2010 RTV 500 repairs

[kmelander]

Good afternoon, new member to the forum. I'm in the throws of repairing a 2010 RTV 500 I purchased and I thought it might be helpful (for myself and others) if I posted about my "journey".

I bought this machine from a public school auction. Had a good battery and turned over ok but wouldn't start. I believe I got a fair deal and assumed there was potentially something major wrong with it because I paid about 1/5 of what it looks worth. It has 1400 hours on the clock.

Got it home and started trouble shooting. Pulled the spark plugs and did a compression test. 190# on each cylinder...promising. I was lead to believe it likely had a blown head gasket by the staff at the location I picked it up from. Checked for spark, put some gas in it, turned it over and it stumbled, tried as best it could to start, unsuccessfully.

It was around this time I twisted the coolant cap off, because I couldn't think of anything else to do at that moment. High pressure shower of coolant is what happened next. Darn. I guess it does have a bad head gasket.

So...this engine is really strange to me. I've worked on plenty of small engines but never a Kubota gasoline engine. This should be good, I'm definitely going to learn a lot on this one.

In the interest of continuity, Ill advise that Im now putting it back together. It was the last "setback" I experienced which convinced me to post as much as I can remember here for future shade-tree mechanics like me.

 

[kmelander]

So, I have to get the head off this engine.

I start disassembling. I pull the bed off it 1st, pretty easy. Just have to be mindful of the wiring for the rear tail lights. There are connectors which make it simple to disconnect. Seems like the bed hinge was slightly odd to remove but its been about 3 weeks now so I can't really recall. No big deal anyways.

After the bed was off, I removed the seat and plastic cowl underneath seat. Also, I did remove the battery before starting any of the disassembly. That's important.

I think I removed the exhaust components next, making notes about what gaskets (and other parts) I needed to order for reassembly. The exhaust system for this little motor is "robust". No issues though, everything comes apart without objection.

After that I think I drained the coolant and removed the large coolant hoses from the engine. Also the coolant reservoir. All the cooling system components were both filthy from combustion gases and some heavy scaling. I surmise poor cooling system maintenance at this point. The hoses were on the fringe of ok and replace with signs of dry-rot. One of those deals where if I don't replace them, they will likely fail. If I do, I'm probably wasting money. I'd rather waste money than break down I guess.

Anyways, you get the picture. take everything apart so I can remove the head. No big deal, no drama really. Just have to be patient. Alternator, carb, timing cover, make notes, take pictures.

 

[kmelander]

Finally get the head off and inspect everything. Found that the head gasket had succumbed but everything else looks good. The cylinder walls weren't perfect, they showed some visual signs of discoloration but felt smooth to the touch. Pistons looked good, no wiggle. the crank turned freely, and the connecting rods were free of any bearing slop. Good enough for me.

The most interesting thing I discovered was that both pistons move on the same plane. They don't alternate and that surprised me. I haven't researched that design and there are probably other twin cylinder engines out there that work on the same principal, but it is perplexing to me for some reason. I don't get it. Why not just 1 large piston? What is the advantage of 2 smaller pistons acting as one? maybe the ignition is alternating? I don't know the answer to that. Is this design better somehow?

 

[kmelander]

Forgive the slew of posts but I'm trying to get "caught up". I do have one very important question that I hope someone can help me with, but I'll save that for last.

Next is ordering parts. I ordered the new head gasket plus any other gaskets I think I'll need, which is all of them. The one gasket I didn't buy was the timing cover gasket simply because it was ridiculously expensive, and thats a dry compartment. Also, the old one is still in decent shape.

The timing belt was questionable and the alternator belt was badly worn and cracked. I spent some time researching alternates for these because again, Kubota $ was out of line, in my opinion. I ordered the timing belt from Misumiusa.com (part #HTBN800S8M-150) for about 1/2 the cost I think, and the alternator belt from Advance auto (Dayco 15225). Again, worthwhile savings.

