The Stovebolt Site Forums The Shop Area Engine Shop Intake/exhaust question

I keep having a problem with a leaking intake/exhaust manifold on my 261. My questions are: do I need to take the intake/exhaust apart to properly seat the two parts? I've had it planned down smooth but it still seems to leak. I have not separated the two units before planing or attempting to mount them. Anyone done this job successfully? I thought it would be easier and simpler to mount it as one. Should I take it apart and try it?

Help???

On the 235 there are 3 alignment rings that go into the intake manifold that position the intake gasket. I experienced some vac. leaks as the PO hadn't bothered to install them. It was difficult to get the intake gasket properly aligned, which would also effect the exhaust gasket. Hence, leaks!

If your manifolds were trued as a unit, they should bolt up properly as a unit.

One of the 261 guys should verify that the alignment rings are or aren't used in that engine. Hopefully, this will steer you in the right direction.

Thanks. I have the three intake rings. I'm wondering since it was trued, are the intake rings now keeping it from sealing completely? What happens "if" I do not use the rings? I'm going to try to mount it again in the morning.

And I've been told that nobody makes a repop version of the intake/exhaust. Anyone know if that new part information is correct?

Virginiafiretruck,

I have seen folks mention grinding down the alignment rings to compensate for material removed when the intake/exhaust combo was surfaced. If lots of material has been removed, the rings have the possibility of keeping the
assembly from fully seating.

Unless the intake or exhaust were broken, replacing it would be for naught. If this intake exhaust was surfaced properly as a unit bolted together, and not disturbed when reinstalled, it MUST be flat. The manifold bolts must have sufficient threads to pull all this down tight.

Stuart

You can check the depth of the three rings in the manifold and head and plane them down as necessary.I would not leave them out as it will suck the gasket in.Loosen the three bolts that hold the intake and exhaust together and then install it on the head.tighten the manifold bolts(to head)from the center out to the ends.Good luck.

If the manifolds are not leaking exhaust between them I would not separate them. It would probably start a new set of problems. The bolts or studs often break & are hard to remove. The fellow bolters have good ideas on the intake rings. You can put a layer of copper RTV on the gasket to help seal it. Also I would replace the bolts with new grade8 bolts & use a flat washer under them.

I'll go one step further than Wrenchbenders suggestion-studs. I had a similar problem (no machining, but leaks) after installing studs and replacing the 2 end pilot studs with bolts, the leaks were eliminated.

Don't over torque the bolts and as gtow69 said, follow the correct tightening sequence.

The torque specs for those bolts is much lower than what most people expect it to be and overtorquing causes the manifold to seat incorrectly.

The torque is 30 lbs for center exhaust bolts,20 lbs for end exhaust bolts and 35 lbs for intake bolts I think, but that should be verified with automarc or someone with a shop manual.

The set rings for the intake manifold should be ground down to compensate for the amount that was machined from the manifold.

Hobert

Center clamp bolts-15-20 ft. lbs., end clamp bolts-25-30 ft. lbs.

Thanks for the info. I'll see what the morning brings as I try to set it again.

Well we tried it several times and several ways without luck. It still leaks. I've ordered a used intake/exhaust manifold(Denton texas) and will have to wait for it to arrive. I hope that fixes the problem as the truck is ready to go to the body shop.

Virginiafiretruck,

Just out of curiosity, did a commercial automotive machine shop surface the intake/exhaust combo, or was it done elsewhere.

Stuart

It was done at a commercial machine shop as one unit. It appeared to have been done before I had it done. There is no surface left to plain down. The manifold is flush all across the entire surface top to bottom and for to aft.

What does the manifold surface on the head look like. If it leaked for an extended period of time or was exposed to moisture for a long time it may be in bad shape, we see this quite a bit on older engines at the shop where I work. It shouldn't show any signs of rusty pitting where the gasket seals. Just a thought.

Sean

It looks smooth but there is no flange mount surface. It looks flush with the entire intake and exhaust pipe face. I've never seen the intake/exhaust from any other chevy but I would think there should be some type of flange mount surface that is built up beyond what I have on this intake/exhaust. I'm hopeful it isn't the head that isn't flat. If that is the case, the back up intake/exhaust I orderd from Denton Texas might solve the leak problem. If it's the head, then I'm in deep trouble...

