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Risers or flapper bellows?

PR-Chapin

Member
I'm wrapping up the conversion from 318 to 360 Chrysler and about to drop the new engine in the boat. The 360 has risers but the 318 did not. Just ninety degree elbows off the end of manifolds. That old 1974 Volvo 270 outdrive originally had the flapper on exhaust port but when that blew off and I tried to replace it, I discovered that technology was discontinued in favor of exhaust bellows with flapper in it so that's what I used as replacement. Now I may have some trouble with steering linkage clearance with the 360's risers putting the down exhaust too close to the transom. My questions are these: Were risers meant to replace the flapper in bellows? If I run the 360 with the flapper bellows do I need the risers? If it's a one-or-the-other situation (and I suspect it is), which is better? Thanks.
 
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I'm wrapping up the conversion from 318 to 360 Chrysler and about to drop the new engine in the boat. The 360 has risers but the 318 did not. Just ninety degree elbows off the end of manifolds. That old 1974 Volvo 270 outdrive originally had the flapper on exhaust port but when that blew off and I tried to replace it, I discovered that technology was discontinued in favor of exhaust bellows with flapper in it so that's what I used as replacement.
OK.... the 270 stern drive lower unit exhaust outlet housing came from the factory with a rubber flapper attached. And yes, it is no longer available.
The exhaust bellows with the internal flapper is too restrictive for your 360. I would not recommend it.


Now I may have some trouble with steering linkage clearance with the 360's risers putting the down exhaust too close to the transom. My questions are these: Were risers meant to replace the flapper in bellows?
What are you calling "risers"?
Risers/Spacers are the rather short exhaust components that fit between the manifold and elbow.


If I run the 360 with the flapper bellows do I need the risers?
Again, what are you calling a "riser"?

If it's a one-or-the-other situation (and I suspect it is), which is better?
Better (less restrictive flow) would be a 280 lower unit (1.61:1 ratio) w/ a flapper at the exhaust outlet. However, the 280 flapper was only available as a production unit.
You would need to go to a 290 (1.61:1) in order to have the outlet flapper.


Thanks.
 
Thanks. A 270 outdrive is what I have to work with. Flapper on the exhaust 270 outtake is gone and replacement is no longer available. Below is a Barr brand Chrysler manifold and 6" riser kit. Riser is what THEY call the extension that lifts the exhaust six inches vertically (https://www.marineengineparts.com/b...ysler-lm-318-360-end-style-standard-exhaust-6). I have circled the risers for your convenience. This kit has 45 degree exhaust elbows after the risers. Mine has 90 degree elbows.
chrysler manifold with 6 inch riser.jpg
 
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To clarify: As you can visualize by using the above image, my 318 had no risers, only ninety degree elbows off the end of the manifolds. With the addition of risers on 360 manifold there is much less clearance between the end of manifold and transom than there is without them. The ball joint pivot for end of steering line is mounted away from the transom and may not allow the clearance necessary for riser. Of course I won't know for certain until I drop the engine in. My question is if it turns out I do have clearance issues for steering pivot (which it doesn't appear I can relocate without putting a lot of stress on the lower unit's steering arm), would it be okay to go back to the old system of no risers and simply ninety degree elbows? Presumably the old 318 was mounted high enough in this deep V 1974 Fiberform boat that Chrysler did not feel they were needed? Do the risers perform the same function of preventing backwash into the manifolds/engine as the bellows flapper valve? I am not worrying about robbing the engine of a lot of power with bellows type flapper valve. This is a 24' pleasure cruiser mostly used for salmon fishing, not a speed boat. I seldom have a need to run it at anything more than moderate rpms.
 
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To clarify: As you can visualize by using the above image, my 318 had no risers, only ninety degree elbows off the end of the manifolds. With the addition of risers on 360 manifold there is much less clearance between the end of manifold and transom than there is without them.
The ball joint pivot for end of steering line is mounted away from the transom and may not allow the clearance necessary for riser. Of course I won't know for certain until I drop the engine in. My question is if it turns out I do have clearance issues for steering pivot (which it doesn't appear I can relocate without putting a lot of stress on the lower unit's steering arm),
The 270 collar steering fork shaft is the small diameter shaft.
The spindle arm will also be the small diameter, and will be the long style.
The short spindle arm will not work on the 270.

It would be very helpful to see a few photos of this area.


would it be okay to go back to the old system of no risers and simply ninety degree elbows? Presumably the old 318 was mounted high enough in this deep V 1974 Fiberform boat that Chrysler did not feel they were needed?
I can't say for certain.

