NorthUp
Active member
Has anybody tried replacing a Yamaha ST421 stern drive with a Mercruiser bravo 3?
Edit- or any other leg that doesn't have Yamaha on it?
Edit- or any other leg that doesn't have Yamaha on it?
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Yamaha sterndrive change
- Thread starter NorthUp
- Start date
[2068]
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Why would you want to do such a thing?
NorthUp
Active member
Six drives in twelve years, countless 23'' props shedding blades or hubs, steering failures, fifty hour oil changes, and now spares are becoming difficult to source.
Mr Googler
Well-known member
Yamaha spares are horrendously expensive. I span up a gimbal bearing on mine and took a few tho off the inside on the transom shield. New shield was £3k just for the part. Secondhand parts are rare too. No more nails did the trick........joking 
. Special oil too but they are cracking when all is right.
. Special oil too but they are cracking when all is right.[2068]
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Wow, and I thought shaft seal changes on VP DPE's was bad news after 10 years.
I've just bought a couple of new Alu 3-bladed props to replace the original ones which had turned to cheese on the edges - they were from 2003!
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Mr Googler
Well-known member
Had a quick read on a few us forums and they reckon bolt pattern and transom holes are the same for mercruiser and yamaha so that's one big issue sorted.
Greg2
Well-known member
Interesting. My understanding is that the Yamaha drives are a quality bit of kit that has been discontinued because they couldn't build them to a cost that the market is prepared to pay. I did quite a bit of research on this as we have them on a boat at work. Sounds like you have been unlucky, which can happen with drives.
Might be worth trying are Redbay Boats (located in N. Ireland) for spares. They are the UK dealer and have the remaining new units as well as lots of stuff for recon.
Might be worth trying are Redbay Boats (located in N. Ireland) for spares. They are the UK dealer and have the remaining new units as well as lots of stuff for recon.
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volvopaul
Well-known member
If you have really used that many drives in that time there was or is something seriously wrong with either the installation set up, or the way you have used it . There is no way the legs would destruct in the time span like that
Tell us more, what boat , engine, twin or single Hours per season etc .
For you to get through them like that there is something not right . We're they serviced correctly ? Those legs are not rocket science at all. I looked after a boat with them on , they are still going now and from 1995 vintage.
Mercruiser isn't the way to go in my view . Sort the problem logically .
Tell us more, what boat , engine, twin or single Hours per season etc .
For you to get through them like that there is something not right . We're they serviced correctly ? Those legs are not rocket science at all. I looked after a boat with them on , they are still going now and from 1995 vintage.
Mercruiser isn't the way to go in my view . Sort the problem logically .
NorthUp
Active member
11metre Delta rib, twin engine, probably around 2000 hours of commercial use. Serviced in excess of manufacturers recommendations as far as oil changes were concerned.
Clutches slipping and failing due to low oil pressure were the main failures, I suspect the pumps are just not up to the job. The oil would be black and burnt sometimes, failure followed eventually, but not at consistent timescale- this with fifty hour changes!
Propellers - shedding individual blades, occasionally all that was left was the hub itself. Switching to 21" pitch from 23" cured that problem at the expense of poor handling at low speed and 8 or so knots at the top end.
Steering- the square on the shaft becomes worn despite regular checks of torque on clamp bolt.
All these failures are duplicated on two other boats to my personal knowledge, (not serviced by same engineers either!) and the net has similar tales of woe.
Yamaha were in denial, despite being presented with physical evidence.
Clutches slipping and failing due to low oil pressure were the main failures, I suspect the pumps are just not up to the job. The oil would be black and burnt sometimes, failure followed eventually, but not at consistent timescale- this with fifty hour changes!
Propellers - shedding individual blades, occasionally all that was left was the hub itself. Switching to 21" pitch from 23" cured that problem at the expense of poor handling at low speed and 8 or so knots at the top end.
Steering- the square on the shaft becomes worn despite regular checks of torque on clamp bolt.
