PT 425 Robin Engine Problem

[mlhunter]

Hi guys! Its been a couple of years since I've been on here and I now have 165 hours on my Pt425 with (EH72?) 25hp Robin/Subaru engine. Overall I've been satisfied with no problems. However, yesterday I encountered something new.

After using the brush cutter for about an hour to mow the remnants of a 1 acre food plot I started cleaning up some bramble choked paths with it. After several minutes of that I stopped to clear some junk out of my left front wheel and the motor rpm went way up! I dropped the throttle back to idle and it remained running near what would normally be full throttle! At that point I decided I'd better quit and put the tractor back on the trailer and went home with it.

Back at home, I studied the engine's throttle linkage and read the online Assembly/Disassembly and Parts manual to see what all is involved. Pulling the tractor's throttle lever back pulls the governor arm toward the carburetor and moves it to full throttle. It appears that the governor arm should pull against its restraining springs to govern how much thottle opening there is depending on the engine load. At rest with little or no load there is no movement of the governor arm to do that which seems to be why the rpms remain so high with little or no load. Nothing appears to be broke and all springs appear to be functioning normally.The governor arm is tight on the vertical shaft that goes down into the block where the governor mechanical parts are.

Right now it appears that I may have to remove the timing gears cover to get to those internal governor parts.

Naturally it couldn't happen at a worse time! I would like to hear from you guys that are familiar with these engines to determine if I'm on the right track and if there is anything else I should be looking at before I start pulling the hydraulics off the engine to to repair it.

 

[washita]

not sure if this helps but I have same setup mine does the same thing occasionally pulled air cleaner off throttle plate was iced up started using additive to gas and problem has not resufaced since hope your solution will be as simple

 

[mlhunter]

not sure if this helps but I have same setup mine does the same thing occasionally pulled air cleaner off throttle plate was iced up started using additive to gas and problem has not resufaced since hope your solution will be as simple

Thanks for responding! That's good to know although its been above freezing when I've used it and its kept in my garage which is usually in the 50s so it wouldn't be iced up.

I talked to Terry at Power Trac and he said he had never heard of one of these engines having a problem with the governor so I'm hoping my problem ends up being similar to your problem

I trailered the tractor to the our local Robin/Subaru service center yesterday so I'll see what they come up with.

 

[washita]

last time I trailered mine to the local small engine/compact tractor repair shop was quite interesting it all started with "that's not a tractor" and no it is not a JD popped the hatch for a look see, I think he is still hiding in the parts room

 

[SnowRidge]

last time I trailered mine to the local small engine/compact tractor repair shop was quite interesting it all started with "that's not a tractor" and no it is not a JD popped the hatch for a look see, I think he is still hiding in the parts room

Take it to a small engine shop. You'll likely get, "My God! That's a tractor." And that was from just a photo.

You just can't win with these things.

 

[mlhunter]

I retrieved the tractor from small engine shop yesterday. The Blue Springs, MO, shop mostly sells and repairs commericial mowers. They are very familiar with these engines and believe they are very good engines. They went through the carburetor twice and while they had the tractor running after the last time it backfired a few times then quit running all together and wouldn't start any longer. They checked compression and valves and that all seemed good. They have seen crankshaft keys break and cause problems like that. They believe the problem is internal to the timing gears and governor and will require getting into the engine to find the problem and fix it.

They were willing to fix it with an estimated 7-8 hours labor plus parts. The only comment they had was how heavy the tractor was (they mostly sell and repair commerical mowers).

To move on with it, I elected to save some money and bring the tractor back home, pull the engine, and repair it myself if I can. I built and re-built hotrods during my hotrod days and got back into it awhile while I had two teenage sons at home to teach them how to do auto repair work.

Robin Subaru has a detailed service manual and parts manual online in PDF format. They seem to be quite detailed.

The tractor was purchased in May, 2005. I'll be talking to Terry at Power Trac when I run into engine removal snags. If anyone has tips on how to move the hyrdaulics out far enough to clear the engine output shaft and get the engine out I would really appreciate it!

 

[washita]

thanks for the feedback keep us posted as to what you find

 

[SnowRidge]

I pulled the engine out of my PT-425 several years back and wrote up the procedure. There are significant differences in the machines, but a read through it will likely provide some useful information. I know some of the things I pointed out should apply to removing the engine from any Power Trac.

PT-425 Engine Removal Procedure

Good luck with getting it out. I hope your model is easier to work on than mine is.

 

[mlhunter]

I pulled the engine out of my PT-425 several years back and wrote up the procedure. There are significant differences in the machines, but a read through it will likely provide some useful information. I know some of the things I pointed out should apply to removing the engine from any Power Trac.

PT-425 Engine Removal Procedure

Good luck with getting it out. I hope your model is easier to work on than mine is.

Thanks for that info, good stuff! I was going to wait until Monday but I couldn't stand it and started working on the PowerTrac about 11:30 this morning. By 4:30 I had the engine out, the rear bearing cover off, and the blown governor in my hands. Some of the parts were laying in the oil pan along side the oil pump filter. I can find no evidence of any engine damage at all and the timing marks (luckily) were almost perfectly lined up indicating no issue there.

I have to say the process was much less involved than what you went through. After removing the battery, gas tank, and heat shield getting the hydraulics off the "engine to hydraulics" coupler the engine removal was simple. Two bolts and the hydraulics pushed back approximately 1.5"-2" and the engine was free, no uncoupling of any hydraulic lines.

Since there were no hydraulics hanging on the engine and it only weighs 100# dry I pulled it with a come-along attached to a heavy chain that was strung between two eye bolts from a previous project. In my younger days I would wrestle 100# around but I don't attempt it any more! You'd laugh at how I got the engine on to a bench beside the tractor but if anyone wants to know the details I can post that info.

The only sticky issue with the whole process was was getting the "engine to hydraulics coupler" off the rear (rear of engine, not rear of tractor) engine main bearing cover after the engine was pulled. It was extremely tight and took quite a lot of persuasion. There appeared to be some light rust on the crank shaft that may have caused that. I'll be cleaning that up before it gets re-assembled!

Since there is no apparent damage to anything other than the governor itself I'm inclined to just replace that and sew it back up. I also found I'm missing an exhaust manifold stud/nut combo and one other exhaust manifold nut so I'll fix that while I'm at it.

I am mystified as to why the engine suddently died on the repair guy as I can't find any reason for that. I did find that the gas tank was completely empty and I'm betting it just ran out of gas!

Anyway, parts will be ordered Monday and hopefully Tuesday I can get it all re-assembled. Thanks again for posting that link to your experience!

 

[SnowRidge]

It's good to know they are easier to work on these days. I think the most important change has been to move all the pumps to one end of the motor. The biggest headache with the Kohler powered version is getting both front and rear pumps clear of the engine, so that it can be lifted out.