lower unit

R

richny

New Member
Sep 9, 2018
24
Boat Info
1992 230 sundancer
Engines
4.3 mercruiser
Well I removed the alpha 1 gen 2 lower unit to replace the water pump. When I separated the lower half, three small triangular plates fell to the ground along with a piece of rubber (looks to been part of a seal). Any idea on the three plates?
 
This could be what's left of it.
shopping

Glenn
 
upload_2018-10-12_15-26-47.png

this is what I found when I split my lower unit. I had overheated the engine and this is what was left of the flapper valve. It's laying against the shaft. ''Glenn
 
Glenn, that is exactly what it looks like! I just bought the boat and the guy said it did overheat on a sea trial and just needed an impeller. So... is it a lot involved in replacing the flapper valve? And what does it do?
 
The flappers prevent water from rushing into your exhaust manifolds when you come to a stop. They are very important... water in your exhaust manifolds can go into your cylinders and cause a hydro-lock.

I've never replaced them, but I don't think it is difficult.
 
Last edited:
JimG is right. As for replacing them, you will have to remove the exhaust elbows to get to the flapper valves which are located in the y pipe. Not too hard of a job.
Glenn
 
Yep, that's an exhaust flapper. Not terribly hard to replace once you disconnect the rubber section connecting the riser to the Y pipe. Also look around in the bottom of the bell housing (while the drive is off) there are probably some more pieces stuck there. Definitely fix it, not a good idea to run an IO without the flappers.
 
Excellent this is likely the obstruction which caused your overheat condition. While you are at it you should change the rubber exhaust tubes add they are most likely damaged due to the overheat and are what is considered critical path for an inboard_outdrive combination . The entire kit for my 7.4 was about 150 bucks . Good idea to do both engines if you have twins . It is not a tough job since you are out if the water . When I did mine in slip I needed to work at removing the old ones from within the lower exhaust tube because the top of the y pipe was half an inch below the waterline so a little more nerve wracking but not impossible . A pretty easy repair and relatively cheap as far as marine repairs go .
 
Want to thank everyone for the great advice and information! Can't wait to get it fixed and in the water.
 
I just replaced both of them on my twin 470s really wasn't that hard once I figured out the trick to do it, also found out I needed two risers and a rubber boot, replaced both of each.
 
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