Slant Six Forum :: We keep blowing head gaskets.

different brand of head gasket.

The Felpro should be fine

You could go to the premium permaseal gasket from Oz, but it has a large bore size.

We have always reused the same head bolts, but they pass a visual inspection and always torque down with no problems. Every blown gasket has been a Felpro printoseal, and it is always a cross-blow between two cylinders (but not always the same two). In fact, we're back on the track right now running on cylinders after pulling the push rods from the dead 2.

Are the head bolts going back into the same spot?

I'm thinking 1 or 2 bad bolts are moving around and that's where you're blowing.

Or you're bottoming out a bolt so it doesn't have a clamp load but torques ok. (1 or 2 bolts could be too long)

I don't recall if the headbolts have washers......

If washers are involved, check the thickness, a thin one might cause that bolt to bottom out........

While the head is off, check the deck with a straight edge.
The factory did not use head bolt washers, but I would suggest using them. It will prevent the bolts from bottoming, and give a better clamp at the same torque reading. I'm also thinkingg you are getting into detonation. When I first started running slants, I had a problem with blowing head gaskets. After I cured the head gasket problem, I started eating pistons. I would rather the gasket act like a fuse (blow), then eat a piston. I had been running too much total advance. A slant does not like as much total advance a most other engines.

Author:	SpaceFrank [ Sat Nov 14, 2015 9:13 am ]
Post subject:	We keep blowing head gaskets.
Last LeMons race in June, we blew a head gasket and thought it was due to a rough surface finish from getting the head decked at a bad machine shop. I had the surface redone at a different shop and it looked much better. After reassembling the motor, we ran the test session at this weekend's race and blew another head gasket after less than an hour on track. We swapped it again and were extra careful to clean the block surface. There were a few spots of corrosion or buildup that I knocked down with emory cloth. We were also very careful to torque in multiple steps (25, 50, 60, 65, 70) and go over each bolt twice at each number. We also torqued to 70 after warming it up this time, which we don't normally do. This head gasket blew after less than an hour on track this morning. We have always reused the same head bolts, but they pass a visual inspection and always torque down with no problems. Every blown gasket has been a Felpro printoseal, and it is always a cross-blow between two cylinders (but not always the same two). In fact, we're back on the track right now running on 4 cylinders after pulling the push rods from the dead 2. The car has a big radiator and coolant never gets above 210 on the track. SCR of 8.8:1 and DCR around 7.6:1, running on 87 octane pump gas. Timing usually set around 5 btdc at idle. I don't know the total advance, but we're running mechanical only, no vacuum advance. Any ideas? The only thing I can think of is that the block surface is warped, but that seems really unusual for a big iron block like this.

Author:	SpaceFrank [ Sat Nov 14, 2015 9:19 am ]
Post subject:
Just to be clear, we're talking about 3 blown head gaskets. The one in June blew after about 8 hours on track, the one yesterday blew after about an hour, and the one today blew after about an hour.

Author:	Rick Covalt [ Sat Nov 14, 2015 10:27 am ]
Post subject:
I would check the block straightness for sure. You can always torque it an extra 5 pounds over spec. Rick

Author:	SlantSixDan [ Sat Nov 14, 2015 11:52 am ]
Post subject:
If you've run out of things to look at on the block, maybe it's time to take a hard look at the head. Maybe it's time to pick a different brand of head gasket.

Author:	Pierre [ Sat Nov 14, 2015 12:09 pm ]
Post subject:
I'd re-measure everything while your in there to make sure those figures are accurate.

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Author:	slantzilla [ Sat Nov 14, 2015 12:34 pm ]
Post subject:
Is it blowing out in the same place all the time? If yes it's the head/deck. If not I would explore possible lean/detonation. Piston tops all look good?

Author:	Rick Covalt [ Sat Nov 14, 2015 12:39 pm ]
Post subject:
Quote: different brand of head gasket. The Felpro should be fine if your surfaces are Ok. You could go to the premium permaseal gasket from Oz, but it has a large bore size.

Author:	SlantSixDan [ Sat Nov 14, 2015 12:53 pm ]
Post subject:
Quote: The Felpro should be fine I've had enough not-fine Fel-Pro gaskets that I go out of my way to avoid them. Quote: You could go to the premium permaseal gasket from Oz, but it has a large bore size. â€¦you could use a Victor-Reinz gasket from NAPA.

