Shift interrupter operation and adjustment after restoration

[Junkyardroad]

I have followed many build threads and searched everywhere for answers to this question.

Background:
1989 Maxum 20' open bow - 5.0 Alpha 1 Gen 1 230 hp s/n 0449447
This boat was our family vacation for 15 years, and that sentimental value has overridden the expense of the resto-mod.

My Thunderbolt IV module failed by every diagnostic I can find. I have replaced it with a HEI with all new OEM internals, I cannot, will not, spend ~$500 for the Merc replacement. I have installed a 350.

The interruptor can kill the motor momentarily by grounding thru the tach sensor. My new shift cable is installed exactly as instructed, and the engine runs and shifts perfectly without the interruptor. (I haven't splashed the boat yet, this part is among the last steps.)

My switch is verified good, normally open. Cables are free and lubricated. The 'rocker' on the manfold for the shift cable is lubed.

It seems that if this mechanism is to ground the coil momentarily, the attachment for the shift cable must be moved by the shift cable casing being pulled briefly by the red cable attached to the shifter handle.

It seems this has to be done by friction, not by cable travel limit, or the switch would remain closed during operation? Thus grounding the coil and killing the engine.

Unless there was some magic in the TV 4 module, the switch remaining closed at full reverse would have prevented the engine from running? My switch 'rocker' never moves unless the boat is full reverse throttle. It cannot be dictated by throttle postition or it would not be momentary.

Seems like I have exhausted all the adjustment variables at this point.

Any advice appreciated.

 

[Junkyardroad]

This boat has been completely reconstructed except for the stingers and a few bulkheads. The block was cracked, interior falling apart, gelcoat faded. My son is an active-duty Marine who asked to use the boat at his base in Arizona 2 years ago, and then was deployed in joint-ops with a friendly navy for almost a year. I decided to do my 'street rod' thing to it while they were gone. Little did I know. The Maxum had 570 hours on it, but ran fine when parked after 2016.

I installed new floors, reconfigured the seating, built in a cooler, and reupholstered by myself. New engine and sterndrive rebuilt on my days off. It has taken almost two years and around $17k. My plan is to drop of the boat to the boys of VMF 211 in a couple of weeks, and I intend it to run as if it was factory delivered.

These boys fly fighters for a living, and I WILL NOT have them wrenching on this boat on their days off. I want it to shift like it used to but i just can't get it to work.

 

[todhunter]

There is no magic in the TBIV. I'm assuming you're trying to see it work while on the muffs? The shift interrupt switch won't do it's thing unless the prop is under load (aka, in the water) and you are coming out of gear and into neutral.

 

[Junkyardroad]

I don't understand. Wouldn't the cables move the same way? I do not have a way to test this unless I'm solo at a small local reservior with high winds and a single lane ramp. It is critical that i not eff this up since i cannot recover it alone.

 

[dubs283]

You can test the operation of the interrupt switch with the boat still on the trailer backed into the ramp. There must be a load on the prop for the switch system to operate properly. You will never simulate the correct load with the boat out of the water.

Check the stickies at the top of the thread page, there is an explanation of how the shift system for an alpha style drive with the interrupt switch works

 

[j cat]

I don't understand. Wouldn't the cables move the same way? I do not have a way to test this unless I'm solo at a small local reservior with high winds and a single lane ramp. It is critical that i not eff this up since i cannot recover it alone.

remove the battery cables then use a ohm meter on the neg coil lug then the other meter probe is on engine block . . fwd- N then rev -n see if the ohm meter is zero ohms when you put it in neutral one sec....
also the switch interrupter move the switch your finger to see if its zero ohms ..

 

[achris]

...The interruptor can kill the motor momentarily by grounding thru the tach sensor.

Incorrect! The shift interrupt switch (SIS) grounds the white/green wire coming from the distributor sensor, it grounds the switching pulses, not the coil.

My new shift cable is installed exactly as instructed, and the engine runs and shifts perfectly without the interruptor.

This is correct. Without a load on the propeller that SIS should NEVER activate.

..My switch is verified good, normally open. Cables are free and lubricated. The 'rocker' on the manifold for the shift cable is lubed.

Rocker? (Please use the names in the Merc diagrams so we are all speaking the same langauge. Nothing worse than one person referring to a part by a name they THINK describes it, like 'riser', when that name actually refers to something completely different.) The only rockers on these engines open the inlet and exhaust valves...

