converting a pre alpha in-line Gimble housing to a V-8 Gimble housing

[thedeuceman]

Replacing the gimble assy on Our balharbor, 77 with 233 (ford 351)
While cleaning it up I noticed the 2 small exhaust holes are blocked off.

 I looked at the gimble assy I put on the 1900 and it's the same.
Question is, is this an alpha 1 thing, or a 4 cyl vs v8.
Is it ok to run it like this or do I need drill these passages ?


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[Rich_V174SS]

That looks like a pre-Alpha in-line 4/6 transom assembly meant to take a single-side exhaust pipe because of the bolt arrangement. Definitely not an Alpha unit. I don't think you can properly bolt on a Y pipe for an 8 cylinder engine. The two side ports are bypasses to allow exhaust closer to the water surface when the engine is idling so there isn't so much back pressure because otherwise it would have to blow through all the way to the prop. I don't know why some assemblies had the ports open and others were closed but just double check that those ports don't open into the main port inside the tube. I think my '67 drive assembly was like that. Also, do I see a single hydraulic line? So is this a lift-tilt only unit. You sure on the year for this assembly, not older than the boat your're putting it on?

[Plugcheck]

     My CVZ utilized the transom plate from the pre alpha 898 and has an identical look to it compared to yours.   I plasma cut a 12g SS cover to bolt on over this opening as I converted to thru hull exhaust.   My 1985 Intimidator has a similar look to it, but has the Mercruiser cover on it since it has its own special exhaust.   I have yet another 898 plate and Y pipe in storage, I will make a point to take a look at them tonight.

[thedeuceman]

it is pre alpha, i was thinking the clamp bolts on the outside of the gimble ring for the steering were exclusive to alpha 1.
both units have serial numbers on them and are both 470 (1980-1982) and after looking at the mecury parts manual i see a different housing called out for a V8.
the inline housing has the bypass ports directly into the main exhaust port where the V8 has them to the 2 lower holes. the V8 y-pipe fits but the 2 bottom holes are not taped, i suspect on the 1900 i just put the 3 bolts in it.
i am considering drilling into these passages as the v8 assembly's are, and at least on the balharbor i can tap the bottom holes as well.
it does have 2 trim hoses, just cant see it from the pix.

[Plugcheck]

Im pretty certain my 898 Y pipe has five bolts(Allen head) that attached it to the transom plate.  All 5 holes were drilled and tapped.  Not certain what the small holes did or what purpose.  Prob assume what rich said, they are bypass for exhaust.  When I get out to shop tonight, I'll give ya a ring.  Still got a crazy idea of putting a 260 in my pontoon with custom third log.

[thedeuceman]

OK maybe the name of this thread should be "converting a pre alpha in-line Gimble housing to a V-8 Gimble housing".
checking the serial numbers what I have on my 1900, and what I have to put on the Bal Harbour is a 70861A1
In the parts manual under the comments it says "in line engines"
70862A1 is listed for V-8 engines.
The 70861A1 has the exhaust relief ports drilled into the main exhaust, and the Lower 2 passages are blocked off.
So I tapped the two lower bolt holes, and drilled the lower two passages to the outside.
You can see the tip of the drill bit inside the passage in this photo

As viewed from the side




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[Plugcheck]

     Nice job Joe, pleasure discussing the project with you last night.  Still, I'm a bit curious why those passages weren't open before, both my alpha and pre alpha (V-8) do have them open, but the inline plate does not?  Would think they need an idle exhaust port just as much.

[thedeuceman]

the inline assy has them drilled to the main exhaust port, where the V8 has them drilled to the lower passages.
now mine have both
this pix explains