exhaust backwash?

[jpohl58]

I have a 1990 Windsorcraft 26 that I keep on a mooring on Lake Tahoe. After a starm last Fall the engine was hydrolocked due to water in several cylinders. This is a new chevy 350 engine with new risers and manifolds that replaced the original. The outdrive is a Volvo Penta DP. I asked a mechanic friend what he thought happened and he suggested that water could have gone up the exhaust and into the cylinders while the boat was leaping up and down on the mooring. If so, how can I prevent this from happening again.? The risers and manifolds are identical to the original and I did not have the problem before or since this one incident. Any ideas on how to prevent this backwash situation?

 

[Scott Danforth]

Do you still have the exhaust flapper on the drive exit? If not, replace it. Thats what its for.

Also check your riser height to the waterline. If your boat is stern heavy, you may need riser extensions

 

[jpohl58]

Flapper is on exhaust above props but not sure about ports that are in area of bellows (idle ports?) I think that is where the water came in. I'm guessing that the riser hieght may be the problem and that it is too close to waterline. Riser extensions may be a problem due to fact that existing risers match up with outdrive portion of exhaust with only about an inch and a half of gap. Not sure how offset created by riser extension would be incorporated in the existing geometry? What would be the typical hieght of riser above waterline? An I maybe looking at new (higher) risers instead of extensions?

 

[Maclin]

When I first got my old DPA the idle relief port flapper was kind of old and did not rest against the ports at all. I took the plate off that was holding it on and flipped the flapper around so it would rest against the ports, worked well. In fact I had to lift it to drain the exhaust on the ramp to comply with the quagga mussel containment rules.

 

[Scott Danforth]

They also sell replacement idle relief port flappers

Regarding riser height and waterline. Measure where you are at currently then if your less than 14" worry about how to change it.

 

[jpohl58]

Out fishing cod in the Bering sea right now but will check hieght on risers and check for flappers on idle ports when I get back in a couple weeks. I will also look closely at old flapper on the drive unit. Thanks for the info!