Mercruiser shift interrupter

colhel

colhel

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My new to me speedboat has a Mercruiser 5.0l carb coupled to an Alpha 1 gen 2 drive. After searching the internet it appears to me that it's possible it only stalls the engine coming out of gear (which seems odd to me). I've had to make adjustments on the shift control cable just to make the boat usable but where the cables are so stiff and need replacing, I think they're still a little out of adjustment. Is there a separate adjustment for the switch or does the cable adjustment set the switch?
 
The switch only activates when you are coming out of gear, the reason is the gears are under load and you need to relieve the load to let them slide out of mesh. The main reason for stalling is that the sort wire down to the drive gets stiff and it adds an extea load to the system causing the interrupter switch to activate for too long, stalling the engine.
I would disconnect the short wire and shift by hand to see if its unduly stiff, if so it needs replacing. If it moves relatively easy then it needs to be set up correctly with equal throw for forwards and reverse, there is a further adjustment on the arm with a slot to get a longer or shorter throw. There is no adjusstment on the switch itself its all done on the cables.
 
Thanks for the kind remarks guys, I am more than happy to share my experience abd knowledge of the past 30 years in the marine branch, I don’t know everything but have worked on most engines and drives.
 
The Alpha has a dog clutch rather than a cone like other drives. Upside is it's very robust, downside it can stall when coming out of gear due to a badly adjusted cable.

I would try greasing the cable where it is connected on top of the engine and shift back and for a few times. There are YouTube videos showing how to measure the cable to see if it needs replacing and adjust it. You can do the final adjustments on the water with the propeller under load, for the perfect setting.
 
I have seen many boats where the cable to the drive has been replaced and routed incorrectly. It comes in just over the exhaust downpipe and then has a sharp bend to the right to clear the flywheel housing, it should then curve 180 degrees back towards the transom then curve upwards BEHIND the steering servo cylinder then forwards to the shift quadrant, if this isn’t followed it induces undue friction which affects the interrupter switch. Also with time the cable gets a kink where it bends past the flywheel housing so when you shift the kink on the inner cable has to force its way into a new part of the outer cable, this the reason for stalling.
 
Grubble said:
The Alpha has a dog clutch rather than a cone like other drives. Upside is it's very robust, downside it can stall when coming out of gear due to a badly adjusted cable.

I would try greasing the cable where it is connected on top of the engine and shift back and for a few times. There are YouTube videos showing how to measure the cable to see if it needs replacing and adjust it. You can do the final adjustments on the water with the propeller under load, for the perfect setting.
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Yes when I first got the boat it was very difficult to find neutral and extremely stiff to shift. . Once I followed the instructions found on YouTube and adjusted the cable, neutral was easy to find and it feels a lot free'er. I still had the occasional stall (and still do but not as often) due, possibly, to the tickover being too low. I found on Internet it should be between 650 and 700 rpm in gear. It was around 400 rpm.

spannerman said:
I have seen many boats where the cable to the drive has been replaced and routed incorrectly. It comes in just over the exhaust downpipe and then has a sharp bend to the right to clear the flywheel housing, it should then curve 180 degrees back towards the transom then curve upwards BEHIND the steering servo cylinder then forwards to the shift quadrant, if this isn’t followed it induces undue friction which affects the interrupter switch. Also with time the cable gets a kink where it bends past the flywheel housing so when you shift the kink on the inner cable has to force its way into a new part of the outer cable, this the reason for stalling.
Click to expand...

Thanks, I'll see if I can check this next time. Thanks again
 
colhel said:
I still had the occasional stall (and still do but not as often) due, possibly, to the tickover being too low. I found on Internet it should be between 650 and 700 rpm in gear. It was around 400 rpm.
Click to expand...

That does sound like the culprit. The engine practically stalls at times when coming out of gear even with the idle speed set correctly, so I would imagine if it's too low plus maybe with a cable past it's best, then it will be even worse.

Mine is the fuel injected version so nothing to adjust for the idle speed - I don't know how the carb version works, but it does sound like it's what you need to look at next.
 
Another tip is to shift in and out of gear smartly, I cringe when I hear people shifting slowly and you hear that horrible dak dak dak sound as the dog clutch bounces over succesive teeth on the gear, which eventually rounds off the 90 degree corner on the dogs. Its best to move the gear lever in one positive movement which means the gear engages first time and also reduces the time the interrupter switch is active as the engine can stall if its operative for too long. The way its designed means it flicks closed for a fraction of a second which is enough to take the torque off the dog clutch allowing easy shifting. Also a pause between going from forward to reverse or the opposite to allow the prop to stop spinning before its made to reverse direction especially if its a steel prop as its weight means it takes longer to stop spinning and making a heavy prop doing 400 rpm in one direction suddenly go 400rpm in the opposite direction makes my ‘engineers’ toes curl thinking of the shock loads on the gears.
 
Yes, get the engine up to temp and put it in gear, I adjust the idle first then fine tune the mixture then the idle again to give 650. Rev it up in neutral a few times to check it comes back down to about 700 if its much higher you get a hard clunk as it goes into gear, then check it goes in and out of gear without stalling a few times.
You may have to do this a few times to get it spot on as carbs can be a bit temperamental. I have a 350 Magnum with a carb but this engine has an idle control system with the ignition module adjusting the timing to maintain the correct idle speed so it doesn’t stall.
 
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