Installing Distributor in 4.3MPI Help

[Gunn]

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 (specifically for 4.3MPI), 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...(1) That it's telling me to do that before Step #1 in the installation below it, or (2) 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

 

[Gunn]

Ok, found another Youtube video which is a little clearer.... If you're interested, see this video from 3:00 - 3:35 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.

What do you think?!

Tom

 

[Nater Potater]

One thing to verify is that not only is the crank at #1 TDC, but that it is at TDC of the compression stroke. Don't ask how I know... See if this helps any: http://www.gmtruckcentral.com/articles/distributor.html

 

[HawkX66]

Don't over think it. It's easier than it seems. Like Nater said, its critical to be on the compression stroke so you're not 180° out. Once you're there you just drop the dizzy in making sure it drops on the oil pump drive correctly. The dizzy won't drop down all the way unless you've done this. Point the rotor to where you want the #1 spark plug wire to be. This can be tricky because you might need to turn the oil pump drive gear to get it where you want. Use a long screw driver and trial and error making small turns. Once it drops down all the way, install the cap and be sure to put the #1 plug wire in the right spot. Follow the firing order putting the rest of the wires on. My Mercruiser caps have the firing order printed on them. Even though I know the firing order by heart, it still helps.

 

[Bt Doctur]

Hawk, that not applicable for MPI motors
Gunn, follow the manual procedure and read "how to install a dist" because the oil pump drive must be lined up also

 

[HawkX66]

Hawk, that not applicable for MPI motors
Gunn, follow the manual procedure and read "how to install a dist" because the oil pump drive must be lined up also

Seriously? My apologies! Didn't realize the six bangers had a different setup.

Edit: @Bt Doctur I just watched Gunn's video, which was pretty decent but the way. Thanks for the heads up.

 

[scoflaw]

MPI 8's as well with the 555 ecm. Mefi's are old school

 

[Gunn]

Hawk, that not applicable for MPI motors
Gunn, follow the manual procedure and read "how to install a dist" because the oil pump drive must be lined up also

Ok, thanks everyone. Definitely overthinking this one! So I already had the #1 cylinder at TDC...confident in that, no issues there (I've rebuilt a couple of small block Chevy's...which is why I'm questioning the manual probably).

I went back and removed the distributor, re-clocked the rotor and dropped it in. After a few trials of tweaking the oil pump, I got it directly lined up with where the manual says:

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 did 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

 

[Nater Potater]

Okay, this is all messing with me, too. If you go back to your first image, it looks like the arrow you drew at 6:30 is where #1 would be. I say go with your gut and align the rotor shaft to match #1 contact in the cap when you're on #1 TDC. I mean, the worst that could happen is that it won't run. Hell, throw a timing light on it just to see if it flashes where you'd expect. If you're worried about something going really wrong when trying this, disable the fuel injection while cranking with the timing light.

 

[Jimmy Buoy]

From watching the video I gathered that the rotor should be pointed towards the "6" for a V6 and the "8" for a V8. If that's the case, your rotor when pointed towards the "6" would pass by the stud in the cap that leads to the #1 wire. Maybe I didn't catch it right, but I thought that was the idea since the same distributor is used for both V6 and V8 engines?

Bottom line, for your V6 it might just be that the rotor should be pointed towards the "6".

Not experienced in this - just watched the video with curiosity since my Formula (new to me) has the V6 EFI's as well so trying to "learn up".

 

[Burg guy]

Rotor should be on #1 cyl at TDC hence the #6 alignment. If not you will get a backfire thru the intake or exhaust on the wrong 4cyl and that would be a big problem. You will still have to adjust timing after getting it running.

 

[Gunn]

Rotor should be on #1 cyl at TDC hence the #6 alignment. If not you will get a backfire thru the intake or exhaust on the wrong 4cyl and that would be a big problem. You will still have to adjust timing after getting it running.

Has anyone actually done this?!

So at first the consensus was the manual was correct and to align it with the "8" pointer on the distributor and don't question the manual. But now, it seems the consensus is to go with the "6"?!!

Burg, that is incorrect for this 4.3MPI engine. I will not have to adjust timing after getting it running. You are thinking of old school, small block Chevy and the likes where you get the distributor close, fire it up with a timing light and then move the distributor as needed. Not with this engine. The distributor is is bolted down, you CAN'T move it. Timing is done with software. Which from all accounts I've read, I shouldn't have to mess with. The ignition software will figure it out and get it set correctly itself.

I'm leaning to changing to the "6" position. However, I already put the damn engine back in the boat. Makes the job that much harder to do now. I just can't physically see that any kind of software magic can get the ignition to fire on the #1 cylinder at TDC of the compression stroke in this configuration!

