Ilmor MV8 Head Gasket Replacement

[jpwhit]

20 hours ago, chrislandy said:

I'm on holiday at the moment and the head gasket just went on the prostar (water/oil mix and cloudy exhaust, plus one cylinder is down to 110psi (no.3) when rest are at 150-160psi.

 

I've got a gasket set coming from MC belgium, (I'm in France)but wanted to check with someone with experience of these engines... its a 2014 mv8 570 (red) with 1500hrs ( 1400 at ski school so 36mph and short line)

 

Do you know if the head bolts need changing or can they be reused, plus what is the torque sequence and stages? And if there is anything to look out for?

 

I've rebuilt dozens of engines but never the ilmor and can't find an engine manual anywhere specific to this one.

 

Responding to this PM on the open forum because it seems like info that others may need at some point. 

Ilmor doesn't provide specs or any info on head bolt tighten sequence in the official service manual.  They are very clear in the official service manual that dealers should just order a new bobtail engine from them for any internal engine issues. 

There are 2 generations of head bolts for the vortec LS engine series. The later generation can be identified by having a captive washer on the bolt. GM specifies not to re-use the 2nd generation head bolts because they are torque to yield. To always replace them. They are less clear about the first generation bolts. 

You're suppose to follow the tightening torque sequence as specified by the bolt OEM. 

This is the procedure for the GM OEM 2nd Gen Torque to Yield head bolts. 

https://help.summitracing.com/app/answers/detail/a_id/5187/~/how-do-i-install-my-ls-cylinder-heads%3F

You also typically need new intake, exhaust, and valve cover gaskets in addition to the head gasket. You can likely get away without a new valve cover gasket. I'd say 50% of the time the exhaust gasket doesn't come apart on disassembly. I've never been able to save and re-use the intake manifold gasket. 

John

[BraceMaker]

Personally I'd be calling up ARP and getting a set of head studs shipped out.

They should know what the proper product would be or the questions about it and on a boat even more reason to skip torque to yield hardware buy once cry once.

[DW]

Bummer on the chocolate milkshake in the pan, that stinks & on vacation.  Pretty sure Chris knows based on some of his posts, don't forget stainless steel ringed marine head gaskets.  Lots of options if you do your own sourcing.  I would suggest a leak down test before one rips it apart to verify where the cylinder is losing air although his post implies he is confident in the analysis.

@jpwhit  On the Ilmor website they don't list the MV8 for a Prostar application, hopefully Chris can provide info on which specific engine is in the boat.  If it is the 570 hp LS7, woo hoo:-)

[chrislandy]

1 hour ago, DW said:

Bummer on the chocolate milkshake in the pan, that stinks & on vacation.  Pretty sure Chris knows based on some of his posts, don't forget stainless steel ringed marine head gaskets.  Lots of options if you do your own sourcing.  I would suggest a leak down test before one rips it apart to verify where the cylinder is losing air although his post implies he is confident in the analysis.

@jpwhit  On the Ilmor website they don't list the MV8 for a Prostar application, hopefully Chris can provide info on which specific engine is in the boat.  If it is the 570 hp LS7, woo hoo:-)

Just the boggo standard 5.7 unfortunately 

 

Can't do any other tests on hols, luckily I brought the torque wrench!

[DW]

@chrislandy - did it get hot at some point?   The siamesed  center cylinders where exhaust valves are adjacent are prime candidates for head gasket failure.  If you find that, check for a cracked block and cracked or holed piston for the water path to the pan.  Hopefully just cylinder to water jacket  breach.

[chrislandy]

Well the head gasket looked ok on the odd side. 

Still thinking it is the head gasket though as it did overheat, just it's not done any real time since though so wasn't really expecting to see a full blow through. The coolant runs in the head were fully clogged with limescale though.

[LeonL]

Torque sequence.   Failing any other source of info, start at inner most bolt and proceed in a semi circular pattern outward.

[DW]

From the latest update I would investigate a cracked cylinder head (white smoke from exhaust) as it must have gotten pretty hot, if not cracked check for warpage.  Low cylinder may also be a warped valve, probably on the exhaust side.

