early 70's Mercruiser 165hp inline 6 w/ MC-1 drive not going into gear (sometimes)

[jimmwaller]

Hi all,
I have an older mercruiser 165hp from... my boat is late 60's but the engine was replaced. I think the engine is early 70's somewhere? It's an inline 6 cylinder GM. It has an old pre alpha drive (MC-1, to be exact). So my problem is, everything works great 98% of the time. It pops right into gear and drives well. But maybe 1-2% of the time (so basically never, it'll happen maybe once over a day of boating), I'll do what I always do and push the throttle forward and the engine will rev but it just won't pop into gear. It doesn't make any noises or anything, the throttle goes forward and there's not grinding, no nothing.... it'll just go forward and there's no pop where there's supposed to be a pop and then the engine will rev but of course the boat doesn't move.

This usually lasts for about 60 seconds, and then all of a sudden it'll be fine. Throttle goes forward and it goes into gear and drives completely fine. So I'm just looking for input on what could cause this and how I might be able to fix it.

Other considerations: I did put on a different drive. It's a slightly smaller MC-1 so the gear ratio is a little different. Went from the drive that was on there when I bought it (so I assume a 165hp drive) to a 120-140hp drive. Iboaters have told me that my old drive was a 1.84:1 and my new one is a 1.98:1. I'm not sure if ratios and/or a smaller drive would affect the shifting but I thought it was worth mentioning. Any guidance appreciated, thanks in advance!

 

[Bondo]

Ayuh,...... 2 possibilities come to mind,......
If the controller was failin', I suppose it could somehow find itself in "Throttle Only" mode, but then goes back to normal,.....
The other is maybe the lower shift cable is failin',....

 

[Scott06]

Hi all,
I have an older mercruiser 165hp from... my boat is late 60's but the engine was replaced. I think the engine is early 70's somewhere? It's an inline 6 cylinder GM. It has an old pre alpha drive (MC-1, to be exact). So my problem is, everything works great 98% of the time. It pops right into gear and drives well. But maybe 1-2% of the time (so basically never, it'll happen maybe once over a day of boating), I'll do what I always do and push the throttle forward and the engine will rev but it just won't pop into gear. It doesn't make any noises or anything, the throttle goes forward and there's not grinding, no nothing.... it'll just go forward and there's no pop where there's supposed to be a pop and then the engine will rev but of course the boat doesn't move.

This usually lasts for about 60 seconds, and then all of a sudden it'll be fine. Throttle goes forward and it goes into gear and drives completely fine. So I'm just looking for input on what could cause this and how I might be able to fix it.

Other considerations: I did put on a different drive. It's a slightly smaller MC-1 so the gear ratio is a little different. Went from the drive that was on there when I bought it (so I assume a 165hp drive) to a 120-140hp drive. Iboaters have told me that my old drive was a 1.84:1 and my new one is a 1.98:1. I'm not sure if ratios and/or a smaller drive would affect the shifting but I thought it was worth mentioning. Any guidance appreciated, thanks in advance!

I would think testing the shift cable by removing it from the shift plate and operating it - does it go smoothly with two fingers, would also remove the drive and make sure the shift shaft is swiveling freely look at how the shift shaft turns on the drive - the angle to make it into gear. Might need shift cable replacement if it is stiff or could be issue inside drive

Ratio of drive has nothing to do with shifting but assuming it was correctly propped (correct WOT rpm) you will need to increase pitch to compensate for the steeper drive gears - probably 2" more pitch

 

[jimmwaller]

Ayuh,...... 2 possibilities come to mind,......
If the controller was failin', I suppose it could somehow find itself in "Throttle Only" mode, but then goes back to normal,.....
The other is maybe the lower shift cable is failin',....

Hi, thanks... I guess I'm not sure what the controller is (is that something that would be on an old engine like this?). I also just replaced the lower shift cable pretty recently (a few months ago) but only noticed the problem in the last week or two

 

[jimmwaller]

I would think testing the shift cable by removing it from the shift plate and operating it - does it go smoothly with two fingers, would also remove the drive and make sure the shift shaft is swiveling freely look at how the shift shaft turns on the drive - the angle to make it into gear. Might need shift cable replacement if it is stiff or could be issue inside drive

Ratio of drive has nothing to do with shifting but assuming it was correctly propped (correct WOT rpm) you will need to increase pitch to compensate for the steeper drive gears - probably 2" more pitch

Thanks, the cable seems fine and the shifter seems fine (shifts by hand). Is there a good video explainer on how the shifter on these old units works? I've only seen inside the drive a few times and I'm still mystified about how the shifter actually operates :/

 

[Eric 3.7LX Alpha 1]

Hi, thanks... I guess I'm not sure what the controller is (is that something that would be on an old engine like this?). I also just replaced the lower shift cable pretty recently (a few months ago) but only noticed the problem in the last week or two

That's your shifter you have at the helm.

