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#1
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Diesel drivetrain conversion
I am starting a project - Atkin-style tunnel stern, of welded aluminum. I have been offered a Datsun pick-up truck with (I think) an SD22 diesel - widely used in forklifts, IH Scouts, and some boats. The truck has been immobile for a few years, but ran ok when it was parked. I have no experience with diesels. Questions: Is there a recommended procedure for starting such an engine, and checking it over? If it's not in reasonable shape, I would want to know ASAP. Any concerns or suggestions for dropping the engine into a boat? Cooling would be fresh-water, through a "keel cooler" integral to the aluminum hull; exhaust (wet or dry) to be determined. Could auto-style vibration mounts be used? I know I need to check on regs for fuel and electrical systems. Transmission - it seems simple (and cheap) to use the 5 speed transmission, with driveshaft attached to prop shaft with CV-joint and thrust bearing. This would allow some variation in reduction ratio, for varying conditions. Am I nuts? For prop sizing and the like, I am assuming 40hp at 3200rpm (intermittent- or heavy-duty operation; a few hours at a stretch). Is this reasonable for this engine? Any suggestions? good info/resources? Thanks - Sal's Dad |
#2
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Sal, starting a small diesel that has been laid up for a short period
of time is not like that of a gas engine. Unburned diesel left on the cylinder walls keeps them from rusting. And because it's going to take a little bit of time to start it because of having to prime the fuel system, the bearings should get plenty of oil before it starts up. As far as cooling, your going to have to get a wet exhaust manifold fabricated for the engine, unless you want a dry exhaust, which I wouldn't reccomend you making yourself. Your also better off getting marine engine mounts and making braclets to fit the engine. As far as the transmission, I would forget about the 5 speed, boat transmissions are very differant, the automotive unit will probably not last very long. This would eliminate the thrust bearing and CV joint as well. Before I got too far into this you need to see if the engine is worth using. How old is it? Does it burn oil or leak? For the size engine your looking at, you could probably buy a used or rebuilt marine engine and marine transmission for the same or less. Take a look at Ebay. |
#3
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I'm not an expert, but I did find a few tricks that work. Once you've
cranked enough to get the oil pressure up, spray WD-40 into the air inlet. Continue spraying until the engine driven fuel pumps have purged the lines. Auto diesels are different, so maybe you don't have to, but both the old Volvo MD7B I bought to play with and the Polish tractor I use to mow like to have the injectors bled if there has been any interruption in the fuel supply. Just unscrew the high pressure lines where they attach to the injectors. One turn or less should do it. You'd think you could wait while the air stopped and your induced leak was just spraying fuel, but I found the pressure to be so high that it was easier to just wait a few seconds and then tighten it back down. Don't get your face or hand in the path of the high pressure spray! Remember! Turning off the "ignition" does NOT stop the engine. If there's no cut-off on the injector pump that you can flip/pull/twist, be ready to put a piece of plywood over the air intake. Do NOT use your hand! A few years ago someone on this list told of starting a boat engine on his garage floor and watching in horror as it bounced across the floor burning off the fuel in the lines. A test stand is worth the labor. Roger http://home.earthlink.net/~derbyrm "Capt John" wrote in message oups.com... Sal, starting a small diesel that has been laid up for a short period of time is not like that of a gas engine. Unburned diesel left on the cylinder walls keeps them from rusting. And because it's going to take a little bit of time to start it because of having to prime the fuel system, the bearings should get plenty of oil before it starts up. As far as cooling, your going to have to get a wet exhaust manifold fabricated for the engine, unless you want a dry exhaust, which I wouldn't reccomend you making yourself. Your also better off getting marine engine mounts and making braclets to fit the engine. As far as the transmission, I would forget about the 5 speed, boat transmissions are very differant, the automotive unit will probably not last very long. This would eliminate the thrust bearing and CV joint as well. Before I got too far into this you need to see if the engine is worth using. How old is it? Does it burn oil or leak? For the size engine your looking at, you could probably buy a used or rebuilt marine engine and marine transmission for the same or less. Take a look at Ebay. |
#4
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On Wed, 8 Jun 2005 11:20:31 -0400, "Sal's Dad"
wrote: // Transmission - it seems simple (and cheap) to use the 5 speed transmission, with driveshaft attached to prop shaft with CV-joint and thrust bearing. This would allow some variation in reduction ratio, for varying conditions. Am I nuts? /// Thanks - Sal's Dad In the matter of a variable gear transmission: yes, probably. Brian W |
#5
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Transmission - it seems simple (and cheap) to use the 5 speed transmission, with driveshaft attached to prop shaft with CV-joint and thrust bearing. This would allow some variation in reduction ratio, for varying conditions. Am I nuts? /// Thanks - Sal's Dad In the matter of a variable gear transmission: yes, probably. Brian W I've done some preliminary calculations, using Gerr's "Propeller Handbook" as a reference. Based on two boats of similar hull design (I'm sure there are more out there, but I haven't located them) and Atkins' estimates, I ran numbers for very light (2,000 lbs hull and machinery, minimal passenger and fuel, no cargo) medium (1,000 lbs load) and heavy (2.000 lbs). The engine claims 55 hp @4,000 rpm, so I've assumed 40 hp @3200 rpm cruising. For medium load, 40 hp should deliver up to about 16 knots, 55 hp about 19. With a 1.4:1 reduction (3rd gear), according to Gerr's formulas, a 10 pitch prop will deliver 15 knots, 19 @4,000 rpm. 12" diameter is ideal Lightly loaded, 40hp should provide 20 kts, 55 hp 26kts. With a 1:1 reduction (4th) a 10 pitch prop would push it at 21/26.5. 10" diameter would be adequate. Heavily loaded, you could expect 14 kts with 40hp, 15 or so with 55 hp. A 2.1:1 reduction would be pretty low, 10.6/12.5 knts, and it could turn a 16" prop (can you say "tugboat"?). In any case, there's no room for a prop bigger than 12"; it is tucked up above the box keel. Seems to me that varying reduction ratios is a reasonable way to improve performance with widely varying loads - 50% of the time would be "normal" operation (with the prop optimized), 25% carrying cargo, a big crew, towing, or heavy weather - and 25% would be just the skipper, out joy-riding in flat water. I don't see how this use would do extraordinary damage to the tranny - it would only be operating a few hundred hours a year. And the separate thrust bearing and u-joint would keep it isolated from the prop shaft. |
#6
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I have not done such a conversation, but I think after you solve the usual
engine marinization issues, the transmission becomes an issue in my mind. I would be concerned about it's reliability in constant heavy load duty. If this is a mud boat for the duck camp? then it's a good fit as it's loaded running would be short? But if this is to be run 1,2or3 hours fully loaded ,then you could run into some trouble. It comes out of a intermittent load duty, air cooled (with plenty air flow) duty, You would be putting it in a constant heavy load little or no air flow. So more lots more load duty with less cooling. If that were the case and you didn't want to find a marine transmission I would think it needs it's own cooler with a circulation pump at a minimum. -- Ron White Boat building web address is www.concentric.net/~knotreel |
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