I also opted to replace the timing idler bearings. This is, I think, the cheesiest setup of the entire engine so far. Even buying the bearings "outsouced" was overly expensive, IMO. No discount here vs. buying them direct from Kubota either. Well, you could save by buying no-name, questionable bearings but this wasn't a place I wanted cheap components. I think I ended up with Koyo. I ordered these from Amazon, part #koyo 60/22-rs. I would have preferred Timken, but I couldn't find them.

I ordered new coolant hoses too. They were very reasonably priced from Kubota.

All in I think I spent around $300 in parts, which didn't seem too bad to me.

Next was waiting for all the parts to show up and reassemble. I was getting excited.

 

[kmelander]

well, this site just hosed up a post and then duplicated the previous one. Thats aggravating. Maybe ill try again some other time.

 

[PoTreeBoy]

The crank seems strange until you think about the fact that you need a power stroke in 720° of crank rotation, or 2 revolutions. Or one power stroke per revolution with 2 cylinders. For equal distribution one cylinder fires the first time up (the other cylinder is exhausting), the next time up the roles are reversed. If the crank throws were 180° apart, you'd have fire at 0-180-720, unequally spaced pulses, instead of 0-360-720, equally spaced.

Is that the Subaru/Robin-designed engine with fuel injection?

 

[lugbolt]

yes parallel twin 360 degree crankshaft

2 cylinders. 4 stroke engine "fires" cylinders at 720 crankshaft degrees. Divide 2 by 720 and you get 360. 360 deg means both pistons travel at the exact same plane, 360 degrees apart (in other words they run at the same direction all the time). Polaris 600, 700, 800 sportsman and Ranger use this design as well. A lot of 4 stroke outboards too.

You can have several ways to arrange the crankshaft/engine on a parallel twin. 360 degree, 180 degree and 270 are the most common.

180 degree, one piston is up, the other is down. 180 degrees apart. But it is an oddfire engine, in that it fires a cylinder, then 180 degrees later fires another. Then the crank must turn 540 degrees before it fires the first one again. It has an odd sound too. Polaris uses this design a lot, on the 900, 1000cc engines used on the Rangers and rzr's.

THe 270 design is a good one, and my favorite. One cyl fires, then the crank must turn 270 degrees to fire the other one, then there is a 450 degree pause til it fires the first one again. Note that the 270 has an exhaust sound very similar to a 90 degree V-twin. And, it runs VERY smooth as long as the counterbalancer is set up right. This design is gaining a lot of popularity. Rzr turbo models are 270, as are the Polaris sportsman 850 and 1000, Yamaha uses it on the Wolverine 850 and 1000, the Rmax 1000, and the 700cc naked bikes. Good design, smooth and very torquey. And is audibly pleasing.

anyway, you're finding out that the 500 isn't easy to work on by comparison. I'd just as soon work on a 900, 1140, 1100, or 1120 before I work on a 500. 500's don't sell well here, never have. Sold a few 400's to compete with the Mule 610 but the 500 was priced higher than the Mules and did not do well. My coworker (when I was at the kubota dealer) bought one. In the 11 years he had it, he complained about it's rough ride and severe lack of power. It was bad enough that he really didn't use it much, I think he sold it last year for $5800 (all he could get out of it). It had 64 hours on it.

 

[kmelander]

Thank you for the information. Interesting design. I have run into a problem with reassembly and it revolves around torquing the head bolts down.

The only torque specs I could find online for this engine are 46-50 ft-lbs and I'm guessing that is not correct or even possible. I managed to get a couple up to about 25 before the fastener began stretching. I looked up general torque specs for a 7mm bolt after that and found they were somewhere around 10-12 ft-lbs. So, Ive ordered new bolts and now I'm thinking I may have ruined the new head gasket with over torquing the bolts. They all went to 20. It was the next sequence where the trouble started. I don't think Ive damaged any threads thankfully. Anyone know what the correct torque specs are on the head bolts? Also, should I buy another new head gasket?

 

[kmelander]

500's don't sell well here, never have. Sold a few 400's to compete with the Mule 610 but the 500 was priced higher than the Mules and did not do well. My coworker (when I was at the kubota dealer) bought one. In the 11 years he had it, he complained about it's rough ride and severe lack of power. It was bad enough that he really didn't use it much, I think he sold it last year for $5800 (all he could get out of it). It had 64 hours on it.

