Need Help Installing Distributor in 4.3MPI

[tmagyar]

I'm to the point of installing the distributor in my brand-new 4.3 MPI engine. I have the engine at TDC on the #1 cylinder, ready for it to be installed. According to the manual, shown below, I aligned the tang of the rotor between the two marks. Between these two marks on the distributor is a little arrow casting, with the number "8" printed on it. So I put the rotor in this position on the bench, aligned the oil pump shaft properly to engage the bottom of the distributor and then installed it.



As the distributor engaged the camshaft, the rotor rotated clockwise, away from this position. It then engaged the oil pump shaft and seated down on the intake manifold, ready to bolt down. This is a photo if it installed. You can see where the rotor rotated to in its finally resting position



My question is to anyone who has done this before...is this correct?! According to the manual, I think it is. Or, should the rotor tang be within those two marks *after* full installation? Because I can read #7 two ways...one being that it's telling me to do that before Step #1 in the installation below it, or as a note that after installation, if the engine is at #1 TDC, the rotor should align between those two marks. I can go both ways in my head!

Or...and now here is where things get interesting. When I went searching for an answer, I found a Youtube video where someone was installing this same distributor in a 4.3 Vortec in a Chevy truck. In the video, he pointed out those "8" and "6" numbers cast into the housing, at these two little arrow pointer things also cast in the housing. If you look at the manual photo you can see where I marked with red arrows these two pointers. The manual makes no mention of these or the numbers within them. The person in the Youtube video said to align the rotor tang with the "6" for a 6 cylinder engine.

But then the Youtube video went on to say that there may be little scribe marks on the tail end of the distributor that give you an offset to position the rotor tang, so when it engages the camshaft and rotates, it ends up where you want it pointing at the 6. Which made me also wonder...should the pointer -end up- when fully seated pointing at the "6" for a 6-cylinder?

So I'm left with a couple of questions and a lot of anxiety now. Is it just plain different for Mercruiser versus GM due to the ignition software? I really want to be confident this thing will fire up when I install it in the boat! I also know it will be very difficult to remove and reposition this distributor with the engine in the boat (near impossible?!). If anyone has done with before, or can offer any help, please let me know!

Thanks,

Tom

 

[tmagyar]

Ok, found another Youtube video which is a little clearer.... If you're interested, see this video at the 3:00 minute mark here:

It says "AFTER INSTALLATION" it should line up at that mark. So I have it installed wrong.

BUT...the video also mentions the "6" and "8" and says the rotor tang should be pointing at that number when installed, for however many cylinders your engine has. But this video is also for a Chevy engine, not Mercruiser (even though the base engine is a GM Vortec). So....is my manual wrong? Or does Mercruiser just do it differently?!

I think I may be able to figure this out because when I continued watching at the 12:18 mark, he goes on to show how you can verify that when the engine is at #1 TDC, the rotor should be aligned with the #1 contact on the underside of the rotor that traces over to the #1 spark plug wire location. With that knowledge, I should be able to see if I need to align to the "6" or the "8" upon final installation.

Tom

 

[nola mike]

Not familiar enough with the MPI engines to give you a definitive answer, however I would stop looking at how to set up a Chevy; you're working on a completely different ignition system. My reading of that manual is that the rotor tang should fall within the reference marks after installation. @alldodge can probably give you a definitive answer.

 

[alldodge]

should the rotor tang be within those two marks *after* full installation?

Should point to the 8 after install.
Don't pay any attention to the other notch

 

[Bt Doctur]

Yep, to have a dist install correctly you need to "back up" the rotor a bit, align the oil pump shaft to the dist using a long flat blade, slip the dist down until seated and have the rotor at the arrow

 

[Scott Danforth]

Start with rotor at bottom notch (at 7 oclock), as you drop it in, it will spin around to notch at 3 oclock. May have to spin motor to get dizzy to drop into pump shaft

 

[tmagyar]

Should point to the 8 after install.
Don't pay any attention to the other notch

Thanks everyone for your replies.

Ok, I went back and re-indexed the rotor so it is now in its installed position and bolted down, just like the manual states, exactly.



But here is where it messes with my head. With the rotor lined up there, it is basically pointing at the #3 cylinder firing on the cap...

Now if I were to align the rotor with the pointer cast into the distributor with the "6" beside it, then the rotor would be pointing at the #1 cylinder on the cap! Which totally makes sense to me (and the way GM vehicles do it)...I mean, with the engine at #1 TDC, you want the rotor close to touching the contact that fires the #1 cylinder plug wire, right?

