STOCK EXAUST MANIFOLD BOLT HOLES

[SY1096]

Are the exaust manifold bolt holes on you guys trucks larger on both ends and a smaller, tighter fit in the middle holes? Mine are. My truck has been down since October. My son is installing my engine for me since I am disabled to do so. The manfolds will not fit now. Will they shrink enough in the cold air off the engine for a few months so as to not fit? Or is it that the stock manifolds are just junk?

 

[TurboTony]

The outside bolt holes are supposed to be a bit larger.

It is very typical for the stock manifolds to "spring" a little bit when you take them off. That problem dates back to the small block chezy roots of the 4.3 and it's manifold design.

You can buy tools called exhaust manifold spreaders to reinstall the manifolds. They are basicly a big forcing screw that spreads the manifolds apart a bit to help get them back on. Without the spreaders I very much doubt you will be able to get them back on. Just be very carefull with them and go slowly, it is possible to crack a manifold with them.

HTH

Tony

 

[CLONE]

I've found that heating them up with a torch on the longer stretches between the ports works. You don't have to get the whole manifold hot, and don't heat the flanges. Also make sure to wear long sleeves and heavy gloves when trying to put them back on.

 

[Sy#26]

Agree w/ the heat trick - I put mine in a 250° oven for an hour or so, they went on fairly easily. Wife is used to the oven being used for odd things....

 

[Falco]

Yep, I put back my manifolds a month ago. Passenger side went back quite well, however for driver side I had to drill up two of the holes a bit to make it fit. Not the best solution, but I can't see any real problem to do it this way...

Later,

 

[SY1096]

Ok. So you drill or spread the exhaust manifold to get it mounted. With the bolt holes being oversized does this not offer the effect of the center point of the ports shifting from location to location on the exhaust port on the head itself? This I think would cause a miss-match wouldn't it? I looked at my old LB4 head. There was a miss-match when looking at the exhaust buildup around exhaust manifold entrance that suggested a miss-match. I also found a residue buildup on the exhaust port on the head also suggesting a miss-match. If all this is happening because of the oversize bolt hole in the exhaust manifold, then we all maybe suffering from uneven flows in our exhaust systems.
What do you guys think is the best way to match these ports properly, short of installing new headers or manifolds? My personal opinion is to port the exhaust manifolds enough to offset any shift that may occur from expansion or contraction while the manifolds are mounted on the head and in use. Feed back would be appreciated.

 

[Falco]

You are right. As far as I remember the ports on the manifolds are much larger than the on the heads. So, even if it's a bit missaligned it should work, IMHO. ALso I had to drill up the holes by one mm only on both sides...

Later,

 

[Sy769]

I had a severe mismatch on my passenger side manifold. It was so tight that it ruined the threads on the bolts as they threaded out. Be very careful drilling as I came through the port on one. I repaired it but haven't put it on yet. I may try the heating method. I am glad someone posted about this problem-hadn't heard of it before on sytys.

 

[SY1096]

I think that once you do heat it enough to allow the insertion of the bolts, this does not automatically align the ports. The size of the exaust manifold ports are not large enough over the size of the head ports to compensate. You guys that have engines pulled down right now, that have not cleaned the surfaces of the exaust ports, check um out and let everyone know what you have found. How much of a miss-match, if any did you find? I found enough to really worry me.