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  #1  
Old 01-07-2011, 12:18 AM
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Default Cracked exhaust manifolds

I am about ready to buy the parts to swap out both exhaust manifolds on my 4.3L. The drivers manifold has about 1" spider crack and the passengers is showing the start of a crack. After looking at manifolds in the wrecking yard I could see this is a problem with about half the cars in the yard. Then I started to think what could be causing this failure on so many cars, and then it hit me the motor mounts might the cause of this. I checked mine and they are cracked and worn out.

So here’s my question: I am going to replace the mounts as I do the manifolds. After pricing used and new manifolds what would be the best idea for the respective price. I can buy new manifolds for roughly 100 bucks a pair, buy used pulled from the car for 80 bucks a pair or pull them myself for 65 bucks a pair. The new manifolds are aftermarket, not sure it that matters, the used parts are genuine chevy - but who knows if there are any hair line cracks on the used manifolds?

Last edited by Cidium; 01-07-2011 at 12:32 AM.
  #2  
Old 01-07-2011, 12:24 AM
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Honestly, if it were me, I'd put headers on rather than replacing with stock manifolds. I mean, if you are going through the hassle anyways...
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  #3  
Old 01-07-2011, 12:31 AM
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Well besides the price, like another 200 bucks for headers everything i read said the stock manifolds flow pretty good. After looking at the manifold they don't seem to restrict too much. But if i had the extra cash i probably would do headers but for now i need to get this problem repaired.
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Old 01-07-2011, 06:19 AM
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Also if you do some research it seems the headers don't do much but really change the tone of your exhaust. Do you know if the brand new ones have any kind of warranty? I used to work for Advance Auto and there's a lot of parts that is better than oem quality. That's not saying every aftermarket part is. Somethings you do need to go with delco on. But if the brand new ones has a decent warranty that'd be the route Id take personaly.
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Old 01-14-2011, 03:42 AM
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Here's the update. I got the motor mounts and all the exhaust gaskets new from autozone. I have the aftermarket manifolds in route from a parts seller on ebay. Total investment: $178.00 this should be final unless I break some collector studs. I have been spraying penetrating oil on the studs now for about a week so I am keeping my fingers crossed they come out. I need to get this done ASAP, both right and left manifolds are showing progressing cracks, once I get all the parts in hand and have a clear day to repair them I'll post a few pics.
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Old 01-20-2011, 12:22 AM
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Arrrgh! I started in on this project today, didn't think there was going to be as much BS to this, but I was wrong. Here's the list of BS so far: The bracket that holds the alt, and power steering pump has to come off, ok no big deal till you need a puller to get the pulley off the PS pump. This bracket is using the front 2 manifold bolts, there is no way around it, the PS pump needs to be removed. Passenger side manifold was cake to remove, just make sure you use a 6 point socket, a couple bolts needed a wobbler to get out. Getting the main bolt out of the drivers side motor mount is a 2 person job, and about 2 1/2 feet of socket extensions, oh and a wobbler too. Getting to the passenger mount is a little easier after you pull the starter, just one problem there, the inspection plate needs to be loosen before you can move the starter out of the way. All GM needed to do was make the starter nose 1/4" shorter to allow it to passed by the inspection plate. The 2 of 3 mounting bolts on the passenger side mount are pretty easy to get to after you raise the engine, the famous 3rd, lower bolt is a pain in the royal ***. I know why some guys have posted they leave that bolt out. What I did to get it out was size up all my 9/16 deep sockets till I found the shortest socket and sized all my ratchets till I found the one with the narrowest head. This combo barley fit and i was able to get the 3rd bolt out. The install wasn't any better, the motor mounts from autozone were slightly different, that ratchet and socket I used to remove the bolt wouldn't fit to install the lower bolt on the new mount. After about an hour and trying a ton of different ways i finally got the passenger mount in place with all 3 bolts. The only thing I had to modify was the heat shield that protects the mount from the exhaust, slotted the holes so it could be dropped in from the top. I'll post some pictures next time of how bad the autozone mount matches to the original parts.

