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Old 16-09-2021, 14:22   #1
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Repowering Tayana 37 with Yanmar 3JH40

I have a Yanmar 3QM30 and am considering replacing it with a Yanmar 3JH40. Has anyone had a 3JH40 installed in their Tayana 37?



If so, please share what engine you replaced and any problems you may have encountered with engine bed modifications, rerouting water strainer hose a/o exhaust hose, onboard diagnostic problems, etc.
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Old 17-09-2021, 05:04   #2
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Re: Repowering Tayana 37 with Yanmar 3JH40

Good morning, Taipe.

At least you are well ahead of most cruisers who post with proposals to change engines. You know that you may be up against bunches of problems if the two are not identical. The 40 is larger, but both are three cylinder and have the exhaust on the port side, so you may be OK.

I am curious as to why you want to make the shift. The 30 should push you along at hull speed or close to it, and the 40 should only add lots of fuel expended for a slight gain in speed.
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Old 17-09-2021, 10:12   #3
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Re: Repowering Tayana 37 with Yanmar 3JH40

Thanks for your reply. The motive for investigating possibilities for repowering is due to ongoing scarcity of some of the parts for the 3QM30. Rebuilt coolant pump replacements are becoming very scarce, no engine heads listed on the internet anymore for replacement of a head with hair-line cracks, and the water pump">raw water pump drive design has always been a potential achilles heel on this engine, as there exists the potential for mixing of seawater with the engine oil to occur if the seal on the end of the engine cam fails. Unlike the 3JH40, the exhaust on the 3QM is actually on the stbd side. In regard to fuel consumption, I am expecting the two engines to be comparable due to the 3JH40's rail line injection affording improved fuel economy, and there is of course the environmental benefit of reduced nitrogen oxide emissions due to the improved combustion. I do agree with you that the 3QM has sufficient power for most sea conditions and also agree with your implication that the possibility of needing to repower in an unfamiliar port is often times not an ideal situation.



So, my query on this thread will be to see if it is feasible to re-route the exhaust hose downstream from the mixing elbow to the starboard side, and to see if there are serious obstacles to accommodating the motor mounts to my engine bed stringers. I'll be back aboard soon to take measurements.
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Old 17-09-2021, 10:17   #4
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Re: Repowering Tayana 37 with Yanmar 3JH40

One person on the forum doing a re-engine actually made a cardboard engine from the CAD measurements, just to see that it would fit.
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Old 17-09-2021, 11:31   #5
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Re: Repowering Tayana 37 with Yanmar 3JH40

It depends on your plans for the boat, but I would be very hesitant to replace the older design engine with a common rail electronic one. If you sail within a few miles of the Yanmar dealer, it will be fine. If you wake up one morning in Vanuatu and your Yanmar computer doesn't, you are going to question your choice.
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Old 20-09-2021, 12:20   #6
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Re: Repowering Tayana 37 with Yanmar 3JH40

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Originally Posted by donradcliffe View Post
It depends on your plans for the boat, but I would be very hesitant to replace the older design engine with a common rail electronic one. If you sail within a few miles of the Yanmar dealer, it will be fine. If you wake up one morning in Vanuatu and your Yanmar computer doesn't, you are going to question your choice.

I appreciate your concern. Assuming that you are primarily considering lightning strikes, according to marine insurance claims the risk of a lightning strike taking out electronics averages about 1:1,000 insured sailboats/year and in the lightning strike infested waters of Florida, the risk is a little over 3:1,000. Though I don't particularly like those risks, they do not deter me from considering engine replacement with one that uses computerized injection. But, before setting out on a blue water cruise, I would want to take along a spare engine computer in a metal box for shielding. For onboard diagnostics, that is available remotely by uploading the data via sattelite phone with a dongle plugged into the engine's computer diagnostics. I don't like this dependence upon circuit boards either, but this is the reality we may need to adapt to.
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Old 20-09-2021, 16:39   #7
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Re: Repowering Tayana 37 with Yanmar 3JH40

It isn't just lightning. I delivered a common rail engined boat up the east coast, On day 2 I tried to start the stbd engine, and was greeted with yellow triangles and see your dealer messages.

