ANOTHER EXHAUST MANINFOLD QUESTION 2F (1 Viewer)

[SHERMAN FJ62]

LAST YEAR AFTER 32 YEARS THE EXHAUST MANINFOLD GASKET GAVE OUT ON MY TRUCK.. TO SAVE TIME I PURCAHSED A USED INTAKE AND MANIFOLD, HAD A MACHINE SHOP PUT THEM BACK IN SQUARE AND REPLACED ALL THE PARTS AND DELETED THE HEAT RISER FLAP IN THE EXHAUST MANIFOLD. I ALSO REPLACED THE EXHAUST FROM THE DOWN PIPE BACK. I HAD A TOYOTA SHOP/ MECHANIC REPLACE ALL THE PARTS AND REINSTALL MY CARB. ONE YEAR LATER THE LEAK IS BACK.

SHOULD I HAVE DOUBLE UP ON THE GASKET LIKE SOME PEOPLE HAVE DONE?
SHOULD I HAVE THE EXHAUST MANIFOLD PUT BACK IN SQUARE AGAIN?
SHOULD I JUST REPLACE THE GASKET AGAIN WITH A OE MANIFOLD GASKET AND CALL IT A DAY.
ANY OTHER RECOMMENDATIONS.

THANKS

TRUCK IS DESMOGGED.

 

[micruz60]

Try torquing down the bolts / nuts again.

 

[CaptClose]

^^^What he said first. Then pull the manifold and measure it up to make sure it isn't warped. You just need a straight edge and a feeler gauge and measure down the center line and then corner to opposite corner, per the FSM. And can't remember offhand what the factory tolerance is, but it's in the FSM and you can look it up. If it checks out okay, there's no need to machine it again.

Make sure you inspect your intake manifold for cracks under the carb too. That's pretty common. Also, if the manifold is true... make sure your block is square and true as well. I've heard that they can warp too.

After all that, throw another OEM gasket on there and see how it seals up. A lot of guys are putting two gaskets on like you mentioned. If it gives you peace of mind, do it. Either way, be sure to come back after several warmup/cool down cycles and retorque the manifold to spec (34 foot pounds if I remember right). Some guys are also over torquing a bit to be sure. Probably the same guys that are doubling up their gaskets haha.

That's about it man. Good luck.

 

[60 toy ota]

Just out of curiosity, why would you replace a manifold if it was just the gasket that went out?

 

[LAMBCRUSHER]

have a spare to machine and the truck isn't down for so long. that's what people who rely on their 30YO rigs do to stay in front...besides, it never hurts to have one on the shelf.

 

[BlueLow]

Have you measured intake vacuum?
What's your definition of a leak?

 

[jestlurnin]

I've done 4 exhaust/manifold to block gaskets on 2 60's over the last decade and my leak always returns....

I've done everything everyone has noted above and more. Literally followed the FSM word for word and several extensive MUD posts and my leaks always come back.

I've had 78' 40 for 7 years that has a double OEM gasket (not my doing) and it hasn't started leaking on me yet.

If I ever do another it'll be double OEM gasket for me....

 

[Output Shaft]

The side of the head that mates to the manifold can warp (a little tidbit left out of the FSM). Until the side of the head gets machined flat again (if it's warped) the manifold will never maintain an air tight seal for long.

 

[jestlurnin]

Well crap. If you gotta machine the side of the head every time you are fixing the intake exhaust leak this job just got very expensive and time consuming....

Like I said, belt and suspenders, next time I'm just gonna double up OEM gaskets...

 

[CaptClose]

I think OS is saying that it's just a "possibility" if you're having chronic leaks, even after changing the gasket. It's something to check out.... But yeah, I would be in the two gasket camp as well!

 

[gregnash]

Yeah I think when I actually get around to replacing the rest of my exhaust system I am going to do the two gaskets. Have had one since I rebuilt the top end and SUPPOSEDLY the shop my headshop farmed out the manifold to knew what they were doing but I have had a slight leak since. At first I thought I was because I put the gasket on backwards and so I purchased a second gasket and replaced completely instead of just flipping (wasn't sure if the old new was damaged or not)... Had thought about doubling up at that point but never did. Oh well.

 

[SHERMAN FJ62]

Just out of curiosity, why would you replace a manifold if it was just the gasket that went out?

Because I know enough to know what I don't know. I didn't want to break everything down and find out that the manifold or intake was cracked and scramble to find a good one, so I acquired a new set and had them ready to go.

 

[Landpimp]

I did the same thing(82 fj40) bought a new OEM manifold set(as well as last OEM carb out theree).........but that was many years ago(and not all that speedy) but those are long gone now.

When I did the 60 last summer I just use OEM gasket, had old manifolds machined together, re-installed......no issues so far.

Because I know enough to know what I don't know. I didn't want to break everything down and find out that the manifold or intake was cracked and scramble to find a good one, so I acquired a new set and had them ready to go.

 

[LAMBCRUSHER]

if the rig has been run for a while with a manifold leak, the chances of a warped mounting deck go up. many of these things have been run for over 20 years without any real attention, so it wouldn't surprise me to find the head needed shaving too. I had my head flat decked on the block surface and the manifold surface.

 

[FJ40Jim]

The manifold bolt holes are out of level because the manifolds were warped. Most (all?) automotive machine shops don't bother to mill spotface them back to level after machining the gasket face flat, resulting in unequal clamp loads on the gasket, which allows the unclamped half to fail.
There are various bandaids to cover up the problem: stacking gaskets, using overly soft/thick gaskets, overtorquing fasteners, machining half washers to make up for the thickness variations at all the bolt holes...
Ultimately, the best fix is to just machine the parts correctly.

 

[jestlurnin]

Jim can you elaborate on what spotfacing the manifolds is. Does that mean the surface where the exhaust/intake manifolds interact (away from the engine block) where there is a gasket that sits in between them needs to be machined flat? Both exhaust and intake manifolds need to be machine flat at that interaction?

 

[FJ40Jim]

Yes, spotfacing Is machining around a bolt hole to provide a flat bolting surface.

 

[gregnash]

So basically what you guys are saying is that due to something not being "tacked" in the bolt surfaces to ensure that the bolt mounting surface is level FIRST before machining the face, the shop therefore machines it incorrectly thus creating and inaccurately machined surface? Crap... well guess I need to order ANOTHER gasket from Onur and double the bastard up.

 

[Output Shaft]

The desired end result is to have the manifold mating surface flat and all the intake & exhaust bolt cutouts flat with each other where the washer & bolt contact both manifolds.

So what you want is when the bolt is tightened up, (or nut on the stud) the bolt head (or nut) clamps down on both the intake and exhaust flanges equally. If one side is sticking out a bit, the bolt/nut won't clamp down on the other side as firmly... = potential leak.

 

[jestlurnin]

This thread is making me feel better about my mechanic skills. It's not that I screwed it up it's the guy that machined it...

Seriously though thanks for that guys. Next time I have a manifold machined I'll know what to ask for.