Gas-Diesel engine swap question

[handirifle]

I have a 20hp lawn tractor that has a Briggs and Stratton flat twin (flat head) 20hp, 750cc engine. It's got a valve seat on the exhaust side of one cylinder, that I have jury rigged back together. It's help for 4-5 mowings (3 acres) so far, but lately it kinda sounds like it's getting a little worse each time.

There is NO short block, long block or direct engine replacement for it, period. Even a similar sized replacement engine, that will have to be modified (the tractor most likely) quite a bit, to mount and set the exhaust system, possibly the fuel system too.

My only option is really to replace the mower, and am NOT going to buy another used one, so looking at about 3 grand for suitable replacement.

OK, that said, I was wondering how much horse power would be necessary in a diesel to replace the 20hp gas. I know it would operate at a slightly lower RPM, but I figure higher torque would offset that some.

I ask this only because I see the import 10hp engines on fleabay ar $600 or so, shipped. That would be worth it, IF it didn't cost a fortune to make the adaptation. The closest gas engine that Briggs and Stratton recommends is $850 plus shipping and tax.

 

[3238dpw]

what is it going in?

 

[handirifle]

Oops. forgot to mention that. It's a Murray riding mower with a 52" cut. Large rear tires and is a perfect size for my needs, but I think the engine is doing well if it's mustering 12-14hp in current condition. Maybe less, but no way to tell. I haven't done a compression test lately, that might give me an idea, but it's kinda like I don't really want to know. Ignorance is bliss you know.

Since there is no further fix for the main problem, it's just a matter of running her till she gives up the ghost.

 

[mjncad]

How old is the mower? Any way you go, you could easily be throwing good money after bad if you're not careful.

 

[oldnslo]

That old of a Murray, what shape is the mower deck in? Seems like they have a tendancy to rust/wear out where ever the grass hits them. I realize $3000 is a lot of money but is sticking $500 or more into existing a good investment? I suspect that the time to mount a diesel engine and get all the pulleys etc. to fit and line up properly may make this task a real challenge.

Engine running at lower RPM will require diffent drive pulley size to get same blade speed. Is there room for a larger pulley? WIll the belt guides and tensioners clear?

ROy

 

[Monster5601]

OK, that said, I was wondering how much horse power would be necessary in a diesel to replace the 20hp gas. I know it would operate at a slightly lower RPM, but I figure higher torque would offset that some.

A diesel rated at 18 HP @ 3200 RPM (typical RPM for a small diesel) would provide about 30 ft.lbs. of torque which is equivalent to your gas engine assuming it delivered its rated horsepower at 3600 RPMs.

As mentioned, your are going to need to adjust the blade drive-line to increase the blade speeds.

 

[handirifle]

All good questions and feedback. An 18hp diesel would more than likely drive the cost up well beyond what would ever be considered prudent, I am afraid. Took it out this AM wioth the trailer to pull my tree watering buckets, and it ran like total crap, so hopefully there will be no more mowing required this season, cause I don't think this engine is up to the task.

I figured pulley speeds would be different but didn't consider clearance issues. There are some tight areas so looks like this idea heads to the scrapyard as well.

As for the condition of the mower and deck, everything else is in very good shape. No rust at all on the deck, under or on top. I thought it was gonna be a real good buy this spring when I got it for $500, oh well, live and learn.

 

[David_Kb7uns]

Murray lawn mowers are a dead end for parts in the long run. Everything made before the bankruptcy is no longer supported also .

David Kb7uns

 

[Iplayfarmer]

$500 isn't too bad for that big of a mower if the rest of it is in good condition like you stated. If you're considering going to the effort and expense of a diesel engine for this one, you might consider keeping your eyes out for a similarly sized mower with a good engine and bad everything else. Even if you found a 14 to 16 hp engine it would likely work. The effort to swap engines is nothing compared to the amount of adapting and changing that you'll have to do for a diesel. Around here, old mowers can be had for cheap to free.

 

[Treemonkey1000]

I think if you create a template of the deck mounting holes or the engine holes and find a reasonably close replacement motor any decent machine shop can make you a mounting plate to line up a replacement motor. Exhause doesn't have to be pretty and fuel lines don't vary that much. That's if you really want to spend the time. Otherwise put it on Craigslist for some other person that may need the chasis that has a good motor..Then take the money and go find another mower that fits your needs.

 

[handirifle]

Actually I have found some good sources for Murray parts, at least all that I have needed so far. I have rebuilt the fuel pump and carb, plus the valve work, and those parts were pretty easy. Of course that is engine parts, so nothing specific to Murray. The local mower shop says about the only other thing that could go is the tranny and he's replaced only one or two in about 15years.

I could make an adapter, or drill out the frame, whatever is required there, not a biggie. I do watch CL and am on there about every day looking. Complete mowers here, of decent size are pricey. I think they become gold plated with age, and a higher karat rating as the HP goes up.