I'm guessing the 500's have much smaller sales figures than the diesel units based on the availability of 3rd party information alone.

I bought this one as a gift for my parents living in upstate NY. Originally had the idea of putting a snow plow on it but I'm rethinking it now. It's much closer to a flip vehicle after I work it a bit because circumstances have changed. Based on local classified ads, I'm guessing I can get between $4-5k for it.

I've never owned or operated any Kubota products. I'm very curious to experience what it's like to drive it. I've read that they are an impressive workhorse.

I did once build a modified club car carry all, which was essentially a death trap because it went way too fast for the flimsy chassis, steering and brakes. I couldn't even let my kids drive it. I simply went too far with it. Didn't have any problem selling it though.

 

[kmelander]

I've got new head bolts and a new head gasket on the way. Anyone know what the factory torque specifications are for the head bolts? I'm guessing 18.9 Nm, or 167 in-lb, or 14 ft-lb?

 

[lugbolt]

I'm guessing the 500's have much smaller sales figures than the diesel units based on the availability of 3rd party information alone.

The competition in that segment is pretty stiff. You have the Mule SX (used to be the 600/610), then you had the Polaris 500 ranger, and the John Deere, the Rhino (later on the Viking) and each and every one of them was a better design than the Kubota. The Kubota was their entry level side-by-side, and it was designed to work. The 500 doesn't work. It is GUTLESS. It has no power, and to add to that the transmission eats up most of the power that the little engine can make. Then it has very little ground clearance in comparison, hard to work on, and rides like a log wagon. AFTER the 500 came out, the japenese engineers showed up at the place I was working at, and wanted to compare the 500 to the Mule. There was no comparison. The little Mule destroyed it in every test that they put it through. And it was less expensive than the RTV500. In their trailer they had some computers and such, and a prototype CVT-driven RTV (what later became the RTV400), of which we were strictly told to NOT take pictures. They didn't want the whole world to know they were working on it, as if it was gonna be any "better" than the Mule. IT was about the same cost but still had the terrible ride quality and lack of ground clearance among other things, but at least it gave folks another option.

I'm a professional drag racer as a "third" job (mostly a hobby) and at the time the engineers wanted us to drag race the 500 (and their prototype) in the field next to the store. I was chomping at the bit over that deal. So I agreed, the boss agreed, and we did it. Every single time, the 500 was a loser, no matter who drove. That assumed that the driver could stay in the seat...the suspension and seat are such that you really can't on rough ground at "top" speed of 18 mph. The Mule would do about 23 in that field. Wasn't even close. Then their prototype was actually faster than the 500, but about the same as the Mule-again assuming you could stay in the seat. When I drove it I had to really tighten up the seat belt. That or bounce out.

So yes, the 500 was kind of a sore subject.

us shop guys hated working on them. Not too terrible to work on, but it was a lot easier to work on a Mule and Viking (and for sure the Rhino) than the RTV lineup. What's that mean? It means if you had an RTV, you paid more for maintenance and repairs than you did if you had a mule or rhino.

They classified them by engine size. The Rhino 450 which was smaller engine than the RTV500, would walk it any day of the week, even governed electronically.

So as a sales person talking to a prospective customer, there are few advantages to the 500, when we had rhino's vikings and Mules sitting on the same showroom. The only people that bought them were people who just had to have the kubota-including my coworker at the time. He just wanted it. After a week, he dreaded it. Hated it. Rode rough, no power, a little noisy (but then again so is the rhino 450), slow, and expensive. He kept it for I think 7 years and in that 7 years had to put a fuel pump in it (about $800 as I recall) and a muffler (rusted out). It had I think 54 hours on it-I did the first service at 50 hours, 5 1/2 years after he bought it. Why so few hours? He hated it. But loved it on the pavement running around at work. Just out in the pasture at his place, it SUCKED (his words).

 

[kmelander]

I've got new head bolts and a new head gasket on the way. Anyone know what the factory torque specifications are for the head bolts? I'm guessing 18.9 Nm, or 167 in-lb, or 14 ft-lb?