 

[Eric 3.7LX Alpha 1]

Here is a link from the Adults Only sticky at the beginning of the forum that may help:

HOW TO: How the Shift Interrupt system works
and this one also:

Mercruiser Alpha Shift cable adjustment

 

[achris]

Other considerations: I did put on a different drive. It's a slightly smaller MC-1 so the gear ratio is a little different. Went from the drive that was on there when I bought it (so I assume a 165hp drive) to a 120-140hp drive. Iboaters have told me that my old drive was a 1.84:1 and my new one is a 1.98:1. I'm not sure if ratios and/or a smaller drive would affect the shifting but I thought it was worth mentioning. Any guidance appreciated, thanks in advance!

I'm confused on your wording here. When you say 'slightly smaller MC-1', do you mean physically smaller in size? (All MC-1 drives use the same housings, hence my confusion.)

If you mean ratios, your 165 was originally supplied with a 1.65:1 drive, not 1.84... As already said, you can compensate with a slightly taller (more pitch) prop...

Chris.......

 

[jimmwaller]

That's your shifter you have at the helm.

Ah, thank you. That makes sense. Do these often have a "throttle only" mode? How would that engage or disengage, is there usually like a button or something that typically does that? It's possible I'm accidentally pushing a button or hitting a switch or something?

 

[jimmwaller]

Here is a link from the Adults Only sticky at the beginning of the forum that may help:

HOW TO: How the Shift Interrupt system works
and this one also:

Mercruiser Alpha Shift cable adjustment

Thank you, I will check these out!

 

[jimmwaller]

I'm confused on your wording here. When you say 'slightly smaller MC-1', do you mean physically smaller in size? (All MC-1 drives use the same housings, hence my confusion.)

If you mean ratios, your 165 was originally supplied with a 1.65:1 drive, not 1.84... As already said, you can compensate with a slightly taller (more pitch) prop...

Chris.......

Right, I means smaller as in lower horsepower (confusing phrasing, my fault). They have different ratios but I really only meant HP rating. thanks!

 

[achris]

Right, I means smaller as in lower horsepower (confusing phrasing, my fault). They have different ratios but I really only meant HP rating. thanks!

It's not a horsepower rating, it's just a decal denoting the engine inside the boat. All Alpha style drives (from MC1 to Alpha One Gen II) are rated to 300hp.

When Merc supplied the drives to the dealers they didn't know which engines they'd be put behind, so there was no decal on them. That '120' or '140' or '165', etc.... decal is supplied with the engine, and when the dealer installed the engine he put the decal on the drive. The only thing actually different is the ratios...

Chris........

 

[jimmwaller]

It's not a horsepower rating, it's just a decal denoting the engine inside the boat. All Alpha style drives (from MC1 to Alpha One Gen II) are rated to 300hp.

When Merc supplied the drives to the dealers they didn't know which engines they'd be put behind, so there was no decal on them. That '120' or '140' or '165', etc.... decal is supplied with the engine, and when the dealer installed the engine he put the decal on the drive. The only thing actually different is the ratios...

Chris........

Thanks, that's good context. Sorry for being a pain here but I'm a little confused and I'd like to understand. If Merc just shipped the drives out with no decal and it sounds like any drive could go behind any motor, it kind of sounds like there's no way to tell the ratio from the sticker.

So, like, if drives with the 120-140 ratios were always behind 120-140hp drives, it seems like merc could put the stickers on them from the factory. But if the drives came unlabelled because they could go behind any engine, and you had to put the sticker on based on which engine it went behind, then wouldn't you have, say, drives with a 165 sticker on them that have all different ratios?

 

[dubs283]

It's not a horsepower rating, it's just a decal denoting the engine inside the boat. All Alpha style drives (from MC1 to Alpha One Gen II) are rated to 300hp.

When Merc supplied the drives to the dealers they didn't know which engines they'd be put behind, so there was no decal on them. That '120' or '140' or '165', etc.... decal is supplied with the engine, and when the dealer installed the engine he put the decal on the drive. The only thing actually different is the ratios...

Chris........

Gotta agree with jimmy on this. I have no idea what mercury did in the 60's to 70's.

You make it sound like dealers not manufacturers rigged the boats? Like sea ray, bayliner, slick craft, etc...just left it to the seller to rig.

Can't imagine arbitrarily attaching decals to blank drives behind different engines was the norm anyways. There must have been a pragmatic way to determine the drive ratio/engine package. I know the drives from that era have decals matching the engine horsepower but the ratio is important, or not?????

