Marinized Kubota Engine . . . What Are the Differences ?

[alansmith]

Raymond, thanks for the pics and how your DIY. That is way cool...

[GILow]

Our engine is a marinised truck engine. Marinisation in our case was simply a matter of replacing the radiator with a heat exchanger about one twentieth the size of the original radiator, replacing the exhaust manifold with a water jacketed manifold, and adding a water pump">raw water pump to feed water through the heat exchanger and into the exhaust. Of those items the most specialised is the manifold which is pretty much a custom build for engine, but a chat with a local marine engineer was very reassuring when he claimed he could make me a new one for a few hundred dollars if I needed it. The heat exchangers are not cheap, probably about $1500 for our size unit, and the pump is worth about $400 last I looked. Nothing else was changed.

The thing I don't understand yet is why so many marinisations involve building the raw water pump into the engine in such a complicated way. I accept that a belt drive raw water pump has the potential to fail because of a broken belt but that risk is easily minimised with regular belt inspection and replacement. Compared to the way I have seen (first hand in most cases) seals on various complicated cam shaft driven pumps fail and the results of them dumping raw water into the engine oil (older ford/Volvo penta setup) I just don't see the rationale. Most engines come with the ability to drive multiple belts, what am I missing?

Matt



Sent from my iPad using Cruisers Sailing Forum

[brownoarsman]

Thanks for the pics RaymondR, I always love to see the DIY projects (as well as sailors sticking it to marine manufacturers).


Sent from my iPhone using Cruisers Sailing Forum

[janice142]

Originally Posted by a64pilot

What would be the difference in freeze plugs?

I've looked through the Beta Marine shop manual and cannot find the location of said freeze plugs. Where would I look? I have a Kubota 18hp tractor motor.

Originally Posted by brownoarsman

I think the factory ones are thin mild steel, and subject to corrosion that will then cause a leak in the cooling system. Replacing them with corrosion-resistant plugs eliminates this weakness. Again - can't confirm, just what I was told by a fellow who suggested I just swap the marinized parts on my Universal 5411 to a used Z500 Kubota engine rather than mess around with trying to get the head off.

Thank you brownoarsman.

Originally Posted by RaymondR

I marinized a Kubuto V2203 about five years ago.

I started off with a heat exchanger/water cooled manifold and abandoned it for raw water cooling.

I knocked all the freeze plugs out of the block in order to install threaded inserts into which to screw anodes.

Hello Jim. Why did you go to raw water cooling? What went wrong with your initial setup?

Why did you remove the freeze plugs so you could put in anodes? Is that because you're going with raw water versus fresh?

Originally Posted by GILow

Our engine is a marinised truck engine. Marinisation in our case was simply a matter of replacing the radiator with a heat exchanger about one twentieth the size of the original radiator, replacing the exhaust manifold with a water jacketed manifold, and adding a raw water pump to feed water through the heat exchanger and into the exhaust. Of those items the most specialised is the manifold which is pretty much a custom build for engine, but a chat with a local marine engineer was very reassuring when he claimed he could make me a new one for a few hundred dollars if I needed it. The heat exchangers are not cheap, probably about $1500 for our size unit, and the pump is worth about $400 last I looked. Nothing else was changed.

This is encouraging Matt. Thank you.

[RaymondR]

Hello Jim. Why did you go to raw water cooling? What went wrong with your initial setup

Pretty well all the shop built combination heat exchanger/WC manifolds are made from alloy. Many of the people I spoke to had experienced corrosion problems when the alloy acted as an anode for the other metals in the cooling system. Consequently I decided to build the manifold from stainless steel. Unfortunately the sections available tended to be fairly heavy and after test running the engine and observing it's running vibration levels I decided the manifold studs were not big enough to support the manifold in the long term.

The anodes are to protect the cast iron and steel components exposed to the salt water cooling fluid from electrolysis. Older engines did not have alloy components exposed to cooling fluid however this is often not the case with modern engines and consequently many of them are not suitable for raw water cooling. The Kubuto has alloy timing gear covers so I piped the raw water through this section into the cast steel engine block.

[GILow]

I made the following observations off-line to another CF member, but I think I should post them here for consideration/criticism.


>>>---------------------------------------------snip!--------------<<<<<<<<<<<



At first glance it all appears very complicated but once you get your head around what is going on you realise that marinisation is a very simple process indeed.


Where some of the confusion about engine parts arises, I believe, is that some of the high performance petrol engines do end up with higher grade big-end bearings etc because they are designed to run at full throttle for hours on end. So (an older) Volvo Penta would be a good example, they took a Ford car engine and refitted it with stronger bearings so that it could be run at 100% output continuously.