I checked the fluids and battery and tried again. This time it started right up and ran for the next 10 days. It just wanted to show me who was in charge.
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Old 20-09-2021, 18:08   #8
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Re: Repowering Tayana 37 with Yanmar 3JH40

That's not very encouraging to hear. Last week I did a computer search for alternatives to Yanmar dealers for diagnostics & fault code resets for the 3JH40's on-board diagnostics (OBD) and found it would cost me either $8,000 U.S.D. to purchase the software and additionally pay for online classes to learn to independently do my own diagnostics & repair for this engine or alternatively to upload from the engine's OBD to another company's web page for a charge of $200 per fault code found. The latter doesn't hurt the wallet quite as badly, but for comparison, I recently paid a one-time $200 fee to Ross Diagnostics so that I can diagnose and decide whether to work on my 2013 VW TDI vehicle or take it in to the VW dealer for repairs. In addition to receiving their dongle (a hardwired plug-in to connect the OBD to a USB port in a laptop), they include the dealer parts numbers matched to each fault code problem + prompt tech support via email for up to 3 different vehicles. Too bad they don't include marine diesels, but maybe someone will come along and shake things up for more affordable options.
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Old 20-09-2021, 18:39   #9
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Re: Repowering Tayana 37 with Yanmar 3JH40

Dont know if Betas pass yr emissions test but they have mechanical injection.

Integral salt water pumps always make me nervous too. Beta might have those sadly.


How much does a spare ecu set you back? I'd enquire as the yammer mafia are ruthless IME.
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Old 20-09-2021, 20:07   #10
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Repowering Tayana 37 with Yanmar 3JH40

Just replace it with a Beta. Probably the 35 is perfect for you. When I repowered, I debated briefly on the Yanmar 4JH45 and went with Beta 50 instead. 500 hours of flawless performance now. And, when it shuts down (which it did once) it was due to my stupidity (not reopening the fuel valve after filter change). No holding my breath on whether the computer went bye bye.

I don’t think you can even change an injector on a Yanmar CR without a tech and a laptop
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Old 20-09-2021, 23:07   #11
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Repowering Tayana 37 with Yanmar 3JH40

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Originally Posted by Taipe View Post
That's not very encouraging to hear. Last week I did a computer search for alternatives to Yanmar dealers for diagnostics & fault code resets for the 3JH40's on-board diagnostics (OBD) and found it would cost me either $8,000 U.S.D. to purchase the software and additionally pay for online classes to learn to independently do my own diagnostics & repair for this engine or alternatively to upload from the engine's OBD to another company's web page for a charge of $200 per fault code found. The latter doesn't hurt the wallet quite as badly, but for comparison, I recently paid a one-time $200 fee to Ross Diagnostics so that I can diagnose and decide whether to work on my 2013 VW TDI vehicle or take it in to the VW dealer for repairs. In addition to receiving their dongle (a hardwired plug-in to connect the OBD to a USB port in a laptop), they include the dealer parts numbers matched to each fault code problem + prompt tech support via email for up to 3 different vehicles. Too bad they don't include marine diesels, but maybe someone will come along and shake things up for more affordable options.


I fitted a new Beta 30 to a Tayana 37 and it was a fairly snug fit. I had a bit of trouble with the exhaust , bugger all access up in the stern to remove the old swan neck and then run new hoses, also the aqualock was hard to deal with in the difficult space aft of the engine bed because it had an “aquadrive”on the propshaft. Your 3qm must have been tight in that space.
I’m not in favor of common rail engines in cruising yachts but if it’s a marina based short journey sailboat with access to a Yanmar dealership then fair enough BUT, if you’re planning on serious voyaging avoid em like Covid. I did an estimate of all the spares needed to cover every theoretical electronic engine failure for a Volvo D3 110 once and the cost was over $10,000. That 10k guarantees that you have everything needed to bring a green monster back to life if it happened to not start at “Chagos” or somewhere equally devoid of Tech support.
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Old 21-09-2021, 06:38   #12
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Re: Repowering Tayana 37 with Yanmar 3JH40

I appreciate everyone's input and will most likely focus on keeping the 3QM. Btw, in regard to the potential saltwater-oil seal failure for the 3QM30's internal-driven saltwater pump, to convert it to external belt drive, I purchased a bronze Jabsco pedestal pump to replace it with. A marine diesel mechanic told me had done this conversion on the 3QM30. It requires adding on an idler pulley to drive it together with the fresh water pump. A bolt-on aftermarket double grooved pulley attaches onto the face of the original crankshaft pulley for two belts dedicated just to the alternator. In all, the conversion reduces bearing wear to pumps, alternator and crankshaft main bearings by allowing less tension on all belts.
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Old 21-09-2021, 12:53   #13
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Re: Repowering Tayana 37 with Yanmar 3JH40

IMO you have made the right decision as compared to going to ecu controlled common rail. As I understand it the 3qm30 is essentially indefinitely rebuildable being a wet sleeve motor. Diesel mechanics everywhere should be able to deal with any issues that arise. I applaud the conversion to external saltwater pump. If the 3qm30 gets rebuilt properly it should last as long as it originally did. Will you?
Sure it's nice to have a lighter, less polluting motor but you have a yacht ( sailboat ) you are low on the list of planet destroyers assuming you use wind power mostly.
I may be able to find a new replacement cylinder head but no guarantee. PM to follow
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