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Volvo 280 drive noise

"Agree!
And even for us with

"Agree!
And even for us with a mild 260/280 HP V-8 (and down and through the drive exhaust), we should not be using the bellows w/ a flapper in the first place."
 
"Michael, one more thought for

"Michael, one more thought for you:
I over-haul a fair amount of these V/P transmissions each year.
What I am seeing (and have for a while now) are more of them in need of main drive gear bearings (#30207 and #31307).
I make this protocol to remove the main drive gear from the bearing box so that I can inspect the bearings.
The 31307 (aft most bearing) takes quite a load!
As of ten years ago, I was not seeing these bearings in great need of replacement..... not very often, but do now days.
I wonder if you have a bad or worn 31307 bearing?

Easy to install, and it only involves re-shimming for rolling torque, contact backlash and of course correct clamping collar/bearing box clearance."
 
"RE:"Agree! And even for u

"RE:"Agree! And even for us with a mild 260/280 HP V-8 (and down and through the drive exhaust),"

and as I've stated before, I have my doubts about 5.7L exhausting thru the drive even without the flaps in the bellows."
 
"Gents, sorry for throwing a w

"Gents, sorry for throwing a wrench in here, but the 5.7 (around 300 HP) exhausts just fine through a 280 even with a flapper bellows. The double bypass relief holes in the Y-pipe and transom shield can more than take care of any excess in back pressure that the flapper may create."
 
"El P, agree re; the exhaust r

"El P, agree re; the exhaust reliefs, but respectfully disagree re; the bellows flapper..... and I don't want to lock horns with anyone here.
IMO, the V-8 should never have a flapper in the bellows.
When Volvo started using the higher HP V-8 engines, the exhaust flapper could be found on the lower unit. Even the 280 production model offered the flapper on the drive. The 280 flapper could not be purchased over the counter, but it was a factory production unit.

Then of course, the 290 offered the flapper on on the lower unit for all engines.

But that's just my take on it.
I don't use them, and I remove them if I were to find one in an exhaust bellows for a V-8.

."
 
"Ricardo, not "locking hor

"Ricardo, not "locking horns" with anyone here, just exchanging thoughts or philosophies.

The exhaust outlet in the 280 is about 6 square inch, and the restriction that may be caused by the bellows flapper is not substantially different from the restriction created by the factory installed flapper in the drive outlet. But the effect of the relief holes combined adds another 1.5 square inch (or 25%) to the exhaust, and that added surface becomes your saviour when it comes to preventing excessive back pressure.

Ideally, I agree that there should be no restrictions whatsoever in the exhaust. But also (ideally), water should never be able to reach the cylinders through the exhaust. Back to the real world, where the conditions are far from ideal, one has to make a balanced approach and consider the pros and cons of having (or not) a flapper installed. From my perspective, I'd rather prevent damage to the engine by stopping water ingress, and I'd settle for having the flapper installed, especially after not having observed any adverse effects. And if I found that a mechanic had removed the flapper from my boat exhaust without previous consultation, I suggest that loosing me as a customer was the least that would happen, especially if water ended reaching the cylinders.

Right or wrong, that's my take on it."
 
"El P, I fully agree with you

"El P, I fully agree with you re; what we call engine "water intrusion" or "ingestation"!
You may have misunderstood me! And my apologies if I was unclear!

I'd never run a marine engine/drive without back-flow prevention.
Never would I send a customer away without one or the other.
I'd also never remove a bellows flapper without having protection on the drive itself.

I've seen both... a Bellows flapper installed AND a flapper installed on the drive on the same boat!!!!
There is no need for both, IMO!
For me, and on a V-8, the one that goes by by is going to be the one in the bellows!
If it were my boat, and it has bellows flapper only, then I am going to retro-fit a flapper onto the drive and remove the bellows flapper!


Sorry if I was not clear on that earlier.


"
 
"Re: "The exhaust outlet i

"Re: "The exhaust outlet in the 280 is about 6 square inch, ...... But the effect of the relief holes combined adds another 1.5 square inch"

While the port in the cav plate may be about 6 sq inches, the limitation in the system is the diameter of the hole thru the transom at the Y pipe. The area of that hole plus the area of the two bypass holes TOTALS 6.8 sq inches (by my measurement).
The MERC engine installation/shop manual (available via a free link on the MERC forum)specifies a single minimum 4" dia exhaust port or dual 3" ports. The area of a 4" port is 12.5 sqin... Regardless of who makes the engine, a 5.7L at a given HP and RPM flows the same amount of exhaust gas.
This weekend, hopefully I'll start working on the thru hull conversion on my boat as I finally have some parts in hand. To complicate matters, NJ requires mufflers and I don't like external ones."
 
"Ricardo, thanks for the clari

"Ricardo, thanks for the clarification. Like you, I don't see the need for two flappers in series. But there should be one, and for the ones who don't have the factory flapper, I personally think the one in the exhaust bellows does the job just fine.

Robert, your measurements are quite close to mine (2.65" diameter in the Y-pipe exhaust + 1" each relief hole equals 7.08 square inches). It has been almost 14 years since I last worked with Mercruisers, but I recall the exhaust being through the prop. I never took the time to measure the ports in the lower unit and prop, but I think I could safely bet a few beers they won't add up to 12.5 square inches.
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