By contrast, our engine was originally rated to 96 HP @3200 rpm in the truck it was made for in Japan, but it has been fitted with a propeller that only allows it to rev to 2100 rpm and put out a maximum of about 82HP at those revs. So actually it is under less strain in the boat than it was in the truck. Combine this with the fact that it cruises at around 1250 rpm (50HP) and you can see that the engine is actually in a very easy job.


<<<---------------- end snip! ------------------------------>>>>>>>>>>>

[janice142]

Thanks Jim for the reply. My heat exchanger is copper so I'm good there. The manifold is stainless, so if everything goes according to Theory...

I should have named my boat Theory. Everything works there!



It's great to know it works well for you Matt and thank you for your reply. I'm still up to my transom in this engine swap.

With the copper heat exchanger (it's huge -- came from a V8, however it was Free, and that's why it's perfect) as one component, keeping the engine cool ought not to be a problem.

Cooling the exhaust is another matter.

Like Jim I am concerned about the weight of the stainless manifold. There are four bolts much lower where the brace will attach, supporting the weight of the unit and the water in it.



That support brace has not been made. It was going to be steel when I had access to a welder however here it will be made from hardwood. Red oak possibly -- I'll take the advice of the fellow making that part.

I am concerned where the manifold attaches to the exhaust pipe (left side, previous photo)

It's been suggested that I have a piece of wire reinforced rubber between the two pieces to allow for give/vibration. There is a gasket however I'm not so certain it's "enough"

Anyway, thanks for your advice/wisdom thus far.

My mechanic has been out of the state for a month (his mom has cancer) and I'm looking forward to his arrival back in town. I'm anxious to have the job completed. Yesterday!

[GILow]

I am a bit surprised by that manifold, if that's what you are calling the silver box?


To me a manifold is where multiple pipes are combined into one pipe.


So our manifold is a rectangular steel box with the four exhaust outlets from the engine entering it from the side, wherein they are combined to one larger pipe that exits the box from one end. The purpose of the box is to surround the four entry pipes and the exit pipe with cooling water (fresh water with coolant) and thus keep the whole assembly cool. The distance between the "box" and the engine head is about an inch, simply to facilitate access to the bolts that hold the four manifold pipes to the head. Because the pipes are so short, the leverage of the box on the bolts is minimised.


The way that box is constructed, the leverage will be enormous and bound to fail. Also, that box apparently cools only a small section of the exhaust pipe, and leaves the initial (hottest) part exposed with all the problems that entails. Also, the box seems a bit short to provide enough surface area on the exhaust pipe to do much in the way of heat transfer.


Have I misread how all that works?


Finally, that heat exchanger looks very much like the units fitted to one of the old Mercruisers. True, they are big high HP engines, and it is probably more than adequate, but I read somewhere, and I can't remember where, that you cannot do a 1:1 mapping of hp between petrol engines and diesel engines. I cannot remember which engine produces more heat per HP but I do remember it was different.


Matt

[Sailmonkey]

I have two problems with that stainless box.

1. The lever arm is huge. And seemingly without purpose. What does this piece do exactly?

2. If the stainless "manifold" is cooled with seawater it's inviting a failure. The current setup appears to be set to flood the engine if the water jacket fails (and it will if filled with seawater). You always want a seawater leak in the engine exhaust to flow downhill away from the engine.


Sent from my iPhone using Cruisers Sailing Forum

[janice142]

This is the interior:



The Red (I'm not good with Paint) is supposed to illustrate the hot air/exhaust pipe extension as it exits the engine and runs through the box. The exhaust pipe runs through the stainless box as illustrated in red. Hot air is White in the above picture. Just prior to exiting the stainless box, there is a raw water nipple that puts salt water (blue arrows) into the pipe to cool it (the pipe) .

A black hose then carries the water/hot exhaust to the Vernier lift water muffler and then out of the boat.



The box itself is filled with a combination of fresh water and antifreeze (50/50)
That's shown in the green stars (and arrows pointing direction of water flow) above.

The fresh water/antifreeze combination is pumped into the box at the bottom and exits at the top, moving next through the heat exchanger, and then the engine.

No salt water will ever be in the Kubota.

At least that's how it's been explained to me. My mechanic (#2) is due back in town at the end of this week. I look forward to this engine running inside my boat. It ran fine in the bench test.

