Merc 260 camshaft

[mitchcraft15cc]

I am rebuilding the 260 merc/Chevy 350 in my 1980 searay srv 240. Just a basic rebuild, new flattop pistons, three angle valve grind, new crankshaft. I know that the factory cam for this motor is the mellings 22124, but was wondering if there is a better choice for this engine and boat combo. The mellings cam is a design that is 30+ years old. I am using the stock exhaust, true compression is going to be 9.04/1, stock heads, Edelbrock performer intake, and stock Q-jet carb. I am upgrading the stock point ignition to a Thunderbolt IV. There is not a lot of info for marine camshaft selection and the tech people that I talk to don't seem to know anything more than what they can access on their computer screen, which is no more than what I can google. If anyone else has been down this road and has some input that would help me I would appreciate it, thank you.

 

[spdracr39]

Re: Merc 260 camshaft

There isn't a lot of choice because of the specific need for the powerband. An rv cam or truck cam is the best choice because it makes low end torque. This is where you want your max power to be. Any other automotive cams will make the holeshot suffer.

 

[series60]

Re: Merc 260 camshaft

I am rebuilding the 260 merc/Chevy 350 in my 1980 searay srv 240. Just a basic rebuild, new flattop pistons, three angle valve grind, new crankshaft. I know that the factory cam for this motor is the mellings 22124, but was wondering if there is a better choice for this engine and boat combo. The mellings cam is a design that is 30+ years old. I am using the stock exhaust, true compression is going to be 9.04/1, stock heads, Edelbrock performer intake, and stock Q-jet carb. I am upgrading the stock point ignition to a Thunderbolt IV. There is not a lot of info for marine camshaft selection and the tech people that I talk to don't seem to know anything more than what they can access on their computer screen, which is no more than what I can google. If anyone else has been down this road and has some input that would help me I would appreciate it, thank you.

Stock merc flat tappet cam pn 431-5943 that was put in most 350s is: 0.05 duration (intake/exhaust) 200/212, lift .400/.410, centerline 108/112, lsa 110. For future reference, for an off the shelf cam to use in a near stock or slightly modified 350 - especially with stock exhaust, something like a comp xm-256 grind is a good all around cam and a pretty safe bet. In addition, I think for comp cams it's recommended to go 1/2 turn past zero lash on valve lash adjustment. That'll make a little difference in power on your current set-up.

Marine Chevy: Duration: 200/212 (I/E) @ 0.050
Lift: 0.400/0.410 (I/E)
Lobe Separation: 110 degrees.

 

[FreeBeeTony]

Re: Merc 260 camshaft

If you looking for more power I would suggest switching to Vortec heads........you'll also need a Vortec style intake.

 

[mitchcraft15cc]

Re: Merc 260 camshaft

If you looking for more power I would suggest switching to Vortec heads........you'll also need a Vortec style intake.

I was thinking about using vortec heads, but they would put the compression near 10 to 1 with current pistons and .028" head gaskets. I could use a thicker head gasket, but then the quench clearance would be excessive. This would further promote detonation, which may already be an issue with the higher compression and available fuels.

 

[QC]

Re: Merc 260 camshaft

The cam discussion in marine engines with stock wet exhaust is not about performance, it is about Reversion. Do a search here, but basically overlap can cause the engine to suck water back into itself through the exhaust. It's about harmonics, pulses, etc. and some voodoo too. This is why there are limited choices. The RV/Truck cam grind just happen to be right. It is not as much about torque as people believe although it does help with hole shot.

 

[mitchcraft15cc]

Re: Merc 260 camshaft

The cam discussion in marine engines with stock wet exhaust is not about performance, it is about Reversion. Do a search here, but basically overlap can cause the engine to suck water back into itself through the exhaust. It's about harmonics, pulses, etc. and some voodoo too. This is why there are limited choices. The RV/Truck cam grind just happen to be right. It is not as much about torque as people believe although it does help with hole shot.

Thanks, good information. I am not really looking for a cam with more duration, but with more valve lift, and maybe more modern opening/closing rates. I am going to stay flat tappet for budget reasons, but I just thought the aftermarket had something that would be a better choice than stock. Stock cams are usually ground very conservative for longevity and reliability, and are a compromise. Thanks for the input.

