Merc 260 5.7 backfiring, timing or electrical?

[Bt Doctur]

Not a trick question , when you installed the cam, what did you use to line it up correctly when you installed the timing chain.

 

[NHGuy]

If you read the Mercruiser (or Seloc) manual to install the timing chain you would line up the dot on the crank sprocket with the dot on the cam sprocket. That's correct for the timing chain to keep the valves in sync, but it's not where you should have the rotating assembly to install the distributor. If you stabbed it there you are off. It's a very easy mistake. You missed the step that says to THEN turn the crank to get both #1 valves closed and then bring the timing mark up to zero before you install the distributor.
BTW I bought a Seloc before I found this forum and realized Seloc is often short on information. I just pulled it out and looked up their distributor installation. Seloc says to do the same thing I just wrote, It's on page 5-29.
Also I hope you did not install the cam sprocket with the dowel pin facing straight down as Seloc shows. That would put your cam off by 90 degrees. They must have been showing a different cam or engine than ours. On the GM small block the pin is at 3 oclock when the dot is straight down (as you look at the front of the engine).
So if you installed the chain with the sprocket dots aligned you can do valves closed, timing mark to TDC, rotor toward #1.
But Bondo's right, 180 the distributor, bet it's fine. I just thought an explanation might help.

 

[Bt Doctur]

Cant figure out some of these manuals either. Such mis-information that's printed not to mention leaving important steps out.
Building an engine is not that hard if you know a little about the engine and have quality manuals to refer to. Having all the correct tools is a plus too.
Most valuable is the piston stop tool to verify TDC of a piston to match this to the harmonic balancer timing marks. Second on the list is a cam degree wheel to verify that you have the cam installed correctly and to verify when and how many degrees the valve is open and when it closes.
Saying that you checked the timing and found it correct and then say the intake valve is opening where you stabbed the dist tells me your mis-informed or have no idea how a motor works.
We don't know how much knowledge you have or what your mechanical skill level is. A lot goes into building a motor and have it run for the first time.
lubing the rotating items during assembly, correct torque values and patterns, pre-oiling thru the dist hole BEFOR you even try to fire the motor.
pre-oiling the lifters to pump them up, pre-setting the hyd lifter valve lash or torque setting . And a whole lot of other items .
Done correctly you have a motor that will go 1800 hours, done incorrectly you have a motor that will last 15 seconds.
Like I said I`m not poking a stick .

 

[DJ Jaws]

If you read the Mercruiser (or Seloc) manual to install the timing chain you would line up the dot on the crank sprocket with the dot on the cam sprocket. That's correct for the timing chain to keep the valves in sync, but it's not where you should have the rotating assembly to install the distributor. If you stabbed it there you are off. It's a very easy mistake. You missed the step that says to THEN turn the crank to get both #1 valves closed and then bring the timing mark up to zero before you install the distributor.
BTW I bought a Seloc before I found this forum and realized Seloc is often short on information. I just pulled it out and looked up their distributor installation. Seloc says to do the same thing I just wrote, It's on page 5-29.
Also I hope you did not install the cam sprocket with the dowel pin facing straight down as Seloc shows. That would put your cam off by 90 degrees. They must have been showing a different cam or engine than ours. On the GM small block the pin is at 3 oclock when the dot is straight down (as you look at the front of the engine).
So if you installed the chain with the sprocket dots aligned you can do valves closed, timing mark to TDC, rotor toward #1.
But Bondo's right, 180 the distributor, bet it's fine. I just thought an explanation might help.

Thanks, I was going to write all that, but you saved me some time. I went back in the book and read it about six times. The instruction is there, it's just very poorly worded, so it comes across quite vague.

 

[DJ Jaws]

So I think I got my answer. I rotated the crank to TDC after the #1 intake valve closed. I opened the distributor cap and it was pointing at #6, which is the exact opposite of where it should be. Simple fix, I pulled it out, gave a twist, had to rerout a few wires and a few minor tinkers, and viola! She kicked right off. My god this thing roars!

Thanks for all the help guys. For the record, I do have lots of experience with engines, both gas and diesel and even a few propane engines, I've been working ont hem since I was literally six years old. I never really learned a whole lot about timing though, the guy I worked with usually did it, and he died before he taught me much about it. The boat world has been an experience for me in the past few years. I have learned that some aspects carry over to boats from the automotive/industrial world and some don't. The basic principles are the same though. Follow the book and you should be cherry. Except when the book sucks. Then you ask the experts. But that carries over to just about anything.

 

[Bt Doctur]

Glad its running, never overlook the obvious

 

[DJ Jaws]

Glad its running, never overlook the obvious

Don't worry, I'm sure I'll have more questions.