This is the cap, flipped upside down:



And this is it, right side up, mounted on the distributor:



I'm trying to figure out how the Mercruiser ignition software deals with this, but I can't make sense of it.

Bottom line, I installed it like the manual states, but I'm still not clear on if that is right. I know, I know...

I did put the engine back in the boat yesterday, so it should only take me a few hours to get everything hooked back up and fire it up and see what happens, once I get the time.

Thanks,

Tom

 

[alldodge]

Its like the wizard of OZ, don't pay any attention to the thing behind the curtain

 

[nola mike]

Thanks everyone for your replies.

Ok, I went back and re-indexed the rotor so it is now in its installed position and bolted down, just like the manual states, exactly.

View attachment 351970

But here is where it messes with my head. With the rotor lined up there, it is basically pointing at the #3 cylinder firing on the cap...

Now if I were to align the rotor with the pointer cast into the distributor with the "6" beside it, then the rotor would be pointing at the #1 cylinder on the cap! Which totally makes sense to me (and the way GM vehicles do it)...I mean, with the engine at #1 TDC, you want the rotor close to touching the contact that fires the #1 cylinder plug wire, right?

This is the cap, flipped upside down:

View attachment 351971

And this is it, right side up, mounted on the distributor:

View attachment 351972

I'm trying to figure out how the Mercruiser ignition software deals with this, but I can't make sense of it.

Bottom line, I installed it like the manual states, but I'm still not clear on if that is right. I know, I know...

I did put the engine back in the boat yesterday, so it should only take me a few hours to get everything hooked back up and fire it up and see what happens, once I get the time.

Thanks,

Tom

This is one of them fully automated 'puter controlled ignitions. As long as the box knows where the rotor is, it can figger out when to fire.

 

[tmagyar]

This is one of them fully automated 'puter controlled ignitions. As long as the box knows where the rotor is, it can figger out when to fire.

I kind of figured this was the answer. But I just can't figure out how physically, in this configuration, the #1 cylinder spark plug will fire when the #1 cylinder is at TDC of the compression stroke, as it is setup right now. The rotor that carries the current from the center coil contact to the pathway that will go to the #1 cylinder is not in the right position!

This surely must be a typo in the manual, copied from the 5.7MPI engine manual and put into my 4.3MPI manual.

Unless there is someone here who has actually dropped a distributor into a 4.3MPI that can explain this to me!

Tom

 

[Fun Times]

Although it's for a V8, See if the following guide helps any,

https://forums.iboats.com/attachments/installing-hvs-pdf.87763/

 

[Bt Doctur]

 

[tmagyar]

Although it's for a V8, See if the following guide helps any,

https://forums.iboats.com/attachments/installing-hvs-pdf.87763/

That is very interesting. Notice how that manual mentions to align the rotor with the "8" cast into the distributor base for the 8-cylinder engine...

Anyway...problem has been SOLVED! The #32 Service Manual I am using is WRONG! I decided to contact Mercruiser directly...for some reason, I figured they were out of reach. But a quick visit to their website had me find a form to fill out. I did that late last night. By 8:30am this morning, I had a response!

The manual I was using, #32 Service Manual, 4.3MPI Gasoline Engines had been updated. They sent me a snippet from the manual, August 2013 edition for installing the distributor. My original manual had a 1/2 page very brief writeup. The updated manual has THREE pages of very detailed steps. And right in there it states:



So there you have it. For the 4.3 liter MPI 6-cylinder engine, the rotor should be pointing at the "6" cast into the distributor when fully installed.

And with the rotor in that position, it will be directly below the contact in the cap for the #1 cylinder, as I mentioned in a previous post.

Sheesh. I'm glad I questioned the manual. It just didn't make sense to me whatsoever. There just seemed no way possible the ignition software could modify the mechanical path the spark had to take, that I saw when I installed it according to the manual I had.

So now I get to remove and re-install the distributor with the engine in the boat. Oh well, at least now I'm confident I have it right!

Thanks for all the help,

Tom

PS> Attached is the full installation procedure that Mercruiser sent me.

 

[QBhoy]

I’m sure there might be an old school way of doing it…but on an mpi like this and if you’re starting from scratch…as far as I know, you might need to put her into a base timing type arrangement first off with a rinda or similar. Then the whole between the two lines things etc. I’ve never had to do this to be honest. Only just changed the assembly a few times and lots of caps. But without anything else being disturbed. Ignore anything else about anything other than an mpi GM.