The basic problem was in cooling the engine. It's a tractor motor and much discussion was made regarding the radiator (should we or not? is there room in the engine room? there is, but would require front panel off and that would mean my cabin would be an oven after running all day, etc.)

Dry stacks were brought up too -- I'm in Florida, in a small boat and don't need the extra heat. There was no good place to put one either. A keel cooler was also run by the gauntlet. The gift of a bonafide heat exchanger, albeit "too large" is an added component.

There was talk of including a hot water heater and a heater with the set-up but frankly, that reeked of Job Creep. I cannot financially afford Job Creep. Still, I'd have to be honest to admit those possibilities might just be explored down the waterway...

The tractor ( from Japanese Diesel Engines and Yanmar Parts ) is a wonderful engine. Their prices are the best I could find. Ask for Dennis.

Regarding the flow of water Sailmonkey, you're absolutely correct. Where the water/hot exhaust exits is a downhill slope to the water lift. From there the water goes through another loop and then out the side of the boat.



GILow: the stainless box attaches where at a flange on the left side of the photo. That's all factory. There was discussion about going with a regular riser. MUCH discussion about that -- and honestly I wish I had gone with one. The tried and proven has a definite appeal.

The advantages are easy access to see when stuff is going to fail. Supposedly this box will outlast me and the boat. I like that idea.

However, to be able to see where the water injects is a good thing though to view it would require unwrapping whatever heat shield is surrounding the junction. I've got a boroscope on order too, for an additional double-check.

At this point I'm leaning towards using the stainless box -- at least for the short term. I'd also like to have made a riser and have that option ready to go.

You are quite correct that it's going to be heavy, especially filled with fresh water/antifreeze. That's why the support will be made. Originally that was supposed to be a steel brace from below. Now, it's going to be wood. Also, it (the stainless box) could be supported by a bulkhead that is directly aft (in the foreground -- photo taken from stern) with the bulkhead out.

Side Note: I'm saying "bulkhead" but it's actually a piece of wood that supports the sole in the pilothouse. It's bolted to a structural bulkhead that runs athwartships in Seaweed.

There will not be just one support point. The bulkhead that is closest (one inch away) is 3/4" plywood. I'd of course use a backing plate and thru-bolt it.

And thanks for your input.

P.S. - I'm still curious about freeze plugs.

[GILow]

I am now more worried.


You want to fix the box to a bulkhead, but the engine is on what appear to be flexible mounts.


You are going to break something. For sure. Seriously.


The only way to avoid it that I can imagine is to make a very strong bracket that attaches to the transmission and the engine head and mount the box on that. (This is what I have done for our setup when I switched it from hard mounted to soft mounted, and all I was protecting was the big inverted U bend cast iron exhaust pipe (less than 10 pounds weight), not a whole box including water.)


As soon as you attach that box to part of the boat it will want to stay still, while the engine is going to be bouncing around like engines do. (unless they are horrendous hard mounted things like mine was. And I concede, soft mounting my engine turned out to produces a whole lot of problems I had not considered until I was well into the job.)


As for your exhaust manifold, it is going to get very, very, very hot. Remember most tractors have huge airflow through and around the engine bay. Boats, generally, do not have any airflow, mainly because of the noise implications.


I am quite worried for you now.


Matt

[janice142]

Matt. The main support is exactly as you stated (from below, next to and behind the Hayes bell housing. I wonder why an additional weight bearing shelf support would be inadvisable?

I did look (there are two places where a support can be affixed by the tranny, so that is an option. Thank you for your advice re the bulkhead. I tend to overcomplicate stuff. Thanks for the "catch" -- it's appreciated.

I don't know about the heat though. Would not the water/antifreeze combination cool that exhaust pipe? That's my understanding, but perhaps I misunderstood. I know an additional blast of raw water goes in just prior to the end where the black exhaust hose attaches.

Previous conversations had indicated the box should not be hot. I wondered about that because of it's proximity to the bulkhead.

As for air, Seaweed has two 4" blowers (one pulls and one pushes) so ventilation is not an issue. There are two vents (port and starboard) one faces forward and the other aft.

Even when the Beast (gasoline engine) was running, the engine room was cool. Ditto BOB (the Volvo) ...

The engine room is 7' across, by 3' x 3' (aft of the engine is another bilge (open air) that runs about 8' to the transom. Yes, I have batteries on the port side however the starboard bilge is entirely empty.

I don't like storing stuff in the bilges.

Thank you again Matt. Your input is welcome.

Tell me about your soft-mounting issues. I'm curious.

