mbrule
Gold Member
Given that the diesel will achive more power at lower RPM than the gas, will it be necessary to change the pulley configuration on the mower deck to get adequate blade speed?
Switch 22hp gas to 18hp diesel, will it be less powerful?
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ME83
Silver Member
Yes, you would have to change pulleys to get the same blade speed. You also have to realize the tractor is geared for more rpm, so you won't be able to go as fast either. I would swap the drive pulley also; if it is belt driven.
JerryG
Super Member
That was what I was thinking about while reading this thread. The difference in speeds of the two engines may be the only problem with the switch.ME83 said:
OP
Superduper
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Transport speed is not a concern. Going a little slower won't bother me none. I never mow at anywhere close to hi range anyhow because it feels dangerous, especailly if you hit a rut. The concern is maintaining blade speed to allow the deck to clean and fill up the rear bin attachment, when used.
Switching pulleys might be a more difficult mod than it appears. It may be possible to find a larger drive pulley but finding one for the mower will be more difficult. The electric PTO's have integral pulleys and it's doubtful that ones with differing pulley sizes will be available, if at all. I suppose modifying the deck to accommodate smaller pulley's might be an option but when the pulley's get too small, it will be more likely for them to slip and burn up the belts.
I looked at my John Deere's tach and found the marking indicating that the engine should be operated at 2650 rpm to obtain proper PTO speed. I believe the Yanmar is rated at top range of 2800 rpm so I am close. The replacement donor that I'm considering is probably also rated for 2800 - 3000 rpm so I think it should work.
The question is what RPM the Craftsman is currently running at in HI with the gas engine. Since most lawn or garden tractors do not come with a tachometer, it's a guess at best but if my ears don't deceive me, I doubt very highly that it is more than 3000 rpm. I will confirm when I get a chance next week.
Switching pulleys might be a more difficult mod than it appears. It may be possible to find a larger drive pulley but finding one for the mower will be more difficult. The electric PTO's have integral pulleys and it's doubtful that ones with differing pulley sizes will be available, if at all. I suppose modifying the deck to accommodate smaller pulley's might be an option but when the pulley's get too small, it will be more likely for them to slip and burn up the belts.
I looked at my John Deere's tach and found the marking indicating that the engine should be operated at 2650 rpm to obtain proper PTO speed. I believe the Yanmar is rated at top range of 2800 rpm so I am close. The replacement donor that I'm considering is probably also rated for 2800 - 3000 rpm so I think it should work.
The question is what RPM the Craftsman is currently running at in HI with the gas engine. Since most lawn or garden tractors do not come with a tachometer, it's a guess at best but if my ears don't deceive me, I doubt very highly that it is more than 3000 rpm. I will confirm when I get a chance next week.
joe48
Gold Member
1.yes the diesel has less hp, as stated 18.5 is less than 22! But the torque or ability to apply that hp is much greater.
2. unless you have the 18.5 sitting in the garage and this project is a challenge you just HAVE todo, i sure as H--- wouldn't waste the time or money putting a good engine in a barely ok Crapsman tractor!
3.take some time and cruise all the local compact tractor dealers, especially Kubota. I bet it won't take long to find a nice Kub GT (diesel garden tractor)
that someone traded in on a bigger Kub.
4. now you'll have a tractor made to last with iron and aluminum castings instead of sheet metal and 20yrs from now you'll still get parts for it.
5. and I'll bet you wouldn't have any more money invested than if you tried a swap.
good luck , either way ,Joe
2. unless you have the 18.5 sitting in the garage and this project is a challenge you just HAVE todo, i sure as H--- wouldn't waste the time or money putting a good engine in a barely ok Crapsman tractor!
3.take some time and cruise all the local compact tractor dealers, especially Kubota. I bet it won't take long to find a nice Kub GT (diesel garden tractor)
that someone traded in on a bigger Kub.
