Question...

[THEFERMANATOR]

The engine you describe sounds like a 60 degree looper OMC which is like Spare said an optical ignition system engine. VERY good engines, and easily argueably the best engine OMC EVER turned out. They are also one TOUGH SOB. As for the extension on your MERC driveshaft, this is pretty unadviseable even from BAY who makes the adapter kits. It is ALWAYS best to go with a 25" lower unit with the spacer kit.

[Destroyer]

Originally Posted by THEFERMANATOR

The engine you describe sounds like a 60 degree looper OMC which is like Spare said an optical ignition system engine. VERY good engines, and easily argueably the best engine OMC EVER turned out. They are also one TOUGH SOB. As for the extension on your MERC driveshaft, this is pretty unadviseable even from BAY who makes the adapter kits. It is ALWAYS best to go with a 25" lower unit with the spacer kit.

Do you know what the normal compression is on one of those engines? The dealer told me that this engine has 80-85 psi on all cylinders. I know that my 91 has 93-95 on all cylinders, but 80 sounds a bit low?

As to the Merc, I have no doubt as to the accuracy of your statement that it's advisable to go with a 25" lower unit with a spacer kit, but the engineer in me has to know why. Aren't the gears and such identical in the 20 and 25's, the only difference in them being the length of the drive shaft? What is it I'm missing?

[THEFERMANATOR]

Originally Posted by Destroyer

Do you know what the normal compression is on one of those engines? The dealer told me that this engine has 80-85 psi on all cylinders. I know that my 91 has 93-95 on all cylinders, but 80 sounds a bit low?

As to the Merc, I have no doubt as to the accuracy of your statement that it's advisable to go with a 25" lower unit with a spacer kit, but the engineer in me has to know why. Aren't the gears and such identical in the 20 and 25's, the only difference in them being the length of the drive shaft? What is it I'm missing?

The compression on the 60 degree loopers should be up around 110-125 I believe, but it can vary from year to year depending on what style porting and pistons were put in it. The problem with using the 20" lower is the driveshaft extension you have to put onto the driveshaft of the 20" lower. They can get looose and cause vibrations over time is what I was told.

[phatdaddy]

like ferm says, you want to avoid a 2 piece driveshaft if possible.

[brisboats]

Personally I hate the look of a merc V-6 with the spacer plate , so much in fact that I often swap out the midsection. 25" clean mids are easier to come by than 20" and the look especially with twins just looks "right" to me.

B

[Destroyer]

Ok, that's what I was missing.. I thought that it would use a new 1 piece driveshaft, not an extension piece on the existing 20". Makes perfect sense to me now. No way would I want a 2 part driveshaft.. sounds like it's just asking for trouble that way.

Now, the question is, which way to go... Jackplate or extension?

[spareparts]

Merc uses two piece drive shafts on the service replacement lower units now, it may not sound great , but it works. There are a ton of used 25" lower around, 20's are hard to find. I've got a spacer on an older 2.0l, I'll see if I can get it off with out destroying it. I think I have a good 25" lower I'll trade you for a 20. Give me a little time on it, I still have this "other" boat in my back yard I've got to do something with