 

[mitchcraft15cc]

Re: Merc 260 camshaft

Ok, I went with a K1102 cam from summit racing. It has nearly the same timing numbers with a little better valve lift. I will let everyone know how it works as soon as I get the motor back in the boat.

 

[helimech2003]

Re: Merc 260 camshaft

Thats a good lookin engine.
Definitelly let us know how it runs. I'm thinking about repowering this next winter and am thinking about building an engine similar to yours

 

[mitchcraft15cc]

Re: Merc 260 camshaft

Well, I finally have taken the boat out to the lake. The new engine runs awesome. Starts real easy, idles in gear at 650 rpms smoothly, and gets this heavy old searay on plane easily. I want to break it in for a while before running it hard, but it cruises 30 mph at 3k rpms. Should probably see 40+ wot. A lot faster than what I expected based on other threads that I have read about these 240srv's. it's very throttle responsive and feels to have @300 hp based on my experience with other boats I've owned. Now we just need some warmer weather so I can enjoy it more...lol.

 

[Bondo]

Re: Merc 260 camshaft

Well, I finally have taken the boat out to the lake. The new engine runs awesome. Starts real easy, idles in gear at 650 rpms smoothly, and gets this heavy old searay on plane easily. I want to break it in for a while before running it hard, but it cruises 30 mph at 3k rpms. Should probably see 40+ wot. A lot faster than what I expected based on other threads that I have read about these 240srv's. it's very throttle responsive and feels to have @300 hp based on my experience with other boats I've owned. Now we just need some warmer weather so I can enjoy it more...lol.

Ayuh,.... Sounds Great,.... I also love a Happy endin',... thanks for keepin' Us posted,....

 

[mitchcraft15cc]

Re: Merc 260 camshaft

Hi, another update to the project. I have put 34 hours on the new engine and it runs perfect. It gets 2.9mpg at cruising speed of 23-25mph. I have also played with props and found one that works all around the best. 4 blade merc aluminum 14.5x18, planes easily when loaded, stays on plane at 17 mph 2700 rpms, cruises nice at 23-25mph and has top end of 41mph on gps at 4500rpms. This boat has been a lot of fun this year, even with the less than optimal weather that we have had around here.

 

[NHGuy]

Re: Merc 260 camshaft

Good, results. Nice. 41 is darn good for a big boat like that. Ditto on the nice motor paint.
How much total timing did you go for? I have a stock 1988 5.7 and am interested in getting what's in there. My research says with the earlier heads like we have that 32 is good.

 

[mitchcraft15cc]

Re: Merc 260 camshaft

Good, results. Nice. 41 is darn good for a big boat like that. Ditto on the nice motor paint.
How much total timing did you go for? I have a stock 1988 5.7 and am interested in getting what's in there. My research says with the earlier heads like we have that 32 is good.

Thanks, I'm running 34 degrees total timing. It is a lot faster than I expected it to be, considering speed wasn't the goal. I was just looking to build an efficient reliable engine on a reasonable budget. The only "speed" parts I used were the cam and the edelbrock performer air gap intake. I also added a thunderbolt4 ignition. The rest of it is just attention to detail and clearances.

 

[NHGuy]

Re: Merc 260 camshaft

I have that ignition, it's very steady. I think you will enjoy the relative lack of maintenance it requires. Never even get a hiccup.

 

[Wackyduck54]

I have problems with my shifter i have it in forward i can't pull it into natural and reverse i was told that i have the lower unit off i removed the lower unit and i
tie up the dog tube up turned the star gear till it locked prop is turned right lock why can't this alpha 1 260 engine size i/o 1991 still won't allow me to shift Went the lower unit off its goes good Went the whole thing together can't New Cable only have three cables New shift cable below plus New cables from the side mount shifter control quick sliver can someone answer this question please

 

[GA_Boater]

I have problems with my shifter i have it in forward i can't pull it into natural and reverse i was told that i have the lower unit off i removed the lower unit and i
tie up the dog tube up turned the star gear till it locked prop is turned right lock why can't this alpha 1 260 engine size i/o 1991 still won't allow me to shift Went the lower unit off its goes good Went the whole thing together can't New Cable only have three cables New shift cable below plus New cables from the side mount shifter control quick sliver can someone answer this question please

What does your question have to do with a camshaft for a Merc 260?

Start a new thread with your question instead of tagging a 6 year old thread. Thanks.


Closed.