Yamaha 30hp 3 cyl Lower Unit Compatibility

[wmk0002]

Let me start by saying this is my first post here. I have lurked on this site over the years as I stumbled upon it originally while looking for how to "mod" 9.9 hps to 15's lol. Since then I have found my way back numerous times but never had any questions worthy of the board due to the small outboards I run on jon boats. But finally I had a reason to join and am happy to be here. I hope I can contribute to some degree.

To my issue at hand... I am looking to purchase a 1988 Yamaha 30hp 3 cylinder. The motor has duck hunter influences and was damaged due to the point it needed to be rebuilt. Powerhead and lower were rebuilt and packaged with a new Edge boat to the current seller. Story goes dealer never replaced the lower oil upon the sale and seller basically ran it dry. Obviously he had lower issues and that's when he discovered a bone dry lower. Seller and a friend rebuilt it themselves where they also discovered the lower unit had been cracked and welded. After fixing he said it worked fine until it failed again and now will engage in reverse but not forward. A cracked lower paired with a rebuild does raise my eyebrows but if this was a duck motor I can see it happening. Was told it has 40 carbs fwiw. No clue on tuned exhaust, shaved heads, lighted components, etc though.

I say all of that to say that while I'm confident I could get a good quality lower casing rebuilt, I am not as confident on one that has previously been cracked. So I'm basing my offer on the assumption that a new lower unit or lower unit casing will need to be purchased. So far I have had poor luck locating any for sale that aren't already professionally rebuilt which are well out of my price range.

The real question becomes, will a lower from any other model fit this 1988 30hp aside from other 30hps in the 87- 90 something range? Are there any that are direct bolt on with identical gear ratios? There are a good bit of 40/50hp ones available. I would assume there is not much crossover, however, I do recall seeing posts elsewhere that I can not find now that said the 30hp lower gearbox was a weak link and many upgraded to a 40/50 lower but required slight modifications. But I could be totally off. Any help would be very much appreciated and thank you in advance.

[Motv18]

I can’t remember much from that era, but typically in the same block family mids and lower will CrossFit I don’t know if it’s 20-30 or 30-50 though.

Also cant remember if it was omc or merc they cross with, Nissan ran a lot of omc parts can’t remember what Yamaha ran at that time

[wmk0002]

I can’t remember much from that era, but typically in the same block family mids and lower will CrossFit I don’t know if it’s 20-30 or 30-50 though.

Also cant remember if it was omc or merc they cross with, Nissan ran a lot of omc parts can’t remember what Yamaha ran at that time

Based on the parts site I was using, the crankcase part number is for 30hp models years 1987-2002. It also is the same crankcase for the 3 cylinder 25hp model years 1999-2001 (there were also 2 cylinder models made those years). So for that 87-98 year range, the 30hp appears to have been its own unique motor with its powerhead part number be exclusively its own. I also saw where the 1988-X 30/40/50hp all had the same gear ratio of I believe 1.85.

[Motv18]

Power head assembly part number change can be as simple as porting or a different bolt hole. If you have a service manual it will normally have the same block series in one book.

It is is possible that it’s just that one engine.

[wmk0002]

Power head assembly part number change can be as simple as porting or a different bolt hole. If you have a service manual it will normally have the same block series in one book.

It is is possible that it’s just that one engine.

You are probably right. In the meantime, I think the lower unit with this motor will be ok or at least serviceable once I fix what turned out to be a broken shift rod. Its been removed along with the shift cam so it allowed it to engage in forward gear just fine. I believe technically I could plug the shift rod hole and actually run it in the water, just be in full time forward. I may do that just to test and then fix it the right way by pulling the bearing carrier and prop shaft out and installing a new one.

[wmk0002]

To update this, I did purchase this motor. It tested 140 psi on all cylinders (was rebuilt 2 years ago) and is in overall great shape aside from the lower unit issue I originally posted about. I'm going to try fixing it myself, however, I'm still open to finding another one, especially if if has a short shaft driveshaft in it already. I mentioned this is a long shaft motor and I really need a short shaft...I have a nice Vance jack plate not yet installed to help remedy this, however, Im not sure the Yamaha transom bracket fits on this mini jack plates motor side profile. The Yamaha has 4 locations for security bolts and although they aren't a true B.I.A. pattern, I think they exceed the jack plates area. I can easily sell this one and get a larger hp capacity plate so its not a big deal but I would still prefer a short shaft. I guess if anyone sees a midsection or upper casing for sale let me know.

[wmk0002]

Another update: I pulled the lower unit bearing carrier and found that forward gear was missing a tooth. All of the bearings seemed to be good though so I'm not sure what happened to the remnants of the tooth. The oil was drained prior to me buying it so its possible it came out on the magnet. Assuming the bearings are good, I may be able to get by with a new forward gear (~$100) a new shift rod assembly (~$60), prop shaft seals ($10), and a new claw washer and retaining ring ($25). That's best case at this point and about $200 in total. I think the clutch dog is in good enough shape but being only a $50 part it may be best to go ahead and swap it out too. Regardless, the cost adds up pretty quick, so I'm still going to keep an eye out for a used lower while I wait on my service manual to come in. So I'm still interested in what lowers are compatible with my motor, especiall interested if the 40/50hps are as they are more readily available used.

[Motv18]

Coolbeens

[wmk0002]

Through a little more digging it seems many state a 40/50 lower will bolt up but need to make sure it's the era with the push/pull vs rotating shift rod. Needed modifications include shortening the driveshaft slightly and extending the splines down along with boring and tapping the bottom side of the shift rod coupling barrel nut to match he 40/50 shift rod size/thread. Wondering if anyone can confirm this and if so what kind of cost would you be looking at to cut a respline a shaft like that?