Exaust reversion Formula thru hull W/ swim platform exaust system


B

Bt Doctur

Member
Hello boaters, a new member with a old problem. Trying to find the answer to this problem for the owner.Boat had BB motors are they were removed for 6.2 SB W/ 3 inch riser extentions. When first serviced for a bad starter we found the manifolds heavily rusted .Motor is very poor condition and it was pulled for a rebuild at the end of 2015. For 2016 no reported problems and was winterized. Fall of 2016 port motor pulled for rebuild, same conditions of the manifold. Heavily rusted but no water in the oil.

Fast forward to spring of 2017. New port motor installed and tested on land 2X. stbd motor started and it had some stuck valves.?????
Removed heads and they were just ugly. No issues found in the heads and motor was new so new heads installed.Boat put in service.
2 hours later port motor takes a dump. 3 valve hung wide open????

Shop keeps saying water ingestion but oil remains clean so we then suspect exaust reversion. Cannot raise the risers or use dry headers,
cannot lower the exaust or swim platform so we did the next best thing , extended the riser outlet.Not knowing how long they should be I used 12 inch tubes hammered in 2 inches leaving 10 inches exposed.

The manifold and riser pics shown only have about 2 hours run time and were loaded with what looked like rocksalt debris. So being a test engine were guessing on the length. The tubes are 2 inch OD SS thinwall 12 inches long .Our "Think Tank" says it should work to prevent the reversion .If this is true I should find nothing but carbon in the manifolds and risers when I remove one for inspection at the end of this season.

Stay tuned for a update and pictures soon




 
I had the exact same issue with a 280 SS Sea Ray. I bought the boat with 340 hours and it was on it's 3rd set of motors - all damaged by salt water intrusion. That boat had water mufflers. I ended up tearing out the water mufflers and installing "Y" pipes to push the exhaust through the drive below the waterline. Ran perfectly for 250 hrs when I sold it. I've heard the 6.2's with their cam timing are more susceptible to the inversion issue. While I wasn't excited about the "Y" pipes solution, I didn't want to fight the reliability issues with the motors.
IMG_0714.jpg
 
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A little selection of what I had to replace after 450 hours of mixed salt water usage. Alas the pervious owner had neglected the basic concept of servicing and had no clue of mechanical issues and the suchlike. This isnt pretty.
 

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They are in much better shape than the ones we replaced originally
Send me the brass hose fittings !!!!!!!!!!!!!!!!!!!

Remove the pullys off the pump with a GM power steering pully kit, they dont come with the new pump or PS pump.
 
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An Update 4 hours run time at power

Burned a small hole thru the exaust hose but it was expected because I`m in uncharted waters with the length of the tubes. Remove the risers and shortened then 2 inches and repaired the hole for now. You could see where the tube was pushing down on the hose because it was shiny clean.

The good news is there was no sign of any moisture and the manifolds, the extention or the risers .There was a nice black coat of carbon deposits and no white salt residue.

Finally some sucess.
 
The hose was not the problem the ends of the tubes were right against the rubber, shortening them should allow some water to pass under it to cool the hose.exaust shutters are new .Problem was reversion not ingestion.
 
Another weekend gone and the motors ran perfectly. No holes burned thru the hoses so far on the port motor. Starboard motor still has the longer uncut tubes but has not burned thru yet. Only a few weeks left untill I remove the risers for inspection and photo`s but I`m going with the fact that making the risers exaust point further back has stopped the reversion .
Stay tuned for the end of season pics
 
Ya know as with your other thread I would like to know what boat were talking about, also from the pic the risers are not high enough

DSCN3491_zpsgna5g4ka.jpg
 
It is a Formula with Silent Thunder swim platform exaust.
the height is 15 inches from the water level to the top of the riser, extention blocks are 3 inch, its the highest it can go due to the engine hatch. Using the extention tube was our only other option and it seems to have cured it.
 
Update, motors ran clean for the remainder of 2017, plugs look perfect with no signs of water or rust. The tubes were shortened to 10 inches to just be above the bottom of the exaust hose. For future application I would notch the top and put a 10 or 15 degree upsweep to have the tube be in the center of the rubber hose and not that close to the bottom of it.
Anybody else with this problem feel free to contact me.photo hosting
 
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