Do the risers perform the same function of preventing backwash into the manifolds/engine as the bellows flapper valve?
Well..... Yes and No!
The low point within the turn of riser is to be at a higher elevation than that of the water line.
Back-flow prevention flappers primarily protect against wave surge.


I am not worrying about robbing the engine of a lot of power with bellows type flapper valve. This is a 24' pleasure cruiser mostly used for salmon fishing, not a speed boat. I seldom have a need to run it at anything more than moderate rpm.
An exhaust restriction will also hinder low speed operation. It's not all about power.
 
I think I posted an image of inside transom before. Let's see ... yes here it is. This was with the exhaust Y-tube that came with 360 engine that I elected to not use because the exhaust bypass is plugged and because, as you can see, it definitely does not allow for clearance of the steering knuckle which is in view at upper left. The white part is the socket for ball joint that's attached to transom.
new exhaust plug.JPG

Apparently the flapper in bellows has replaced flapper on exhaust port. At least that's what the parts suppliers told me. Too bad as I think the exhaust port flapper makes a lot more sense. You can see when it's broken. The one in bellows falls apart and can get stuck.
 
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I think I posted an image of inside transom before. Let's see ... yes here it is.
Yes, that is the interior of your Transom Shield!

This was with the exhaust Y-tube that came with 360 engine that I elected to not use because the exhaust bypass is plugged and because, as you can see, it definitely does not allow for clearance of the steering knuckle which is in view at upper left. The white part is the socket for ball joint that's attached to transom.
View attachment 18816

There are several things wrong with this set up for a 360 cu in engine.
1..... that small Y-pipe is going to hinder performance.
2..... without the low-pressure-relief connected to the exhaust elbows, your engine may "load up" up low speeds.
3.... if this is a 270, you will have the small diameter collar steering fork shaft.

The 280, 285 or 275 transom shield, along with the 95mm Y-pipe would certainly make things easier and better for you.
Note the bell crank arm style steering linkage arrangement. Nice and tight against the transom.
Note the double relief ports that correspond with the 95mm Y-pipe. The reliefs are within the exhaust porting.
While you cannot see it, the collar steering fork shaft is of the larger diameter.

volvo penta 280 shield .jpg


Apparently the flapper in bellows has replaced flapper on exhaust port. At least that's what the parts suppliers told me.
For the 4 cylinder engines this is OK, but NOT for a V-8. Too restrictive!

Too bad as I think the exhaust port flapper makes a lot more sense.
Yes!

You can see when it's broken. The one in bellows falls apart and can get stuck.
 
I'm not using that Y-tube. I'm using the old style setup for 318 with 3" hoses and 90 degree fiberglass elbows (added those so hose is not stressed at the bend). The transom fitting for exhaust joins the two hoses and has single self contained exhaust relief port.
 
looking for some one with experience replacing freeze plugs on a Chrysler 318 1970 in a hard top Uniflite. Can you move the bell housing back far enough without removing the engine or hard top?
 
I'm not using that Y-tube. I'm using the old style setup for 318 with 3" hoses and 90 degree fiberglass elbows (added those so hose is not stressed at the bend). The transom fitting for exhaust joins the two hoses and has single self contained exhaust relief port.

I would need to see a few pictures of that.

Meanwhile..... this is what VP did with the early GM V-8s with a single relief transom shield.

The Y-pipe shown is yours, and is slightly different from the AQ200B and AQ225B Y-pipe.
The 1 pc exhaust manifolds offer a port directly into the exhaust gas chamber. This port feeds into the cross pipe T fitting.
The T fitting directs the low pressure exhaust gasses into the vertical tube (where you have drawn the red circle) where it then enters the transom shield's single relief port.

Later they went to a transom shield with a double relief port and double relief Y-pipe.
By the way..... the two Y-pipes (single or double relief) will not interchange!

Bottom line..... if you are using a Y-pipe with the vertical relief tube (i.e., NO internal relief path), you will need to do one of several things:
..... tap into the exhaust elbow's main chamber and direct that to the
vertical relief tube.
..... somehow fit a ported elbow into the system, and direct that to the vertical relief tube.

Otherwise, you will have no low speed exhaust relief.


volvo penta AQ220B exhaust.jpg
 
Hi again:

My old 318 had only a cast aluminum Y-fitting (NOT a Y-tube) to connect to transom plate. Approximately 18" long 3" inside diameter hoses from each side exhaust manifold clamped to the fitting. The fitting has a self-contained exhaust relief chamber cast in it just ahead of the union of two exhaust lines. This mates to the single relief port in the transom shield which contained the relief exhaust hose. This was factory equipment setup in that boat when it was almost new, not something someone jerry rigged. Originally it had 3" flexible exhaust hose but that stuff didn't last. For one thing, bending it stressed the hose making it crack. I eliminated this by adding ninety degree fiberglass elbows.

