Is my exhaust riser correct?

[Dunromin]

I am reassembling a 1980-82 Mercruiser 470 after an engine rebuild. My question involves the face where the riser clamps on to the exhaust. Can anyone tell me why the exhaust has a water port on all 4 sides, but the riser elbow only on one, (casting #98561). Does this not limit cooling? The old gasket effectively blocked off the 3 unused ports. The engine was rebuilt due to a damaged piston, but the machine shop told me that all the pistons showed signs of overheating, and he blamed a lean mixture. Also, the oil was milky from water. This is my first venture into marine engines, and I would welcome any help in putting my mind at rest.

 

[dubs283]

Re: Is my exhaust riser correct?

all of the slots in the manifold are part of one cooling chamber, the one slot on the riser is there to exit exhaust cooling water out through the transom

since the engine is equiped with a closed cooling system, sea water is only needed for the heat exchanger and exhaust cooling - so, no the one slot does not limit cooling

milky oil may be a sign of a cracked head/bad head gasket due to overheat

the 470 is not a good engine to have for your first adventure in marine engines - do a quick search on "470" here in the forums and read on...

 

[Dunromin]

Re: Is my exhaust riser correct?

Thanks for the help regarding the riser. I started to figure out the 470 might not have been one of my smarter moves when I realised I had to remove the engine for a rebuild. Hopefully, it will run like the proverbial swiss watch from here on.

 

[dubs283]

Re: Is my exhaust riser correct?

it will never run like a swiss watch

it will run like a tractor - sorry

 

[Bt Doctur]

Re: Is my exhaust riser correct?

the slot you have in the riser/res. is to allow the A/F to enter the closed cooling system, it has nothing to do with the water coming out of the heat exchanger.That water gets out the riser thru the hose connection.

 

[dubs283]

Re: Is my exhaust riser correct?

the slot you have in the riser/res. is to allow the A/F to enter the closed cooling system, it has nothing to do with the water coming out of the heat exchanger.That water gets out the riser thru the hose connection.

bug!

didn't think those used the A/F to cool the exhaust

shows what i know, damn 470's haunt ya even when yer not near em!