Your friendly internet has volumes of build articles, data and information on rebuilding your trusty SBC or 'boggo standard 5.7' 🙂

[BraceMaker]

1 hour ago, LeonL said:

Torque sequence.   Failing any other source of info, start at inner most bolt and proceed in a semi circular pattern outward.

I mean yes but this is 2023 - failing any other source.... find a source.

SBC have two different sizes of hardware and a torque sequence that is a torque amount and then a torque angle, you bring them to torque with a torque wrench and then switch to a torque angle gauge and then you go around twice with that torque angle gauge to the correct setting IF you are using the torque to yield hardware.  Its 22ft lbs and then a 90 degree torque and then another torque to 50 or 90 degrees depending on the hardware and then a final pass to torque the small bolts around the outside.  This is not a go inside out semi-circular motion type of guess work.

My suggestion about studs is based on if you're going to take them off the studs are re-usable and stronger.

Edited August 2, 2023 by BraceMaker

[DW]

A few sources:

https://help.summitracing.com/app/answers/detail/a_id/4925/~/small-block-chevy-torque-specs

https://www.jegs.com/tech-articles/small-block-chevy-sbc-torque-specs-info/

https://arpinstructions.com/instructions/134-3604.pdf

[jpwhit]

5 hours ago, LeonL said:

Torque sequence.   Failing any other source of info, start at inner most bolt and proceed in a semi circular pattern outward.

The tightening sequence is in the link I posted in the initial post of the thread.  

[jpwhit]

19 hours ago, chrislandy said:

Well the head gasket looked ok on the odd side. 

Still thinking it is the head gasket though as it did overheat, just it's not done any real time since though so wasn't really expecting to see a full blow through. The coolant runs in the head were fully clogged with limescale though.

I didn't realize it had overheated. If that's the case, even if the head gasket is the cause, it'll be likely the heads and/or the block will need to be resurfaced. This will be even more true if it had TTY fasteners. That's because the advantage of TTY fasteners is that they have a bit of elasticity. That keeps the pressure on the head gasket more consistent with changes in temperature. Whereas when an engine overheats with non-TTY fasteners, such as studs, the expansion of the head and block at high temperature tends to crush the head gasket. Then when it cools back down, you no longer have good even pressure on the head gasket and leaks form. 

With TTY fasteners, that does't happen as much. So, when the head gasket leaks, it's more often due to some warpage of the mating surfaces. 

What caused the boat to overheat and how hot did it get?

[chrislandy]

It overheated on tickover when it ran with the seacock closed for 5 mins. The impeller was near perfect and the antifreeze was still in there from winterising.

 

Putting it all back together now, it turns out this era of ilmor mv8 is just a SBC same as any indmar or mercruiser block, 9 staggered bolts under the rocker cover and 8 short below the plugs. 

Inspecting the gaskets, there looked to be a small leak between the inlet manifold gasket and interior of the block which may have been the source of the oil in the water.

 

We'll see how it runs afterwards, might be a fix for the holiday then winter full rebuild (see pic of bore!)

[jpwhit]

Good luck! I hope you can get it running for the rest of your vacation. I guess this is the first you're using it this year if it was winterized. 

[chrislandy]

Just exhaust manifolds and new oil to go, but lost the light this evening (10pm here in france)

 

Fingers crossed for tomorrow morning 

[chrislandy]

Well it worked, happy faces all round 🙌

Just got to plan for a full rebuild over winter now... 

 

I didn't need to this time as I marked everything up, but how do you set the timing on the ilmor? (This one has a dizzy), on previous engines I've just had to bridge some pins on the harness to put it in service mode and adjust the timing to 10deg btdc. Can this be done through the screen or do I need some software?

[Jody_Seal]

you will need to set it with a computer.

[jpwhit]

Even though it has a distributor, the timing is controlled completely electronically by the ECM using the crank and cam position sensors. Rotating the distributor doesn't change the timing, but it does change what they call Cam Retard Angle. You can only set Cam Retard Angle using Diacom. It basically setting the distributor position such that the rotor lines up with the right spark plug terminal in the distributor cap as close as it can over the typical range of the electronically adjusted timing. If it's off, you'll get the spark jumping to the wrong terminal within the distributor. 

Edited August 6, 2023 by jpwhit