Here is a great one-piece gasket and studs kit for 235/261, that works really well without any leaks. The gasket is really thick.

http://www.merchantamerica.com/chevyhotrod6/index.php?ba=product_enlarge&product=57209

The owner is a well known and knowledgeable builder, who can make just about anything.
Great to talk to over the phone.

I'll need a new gasket so I ordered the problem kit. Thank you for the contact link.

Question #2: Do the studs/guides on each end of the exhaust manifold mount location screw in(threaded) or are they pressed in non-threaded studs? BTW: I'm askng about a 235/261 motor. Thanks.

They are threaded and unscrew easily with a pair of vise grips.

Thank you!

They do unscrew. They can be frozen in the head though, so before you cinch your vise-grips down and start 'oinking'..do some wiggling and apply some penetrant. Busting one off in the head can ruin a good day.

Double nutting the studs for careful removal with a wrench could be an option too.

Stuart

Thanks. I guess the studs would actually turn clockwise to unscrew from the head?

As Toyvo would say..lefty loosey, righty tighty! Lefty loosey being CCW.

Stuart

They're also 3/8" coarse thread. Mine actually came out really easy, but do be carefull, don't want to break one off in the head.

Thanks again. It is nice to have folks who have experiance on the stovebolts.

i wouldn't use vice grips, double-nut it and use a wrench. if they are really tight, heat em up with a torch at the head. every one i've heated came right out.

Can't double nut the stud/guides on the ends...
They usually come out easy, unless you got a badly rusted head.

I'm with Darin367 on this one. try the vice grips but if they don't come out easily ( and they probably won't) Heat them very hot, they don't have to be red hot. Let cool some and they will usually come right out.

Thanks. I'll try that when the replacement manifold arrives.

Does this trick work with the studs/bolts on the flange side too?

Mine are threaded right up to where the nut would cinche down...and then stripped so you get close to tight but not all the way.

Thanks

usually heating up any stuck bolt does the trick..not always but most the time..

The replacement manifold arrived this morning! I can clearly see a flange around the exhaust ports. I guess the one that is leaking on the truck has been plained atleast .25". The repacement one needs to be cleaned up and painted before I try to mount it. In looking at the replacement, it would seem to me the "problem kit" with the thick gasket, new intake rings and the new bolts/nuts vs. the alignment studs (on each end) will do the trick and stop the leaks.

I'll work on it over the weekend and get ready to put it on the fire truck come Monday morning. Thanks for all the help and advise. I'll let you know all if it works! Thanks again.

One more question before I try this again on Monday morning: Do you use a gasket sealer on this gasket? It would seem the answer is "no" but I figured I'd ask before I give it a shot.

My answer would be the same as your answer. Nothing looks more ameteurish than Kopper-Koat smeared all over everything...everyone has their opinion, and that's mine.

Stuart

I'll second the cheesy look of sealant, but then I only ever use Aviation Form-a-gasket in proper amounts. Great stuff, even used it on a plane or two.

So anyway, the manifold assy on my 270 is more crooked than my teeth, both end studs are broken off in the head, and the exhaust manifold is in sorry shape. I'm hopeful that some machine work & prayer will get the manifolds apart & back together with a new gasket & off to be machined flat. Gonna get the head match machined to the manifold while I have the beast apart. In case it doesn't work out I have been eyeballing the two piece exhaust manifolds on E-pay.

Here's an issue I have tho, I'm short two of the clamps that go between the manifolds at the 1-2 & 5-6 cylenders. Yanno, the lil rocker arm looking bits?
Anyone know where I might get a couple of those?
Thanks!

I might have a couple at the garage. Send me an email or PM and I'll look on Monday when I go down to the garage.

Freq2002: I have those "lil rocker arm" looking things if you are interested. Let me know.

Anyway, I used the problem kit bolts with the thick gasket this morning. It appeared to solve the leak issue. I had to leave early but I'll try it again in the morning (instructions say to heat it up and tighten the nuts three times)when I have a little bit more time to warm up the truck. Question: How in the world do you reach the last bolt on the manifold(closest to firewall) with the motor in the truck? I had a beast of a time trying to tighten that bolt down. BTW: The studs on the ends of the head unscrewed with vise grips very easily. Thanks for the tips. I couldn't do this without you all helping me.