Mercruiser 4.3 cracked intake manifold

[nola mike]

Glad to help out. The 35 ft lbs is for the pre-vortec that I have. I saw that bulletin as well, I'm not sure who made the mistake (GM or Merc) but yes there was confusion about that. Its because the composition of the gasket changed, the older ones were not as sensitive to overtorquing, the new ones are a plastic/rubber type composite and over-torquing them can distort the rubber or break the plastic.

Or snap a bolt off in the head (ask me how I know that one)

 

[LWD]

As I prepare for installing my intake and putting my boat back together, I have a few questions.

1. - My intake manifold bolts look like they had some kind of greenish looking loctite on them. Do I need to use loctite on any bolts, and what kind? (intake, distributor clamp, thermostat housing, carburetor)

2. - What type of gasket maker should I be using for the intake manifold front and back ends, the China walls? The gasket material I removed was black and rubbery.

3. - Do I need to drain the water with each oil change, what's the purpose for that? When I drained the block after this happened, I did not see any oil in the water that came out.

4. - Is it a good idea to use temporary guide bolts when setting the intake into place?

As always, thank you for help!

I haven't worked on a motor like this in a long time, my stress and anxiety levels are slowly rising...

 

[Lou C]

I doubt it is loctite, it might just be gasket sealer, I'd clean it off to make sure your torque readings are accurate, anything that puts a drag on the threads can result in your inadvertently overtorquing things. When I did mine I just put a light coat of OMC gasket sealer on the threads (this is mainly to prevent corrosion and make any future dis-assembly easier, as I'm in a salt water region). If you want to be really fussy you can use thread chaser to clean out the bolt holes in the cyl heads. When you do a head gasket or replace cyl heads like I did, this is a must, those head bolt threads get gunked up with junk because of the raw water cooling.
*HOWEVER* this is just my opinion, I don't have a current or past Merc manual or GM manual that covers the newer Vortecs, if I was working on one I'd follow exactly what they say.
As far as guide bolts, not a bad idea but you'd have to take your manifold bolt to a hardware store, buy a longer one, cut the head off and cut a groove in the end to remove it with a screwdriver after setting down the intake. The Vortec bolts go straight in so this might work, on the pre Vortec you can't because they are at an angle. There are guide pins on the gaskets and 2 holes in each cyl head to hold the gasket in place, so for that reason its easier on the Vortec than on the Pre Vortec.
The only reason to drain the water out with each change is if your water in the engine issue is not resolved. Once you fix this you should be good, run it for about an hr to burn off any residual moisture.
I did that because I couldn't take the engine apart right away, and had to pickle it for a few months before pulling it apart. When I did there was no rust in the cyls, or anywhere else for that matter surprisingly.

 

[LWD]

When I did mine I just put a light coat of OMC gasket sealer on the threads (this is mainly to prevent corrosion and make any future dis-assembly easier, as I'm in a salt water region).

Maybe this is corrosion, it is inconsistent on the bolts. I wire brushed them down, and I have a different bolt that I ran in and out of the holes to make sure they did so. I shop vac'ed the holes out.

 

[LWD]

I installed my intake manifold, and I'm on my 3rd oil change so far.

Trying to think ahead, which I should've done sooner... I will need to check the timing, and according to the service manual there's an EFI Timing Tool that I need to use, part # 91-805747A2. It will take at least a week to get one off the internet. It's basically just a jumper, and if I remember right, there's a way to make a jumper. Has anyone done this, and where is the DLC?

 

[LWD]

I got everything squared away with the motor, and so far I've put over 3 hours on it. My oil pressure fluctuated some to start, then steadied out, and ran great this weekend. I appreciate all the help getting my boat back on the water, this is a great group. Thank you!