So after today here's what i got done so far, removed the passenger manifold, removed and installed the passenger mount. Got all but the (2 bracket bolts) off the drivers manifold and removed the main bolt from the drivers mount. So far have about 8 hours and a crap load of yelling into this project.

I should mention my blazer has a 3" body lift - FOR THE LOVE OF GOD - thank you whomever put the body lift in. I can't imagine doing this without a body lift.
  #7  
Old 01-21-2011, 12:10 AM
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Day 2:

Things didn't get much better today. Got the pulley off the PS pump and removed the pump bolts, with this done I could lift the pump and bracket above the manifold bolts.

Click the image to open in full size.

I got the manifold out by moving the front driveline and removing the shifter arm from the trans. The drivers side motor mount was toast, hard as a brick and cracked. In these pictures I am showing the difference between the stock mounts and the autozone replacement mounts. Big problem is where the top half, motor side, bracket is bent. They shorted the base material by a 1/4" so the square washers don't line up with the bracket holes. I just made sure to wrench them down good. The heat shield was also having placement problems so I just slotted the holes and installed from the top. I like this better for a couple of reasons, these shield are freaking sharp so installing at the end seems better and with the shield now protecting the mount metal it might give some longevity to the mount.

Click the image to open in full size.

this pic shows how far off the washer is to the hole

Click the image to open in full size.

here's a couple of pics of what started this whole nightmare. Come to find out the passenger side had 2 cracks, one at each end. The drivers side had almost a complete 360 crack.

Click the image to open in full size.
Click the image to open in full size.

So, end of day two, I got all the old parts out and have both new mounts in place. Also have the drivers manifold in place, just needs to be bolted in. Still need to install the passenger manifold but after the drivers side it should be cake. Should have the blazer back and running by tomorrow - LOL
  #8  
Old 01-23-2011, 12:56 AM
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I can put this project in the "done" list. Yesterday was a rain-out, working in the driveway, so I finished up today. Ran into a big problem today with the passenger manifold, this is not fault of the supplier, just a crappy casting mold. First thing i noticed on these aftermarket manifolds was in huge letters the word, "CHINA". Overall the casting thickness is thinner than the GM parts, but for the price some corners were surely being cut. Here's where the problem is, cylinder #6 exhaust port is shaped different from the GM part. GM has a nice arc on the inside of this port but the aftermarket comes down to a corner which makes getting the heat shield and socket - impossible - sure this makes one of the weakest points a little stronger but also makes changing that plug a nightmare. I had to loosen the manifold, removes the two bolts holding the heat shield and then screw the plug in by hand. Then I could get a socket on it to finish tightening it, and then installed the shield and bolts. In the long term the problem is going to be the heat shield resting on the manifold and the sparkplug boot resting on the heat shield. (I'll post some pics in the next couple of days)

Something that is still baffling me is that lame-*** power steering/alt bracket that I pictured above. After assembly of the PS pump and pulley, the alt wouldn't line back up with this bracket. I have no clue why the position of that bracket would have changed, it was off by almost an inch from the back of the alt. After scratching my head for awhile I decided to grab a 12" crescent wrench and bend the crap outta this bracket till it matched.

I feel really lucky, only busted on flange bolt, and at a cost of 6 bucks a bolt assembly that put the total investment for both manifolds, both mounts, and gaskets at around 184.00 bucks. I am not a speed wrench, I like to take my time check stuff out, had 3 days into this project but someone could do this same project in about 10-12 hours.

First thing I noticed was better low end power from a stop. Since both mounts were busted, there was alot of torque getting lost. The sound of that exhaust leak is gone, one of my pet pevs is a leaky exhaust. There is alot less vibration at standing in gear too. Here's my final thought: If you are on a budget, like me then these parts will do. Just be prepared to make some mods and find something to throw a wrench at when you get pissed. Otherwise, if you got the bank spend the money on "quality".
Old 01-23-2011, 12:56 AM
 
 
 
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1995, 95, 97, blazer, bolt, brace, chevy, cracked, exhaust, heat, manifold, manifolds, motor, mount, remove, shields, size, starter


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