Clutch or throttle issue?

[Catch95]

Hi, looking for some mechanical advice on my Jinma 204 which I've had for 8 years. Now has 750 hours on the clock. I was coming down a steepish hill the other day, which I do regularly, in 2nd gear in low range. No implements on. The tractor began to "run away". Didn't lose traction, but the engine compression wasn't holding it, which it normally would. Bringing the revs up (which is slightly counter intuitive as you start hurtling down a hill...) made the engine compression grab it and slow it down.

Is this an issue with the clutch or just operator error? No other signs of a slipping clutch. Moves off fine.

Other thought is that the hand throttle isn't working (caught on a tree branch). I would normally have this above idle and I'm wondering if the lower end of the revs are too low when I take my foot off the accelerator?

Any thoughts, advice.

Thanks

Mark

 

[RonMar]

Might be an engine issue. Dosn't sound like a clutch as if it were, the speed would increase but the RPM would not. It may be that you are seeing high hours wear provided the engine wasn't overly hot and you were in low range. It sounds like the rings were not sealing, and adding fuel and the associated pressure build from combustion caused them to seal.

 

[Catch95]

Ron,

Thanks for your thoughts. I don't think the revs increased as the speed picked up. I increased the revs after a bit and that seemed to help the engine re gain compression and slow it down.

Engine was hot - not in the red on the gauge, but nearly there. About a 100 degree Fahrenheit day.

Mark

 

[greg_g]

Any chance that it simply slipped out of gear? I've had that happen. Please describe what actions you take immediately after the tractor starts to arbitrarily gain downhill speed. Do you brake? clutch? grab another gear? or just let it run?

//greg//

 

[Catch95]

Greg,

Definitely didn't jump out of gear and did it again on another hill later. I've been going up and down these hills for 10 years and always do the same - in low range and let the engine slow it down. Re what I did. I'm pretty sure I braked but they wouldn't hold it so I let it run and gave it some revs which seemed to let the engine compression slow it down. Didn't change gear as I was going too fast anyway and felt that if I hit the clutch to change gear it would runaway completely.

Did some reading and saw this article Overland Expo - Overland Tech & Travel - The Myth of Compression Braking - does this apply to a TY290 engine?

Appreciate your thoughts

Mark

 

[greg_g]

Yeah, the phrase "compression braking" is often misapplied. Engine braking is usually more appropriate. Downhill "coasting" speed is more realistically being limited by the throttle setting and the governor. Uphill/downhill/level operation should not vary much, as long as the throttle setting is not touched. Yes, gravity plays a roll; there will be a little slowing down uphill and a little speeding up downhill. At any given throttle setting, it's the governor that trys to keep the ground speed as consistent as possible.

But before blaming the governor, is your tractor climbing hills normally? Do you still get momentary black exhaust when the engine has to suddenly pull hard? Sorry for the 20 questions, but resolving issues like this is sometimes a matter of elimination.

//greg//

 

[Catch95]

Greg, thanks for staying on this.

Had me thinking re the two questions. I would say yes to both. Still see a puff of exhaust smoke when I punch the accelerator and climbing hills is ok. Haven't had a situation where I felt like the clutch was slipping as I pulled away up a rise.

Could the broken hand throttle have anything to do with it? Without it, once I take my foot off the accelerator, the revs drop back to idle, instead of to where the hand throttle was set?

Mark

 

[quicksandfarmer]

Greg, thanks for staying on this.

Had me thinking re the two questions. I would say yes to both. Still see a puff of exhaust smoke when I punch the accelerator and climbing hills is ok. Haven't had a situation where I felt like the clutch was slipping as I pulled away up a rise.

Could the broken hand throttle have anything to do with it? Without it, once I take my foot off the accelerator, the revs drop back to idle, instead of to where the hand throttle was set?

Mark

That sounds like your problem.

Tractors don't have a "throttle." In the literal sense, a gas-powered engine regulates the amount of fuel burned by "throttling" the intake manifold, restricting the amount of air allowed in, and the carburetor or fuel injection matches the fuel to the air. Diesel engines don't have throttles. The air comes in unimpeded. The fuel injectors inject an appropriate amount of fuel. In a conceptual sense the "hand throttle" isn't a throttle at all, it's a speed setting. Tractor engines are regulated, you set the speed and the regulator provides fuel to maintain that speed. The hand control is where you set the engine speed. The foot control is used to temporarily override the hand control.

With the regulator working, you shouldn't need to "punch the accelerator" to get up hills, the regulator does that for you. It also cuts off the fuel going down hills to maintain speed.

 

[greg_g]

Yeah, I think you have a governor issue. Good chance it's not the governor itself, more likely just a mechanical linkage issue.

//greg//

 

[Catch95]

Yeah, I think you have a governor issue. Good chance it's not the governor itself, more likely just a mechanical linkage issue.

//greg//

Greg, Excuse the ignorance. Where should I go looking for possible issues in the linkage? Do I follow from the accelerator pedal back? I've also had a go at trying to fix the hand throttle but can't figure it out. It got caught on a tree branch and bent fully over - I think it was backwards. I now can't get it to work. It doesn't seem to engage on the small semi circular piece. Tried to figure it out but no go. I'll be back at the property next week so will take some pics. About to do the repair on the leaking front axle (thanks Tommy - parts arrived safely). Did one side a year ago and not a drop leaked out so hopefully will get the same result on the other side.

Mark

 

[quicksandfarmer]

The foot throttle isn't normally used in tractor operation. Leave that out for now.

For the hand throttle, I would start with a parts diagram. See what parts are supposed to be there and what they are supposed to look like. These tractors aren't complicated, they're the kind of things you can take apart by just looking at what's connected.

 

[greg_g]

I used the foot pedal quite often. Most of my operation was with the lever set to obtain 540 PTO revs. There were still several hundred RPMs left before hitting the governor stop. If I needed some more throttle to maintain the desired 540 PTO revs - on an uphill pull while mowing for example - I'd just add it with the foot pedal.

There are at least three variations of what Jinma calls the "Engine Control Mechanism" for the 200 Series. I have diagrams of two of them. But the foot pedal/hand lever/shutdown pull rod on both are interdependent. If something goes wrong with one, it might adversely affect one or both of the others. Depends upon the nature of the issue. But as quicksandfarmer suggests, there's no substitute for the proper manuals. Are you working towards obtaining a set yet?

Below is a diagram of the setup I had on my own 200 Series. Let me know if it doesn't apply to yours, and I'll upload the other diagram. What you won't see, is the return spring. That's considered part of the governor.

Whatever you bent, may be affecting normal motion of another segment of the assembly - they interact. As I recall, the issue you're addressing is why the tractor has started going faster downhill that previously. I'm guessing whatever piece you bent is interfering with normal governor operation by over-riding the amount of fuel specified by the relationship between the governor and the lever setting. Start with the return spring, watch to see what it's doing as this downhill acceleration occurs. What you want to see is a spring that either doesn't move at all, or works to unwind in its effort to maintain revs.

//greg//

 

[Bob Rooks]

I read that RV article about diesel engine compression braking and almost cried. He says diesel engine compression braking is minimal and then goes on to describe how compression forces "cancel out". He then goes on to describe the Jacobs Engine Brake, but he failed to state the key phrase that encompasses diesel engine compression braking (the Jake Brake only intensifies this), and that is NET ENERGY LOSS. I'm not going to go into a dissertation about this :zzz:
As long as no fuel is delivered to the injectors there will be quantifiable compression braking. You can perform a simple test to verify this: Climb a hill in an appropriate gear range and governor setting, then go down the same hill in the same gear range but with the governor set to the idle or no fuel setting.