Author:	emsvitil [ Sat Nov 14, 2015 1:03 pm ]
Post subject:	Re: We keep blowing head gaskets.
Quote: We have always reused the same head bolts, but they pass a visual inspection and always torque down with no problems. Every blown gasket has been a Felpro printoseal, and it is always a cross-blow between two cylinders (but not always the same two). In fact, we're back on the track right now running on cylinders after pulling the push rods from the dead 2. Are the head bolts going back into the same spot? I'm thinking 1 or 2 bad bolts are moving around and that's where you're blowing. Or you're bottoming out a bolt so it doesn't have a clamp load but torques ok. (1 or 2 bolts could be too long) I don't recall if the headbolts have washers...... If washers are involved, check the thickness, a thin one might cause that bolt to bottom out........

Author:	CNC-Dude [ Sat Nov 14, 2015 1:58 pm ]
Post subject:
The blocks deck surface is often overlooked as needing to be resurfaced when a gasket blows. Sometimes you can get away with not doing it, but in performance or racing situations, its a necessity to at least check it if not resurface it also when you blow a gasket. It takes both surfaces to be flat and straight to seal, not just the head because its the easiest to remove and resurface.

Author:	Dart270 [ Sat Nov 14, 2015 2:56 pm ]
Post subject:
My thoughts: Check block deck for sure. If you don't know your max mechanical ignition timing (shoot for 27-30 deg), or haven't tested for max power or detonation (ideally on dragstrip) then I'd say you shouldn't be running the car at all. Idle timing doesn't mean squat. I wouldn't run 87 octane in an 8.8:1 motor myself for 15 hrs endurance - asking for trouble. Go 91-93 for cheap insurance - how much does a race weekend cost you in $$ and time?? I've reused head bolts many times with no problems. I always overtorque them (usually 85+ lbs) with a beam type torque wrench (not click type). Yes, in several steps. Lou

Author:	spacecommander [ Sat Nov 14, 2015 3:38 pm ]
Post subject:	Re: We keep blowing head gaskets.
Quote: Are the head bolts going back into the same spot? I'm thinking 1 or 2 bad bolts are moving around and that's where you're blowing. Or you're bottoming out a bolt so it doesn't have a clamp load but torques ok. (1 or 2 bolts could be too long) I don't recall if the headbolts have washers...... If washers are involved, check the thickness, a thin one might cause that bolt to bottom out........ I was wondering the same thing. If you have milled the head and decked the block and possibly gotten some garbage down in one of the bolt holes . . . Can you fully thread the bolt down without the washer on it? If you can't- you know you are bottoming out.

Author:	Charrlie_S [ Sat Nov 14, 2015 5:11 pm ]
Post subject:
While the head is off, check the deck with a straight edge. The factory did not use head bolt washers, but I would suggest using them. It will prevent the bolts from bottoming, and give a better clamp at the same torque reading. I'm also thinkingg you are getting into detonation. When I first started running slants, I had a problem with blowing head gaskets. After I cured the head gasket problem, I started eating pistons. I would rather the gasket act like a fuse (blow), then eat a piston. I had been running too much total advance. A slant does not like as much total advance a most other engines.

Author:	spacecommander [ Sat Nov 14, 2015 5:25 pm ]
Post subject:
Quote: While the head is off, check the deck with a straight edge. The factory did not use head bolt washers, but I would suggest using them. It will prevent the bolts from bottoming, and give a better clamp at the same torque reading. I'm also thinkingg you are getting into detonation. When I first started running slants, I had a problem with blowing head gaskets. After I cured the head gasket problem, I started eating pistons. I would rather the gasket act like a fuse (blow), then eat a piston. I had been running too much total advance. A slant does not like as much total advance a most other engines. Interesting comments on spark advance. Guess I'll be retarding mine when I put the rebuilt & milled head on as mine is as advances as it will go without backfiring on starting. I'm at 5500 feet. The more advance I have dialed in - the more power it makes. I run only 91 octane. The 400CFM Carter AFB was re-jetted to lean it out as it was running too rich at this altitude.

Author:	Dart270 [ Sun Nov 15, 2015 1:58 am ]
Post subject:
High altitude means less dense air and thus fuel burns more slowly, so you can run more spark advance and not detonate on the same fuel (or comp ratio) compared to at lower alt. This is why gas stations at high alt sell lower octane fuel in general. Lou

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