I am going to have to remove the risers. There is simply no way I can modify the transom steering ball joint pivot to accommodate them. Not enough clearance between riser and transom. If I try to relocate the transom pivot above the riser, the increased angle on steering line will put too much strain on the steering arm pivot. Factory equipment for that boat had no risers so presumably I can get away without them. I don't see how changing from 318 to 360 will make that much difference in the need for risers. If the need wasn't there to start with, I can't see that changing the engines would create one now. Presumably the engine is mounted high enough in this fairly deep hulled boat to eliminate the need for risers. Hopefully, that is the case. I am stuck with bellows flapper valve unless someone starts making after market exhaust port 270 flappers. I was told they were bad engineering idea and that's why Chrysler/Volvo went to flapper valve inside the bellows.
 
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Hi again:

My old 318 had only a cast aluminum Y-fitting (NOT a Y-tube) to connect to transom plate. Approximately 18" long 3" inside diameter hoses from each side exhaust manifold clamped to the fitting.
Yep.... and it required wet exhaust hose that connected each side of it to the exhaust system.
The issue is..... a large portion of the wet exhaust hoses are below the water line.
If you plan to moor this boat, your insurance company might have an issue with this!


The fitting has a self-contained exhaust relief chamber cast in it just ahead of the union of two exhaust lines. This mates to the single relief port in the transom shield which contained the relief exhaust hose.
Yes. That would be the inlet for the exhaust relief. It should connect to the main chamber within each exhaust elbow.

This was factory equipment setup in that boat when it was almost new, not something someone jerry rigged.


Originally it had 3" flexible exhaust hose but that stuff didn't last. For one thing, bending it stressed the hose making it crack. I eliminated this by adding ninety degree fiberglass elbows.
Above or below the water line????

I am going to have to remove the risers. There is simply no way I can modify the transom steering ball joint pivot to accommodate them. Not enough clearance between riser and transom.
Actually, I have suggested how this could be done!

If I try to relocate the transom pivot above the riser, the increased angle on steering line will put too much strain on the steering arm pivot.
Are you talking about the "spindle arm"?

Factory equipment for that boat had no risers so presumably I can get away without them. I don't see how changing from 318 to 360 will make that much difference in the need for risers. If the need wasn't there to start with, I can't see that changing the engines would create one now. Presumably the engine is mounted high enough in this fairly deep hulled boat to eliminate the need for risers. Hopefully, that is the case. I am stuck with bellows flapper valve unless someone starts making after market exhaust port 270 flappers.
Sorry......... No longer available.

I was told they were bad engineering idea and that's why Chrysler/Volvo went to flapper valve inside the bellows.
As said earlier..... the exhaust bellows with the internal flapper is too restrictive for the V engines.
You can solve this issue by picking up a 290 or later 1.61:1 lower gear unit.... or, a rather rare 280 with the exhaust outlet flapper.
 
Thanks. I magnified image of that exhaust housing on E-Bay and it appears the rubber flapper is cracking at the joint. I doubt it will last long. Too bad.
 
Finding a 280 transom shield and Y-tube up here could be dicey. I'll see what the local marina mechanic has thrown out back in his junk heap. The million dollar question is will the 270 outdrive bolt up to it? I can't see the other side in the image you posted. Let's see if I can find one on the net to look at ... yes, looks like it's doable to mate a 270 outdrive to 280 transom shield. Replacing the entire outdrive would be more money than I want to spend on this old boat.

I'm not overly worried about exhaust hose rotting out. The boat is mostly trailered (Lake Superior is a few blocks away and I have the space to store it here and my roller type trailer is EXCELLENT). Also it is now only used in fresh water so I doubt the hose will decompose as quickly as in marine environment. At any rate, with the ninety degree fiberglass elbows I have just added there is now very little hose below the water line that is exposed to water. Just an inch maybe on each side between elbow and the junction fitting that mates to transom plate. Now no longer any significant bends in the hose as was the case with original design. That will definitely increase life of what little hose is now used! I should mention that the 360 I just bought came with very good flexible rubber extensions off the exhaust risers and these will also eliminate any stress on hose that formerly existed with old 318 primitive setup (shown in below image). A short piece of exhaust pipe joins the extensions to the ninety degree elbows I've just added so again here there is also very little hose left exposed to wet exhaust. Mostly the hose is used to tie solid exhaust fittings together. It's not a one piece metal Y-tube setup ... but almost one piece.

