merc 260 rebuild and upgrade in parts

[kwebster1]

Hey all,

So I've decided to do a total rebuild on my 1983 merc 260 since I had an oil pan leak and had to pull the engine anyway. I wanted to just run my thoughts through your heads and see if you have any extra ideas or input. I really want to keep the engine somewhat close to stock so I don't overpower the sterndrive. I'm not sure exactly which it is be I want to say its pre alpha probably. She's old. But I do want to try to give the boat a little more spunk. Top speed isn't a major factor for me, I care mire about the hole shot for skiing wakeboarding etc. So o was thinking of doing what I would call just a one step up in camshaft, switching to roller rockers, upgrading a step to aluminum intake manifold and swapping the quadrajet to a holley 600 or 650cfm carb. Would yall think this will be beneficial or am I just wasting money? This was my gpas boat he bought new in 83 and its still in great shape so I'd like to keep her goin for a while.

Regards

 

[Bondo]

Re: merc 260 rebuild and upgrade in parts

Hey all,

So I've decided to do a total rebuild on my 1983 merc 260 since I had an oil pan leak and had to pull the engine anyway. I wanted to just run my thoughts through your heads and see if you have any extra ideas or input. I really want to keep the engine somewhat close to stock so I don't overpower the sterndrive. I'm not sure exactly which it is be I want to say its pre alpha probably. She's old. But I do want to try to give the boat a little more spunk. Top speed isn't a major factor for me, I care mire about the hole shot for skiing wakeboarding etc. So o was thinking of doing what I would call just a one step up in camshaft, switching to roller rockers, upgrading a step to aluminum intake manifold and swapping the quadrajet to a holley 600 or 650cfm carb. Would yall think this will be beneficial or am I just wasting money? This was my gpas boat he bought new in 83 and its still in great shape so I'd like to keep her goin for a while.

Regards

Ayuh,... Ya want a cam that makes Power, from idle, to 4800 rpms,...

Roller rockers won't help,...

If yer in freshwater, an aluminum intake is Ok,...

'n,... If the Quadra-jet is Beat, I'd go with an Edlebrock 1409, which is a carbon copy of Merc's current production 4bbl. carb....
It'll make linkages available to ya for the swap,...
Not so goin' with a Holley...

All in all, None of this is gonna up yer horsepower....

 

[NHGuy]

Re: merc 260 rebuild and upgrade in parts

I"d check compression and try to determine if the motor uses any oil. If it uses oil or has low comp or uneven comp, then you might want to tear it down for a true rebuild. But if it just leaks some oil and has good compression just replace the exterior gaskets. You could do the oil pan, front cover and crank seal, fuel pump seal, valve cover gaskets, rear main seal, and the intake & exhaust manifold gaskets to get a dry bilge.
The carburetor alone will probably make a huge difference. Left untouched they can deteriorate and get dirty. The carburetor and some good tune up stuff can do wonders for your torque and power.
There are some different cams, but you have to stay conservative to avoid reversion problems, so if you need one stay only a little hotter than stock or actual stock. Roller rockers are normally paired with a roller cam & lifter set. Rollers cams are for higher revving motors which you really shouldn't do without 4 bolt main bearings. The 83 probably does not have that. Converting gets expensive.
How big of a boat is this?
I have a 350 inch, 260 HP in a 19.5 footer with a kinda go-fast bottom, it weighs around 2400 near as I can tell.
It's plenty fast, and I just did the carb over this fall, haven't even had a chance to run it without a vacuum leak I discovered while doing the carb over. That's why I say take a look at what you have first, it could be just great.
Maybe you could keep your money for fuel, drinks, food, and towables!

 

[tazrig]

Re: merc 260 rebuild and upgrade in parts

Instead of opening up a whole can of worms not to mention your wallet if all you want is a better whole shot then why not just put a different propellor on it?

 

[kwebster1]

Re: merc 260 rebuild and upgrade in parts

I"d check compression and try to determine if the motor uses any oil. If it uses oil or has low comp or uneven comp, then you might want to tear it down for a true rebuild. But if it just leaks some oil and has good compression just replace the exterior gaskets. You could do the oil pan, front cover and crank seal, fuel pump seal, valve cover gaskets, rear main seal, and the intake & exhaust manifold gaskets to get a dry bilge.
The carburetor alone will probably make a huge difference. Left untouched they can deteriorate and get dirty. The carburetor and some good tune up stuff can do wonders for your torque and power.
There are some different cams, but you have to stay conservative to avoid reversion problems, so if you need one stay only a little hotter than stock or actual stock. Roller rockers are normally paired with a roller cam & lifter set. Rollers cams are for higher revving motors which you really shouldn't do without 4 bolt main bearings. The 83 probably does not have that. Converting gets expensive.
How big of a boat is this?
I have a 350 inch, 260 HP in a 19.5 footer with a kinda go-fast bottom, it weighs around 2400 near as I can tell.
It's plenty fast, and I just did the carb over this fall, haven't even had a chance to run it without a vacuum leak I discovered while doing the carb over. That's why I say take a look at what you have first, it could be just great.
Maybe you could keep your money for fuel, drinks, food, and towables!

Im doing a complete rebuild all the way to getting the block hot tanked honed cam bearings piston rod bearings, everything. So while I was in there I was thinking about doing just a little bit of upgrading. I dont want to get to far above stock but maybe one notch up from stock. The boat is a 1983 cobalt open bow 19' I think. I'm not sure what it weighs but I know it is pretty freakin heavy. The reason I was thinking about going to the roller rockers is to have less friction on the valvetrain and perhaps make it last longer.

I have put a different prop on it. The guy at the midwest prop said that it would be a good one for wakeboarding etc.

 

[achris]

Re: merc 260 rebuild and upgrade in parts

I have put a different prop on it. The guy at the midwest prop said that it would be a good one for wakeboarding etc.

Which probably means it's 'short', lower pitch, so you have good hole-shot. Just be aware that it could be pushing the engine to beyond the top of the recommended max revs at WOT with a light load. I have no idea what prop you have, but if hole-shot is your goal, have a look at a Hi-Five or a Laser II. Both were designed with what you're looking for in mind....

As for upgrades, about the only thing worth anything is a pair of Vortec heads, and an intake to suit...Worth about 20-30 hp.... But remember, usually there is a trade-off for more HP, less low end torque; and that is the very thing you need for hole-shot....

Chris......

 

[Bondo]

Re: merc 260 rebuild and upgrade in parts

Im doing a complete rebuild all the way to getting the block hot tanked honed cam bearings piston rod bearings, everything. So while I was in there I was thinking about doing just a little bit of upgrading. I dont want to get to far above stock but maybe one notch up from stock. The boat is a 1983 cobalt open bow 19' I think. I'm not sure what it weighs but I know it is pretty freakin heavy. The reason I was thinking about going to the roller rockers is to have less friction on the valvetrain and perhaps make it last longer.

I have put a different prop on it. The guy at the midwest prop said that it would be a good one for wakeboarding etc.

Ayuh,.... In, 'n of themselves, the roller rockers ain't worth the cubic dollars, for any of those terms...

Chris is on the money,...
If ya wanta do Any kinda up-grade on a full rebuild,...
Vortec heads, 'n matchin' intake is the best bang for the buck, especially with a New carb sittin' on the intake....

'n seein's yer doin' a Full rebuild, you can squeeze that combo abit more by usin' Matchin' pistons, 'n deckin' the block for the minimum quench...
Shoot for 'bout 9.5:1 compression ratio..