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Old 02-01-2008, 05:02   #1
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No gasket in cast iron to alloy join = corrosion !

The heat exchanger in the Nanni 30 hp is an alloy box with a cast iron exhaust mixer at one end and a cast iron water intake at the other. The intake end is a bit corroded but the exhaust end is very pitted on the machined surface where the face meets the alloy exchanger. There is no gasket. Should I make a thin one to go on here or is there sealants that cope with both hot water and exhaust contents.
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Old 02-01-2008, 05:36   #2
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I would first 'build up' the corroded parts with ITW Phillybond, Devcon or the like, to get a smooth surface again.
Than you could make a thin gasket out of an old sea chart, and fit with a sealant that remains flexible like Permatex.
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Old 02-01-2008, 06:39   #3
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I have a different recommendation on the exhaust side.

The part you are dealing with should be a dry section of the exhaust. I would get a machine shop to surface the piece flat. Then make a quality thick gasket from gasket paper and coat it with a high temp sealant of you choice.
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Old 02-01-2008, 06:52   #4
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Definitely agree with the surface being machined. Forgot to mention that.
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Old 02-01-2008, 13:24   #5
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The exhaust mixer has both hot exhaust and hot water passing through in seperate ports. I noticed a sheet of gasket material at the local auto parts supplier that is the same as auto exhaust gaskets are made out of, it is a sandwitch of metal foil and something heat proof in the middle then indented with a regular pattern. It could be similar to head gasket material. What do you think of using that with some of the sealants.

Levelling the surface is certainly on the cards as the exhaust mixer need machining in any case due to some slight distortion from expanding alloy corrosion in the old joint.
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Old 03-01-2008, 00:02   #6
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I agree with NM and was going to suggest sourcing the composite gasket material designed for exhaust sections. I am not in favor of sealants on intake or exhaust manifolds. The surfaces should be true and the gasket should be adequate and that's all you need.

1/ Machine/repair the surfaces
2/ Cut a suitable composite gasket
3/ Make sure you are using correct/suitable bolts or studs and nuts
4/ Torque it up evenly
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