The fitting has a self-contained exhaust relief chamber cast in it just ahead of the union of two exhaust lines. This mates to the single relief port in the transom shield which contained the relief exhaust hose.
Yes. That would be the inlet for the exhaust relief. It should connect to the main chamber within each exhaust elbow.

Actually, the inlet for exhaust relief does not connect to each of the exhaust elbows because there aren't any attached elbows. The exhaust relief port is cast inside this Y-fitting which extends only about eight inches on each side of junction to meet the exhaust hoses (I posted a photo some time ago ... here it is again). The self contained exhaust relief port inlet is slightly to the left of where the two sides of the Y join. Given that the relief port exit on outdrive is only slightly below water level, I don't see that a single outlet of this design would be significantly restrictive compared to a dual relief outlet design. Perhaps somewhat but I'm sure it won't make a big difference except POSSIBLY idling when tied up and even that I would not think to be significant.
old exhaust 318 to transom shield.jpg
 
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Finding a 280 transom shield and Y-tube up here could be dicey. I'll see what the local marina mechanic has thrown out back in his junk heap. The million dollar question is will the 270 out drive bolt up to it?
Between the 250, 270, 275, 280 or 285, yes...... the main suspension forks will interchange. In other words, you can interchange drives as long as they are set up with that style main suspension fork.
NOTE: the 250 main suspension fork has a metal insert (one on each side), making it not quite as stout.

What will NOT interchange will be the single exhaust relief Y-pipes and the double relief Y-pipes.... of which includes
the single exhaust relief transom shield and the double relief transom shield as well.
If you have a single relief down tube or Y-pipe, it must be installed on a single relief shield..... and visa-versa.


I can't see the other side in the image you posted. Let's see if I can find one on the net to look at ... yes, looks like it's doable to mate a 270 outdrive to 280 transom shield.
Again..... you can install a 270 drive on a 280 shield, but the exhaust down tube/Y-pipe relief ports must match the shield.

Replacing the entire outdrive would be more money than I want to spend on this old boat.

I'm not overly worried about exhaust hose rotting out............................... Also it is now only used in fresh water so I doubt the hose will decompose as quickly as in marine environment.
It is not necessarily the "rotting out" that is the concern..... it is more so the potential for an over-heat to cause the hoses to burn through and leak!
When these are below the water line, this could become a serious issue.




The fitting has a self-contained exhaust relief chamber cast in it just ahead of the union of two exhaust lines. This mates to the single relief port in the transom shield which contained the relief exhaust hose.
Yes. That would be the inlet for the exhaust relief. It should connect to the main chamber within each exhaust elbow.

Actually, the inlet for exhaust relief does not connect to each of the exhaust elbows because there aren't any attached elbows.
Correct! You would need the OEM exhaust for this connection........ unless Chrysler did not use the relief system.

The exhaust relief port is cast inside this Y-fitting which extends only about eight inches on each side of junction to meet the exhaust hoses (I posted a photo some time ago ... here it is again). The self contained exhaust relief port inlet is slightly to the left of where the two sides of the Y join. Given that the relief port exit on outdrive is only slightly below water level, I don't see that a single outlet of this design would be significantly restrictive compared to a dual relief outlet design. Perhaps somewhat but I'm sure it won't make a big difference except POSSIBLY idling when tied up and even that I would not think to be significant.

If your transom shield has the single exhaust relief port, and since your elbows are NOT ported for Exhaust reliefs, this is the Y-pipe that you need. This

270 Y pipe.jpg

If you were to find a double relief 280 or 285 transom shield, this is the Y pipe that you would need.
This has 95mm inlet ports.

280 double relief Y pipe .jpg




Rick: Apparently Volvo made different steering arms for the same model outdrives. This one for sale appears to have enough "lift" to it and close enough to transom to clear my risers. http://www.2040-parts.com/volvo-pen...met-fork-shoulder-bolts-1-1-2-shaft--i408888/

OK..... first know that the 270 and 275 spindle arms are not the same.
The 270 is small diameter, and the 275, 280, 285 are larger diameter.
The seller is incorrect as he lists 270 and 275. However, what he shows appears to be the large diameter spindle arm.


My steering arm extends much further from transom and not nearly as high as this one. Steering would likely be a bit less responsive with this arm but shouldn't be a big issue.
 
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