1998 Alpha 1 gen 2 Mercruiser 4.3L 6 Cylinder w/ 1.62R outdrive and 14.5 x 19 Prop

[tobyguy]

Hi All,

I just noticed what I believe is a mismatch in regards to my engine and outdrive.

I bought this boat used a year ago and didn't notice the ratio stamped on the outdrive until recently.

I assumed it was 1.81, but it isn't. And a serial number search also noted it was a 1.62R.

I assumed it was all original boat, but I'm wondering if the outdrive was replaced at some point.

The original serial number search of motor showed it had a 1.81 ratio but that's not what's on it.

Trying to fully understand the implications....

Engine Serial number search:
-------
Engine Model Number 4211015N1
Year 1998
809969 98 - 4.3L ALPHA/BRAVO (262 CID - GEN +)
Merc Alpha 1 SD, 1.81
14-1/4 x 21 Prop-Merc I/O
(but I have a 14.5x19 on it and not 14-1/4x21)


Outdrive Serial Number search
-------
1.62R (and it's stamped with 1.62R on the outdrive so it must be)

thanks

 

[Rick Stephens]

I would think you would have to prop down to make that work. A 19 might be just about right, or a 17 pitch. What was your Wide Open Throttle (WOT) RPMs? That would really tell whether you are propped correctly for the lower gear ratio.

Rick

 

[thumpar]

Like Rick asked, what is your WOT? It could be things were switched out.

 

[tobyguy]

Like Rick asked, what is your WOT? It could be things were switched out.

Boats in storage until spring (I'm in Toronto/Canada area), so I'll have to check it out next spring.

I forget where RPMs are at WOT (I believe it's around 4500-5000 or so), but the RPM guage can bounce around quite a bit sometimes (or seems to misread - it isn't to accurate at all, at least **sometimes** at higher speeds). For example, at 3/4 WOT it can be at 5k sometimes and other times at 3500-4000. If I slow down, then go back to 3/4's WOT, it can go back to what appears to be a more normal range (3500-4000) for 3/4's, though it sounds no different (meaning it doesn't sound like the engine is working any harder regardless what the RPM's say on the guage). When the guage said 5k @ 3/4, it definitely didn't sound like it (so I assumed it's just a guage issue).

I believe it's the guage misreading as when it's at 5k at 3/4 WOT since it doesn't sound like it's any higher than sometimes if it's at 3000-4000, so I just assumed it's the guage not operating correctly. I've had it go WOT to what I recall was about 4500-5000, but I'd have to confirm, just working from memory here (I rarely go WOT). I mostly just cruise as I usually have my 2 little girls and wife in the boat (and dog).

EDIT: Guess my takeaway is to make sure that it stays within the suggested RPM limits in the manual, makes sense (funny enough after jotting down these numbers from memory, it does appear to be within the WOT range for V6's). Except of course for the intermittent 5k+ at 3/4's WOT RPM readings, which again, I believe are a guage issue).

In regards to things could have been switched out, do you mean gears and such inside the outdrive?

thanks,

 

[Rick Stephens]

One of the good ways to double check your tach is to use a good shop tach. Easiest way to get one is on a decent timing light. And you can take it out on the water with you. Until you know rpms at WOT you don't know whether you are propped correctly or not.

It is possible that someone used a 1.64 case with 1.81 gears. If so, then everything is same as stock except for the stamp on the casing.

It is also possible someone swapped the entire upper and your gear ratio is 1.64:1 In which case it is still to be determined whether you can prop it into a decent range for your motor. 1.64:1 means the prop is tuning faster than 1.81:1 in relation to the engine. So a lower pitch prop bites less and relieves some of the disparity. 1.64 is usually a 5.0L V8 gearing. 5.0L engines don't necessarily put out more horsepower than the 4.3 V6, but their power band is a bit different. You may be just fine propping down the 1.64 drive. In fact, you probably will be just fine. Only way to tell is knowing WOT RPM and seeing how the boat performs.

If you want to know which gear set you have without opening it up and counting teeth, you can do a turn test with the outdrive in a stand. If you turn the input shaft 16 times and get 10 turns on the propeller shaft, you have 1.64:1. If it takes 18 turns to get 10 turns on the prop shaft, you have 1.81:1.

Easy peasy.

RIck

 

[tobyguy]

Perfect, thanks for the support!

Just the information I needed

thx