It seems that if this mechanism is to ground the coil momentarily, the attachment for the shift cable must be moved by the shift cable casing being pulled briefly by the red cable attached to the shifter handle.

No, the lower shift cable outer is STOPPED from moving by the load on the proeller not allowing the shift dogs to disengage. As the upper (shift plate end) anchor point for the lower shift cable is offset on the lever assy, actuating the lever assy moves, and that's what trips the SIS.

It seems this has to be done by friction, not by cable travel limit, or the switch would remain closed during operation? Thus grounding the coil and killing the engine.

Not friction, load.

Unless there was some magic in the TV 4 module, the switch remaining closed at full reverse would have prevented the engine from running? My switch 'rocker' never moves unless the boat is full reverse throttle. It cannot be dictated by throttle postition or it would not be momentary.

If the SIS is activated at full reverse, your cable is incorrectly adjusted, or you have crud in the bottom of the slide cavity in the drive that the slide is bottoming out on.

Seems like I have exhausted all the adjustment variables at this point.

Nope, I just gave you a few possibilities.

Chris.......

 

[Bt Doctur]

You need to understand how the shift system and interlock work together. Properly adjusted on land, you should be able to shift into F gear with full throttle and into R gear with full throttle.. Engine NOT RUNNING
If you activate the shift interupt switch shifting, the cables are misadjusted.
Adjust accordingly
Now when your in the water, in gear and try to go to neutral, you cannot do this unless the motor stumbles ,removing the torque on the undercut gears to release it . The shift interupt ground the ign momentarily until it shifts, then releases the tension on the cable allowing the switch to open and the motor to run normally.

HOW TO: How the Shift Interrupt system works

Usually in the spring and summer we get a lot of posts regarding the shift system for the MC-1 (falsely referred to as Pre-alpha drives) to the Alpha 1 drives. There are a lot of wrong ideas on how and why the system works and why it's there to begin with. Maybe this will help explain how it...

forums.iboats.com

 

[Junkyardroad]

"start moving the shifter into neutral there is resistance from the engaged shift dogs that prevents them from coming out of gear. The outer sheath of the lower shift cable is attracted to the Y shaped spring loaded bracket"

This might be where I went wrong. Shift cable and outer sheath are used interchangeably sometimes? Very different parts of an assembly.

I have moved every adjustment to every extreme one at a time while not figuring out that the load on the sheath is what is activating the actuating lever assembly. I would compare this to the slack taken up and moving a motorcycle clutch cable when you first pull it in and seeing the cable sheath move.

The interrupter is NOT activated by the shift cable, but the sheath, or casing of the cable when it comes under tension, right? As in the prop is loaded in water?

Now to figure out where it all needs to be reset to...

I will have a look at this in the morning and report back

Attached is a pic of my first ever try at upholstery. Maybe I can do a build thread?

 

[achris]

"start moving the shifter into neutral there is resistance from the engaged shift dogs that prevents them from coming out of gear. The outer sheath of the lower shift cable is attracted to the Y shaped spring loaded bracket"

This might be where I went wrong. Shift cable and outer sheath are used interchangeably sometimes? Very different parts of an assembly.

Yeah. This is why I try to only use names for parts that Merc use. A common dictionary if you like.

'Shift cable' is the whole assembly. The outer (sheath), inner (core), the slide and the guide.

I have moved every adjustment to every extreme one at a time while not figuring out that the load on the sheath is what is activating the actuating lever assembly. I would compare this to the slack taken up and moving a motorcycle clutch cable when you first pull it in and seeing the cable sheath move.

The interrupter is NOT activated by the shift cable, but the sheath, or casing of the cable when it comes under tension, right? As in the prop is loaded in water?

Spot on sir....

Now to figure out where it all needs to be reset to...

Have you watched my video on the shift cable adjustment?

I will have a look at this in the morning and report back

Attached is a pic of my first ever try at upholstery. Maybe I can do a build thread?

Nice!

 

[Junkyardroad]

Incorrect! The shift interrupt switch (SIS) grounds the white/green wire coming from the distributor sensor, it grounds the switching pulses, not the coil.

This is correct. Without a load on the propeller that SIS should NEVER activate.

Rocker? (Please use the names in the Merc diagrams so we are all speaking the same langauge. Nothing worse than one person referring to a part by a name they THINK describes it, like 'riser', when that name actually refers to something completely different.) The only rockers on these engines open the inlet and exhaust valves...

