Hot Exhaust caused by Melted Butterfly/Flapper

[Michael Clemensen]

Almost have “NO Roses" back together after the Overheating and HOT exhaust issues. To recap, twice last year the Power Plant had insufficient raw water flow due to a damaged impeller.

This damaged impeller last year caused the exhaust butterfly/flapper valves to become overheated by HOT exhaust gasses and the PORT butterfly/flapper melted and fused to the shaft and end bushings.

Functional STBD Butterfly/Flapper

Damaged PORT Butterfly/Flapper

This Spring after replacing both the U-Joint and exhaust bellows in addition to a new impeller the power plant was started. It was experiencing a HIGH Temperature on the PORT, what Volvo Penta calls the “UPPER EXHAUST PIPE." At 1500 RPM's hooked up to muffs the temps were normal throughout the entire exhaust system, BUT at idle, 700 RPM, the PORT upper exhaust pipe slowly increased in temp until it read 160+ degrees on the infrared thermometer. After disassembly of the aft bulkhead to gain easy access to the exhaust system.

The above damaged butterfly was found, per Volvo Penta's service bulletin they both were removed and the shaft/bushing holes were plugged with high temp RTV and wrapped with masking tape. The repair went smooth as ALL four of the exhaust coupling hoses and 16 clamps were replaced.
Operational tests conducted yesterday resulted in the PORT upper exhaust pipe to run at 110 degrees at idle with the STBD upper exhaust pipe running at a max of 120 degrees at idle.
Reinstallation of the bulkhead and aft seating will continue upon the clearing of inclement weather scheduled for the next few days.

As a side note the entire RAW water system piping was “BACK FLUSHED" to remove any of the small impeller vane pieces that may have been caught in the Fuel, power steering or oil coolers.

 

[troublemaker]

Very Nice

A job well done good for you

 

[Brite Idea]

So do you have new exhaust flappers or you have removed them entirely? I would not run without them because you can have water run up the pipe into the engine thru the exhaust valves.
Rob

 

[Michael Clemensen]

Bill,
Thanks for the kind comments.

Rob,
They’re no longer available, since 1999 Volvo Penta has not utilized these Butterfly/Flapper valves. The Service Bulletin stated that they were “problematic” and gave the procedure that I followed in their removal.

 

[j-d]

VP discontinued Flappers as Michael noted above. MerC still wants them used. There's a theme among some MerC owners to remove flappers also. I choose to stick with flappers myself.
We towed a boat back to the ramp with a waterlogged VP I/O a couple years ago. I don't know if it had flappers but I do know it was anchored from both ends with its transom facing the waterway and also a light wind driven chop. It seemed to me that wake and wave action would have tried to force water up into the exhaust. So from that, I'd say anchor with the bow into the conditions. Probably with most inboards...