I do have the port side engine I could verify with. Maybe I'll get it to TDC (not sure I can rotate it manually with the spark plugs installed, but maybe I can bump it over with the starter) and then pop off the cap and see where it sits...

Tom

 

[Jimmy Buoy]

Has anyone actually done this?!

So at first the consensus was the manual was correct and to align it with the "8" pointer on the distributor and don't question the manual. But now, it seems the consensus is to go with the "6"?!!

Burg, that is incorrect for this 4.3MPI engine. I will not have to adjust timing after getting it running. You are thinking of old school, small block Chevy and the likes where you get the distributor close, fire it up with a timing light and then move the distributor as needed. Not with this engine. The distributor is is bolted down, you CAN'T move it. Timing is done with software. Which from all accounts I've read, I shouldn't have to mess with. The ignition software will figure it out and get it set correctly itself.

I'm leaning to changing to the "6" position. However, I already put the damn engine back in the boat. Makes the job that much harder to do now. I just can't physically see that any kind of software magic can get the ignition to fire on the #1 cylinder at TDC of the compression stroke in this configuration!

I do have the port side engine I could verify with. Maybe I'll get it to TDC (not sure I can rotate it manually with the spark plugs installed, but maybe I can bump it over with the starter) and then pop off the cap and see where it sits...

Tom

Good idea to confirm with the working engine before going to all the trouble to try and change to the #6 position. Just remember that each cylinder has two TDC - one for compression stroke and one for exhaust stroke. TDC for your purpose is using the compression stroke. Without the valve cover off you can't use valve position to confirm that both intake and exhaust valves are closed, but here's another way. Take a paper shop towel and make a piece of it into a tight ball, just big enough to jam into the spark plug hole and plug it. Then rotate the engine (best by using a ratchet on the crank but you may have to remove more plugs to do that) and closely monitor the shop towel plug. The compression stroke will cause the shop towel ball to POP out. Then put a long screwdriver in the hole and you can then rotate forward or back on the crank to get true TDC. Then remove the distributor cap to confirm if the rotor is pointing to the 6 or 8. That would be definite confirmation!

I would think this might be worth a try before messing with the engine you just reinstalled. Hope this helps you.

 

[ttmott]

Follow the video; it is correct.
Make sure you have the correct cap.
When the distributor is installed correctly is will not be pointing at the #1 post in the cap because it is installed fully advanced. The ECM cannot predict ignition advance and can only retard (delay) the spark; that is why the rotor will be clocked before the number one post in the cap.

 

[Gunn]

Neat idea with the shop towel. But just to be clear, my issue is NOT with finding TDC on the #1 cylinder. That was easy. And I did have the valve cover off, my exhaust manifold, etc. so I could easily watch the valves move, see the piston come up and see the timing mark on the balancer come up into alignment with the mark on the timing chain cover. No issues there. 100% confident on I'm the compression stroke.

Anyway, I have solved the problem. The 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.

 

[Jimmy Buoy]

Glad they were able to confirm/clarify the procedure so quickly! Good luck getting her up and running soon.

 

[Gunn]

Thanks!

It took me less than 30 minutes to label all of the wires, remove the cap and rotor, remove the distributor, reposition it and reinstall everything. I got the distributor in and fully seated on the second try. Nothing like repetition to make you feel like a pro!

This is the position the oil pump shaft needs to be in to align with the distributor. Just a bit clockwise of parallel to the engine crank/cam, etc.

GM makes it very easy to align the rotor to the distributor for installation, taking into account the movement of the rotor as it engages the camshaft. Just align the mark on top with the painted circle on the bottom.

And this is what the distributor and rotor should look like fully installed...pointing at the "6" on the housing (with engine at #1 TDC):

All back together:

 

[Nater Potater]

Well? Does it run??? The suspense is killing me!

 

[89P270]

Great narrative and photo Job Gunn! Yes, I am curious too, does it run? One question -After looking at the last photo, it appears when installed, the tang is actually pointing at Number 5 rather than number 1 or maybe between the two. I often wonder when they say point at if they actually mean point close too. Regardless, great info in this thread!

 

[Nater Potater]

After looking at the last photo, it appears when installed, the tang is actually pointing at Number 5 rather than number 1 or maybe between the two.

It's so goofy with the internal wiring running across the top of the cap the way they do. Looking at his last picture, the #1 lead comes from the 3 o'clock position, then runs across the cap to about 8:30, which is right where you see the rotor pointing in the prior picture.