2F Hesitation/stumbling at various RPMs (1 Viewer)

[Yankee]

If the manifold assembly has never been machined flat by a machinist in the past, it’s guaranteed to be warped and not sitting flush on the head. At this point- all virgin 2F manifold assemblies are warped. Mine was warped in 1988 when the engine only had 42K on it.

Does the bolt holes that connect the intake and exhaust to the engine head need to be machined as well after the front surface has been machined flat? I'm suspecting that my issue might be that since the surface was machined flat, the bolt doesn't sit evenly between the intake and exhaust holes. The bolt, when torqued down to the head, torques the exhaust side down but not the intake as the surface is slightly below the exhaust side. This is making me think that the intake wasn't getting fully bolted down since its bolt holes are not even with the exhaust holes. Does this sound reasonable? If the holes are not even, is there a process to get the bolt hole sides to be even that isn't guess and check?

 

[mattressking]

Does the bolt holes that connect the intake and exhaust to the engine head need to be machined as well after the front surface has been machined flat? I'm suspecting that my issue might be that since the surface was machined flat, the bolt doesn't sit evenly between the intake and exhaust holes. The bolt, when torqued down to the head, torques the exhaust side down but not the intake as the surface is slightly below the exhaust side. This is making me think that the intake wasn't getting fully bolted down since its bolt holes are not even with the exhaust holes. Does this sound reasonable? If the holes are not even, is there a process to get the bolt hole sides to be even that isn't guess and check?

You won't like what I'm going to say but the best method to machine these things flat is to loosen the assembly, put new gaskets in, leave the 3 mounting bolts very loose, then clean the mounting surfaces to head and bolt down tight without gasket to head. Then tighten the 3 bolts that combine intake to exhaust manifold.

Once tight and aligned, then you put on a surface plate and measure run out, not to exceed .5mm. If it does, time to machine, if it doesn't, I highly recommend stock gasket with copper rtv to seal up versus machining.

Folks like the Remflex but they are sensitive gaskets, I'm not much of a fan long term.

 

[OSS]

This is a common issue. The half circle bolt ‘flange’ on the exhaust manifold doesn’t line up with the corresponding intake manifold one— so only one of the manifolds gets clamped tight to the head at that spot.

The workaround is to use half circle washers as shims — set on the low flange to level out the difference so that the bolt or nut will compress the pair evenly.

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@2mbb

 

[Yankee]

I got some washers and cut them in half to use as half circle washers, but the issue is that the washers are too thick (even just being around 1.5mm) and cause the intake flange to be higher than the exhaust flange which would then be the opposite problem. The difference between the intake and exhaust flanges height wise is about 0.5mm. Is there something a machine shop could do to make these flanges even? I tried having the machine shop I usually go to do something about the flanges but the guy I was talking to just said to use half circle washers as well and that they couldn't do anything. Maybe if I talked to a more experienced person at the shop they would know of something they could do. Any suggestions for what I could ask them to do to help?