Exhaust flapper valve (that attaches to the raw water exhaust above prop)

bill91817

Cadet
Joined
Jan 23, 2017
Messages
25
Hi
sorry if this is a stupid question but sterndrives are somewhat new to me!

I have a SP-c drive that has holes at the end of the cavitation plate (top of raw water exhaust) on the leg - realised that they must be for an flapper valve
My engine (5.7l) is mid mounted and drives through a jack shaft to the stern drive. I am running HiTek stainless manifolds - the manifold risers are quite high and then run down to twin 4 inch exhaust tubes that run 1 metre or 3 feet to the stern drive exhaust -

just wondering if I need the flapper or is this height and length of exhaust sufficient when reversing?

http://www.ebay.com/itm/Volvo-Penta-Exhaust-Flapper-Valve-852644-/371355841128
 

jimmbo

Supreme Mariner
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May 24, 2004
Messages
12,944
My self, I wouldn't install it as it requires exhaust gas pressure to open it. Another name for it is, Backpressure. As for water backing up the exhaust without it... All sx drives route the exhaust gas through the propeller hub, some like mine don't even have internal valves in the downpipes to stop water from backing up, and it's a lot closer to the transom and much much closer to the water line, In the 15 seasons I've had it, it has never choked on water from backing up
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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jimmbo, this is an SP-C drive (AQ series) and not an SX. the exhaust is a bit more of a straight path on the AQ style drives

the flapper never slowed down my 5.7 and I may also use it with my 7.4

when the motor is running you wont need it. its primarily there for when your parked at a marina and some schmuck comes rolling thru with his 47' hatteras with the trim all wrong putting out a 6' wake. that is when you get a large wave hitting the aft of your boat. that little flap of rubber is usually all that stands between hydrolock and not

Bill, with the new hitek mannys, what is your static rise over water line? are you over 14"?

find the choppiest day you can go out, either anchor with two lines to ensure waves hit your stern or tie off to a dock, pull the rubber exhaust hoses off your hitek mannys and sit and watch. as the back of your boat bobs up and down and your transom is hit by waves, how many times does water come up the exhaust

the fact your motor is mid-mounted and jackshafted helps with the longer run of exhaust. would love a pic of the AQ style jackshaft arrangement
 

jimmbo

Supreme Mariner
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May 24, 2004
Messages
12,944
I used the SX as a comparison/example of where the exhaust outlet is buried deeper in solider water and still, at least on mine, not ingest water when in reverse. Sitting beached, not running, with waves feeding it, is a scenario I hadn't considered
 

bill91817

Cadet
Joined
Jan 23, 2017
Messages
25
No Title

Hi Scott, thanks for the reply - picture below of the set up (yes that's a merc engine running a jackshaft to a Volvo leg!), I think I will get one (flapper) cheap insurance! - 2 separate questions,

1) is a bit of play in the drive normal (I can grab the leg and move it up about 1/2 inch and there is a bit of sideways slop, it clunks a bit when going into reverse - not badly but noticeable compared to going into forward gear.
2) I replaced my inlet ball valve and in the process had to remove the power steering oil cooler - a bit of fluid escaped and I ran the engine prior to topping up the reservoir (just slipped my mind!) I topped it up straight away but there is a squeal that comes from the power assist unit at the stern drive (not the pump on the engine) - any tips on how to sort this? (I assume I may have to bleed it?)

didn't have a great weekend - i think my raw water pump has chewed an impellor after running dry or me installing it the wrong way :-( still learning!!!
cheers
Bill
 

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Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,299
Yes, there is a bit of slop if the plastic pivot bushings need attention

With motor running, turn the steering wheel full lock side to side and hold in each position for 5 seconds. Repeat a half dozen times to bleed the air

Hart to tel from the pic, looks lime someone cut off a PDS housing to make the jack shaft setup
 
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