No, the lower shift cable outer is STOPPED from moving by the load on the propeller not allowing the shift dogs to disengage. As the upper (shift plate end) anchor point for the lower shift cable is offset on the lever assy, actuating the lever assy moves, and that's what trips the SIS.

Not friction, load.

If the SIS is activated at full reverse, your cable is incorrectly adjusted, or you have crud in the bottom of the slide cavity in the drive that the slide is bottoming out on.

Nope, I just gave you a few possibilities.

Chris.......

Thank you, Chris
Lever assembly, actuating.
I will adjust the operation of this thing and report back. When using an automotive based GM HEI distributor, the engine can be stalled by grounding the tach lead. This happens in automotive applications when the tachometer fails by shorting to ground. I'm going to use that with the Mercury shift interrupter mechanism to hopefully duplicate this feature used in the Thunderbolt IV ignition setup. So far the problems in executing this have been mechanically actuating the switch. Hopefully I can figure this out and post up results for others battling failing 30 year old parts.

I think you guys have got me on the right track

 

[achris]

Using an automotive anything in a boat is the quickest way to an early grave, or being the next 'man on the moon'! Please, please don't use automotive electrical gear on a boat engine (or anywhere else in the boat).... If it's not SAE-J1171 rated, it has no place in a boat.

Chris........

 

[Junkyardroad]

Lots of firsts for me on this project.
First boat. Flake paint. Fiberglass. Industrial sewing machine. Welding stainless. etc

I can still be humbled by things like my own myopic approach to a shift interrupter.

 

[dubs283]

My Thunderbolt IV module failed by every diagnostic I can find. I have replaced it with a HEI with all new OEM internals, I cannot, will not, spend ~$500 for the Merc replacement.....

Any advice appreciated.

I find it odd that you've spent nearly $17k on this restoration yet you refuse to spend $500 for the proper, safe ignition component. This decision could cost you much more than that.

Did you follow the merc troubleshooting guide for the thunderbolt ignition system? While the module can fail I can count on one hand the number of them I have replaced over the years.

The advice provided against using an automotive ignition system is by far the best you've received thus far, I would heed it

 

[Bt Doctur]

achris, the older points motors did ground the neg side of the coil

 

[todhunter]

The boat and interior look great. Nice job!

 

[nola mike]

achris, the older points motors did ground the neg side of the coil

Op had a TB iv...

 

[Rick Stephens]

Thank you, Chris
When using an automotive based GM HEI distributor, the engine can be stalled by grounding the tach lead.

Chris commented towards this, and I must strongly support his comments. Boats are buckets. Gasoline fumes are heavier than air and sink. They have no where to go in a boat bilge - unlike a car or pickup where they drop out the bottom onto the road surface..

There are loads and loads of deadly events that gave cause for the coast guard to mandate operation of a bilge blower before starting up your motor. Additionally, all electrical components in any boat are designed tested and approved by said USCG for boat use (SAE J-1711). The design criteria is specifically targeted to capturing any ignition source.

I do not believe that HEI makes a marine rated ignition system and your install is a high risk move. I had the same issue, my ThunderboltIV module quit. It was cheaper to install Delco EST ignition than to replace the module. Note that the OEM Merc TIV module absolutely has a better advance curve than the EST, but wasn't worth it for me to spend the $$ for the OEM either.

 

[nola mike]

Chris commented towards this, and I must strongly support his comments. Boats are buckets. Gasoline fumes are heavier than air and sink. They have no where to go in a boat bilge - unlike a car or pickup where they drop out the bottom onto the road surface..

There are loads and loads of deadly events that gave cause for the coast guard to mandate operation of a bilge blower before starting up your motor. Additionally, all electrical components in any boat are designed tested and approved by said USCG for boat use (SAE J-1711). The design criteria is specifically targeted to capturing any ignition source.

I do not believe that HEI makes a marine rated ignition system and your install is a high risk move. I had the same issue, my ThunderboltIV module quit. It was cheaper to install Delco EST ignition than to replace the module. Note that the OEM Merc TIV module absolutely has a better advance curve than the EST, but wasn't worth it for me to spend the $$ for the OEM either.

TB 4 modules are 100-150 used on eBay.

 

[Rick Stephens]

TB 4 modules are 100-150 used on eBay.

They were quite a bit more way back when I swapped to EST.