I'd be happy to find a 15 or more HP engine, as since this one is really only running on one lung, it's about 10HP at best. Engines just do not seem to show up around here. I think they are spoken for very early. I have a neighbor that has a 12HP mower that I can have for about $100 he says, that needs some work. I don't think it's engine work, but stuff like tires, starter solenoid, etc.

 

[hawkeye08]

How about a couple of pictures and model and spec of bad engine? There are many ways to adapt, but it helps to know what it has to fit.. thanks.

 

[handirifle]

The engine model number is Briggs n Stratton 460-777 and there are series numbers etc that I do not have right now. I just came across an Ebay source for some decent priced engines in the 22-26hp range so I might pursue that ave.

I don't have pics of the whole engine, just some close up of the valve issue I had earlier. Leavin for Seattle tomorrow afternoon so no time to take new ones.

http://i110.photobucket.com/albums/n82/handirifle/mowervalve3.jpg

This is a pic from the original problem. It's all I have of the engine.

 

[Treemonkey1000]

That sounds like maybe it would work if you can pick up one of the ebay engines. Welcome to Seattle. Bring a rain hat it is supposed to be drizzly here for the rest of the week.

 

[Iplayfarmer]

...Engines just do not seem to show up around here. I think they are spoken for very early...

I don't think you'll find an engine, but you might find a complete mower with a working engine. I have a few lawn mower bone yards around here that I can occasionally get parts from. They aren't something you find in the yellow pages. You kind of have to know where to look and who to ask. Your local small engine repair shop may have someone that comes to pick up the dead mowers, etc. that aren't worth fixing. Whoever picks them up may have parts and pieces.

 

[deereman75]

I dont see how it would be any easier to put in a diesel engine then a gas engine. I would just get a used industrial engine like a wisconsin, and make it fit. It wouldnt be much harder then putting in a diesel, and it would cost much less and last forever.

 

[Soundguy]

Oops. forgot to mention that. It's a Murray riding mower with a 52" cut. Large rear tires and is a perfect size for my needs, but I think the engine is doing well if it's mustering 12-14hp in current condition. Maybe less, but no way to tell. I haven't done a compression test lately, that might give me an idea, but it's kinda like I don't really want to know. Ignorance is bliss you know.

Since there is no further fix for the main problem, it's just a matter of running her till she gives up the ghost.

no way I would sink significant money in an already crippled older machine.

I have a murray rider that is going on 14 ys old. 12.5hpp / 40" cut.

At his point I just put on blades and belts the beginning of the year. As old as it is.. the deck is getting worn, engine is doing good (great actually ), but feel the drive train is beginning to wear as well. rear tires are at about 10%.. fronts 40%

the belts i took off were oem.. so the new ones will last it the rest of it's life.

I typically get 3ys on a set of blades, with 2 sharpenings , ie.. ist year use new, sharpen, use 2nd year, sharpen, use 3rd year.. end of 3rd year they are rounding and wearing.

she's on her 2nd battery.. they are lasting about 6-7 ys of reliable use or so. this one is to the point that it will charge up and then discharde in about 2 weeks. as long as I mow weekly or charge before use it is fine... probably go like this a couple years before it finally gives up the ghost.

looking at a cost / benefit ratio. I decided last year that it was worth the 30$ in belts and blades this one last time.

I won't be putting a new battery in her. I'll just charge up before each use, and I predict by year 3 from now when the blades are worn, the deck will also be used up and the rear tires completely slick or flat or perforated.. with the fronts being slick as well. i've already had to seal them with a stopleak fluid a couple years ago. that is keeping them inflated year to year.. tranny will likely be worn to the point of sipping or skipping by then.

just not worth a 40$ battery, 250$ deck, and 100$ of tires.

I'll likely be able to salvage the engine for something as it seems great..

At that point she will get replaced with another economy unit. If I get as long out of the new one as the old one.. will be nice.

actually looked at the very economy and narrow ( 32" ) small ZTR that some of the box stores have carried on and off. could compair one of the economy ztr to a mid grade rider.. looking at that size.. etc. might do that or stick tot he economy rider thing again. someething small and easy to maneuver.

soundguy

 

[deereman75]

I would probably keep that one limping along until you find a good deal on a used machine that is in good condition and runs well. Some of the old deere mowers will basicaly last forever. Because it probably isnt worth putting the money it would cost to put in a new engine into an old murry mower. Now if it was a deere......

 

[Soundguy]

or.. possibly find a unit with a shelled out deck and serviceable motor.. maybee in the back lot of a mower repair shop. usually I see murray decks go long before the motor does.

leaving lots of 'yard runner' machines with no deck.. just pulling a trailer.. etc..

soundguy

 

[dixstir]

engine swap-- I had the same problem took the briggs of and replaced with a 18 hp vangard its works real good. easy swap got the engine from www.sedkc ( small engine distributors 816 421 6020)engine was about 700. but when the rest of the unit is wore out you would still have the engine worked for me.