Logo
FULL SITE MENU

2+2 Questions

K

klyross

New member
Questions re: the 2+2 2-stroke Mercury - specifically the 115 & 125 circa 1996:

- HP actual for each.
- Feasibility of converting a 115 to a 125.
- Possible to convert either to a 'constant 4' operation instead of 2 cyls. only below ~1800 rpm.

Thanks ...
 
First select the forum that you want to post under.
Then, on the left side a few rows down from the top, click
on the button Post New Thread.
 
klyross said:
Questions re: the 2+2 2-stroke Mercury - specifically the 115 & 125 circa 1996:

- HP actual for each.
- Feasibility of converting a 115 to a 125.
- Possible to convert either to a 'constant 4' operation instead of 2 cyls. only below ~1800 rpm.

The Hp for the 115 and 125 is, 115 hp and 125 hp at the prop.
To convert a 115 to a 125 look on mercs website and find the differences.
No it cannot be converted to run on all 4 under 1800 rpm, the idle is so rough you swear the motor is going to shake itself aprt.
Click to expand...
 
I would be interested to hear if anyone has any experience with replacing the lower carburetors with same carburetors(with idle circuits) that are used for the upper two cylinders.
 
"I would be interested to hear if anyone has any experience with replacing the lower carburetors with same carburetors(with idle circuits) that are used for the upper two cylinders."

Yeah, that is what I was hoping - nothing like 'been there, done that' info. Certainly cheaper than a new motor; but, I am not looking to be a guinea pig, either.

"Some say the motor will shake a lot at idle when all 4 are firing."

Already does that - definitely would not want more.

Thanks ...
 
I have set up a lot of these engines. Leave it the way it is. If it is shaking then it needs to be set up, and by the book. It is not a simple job and the boat has to be in the water to do it.

When set up right, these engine runs very well and smooth.
 
The idle on my 2+2 is incredibly smooth...the transition at about 1800 RPM is annoying...especially when decelerating as the engine makes the 4 to 2 cylinder transition. It seems to takes a while for the bottom two cylinders to completely burn up the residual fuel and stop "contributing" Yes, the linkage has been "synchronized" according to factory specs.
 
In our High School auto shop. we had a 1968 Plymouth 318 mounted and running on a stand. After reading about some of the things that were done during the gas rationing of WWII, we decided to see if it would run on only 4 cylinders. We removed the push rods from alternate cylinders in the firing order and reassembled the engine. The engine ran quite well and quite smoothly on only four cylinders. Unfortunately, the motor was not in a vehicle and therefore we were not able to actually test for power loss or fuel economy. Cylinder de-activation was tried by Cadillac in the 1980's with less than satisfactory result....the motor was called the "4-6-8" . As I remember, the mechanical valve de-activation components tended to wear prematurely and fail.
 
.."In our High School auto shop. we had a 1968 Plymouth 318 mounted and running on a stand. After reading about some of the things that were done during the gas rationing of WWII, we decided to see if it would run on only 4 cylinders. We removed the push rods from alternate cylinders in the firing order and reassembled the engine."

I did that with a '78 Pontiac 350 V-8, and I actually drove it. Powerless but smooth running.

I also permanently removed the push rods on one bank of cylinders of a Buick V-6 I installed in my Pontiac Astre (Vega). Drove it for a year that way. Powerless but smoother running than when it was on all six since it was an uneven fire engine! My plan was to make a linkage to raise or lower the rocker shaft on the dead bank to energize/ de-energize the cylinders, but I never finished it.

Interestingly, the gas mileage was a bit worse on three cylinders since I had to floor it all the way up the long hill going home each day from work.

Jeff
 
I don't think you got the "Fast Jeff" name as a result of driving that Vega. The odd firing V6 was another interesting motor. The V6 distributor rotor was an unusual item specific to that motor alone. General motors sure did some interesting things during the 60's and 70's.
 
They sure did! The 215 Buick aluminum V-8 (one of my favorites) arrived just before the advent of permanent anti-freeze (an era when you drained the methanol crap each spring and ran on pure water 'til winter). Running on pure water caused massive internal corrosion and destructive overheating--I recall seeing molten aluminum one of of those motor's heads when it overheated!

Panicked, Buick rushed a cast iron replacement motor into production; and since it would have been too heavy for the Special, they lopped off a couple of cylinders. Made on the V-8 assembly line, it had to be a 90 degree motor, and that created firing order problems. Like a gigantic Harley Davison, it had an uneven firing sequence--it sort of purred at idle. By 1975, when the motor was re-introduced in cars (Jeep used the originals in the meantime). GM ahad found a way to 'splay' the rod journels and produce an even firing sequence (as has been done with numerous 90 degree V-6s since then).

My beloved 215 aluminum V-8 was sold to Rover in England, ending up in Range Rovers, Morgan Plus 8s, Triumph TR-8s, and a host of cottage industry cars that all had great performance thanks to its outstanding power to weight ratio. (Hell, the Queen herself drove a Rover with that motor in it!)

It was just unlucky over here. Had permanent anti-freeze) been established before the 215 came out, the motor would have been around for decades, as it did in England, a production era that rivaled the S B Chevy!

Jeff
 
Last edited:
Back
Top