1991 70 HP force exhaust plate

Michael Lang

Seaman Apprentice
Joined
Aug 14, 2013
Messages
30
My first thread, please have patience with me. I ordered and received a new exhaust plate with matching part number, but they look different. The old plate has a long deep formed cavity and the new plate is just flat, both new and old have the same hole and cutouts pattern. I talked to all the parts people and no one knows if they are interchangeable. I currently have the power head off and like to know if I can use the new flat plate.
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: 1991 70 HP force exhaust plate

You actually have a stainless plate from a 75. The formed channel in the 70 HP plate reduces exhaust chest volume and restricts flow a little bit to help de-tune to 70.

Yes, they are swappable. No, you should not see any difference in performance.
 

Michael Lang

Seaman Apprentice
Joined
Aug 14, 2013
Messages
30
Re: 1991 70 HP force exhaust plate

You actually have a stainless plate from a 75. The formed channel in the 70 HP plate reduces exhaust chest volume and restricts flow a little bit to help de-tune to 70.

Yes, they are swappable. No, you should not see any difference in performance.

Thank you so much for the quick reply, I will go ahead and use the plate, you guys are great.
 

Michael Lang

Seaman Apprentice
Joined
Aug 14, 2013
Messages
30
Re: 1991 70 HP force exhaust plate

Why were you changing?
Pics?

Good question, I bought a used 1991 17 foot bayliner with the force motor and started fixing it up and it had a cooling problem so I started from lower unit and worked my way up to the power head, found the problem with copper tube connecting to the spacer plate and decided to pull the head and exhaust cover to check the condition of motor so far it looks very good for a twenty two year old motor. I am retired and like to tinker with boats. The old exhaust plate looked really bad so I ordered a new one. Thanks for your help.
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
Re: 1991 70 HP force exhaust plate

The OEM exhaust plates usually get pretty warped after running for a few years. They are exposed to the hot exhaust exiting the combustion chambers. As long as there are no cracks, they should be fine. The only cure for the warping that I've seen is to make one out of thicker stainless steel.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Re: 1991 70 HP force exhaust plate

Yup the stainless plate gets warped pretty bad but if it's tourqed back on right it will work.
Unless it has a hole?? :)
 
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