[GILow]

OK, first, I would not expect the silver box to become very hot, at least not at the sides, but the exhaust entry pipe will be smoking hot, and the exit pipe not a lot better at a guess.


As for heat buildup in the engine bay, I am not saying it will be a particular problem, as you say it has been fine to date, but I am trying say that the lack of significant air movement around the exhaust manifold itself is going to cause the manifold to become extremely hot. Hotter than I would like but I concede there are plenty of dry exhaust guys on CF who assure me it is not a problem. So it sounds like you have a much nicer engine bay than us humble rag and stick merchants have to make do with, but I still think that manifold is going to be very hot indeed. Not a show stopper, but I wouldn't get away with it in my boat, something would catch fire for sure.


The decent engine blower setup will certainly help.


You might want to investigate wrapping the manifold through to the box with some kind of exhaust wrap to contain the heat. I have done this with my big old cast iron riser and it certainly works better than you'd expect, but I had to do it my boat because the space around the engine is quite limited, and without it there was a real fire risk. A downside of exhaust wraps is that they MAY accelerate erosion of the inside of the manifold, I am told.


As for the soft mounting issues, I guess the thing I learned, a bit painfully, when I changed our engine from hard mounted to soft mounted, was that even though the engine only moves the tiniest bit, those tiny movements are a real PITA when it comes to having to connect other things that are not moving. So, for instance, we have a lovely big barrel style water muffler that is bolted firmly to the boat. Originally the exhaust riser went up a good 22 inches higher than the engine, then all the way back down to the muffler, about 30 inches below, where it was connected with a semi rigid rubber sleeve, about 4 inches long. Once I soft mounted the engine, I had to cut away a good 12 inches of the cast iron engine riser on the downhill side and replace it with some horribly expensive heat-proof flexible rubber hose to absorb the movement between the engine and the muffler.


And now we have a new problem because I was advised to fit a new cutless bearing at the top of the drive shaft to better support the drive shaft itself, the argument being the gearbox could now move around so more support was needed for the shaft. I followed the advice, but now that cutless is resisting the movement of the engine, so if I start the engine when leaning over under sail, the slight sideways movement of the engine (which weighs close to half a ton) causes the drive shaft to pull hard against the cutless and suddenly you get lots of engine vibration transmitted to the hull. It's fine when the boat is vertical, but as you'd know, monohulls spend most of their time leaning on their ear. So much so that I actually find it hard to get around out boat if it we are not under sail.


So although I am endlessly glad I have changed to soft mounts, I am still ironing out the issues it created.


Anyway, the relevant bit of this is that you need to be always looking for that situation where you might inadvertently be resisting movement to the detriment of an engine component.


Matt

[RaymondR]

As for your exhaust manifold, it is going to get very, very, very hot.

This is a safety issue. If fuel or any other flammable volatile gets into contact with the hot exhaust manifold it will vaporize and possibly explode. You need to cool the manifold where the exhaust ports exit the cylinder head.

[philocat]

a 4 year old thread resurrected!

Tend to agree with Matt re the manifold. The picture seems to me to be more like an exhaust water lock than a manifold anyway.

I am also currently installing a diy kubota but without a jacketed manifold. Just do not like the raw water separated from the exhaust ports with only one layer of metal between thats impossible to inspect. Exhaust to run dry upwards above w/l via a flexible bellows per photo, then conventional water injection to rubber hose thus not needing a water lock. Will wrap with insulation. I am aware of heat build up in enclosed space so if the insulation isn't sufficient in itself I will run raw water thru copper water pipes in parallel with exhaust(expect to be slightly noisier than a jacket), or an engine blower (more noisier) or even a small "radiator" and fan functioning in reverse which cools the engine bay air. I actually started bending the copper pipes but got lazy so I'll see how the insulation performs first.

For raw water pump unfortunately my jabsco went with the old engine so I'm installing a Fynspray. I was going to also direct drive from engine but supporting it was too hard so I'm going to use a pulley (you can see in first photo). Not an ideal arrangement with plain bearings taking the side load (not ball) but it wont be working hard and I'll have a thermocouple temp sensor hooked up to alarm.

Matt re your flexible mounts-
Have you room to install a flexible coupling(s) to decouple gearbox with prop shaft or better still a flexible/uni joint intermediate shaft with thrust bearing? Commercial ones exist but are real expensive eg Centaflex in Syd. ~$1200 but are very short in required length. You could diy easily with a bit more length if available. Eg Skf sell self aligning spherical thrust bearing housings ~$200.

I note you are just round the bend from me. Perhaps catch up one day.