Fiat Sohc 1.9L stroker head gasket question

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elderair
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Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Sun Aug 02, 2015 8:28 am

Engine is comprised of 1.6 Punto block bored to 87.5mm with 78.4mm Stilo crankshaft.
Rods are forged offerings and stock length for the 1.6 Punto.
Pistons are custom forged Iapel with custom c/h for zero pop up and the block has been decked for .6mm pop up.
Head is a Tipo with 40mm dia. intake valves and 35mm exhaust valves and a stock combustion chamber dimension.
Head gasket in question is a Navalinea with separate fire rings. Gasket is 1.9mm thick with 88mm fire rings leaving a squish of 1.3mm.
ARP head studs are employed and torqued to 61 ft/lb using ARP lube.
Camshaft is a Pittatore #87 42/82 at .016 lash int/exh

Upon start up and initial break in at the 25 mile mark wisps of antifreeze were seen in the exhaust stream. Head was removed after cool down and the following was noted:

Three of the four fire rings were distorted and pushed outward away from the spark plug side of the combustion chamber and into the water port portion of the NavaLinea gasket. Wondering if a single heat cycle retorque of the head studs would have prevented this condition?

No directions for installation of this gasket are included and so I really need instruction on proper stud/head gasket installation/interaction here to prevent damage to another expensive head gasket and perhaps hydraulic lock of my expensive little motor.

The projected compression ratio was calculated to 10.5:1 and these gaskets are said to be used with turbo with much higher cylinder pressure than I am running so it must be a failure on my part to use proper process on installation or failure to retorque upon the first heat cycle.
Attachments
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navalinea head gasket failure
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1.9L Fiat sohc stroker
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Guy Croft
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Tue Aug 04, 2015 10:35 am

that is detonation and most likely caused by excessive intake air temperature.

You need a sealed ducted air intake system, the underhood temperature at your filters is way too high.

G
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elderair
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Thu Aug 06, 2015 5:17 am

Thanks, I will plan on building a filter box and run a duct to one of the side vents for outside air! Or maybe one of the FAZA engine cover air inlets that goes up above the roof line?
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Guy Croft
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Thu Aug 06, 2015 11:47 am

You will also need to strip the engine and examine the pistons, the event may have shattered ring lands/rings.

You can't see this without taking the pistons out.

G
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elderair
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Sun Aug 16, 2015 5:59 pm

The squish is 1.2mm and the Tipo cylinder head chambers are stock 33cc. Would it be a good idea to open up the chambers to the edge of the fire ring to decompress just a bit while keeping the squish to same? Once I have checked the pistons and have it back together and ready to run again do you feel that the venturi size of the 40DCNF's should be upped to 34 instead of the 32's I am currently running. Or should I just enjoy the low end torque and quick response of the 32's. rpm may not be the high point of this engine due to inlet velocity and factors that come with the rod ratios in the 1.6:1 range.
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Guy Croft
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Mon Aug 17, 2015 12:11 pm

won't make any difference, the SOHC gets its fast burn from swirl offset in the inlet ports, not squish..

as for lowering the CR by enlarging the chamber, whether it detonates or not depends not just on CR, but fuel octane, inlet temp, ignition timing, plugs, exhaust configuration, operating temp, so many things...

G
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elderair
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Tue Aug 18, 2015 12:35 pm

So I should select a colder plug with a slightly more shielded electrode, but how much colder?

I never did get any hard core figures for intake and exhaust valve lash for the Pittatore #87 camshaft but read .016 somewhere. Is that figure good for intake and exhaust both. Shouldn't exhaust be several thousandths more clearance? Anyone have the specs for this? Thanks
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Wed Aug 19, 2015 10:50 am

Plugs would need to be B9EGV or slightly hotter B8EGV from NGK Racing, I stock them..

You will need to run Shell V Nitro Plus or BP 98. Most other fuels contain manganese compounds designed to raise the octane rating and the orange deposits that form on the plugs are conductive at the kind of cylinder temps you will see and will cause misfire. Same is true of some aftermarket fuel additives.

The specified clearance is 16thou" inlet and exhaust with that 87 type cam.

G
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elderair
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Thu Aug 20, 2015 5:27 am

Thanks for the spark plug information. Once I get the engine out of the car and back on the stand I will pull the pistons and check it all out. I am planning on building a filter box that will connect to the left side engine compartment/ body vent. Also wondered if the use of a manifold vacuum gauge is an effective method of dialing in the camshaft timing and if so what gauge indication/reading would I be looking for as an ideal. I set F/L at 110 deg. atdc on this camshaft.
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Guy Croft
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Thu Aug 20, 2015 10:35 am

You don't have much freedom with a single cam, 110 deg is OK.



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tmvolumex
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Re: Fiat Sohc 1.9L stroker, leakdown test with no head

Post by tmvolumex » Fri Aug 28, 2015 6:36 pm

I had a sudden power loss in one of my VX supercharged, 2 liter Fiat / Lancia engines and thought it must be a burned valve. I pulled the head and sure enough, I had a burned exhaust valve. I thought I would dig a little further as the engine had almost 100,000 miles on it and my ignition boost retard system and rev limiter had malfunctioned and the engine over revved and then lost power immediately.
I made a 1 inch thick, 6 inch by 6 inch square aluminum plate with a centered threaded hole for a leak down gauge and 4ea , 11mm through holes for bolting it to the 4 bolt holes in the block that surrounded each cylinder. I used an old cylinder head gasket as a pattern for the holes. I bolted this plate to the block with a 1mm thick piece of silicone as a gasket (you also need to punch a hole in the middle of the silicone sheet where the leak down gauge is). This fixture allowed me to run a leak down test on each individual cylinder, without a cylinder head. The good news is this leak down fixture worked well, the bad news was, I had 2 cylinders that had a lot of leakage. Time to pull the pistons. Pulling the pistons and rods revealed, 2 broken top piston rings in the cylinders that had excessive leakage.
I am glad I took the effort and investigated further as there was no visible detonation evidence on the top of the piston, chamber or spark plug.
Tom
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Guy Croft
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Sat Aug 29, 2015 11:48 am

good post Tom and it just bears out what I said,

G
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tmvolumex
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by tmvolumex » Sat Aug 29, 2015 4:52 pm

Here is a picture of the leak down fixture I made and the leak down test results on one cylinder.
The air pressure source is at 100 PSI and the cylinder pressure is at 70 PSI, that equals 30% leakage.
Once I pulled the piston, it was obvious that I had broken a top ring.
Tom
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Sat Aug 29, 2015 6:43 pm

MODEL POST BY TOM

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elderair
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Thu Sep 10, 2015 10:11 am

I pulled the pistons and found all rings to be in perfect condition but number three piston had minor scuffs above the top ring land. I removed the aluminum that was deposited from the top of the bore and de glazed the cylinder and cleaned up the small amount of damage to the piston. cleaned all parts and reinstalled the pistons into the bores and installed the new head gasket. Reassembled everything and readjusted my valves. My current setup is with a BOI performance cold air box that ducts down to the left side body vent. I am now running Sonoco 110 to get me to the dyno and I will see what this beast is putting to rear wheels. I am in the process of hooking up the wide band A/F meter. Jetting at the moment is mains: 130. A/C 190. Idles 53. Venturi 32. Emulsion tubes: F22. Spark plugs are the NGK racing 9 series you mentioned earlier. Ignition set to 10 degrees btdc. and a computronix ignition system giving me 28 degrees total timing above 3800rpm. I feel it is ready for the dyno but will wait a few more miles and see what the wide band shows. Any need to install the 34mm venturis' that I have on hand. Thanks
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