 

[kmelander]

i've gotten the engine back together plus flushed the cooling system several times to clean out the combustion pollutants. The engine starts and runs but has a fairly bad miss. I notices immediately that the speed governor was fluttering the throttle body excessively. It idles and drives, enough to bring it up to temperature anyways.

It smelled of a rich condition and the plugs were badly carbon fouled following the heat cycles. I was initially concerned that I somehow missed a bad cylinder(s), but the dry soot on the plugs was pointing towards a fueling issue. That and the smell. I decided to pull the injector and test it as best as I could. Based on its bench behavior with a battery, it's bad. It was unreliably and intermittent cycling, sometimes clicking multiple times and others not at all. It showed 17 ohms across the coil if I remember correctly which seemed high but within spec of a high impedance injector. Bottom line, it seemed sketchy enough to warrant the absurdly high cost or a new replacement. I feel like there is a substitute out there for this part, but good luck figuring out what it is. I don't even know if the one in there is the correct part, one of the retaining screw heads was badly stripped, so someone has been into this before. I'll know more when the new one arrives. I notice also that this fuel system does not have a filter. Seems like a good idea to add one at this point to better protect this rare and precious injector.

 

[kmelander]

Well damn! It wasn't the injector. So now I'm wondering what the heck is causing this persistent misfire. It seems like a 50/50 chance it's either the coil or the fuel pump...maybe both, or neither for all I know at this point. I'm guessing that I can check the fuel pressure which admittedly, I'm less inclined to think is the problem. It's hard for me to comprehend that a low fuel pressure condition could cause a rich A/F mixture but I'm not well versed in this discipline, as my misdiagnosis of the injector demonstrates. Also, I don't know what the fuel pressure should be and I don't understand the fuel line plumbing. There are a couple of plastic fittings in there that I could only guess about their purpose. One is a tee which by itself is simple, but why is it there? Then there is a small green disc in one of the lines, routed up and bolted high on the seatback that is what? A check valve or pressure regulator/restrictor maybe? It was all factory looking and seemed unrelated initially but now my scope is broadening.

I'm leaning towards the coil as a prime suspect now, but throwing parts at this thing stings the wallet a bit.
It could be an engine speed control adjustment somehow, with the throttle blade fluttering like it is, even idling. I am under the impression that the misfire is causing this condition, not the other way around.

I guess I need to do another compression test, which is a scary thought. I'm guessing that a low compression condition could cause this issue. I don't know if I'm leaning away from that because the issue is affecting both cylinders equally, to the best of my judgement, or because it will mean I made a critical error at the start of this project. I know I saw 190# on my gauge with both plugs out and about 5 revolutions on each side. How that happened with a blown head gasket - I don't know. This is the one afterthought about that test that has me doubting the readings. I'll do another test with baited breath.

I could use some help on this one if anyone has any ideas/thoughts/experience with this odd little engine. My mind is is going in about 15 different directions at this point. All I can think to do is test the fuel pressure and the compression (again) and go from there. Is there a way for me to test the coil? One thing is for sure, everything @lugbolt has said about this unit in this thread is absolutely correct. So far, it's been tedious, odd, expensive, and now elusive to work on.

 

[kmelander]

I don't believe it's a compression issue. 200# on each cylinder again. This time I warmed it up, pulled the plugs, disconnected the injector and coil control wires, held the throttle to the floor, and turned it over a few times. 200# actually seems high to me but it is what it is. I have to figure out how to test the coil next.

 

[kmelander]

I finished putting the RTV back together and moved it away from my shop. I may remove the coil and put a multimeter on it but I don't have any specs on it at this point. I still need to verify fuel pressure too. It really seems like an ignition or timing problem and there is a black box, which I have no access to, in the mix. Maybe the fuel map is somehow messed up and it's just too rich a mixture. Maybe the timing map is messed up, maybe the MAP sensor is not reading correctly or perhaps the crank trigger is faulty. I assume the dealer has a software tool and it seems like it may be a good time to let them scan it. None of the dash lights are on when it's running so the ECU seems to think everything is nominal. I'll be calling or stopping by the local dealer this week to discuss and see what their recommendation is.