Remove Sheared Exhaust Flange Bolts

[BonChance]

Dear AFourians,
This is my first post. I am very grateful for all encouragement. I'd like to bolt on a new MMI exhaust hot section with water entry fitting, Catalina 27 style. The outboard bolt sheared off and it looks as though the inboard bolt had already rusted through. My plan is to use a screw extractor kit then drill and tap new threads for the new bolts that came with the new hot section. Please weigh-in? Thanks so very much -- Art

[BonChance]

Photos

[zellerj]

I would caution against a screw extractor, they are hardened steel and prone to breaking also because hardened steel is brittle. The broken bolt is fairly soft so can be drilled out quite easily if you have access. Use a center punch to avoid the drill wandering. Use a small drill bit and increase size. If the threads are ruined, just re-tap with a slightly larger tap.

For the bolt sticking out, I would get it cherry red with a torch and quench with water. That will break the bond. Then with patience, try to unscrew using a vice grips. May have to do the heat/quench cycle a few times.

[Dave Neptune]

BonChance, the manifold end looks pretty poor. The end will need to be filed or machined flat for a good exhaust seal for safety reasons. Per Jim a good deal of patience MAY break the studs loose as well as drilling carefully.

I would do a pressure check on the manifold before proceeding with the possible extractions. It is an easy test and can be done with the manifold still attached to the block. With the amount of rust outside it will be worth checking first as a leak is a no good manifold.

Dave Neptune

[BonChance]

Manifold Pressure Test

So grateful for all the suggestions. Would you please say more about how to pressure test the manifold?

[tenders]

There are various ways to effect this testing, from refined to redneck. My approach tends towards the latter.

https://www.moyermarineforum.com/forums/showthread.php?t=11068

https://moyermarineforum.com/forums/showthread.php?t=7221

[JOHN COOKSON]

If you get the bolts out of the old manifold or end up getting a new manifold studs instead of bolts are an option.

ex TRUE GRIT

[ndutton]

How much time does anyone estimate it will take to drill/extract and re-tap the manifold holes and dress the flange mating surface? What is that time worth compared to - or put toward - the cost of a new manifold?

[Al Schober]

Is this a crack?

[BonChance]

Is this a crack?

Thank you -- I'll check today. I was able to drill out the centers of the bolts with progressively larger drill bits. I'm up to a 1/4" hole in each. Some issues with the manifold crumbling some beneath the bolt that was in particularly rough shape. I want to get the boat in the water for the rest of the season then see about pulling the engine this fall for overhaul or replacement. So I drilled into the manifold (plenty of solid metal even after crumbling because appears to be no water jacket around the inboard bolt) and planning to use longer bolt with sealant on it after re-tapping new hole. Slip already paid for, ugh! Any other help gladly received. Thanks all!

[TimBSmith]

I found this hot point and failure point on an old manifold....

Worth poking around this area that thinned out on this old manifold.