MTD 990 Diesel Repower

[bulldogmack407]

So I have been playing with the idea of repowering my MTD 990 with a diesel engine since I bought it several years ago. Long story short I finally did it, I used a air cooled Yanmar diesel from a fire pump I had laying around. The engine is a 100% genuine Yanmar not a china diesel copy. I still have lots of odds and ends to finish but the the drive-line is all back together and it moves under its own power. The swap took me about 4-5 hours total. So far I am very happy with it, now I need to repaint the tractor and make her shine again! Next swap will be my Case 444 with the same type of engine.

 

[CincyFlyer]

That's my kind of project! How's the performance compared to the gasoline engine? Did you change the pulley ratios to keep the speed to the hydrostat the same?

 

[Spanner]

2 things came to mind when I read your post earlier and I 'subscribed' while I thought about it for a while... CF has covered one which is the RPM's for the HST going from petrol to diesel which develops its power at lower rev's.

The other Q is regarding the weight distribution with the heavier diesel mounted over the front axle. Could it have been moved rearwards for better steering weight?

I see it's electric start - which is nice to have.
I fitted one of these 1-cyl Yanmars to a Cricket Pitch Roller some years ago (in the UK) and it was recoil rope start. (Budget restraints.) Surprisingly easy to start.

Anyway, thanks for posting.

 

[bulldogmack407]

I am not sure 100% on the difference in performance but it certainly doesn't seem to be much different. As far as changing pulleys the 990 has a solid drive shaft straight from the engine to the transaxle so no pulleys. The Yanmar is rated for 3600rpm just like the original Briggs so RPM shouldn't be an issue. As far as weight is concerned I am pretty sure the original Briggs is heavier than the new Yanmar. Online it says the Briggs weighs 113lbs but I dont think thats exactly accurate however is is CERTAINLY VERY heavy! I still have not tried mowing with it yet, that will be the true test in power comparison to the old engine.

 

[TMGT]

Always like the diesel repowers, I have a 3cyl kubota going into a Deutz 1920 Ultima (Simplicity Sunstar), the projects has been on the back burner for the past few years but hopefully I can finish it once the new shops built.

I also have a Case 444 in need of a new engine, keep going back and forth on doing a diesel or not, I have a couple more smaller Kubota 3cyl laying around.

I imagine that yammer is lighter then the B&S if it had the 16hp single cylinder engine originally, I had one in my pulling GT and it was a heavy beast.

 

[daugen]

First I scratched my head as to why anyone would want to go to all the effort to
seriously upgrade an MTD garden tractor, since they are known to be lightweight and built for price.
Well....instead of jumping to conclusions I found out that this model is old enough they really did make them better.
This model is also called a Farm King?

I'm very impressed with your job. Did you have to fab a mounting adapter? Shaft size issues?
from Garden tractor forum:
Sounds like a 990 mother load. I just rebuilt one, they are one of my favorite tractors. One problem with these they are so reliable & hard workers most are worn out when sold. Anything can be fixed but at what cost & time frame do you have to have a good runner. The biggest problem with these some have a hole in the side of the frame near the brake pads. This hole is a weak point & will cause the frame to break. Three bolt front spindles are on some, these have ball bearings versus the sleeve bearings that have the single spindle. All 990's are Hydro the 960's are manual. The 990's came in a lot of different colors & badges but same tractor. Most have the plastic dash pretty much destroyed because of the stress & alignment between the front grill, hood & dash. The B&S engines are bullet proof & parts are still out there.

also:
MTD 99 update - YouTube

and I had to chuckle when I read the title of this one, I am not alone...
Never Seen A " Heavy Duty " Garden Tractor From MTD Before..... - YouTube

We will all anxiously await your YouTube video Bulldog.
And...I grew up on a farm just South of New Hope.
Pennington is gorgeous, beautiful dairy and horse farms. land of high taxes...probably
becoming house farms now like across the River.
So howdy ex neighbor, I had to move to NC to afford to retire...

 

[daugen]

Always like the diesel repowers, I have a 3cyl kubota going into a Deutz 1920 Ultima (Simplicity Sunstar),

Now that sounds very cool, plus those Sunstars were really early SCUT's. Does your Deutz have 3 pt hitch? Plus I think they made a loader for that.
Now if they weren't so big you could put an air cooled Deutz diesel in there...

I'm curious where used Kubota engines come from, seems their tractors rarely die.

Having repowered my Gravely 8199G with a 23hp Vanguard, I'm a real believe in repowers.
Can't wait to hear/see Bulldogs run.
Also Spanner's question on engine hp/torque and the HST is a good one. Really a torque and rpm issue.
But that's a smaller hp (?) high speed diesel and the issue is where is the torque curve. I'm guessing that big thumper gas engine
produced decent torque down low too, but you always think the diesel will do better. For sure if it's turboed which this isn't.

fun to speculate...
One thing, haven't found/read any complaints over durability of that HST unit. So if the diesel is a little more powerful should be ok.

 

[TMGT]

I have a 3pt on my Sunstar 20 but not on the Deutz, plan to make a stronger one for the Deutz once it's done.

The engine going in the Deutz is a D662 that cam out of a harvester overseas. It's rated up to 3600rpm so no problems with matching speeds with the gas.(most of the Kubota engines are rated for 32-3800rpm in different applications)

The engines are used in all types of applications, I have 4 other small Kubota diesels, 3 came out of comercial reel mowers that were retired, the 4th came from a Kubota GT that had the rear section catch on fire so they are out there.

 

[bulldogmack407]

Sorry everyone I have been off the forum for a few days. I am playing around with the idea of putting a turbocharger on it. I have read about people turboing this engine with great results. One thread I read the guy said after the turbo install his Cub Cadet would out perform his other 18hp!

daugen:

Yes this model is also badged as a Farm King, mine is VERY rare as it is branded as a STC (Storr Tractor Co) and painted a metallic blue.

To mount the new engine all I had to do was drill 4 new holes near the old engine mounting holes. The shaft on the diesel was the same size as the former briggs, the only difference was the diesel had a shorter shaft and no roll pin hole. The former briggs actually has a hole through the shaft where a roll pin goes to hold the double pulley for the PTO on, To make sure I drilled the new hole correctly I put the PTO pulley on the shaft and used its hole as a guide. Unfortunately the shaft on the diesel was not long enough for the PTO pulley and the driveshaft so I actually welded the drive shaft universal to the pulley. If for whatever reason this method fails I have a backup way to lengthen the shaft.

Yes Pennington is great, the taxes are unbelievable though! My shop where I do most of the work is in Lambertville, absolutely love the area out there!

The project has taken an unexpected turn in the last week but I will let the pictures do the talking!

 

[daugen]

Marvelous! Nice job on taping and not painting what shouldn't be painted. More old stuff gets wrecked that way.
Great project, can't wait for the running YouTube video.