All these failures are duplicated on two other boats to my personal knowledge, (not serviced by same engineers either!) and the net has similar tales of woe.
Yamaha were in denial, despite being presented with physical evidence.
volvopaul
Well-known member
The yanmar is a copy of mercruiser in the transom shield so you won't escape that if you swapped over and the merc won't last long with the Yamaha 6 pot engine as it's the same lump as the yanmar 6 lp.
I wonder if the wrong grade of oil has been used in the legs?
Personally if this is your living I'd ditch the lot and go for the Volvo repower which you can get some deals on.
What hp do your require? You could get away with the D4 260 set up or go for the 300 .
These problems sound like a bad calculation of prop sizes relating to the whole set up being overloaded at cruise speed.
Beamishken
Member
mercruiser bravo range is the same pattern of drillings as the Yamaha so should bolt in & im fairly sure (but not 100% as it was a few years back) I tried a yam coupling on a merc spline & they were the same so in theory & subject to checking you could probably swap to a merc drive & use the yam inner transom shield so the rear mounts will match up & it would be pretty much a nut & bolt job, possibly have some work to do on the steering set up though
the other way to go would be to find yanmar bellhousings to bolt to your engines but there crazy money new & hard to find used
b3 doesn't get a great rep on yanmars but yamahas are turbo'd differently as they run a smaller diameter turbo compressor housing so tourque shouldn't come in with a rush like the yanmars so the drives may fare better.They don't seem as fragile when fitted to mercs own engines but that could be down to the engines not being as potent or could be down to the different tourque delivery
generaly the bravo drives are fairly easy to get hold of & cheaper & spare drives often come up for sale so you could keep spares easier than the yam items .They do suffer from the same problem with the steering square though but you can get external steering & external link bars to help with that look at imco they do loads of uprated stuff for the American race scene inc stainless gimbal rings & steering pins
personally id wouldn't thank you for a Volvo installation as there's too much electronics to go wrong at least if you have a problem with those Toyota based lumps you don't need an electronics degree & the Toyota service bits are readily available at a fraction of dealer parts prices
you could also look at the konrad drives which are supposed to be stronger than the bravo range but pricey & imco do their own beefed up drives aimed at the us race scene too
you have a few options before you need to bin the complete engine & drive package personaly id look at a bravo 2 set up & see how you get on as the single prop bravo two seems more robust than the b 3 but id fit drive showers to cool the drive & stop the burnt oil scenario
where are you based? I've got loads of bravo bits lying around if you wanted anything measured or compared to see how compatable its going to be with the yam engines
the other way to go would be to find yanmar bellhousings to bolt to your engines but there crazy money new & hard to find used
b3 doesn't get a great rep on yanmars but yamahas are turbo'd differently as they run a smaller diameter turbo compressor housing so tourque shouldn't come in with a rush like the yanmars so the drives may fare better.They don't seem as fragile when fitted to mercs own engines but that could be down to the engines not being as potent or could be down to the different tourque delivery
generaly the bravo drives are fairly easy to get hold of & cheaper & spare drives often come up for sale so you could keep spares easier than the yam items .They do suffer from the same problem with the steering square though but you can get external steering & external link bars to help with that look at imco they do loads of uprated stuff for the American race scene inc stainless gimbal rings & steering pins
personally id wouldn't thank you for a Volvo installation as there's too much electronics to go wrong at least if you have a problem with those Toyota based lumps you don't need an electronics degree & the Toyota service bits are readily available at a fraction of dealer parts prices
you could also look at the konrad drives which are supposed to be stronger than the bravo range but pricey & imco do their own beefed up drives aimed at the us race scene too
you have a few options before you need to bin the complete engine & drive package personaly id look at a bravo 2 set up & see how you get on as the single prop bravo two seems more robust than the b 3 but id fit drive showers to cool the drive & stop the burnt oil scenario
where are you based? I've got loads of bravo bits lying around if you wanted anything measured or compared to see how compatable its going to be with the yam engines