New exhaust manifold

[Snowbird]

I bought a new exhaust manifold as mine was trash. However the 2 bolt holes on the front and rear tracts are not 5/16 but are 1/2" diameter.The 5/16" studs look lost in those big holes. Am I missing something?

[Arjan]

Good Morning,

What engine, what fuel and some pics please.

[secondjeremy]

Its probably to provide for expansion - which can cause manifolds to crack.  This is why many manifold fixings (like 2 inner combined ones on the LR 4 cylinder petrol) are lugs cast into the manifold and cast steel clamps to secure the manifold - and allow it to expand and contract.

If its a petrol the register of the manifold on the head is controlled by dowels - and the exhaust is rigidly fixd to the inlet at the centre - form which it will expand outwards.

When re-fixing used manifolds its always a good idea to make sure that the movement isn't restricted by rust in the bolt holes - ie clean them out thoroughly.

 

[Bowie69]

Very common to use large washers on manilfolds, e.g. The old A series engine, as above it allows things to move to allow for expansion, as well as poor manufacture

[Snowbird]

Thanks guys for the info, you guessed right it's a series 3 petrol. Will get some large thick washers to put on those 4 mounts. The old one had normal 5/16 bolt holes and was a sod to get off and was cracked in numerous places. Will take pics Arjan and post.