[turbo camino]

OK, I am starting to figure it out.

With the old-style intake bolt orientation, overtightening the bolts (all, equally) would tend to pull the cylinder heads in closer together, but the Vortec with its vertical bolts, overtightening would make the manifold act as a wedge being driven down between the heads and spreading the heads apart. Higher torque on opposite corners would apply the wedge forces diagonally across the block. It's not about the torsional stiffness of the manifold casting, it's about the casting, in compression, acting as a wedge. Is that about right?

[modok]

Hard to say who wrote that and specifically about what.
On the one hand I believe it, but then again if it was specific to that engine might be doubtful. It was probably already known long before, or should have been.
Ford was using that same kind of design, on probably less sturdy blocks, and I've read some cryptic torque instructions about it.
the ford essex v6 (if I recall correctly, which is quesionable) had you torque the heads and intake at the same time, using a complicated sequence, Seemed like they wanted you to snug the intake to 'square up' the heads, as if the alignment dowels were not accurate, and that was just a little over the top IMO

On machining setups I often have situation where the part might teeter-totter if I tighten one side ahead of the other, but I just torque both sides at the same time. I have two hands, and two wrenches, it's easy. took a while to think of it tho.

[chevyfreak]

.
the ford essex v6 (if I recall correctly, which is quesionable) had you torque the heads and intake at the same time, using a complicated sequence, Seemed like they wanted you to snug the intake

If you are refering to the english essex v6 , you fit the heads, hand tighten bolts then fit intake and tighten down so that intake seals up then you torque headbolts. If you torque heads first the intake doesnt seal properly. (Ask me how i know this )
Bit of a rush to get done if you have spray sealer on headgaskets.

Chevyfreak.