 

[achris]

Ah, thank you. That makes sense. Do these often have a "throttle only" mode?

All single lever controls should have some form of 'Throttle only' operation.

How would that engage or disengage, is there usually like a button or something that typically does that? It's possible I'm accidentally pushing a button or hitting a switch or something?

The early control had a lift up level at the back of the control, with (Fast Idle sticker on it)... Later controls had a button in the centre of the lever that disengage the gear shift cable.

Chris....

 

[achris]

Thanks, that's good context. Sorry for being a pain here but I'm a little confused and I'd like to understand. If Merc just shipped the drives out with no decal and it sounds like any drive could go behind any motor, it kind of sounds like there's no way to tell the ratio from the sticker.

So, like, if drives with the 120-140 ratios were always behind 120-140hp drives, it seems like merc could put the stickers on them from the factory. But if the drives came unlabelled because they could go behind any engine, and you had to put the sticker on based on which engine it went behind, then wouldn't you have, say, drives with a 165 sticker on them that have all different ratios?

The ratio and serial number of the drive is on the rear decal. The reason the engine designation wasn't always on the drive was often a dealer would want to fit a different ratio than 'standard', like for high altitude, or when an engine was fitted to a small boat (for that engine), like if a 350 was fitted to a 17 footer. The standard ratio for that engine was 1.5:1, but in such a light boat a 1.32:1 may have been a better fit.

You make it sound like dealers not manufacturers rigged the boats? Like sea ray, bayliner, slick craft, etc...just left it to the seller to rig.

More often than not, it was dealers. Not a lot of boats come from the manufacturer with the engine already fitted. It's usually the dealers who fit engines.. (Well, at least here in 'Straya...)

Can't imagine arbitrarily attaching decals to blank drives behind different engines was the norm anyways. There must have been a pragmatic way to determine the drive ratio/engine package. I know the drives from that era have decals matching the engine horsepower but the ratio is important, or not?????

The ratio is stamped into the side of the drive shaft housing (under the side decal) as well as being on the rear decal itself. Usually when a dealer ordered an engine they would also specify the drive ratio to be shipped (from the warehouse) with that engine. It's not like a dealer would have (or could afford to have) a dozen engines and drives laying around!

Chris......

 

[jimmwaller]

The ratio and serial number of the drive is on the rear decal. The reason the engine designation wasn't always on the drive was often a dealer would want to fit a different ratio than 'standard', like for high altitude, or when an engine was fitted to a small boat (for that engine), like if a 350 was fitted to a 17 footer. The standard ratio for that engine was 1.5:1, but in such a light boat a 1.32:1 may have been a better fit.

More often than not, it was dealers. Not a lot of boats come from the manufacturer with the engine already fitted. It's usually the dealers who fit engines.. (Well, at least here in 'Straya...)

The ratio is stamped into the side of the drive shaft housing (under the side decal) as well as being on the rear decal itself. Usually when a dealer ordered an engine they would also specify the drive ratio to be shipped (from the warehouse) with that engine. It's not like a dealer would have (or could afford to have) a dozen engines and drives laying around!

Chris......

View attachment 366209

Good enough for me. Really appreciate you taking the time to explain all of that, very cool to hear all of this history that is probably extremely rare knowledge nowadays

 

[jimmwaller]

All single lever controls should have some form of 'Throttle only' operation.

The early control had a lift up level at the back of the control, with (Fast Idle sticker on it)... Later controls had a button in the centre of the lever that disengage the gear shift cable.

Chris....

Hm... I did not know that, but this seems like the simplest (and most likely) explanation of what's happening. This matches the symptoms exactly... I assume if it were more of a shifter issue or cable issue, I would hear or feel something but since it throttles up so smoothly with no noise, it feels much more like it's designed to happen. A throttle only switch seems like a likely culprit. I'll inspect the throttle lever and report back, thanks to all who have contributed so far! Fingers crossed for some good news about the issue being my own stupidity

 

[achris]

If the control on your boat is original, then it will look like this... (pink arrow is 'Fast idle'/'Warm up' lever).

 

[dubs283]

Wow, can't imagine a dealership having to rig an mcm. Outboards, yes but an i/o package would be a tall order for a boat and engine manufacturer to trust proper install. I guess today, in America at least we get stuff from various boat manufacturers already rigged (sterndrive/inboard/v drive). I've never heard of a dealership having to install any propulsion package other than outboard, warranty aside

I absolutely know drive shaft housings are stamped with ratios and s/n. Been working on boats long enough to visually i.d. most brands, models, years and styles without number confirmation. Shop works on boats ranging from 1950 to present day, mostly sterndrive/inboard. Think all gas powered manufacturers in that year range and it's a good bet we lay wrenches on it.....