4. now you'll have a tractor made to last with iron and aluminum castings instead of sheet metal and 20yrs from now you'll still get parts for it.
5. and I'll bet you wouldn't have any more money invested than if you tried a swap.
good luck , either way ,Joe
joe48
Gold Member
oh and something else I thought of why not to do.
that yanmar engine is going to weigh 2x or 3x what the gasser does because unless you find one out of a refer truck it will be a cast iron block and heavy.
I doubt you have powersteering on your tractor.
also the diesel will be a horizontal crank and I don't think Sears has had a tractor in the last 30yrs that has anything but vertical cranks, so now you'd have to have a 90* gear box to connect to your drive train. plus this would cause the diesel to be located farther forward to line up your vertical shafts in the original location. now this puts that heavy engine out over the front axle farther , making the steering worse.
that yanmar engine is going to weigh 2x or 3x what the gasser does because unless you find one out of a refer truck it will be a cast iron block and heavy.
I doubt you have powersteering on your tractor.
also the diesel will be a horizontal crank and I don't think Sears has had a tractor in the last 30yrs that has anything but vertical cranks, so now you'd have to have a 90* gear box to connect to your drive train. plus this would cause the diesel to be located farther forward to line up your vertical shafts in the original location. now this puts that heavy engine out over the front axle farther , making the steering worse.
Blackbird_BX
Bronze Member
I'd pass. The diesel will put out a lot more torque to the wheels, but even if you could get a diesel to match up, the extra engine weight would crush the front suspension and you'll need a lot more "armstrong" power steering.
Unless the new engine was an option for the model, you're probably into a major job of fitting it to the tractor. That's why there are a few outfits selling repower kits. I haven't seen anyone offer a gas to diesel repower kit. The kits I've seen for garden tractors have been for replacing old, cranky, iron block, splash lubed gasser to newer, lighter V-twin aluminum block with pressurized lubrication. One of the biggest selling points is how much easier steering would be after the from the weight reduction.
Unless the new engine was an option for the model, you're probably into a major job of fitting it to the tractor. That's why there are a few outfits selling repower kits. I haven't seen anyone offer a gas to diesel repower kit. The kits I've seen for garden tractors have been for replacing old, cranky, iron block, splash lubed gasser to newer, lighter V-twin aluminum block with pressurized lubrication. One of the biggest selling points is how much easier steering would be after the from the weight reduction.
milkman
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Joe, think you missed this part of his post. "I noticed that the 18.5hp vertical shaft yanmars could be had complete for between $1200 to $1700."
OP
Superduper
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Joe, Blackbird: I value everyone's opinion and your inputs/suggestions are all great. I will take them under advisement. However, one of the greatest shortcomings and assets in my character is stubborness and trust me, I've done a little research to get to this point. I will be replacing it with a VERTICAL shaft motor so the conversion is easier. Yanmar does make one. It's apparently rated at 3600 rpm with max 3800 rpm so looks like speed will not be an issue, both for transport and blade speed. It does weight more than the gasser but not by as much as you think. About 125 compared to 90 for the gasser.
Milkman, thanks for the heads up and the support. I'll post what I can when something breaks (not the tractor, the situation).
Milkman, thanks for the heads up and the support. I'll post what I can when something breaks (not the tractor, the situation).
MJPetersen
Veteran Member
I think that the marriage will work and quite easy accomplished--relatively speaking. The thing that I fore see is the greater torque and longevity of the diesel. The torgue could over-stress a trany not designed for it and the the diesel will still be running when the tractor has returned to the ground. Sears really did not design their tractors with longevity in mind. They make them as "disposable" units. Already very often the gasser engine outlasts the frame and other components. The diesel will out last the the unit far and away.
However, it would be great to have the power to wade through the tough stuff without bogging the engine and to have half the fuel consumption. It would be sweet and unique.
Mike
However, it would be great to have the power to wade through the tough stuff without bogging the engine and to have half the fuel consumption. It would be sweet and unique.
Mike
