Magnum 12 engine

[Dennis C. 142]

Recently I picked up a1987 312-8 with 1600 hours on the meter. tractor starts right up and runs well. I did drain and flushed the transmission and installed a new brake pad.  My neighbor cut a tree that has fallen on his property and i hauled the wood out with the tractor and a small cart to his house up the hill. We made several trips over the next three days with no issues. Yesterday as I was driving up the hill with a load of wood, this is a small country road, the tractor visibly slowed down and I need to continue to give more throttle to get up the hill. Next load same thing as these loads were smaller than i was hauling the day before. Where should i start looking for the problem? Belt slipping, poor compression, if poor compression how can I check this.  After hauling wood I went on to mow my lawn with no issues. Thanks, always great help at red Square.

 

Edited October 3, 2020 by Dennis C.

[ebinmaine 72,669]

2 hours ago, Dennis C. said:

tractor visibly slowed down

Did the engine slow thereby slowing the tractor or did the engine speed stay steady?

 

When you say more throttle what was it at?

Remember these are air cooled engines and should not be worked at low rpm. 

 

First thought is carb needs a cleaning....

[Dennis C. 142]

Engine speed remain constant but the tractor visibly slowed down. Throttle was a half throttle like the day before. The day before i was hauling heavier loads in 2nd gear at half throttle climbing the same incline with no issues.  This time  I was in 1st gear. The previous owner just installed  fresh fuel line, in line fuel filter, new in tank fuel shut off and carb cleaned.

Edited October 3, 2020 by Dennis C.

[ebinmaine 72,669]

28 minutes ago, Dennis C. said:

Engine speed remain constant but the tractor visibly slowed down.

Half throttle is reasonable but 3/4 under a load should be used. 

 

If the engine is constant but you had to increase throttle to maintain that constant I'd still consider carb/fuel first. 

 

How old is the spark plug and wire?

 

Mowing would be considerably less load than pulling a heavy weight so I could understand why behavior would be different. 

[The Tuul Crib 7,339]

How big of a load are we talking here

and about how big was the grade?

[Ed Kennell 41,959]

1 hour ago, Dennis C. said:

Engine speed remain constant but the tractor visibly slowed down. 

This tells me there is no problem with the engine.

The engine torque is not getting the power to the ground.  This could be due to belt slippage caused by a bad belt, dirty engine or transmission pulleys, bad idler pulley, or weak idler pulley spring.       Power can also be lost in a loose axle hub with a sheared key in the hub or the transmission pulley.

There is also a 1/8" roll pin fastening the clutch lever to the cross shaft to the idler pulley. This pin can shear and cause the lever to slip and not transfer the spring load to the idler pulley.

 

If the belt is slipping for any length of time, there should smoke and smell from the burning belt.         I would look for a loose hub first, then the sheared key in the cross shaft lever.

Edited October 3, 2020 by Ed Kennell

[peter lena 9,271]

DENNIS C ,  I would go thru basics to verify their function, I would check out the drive belt area , the possibility of a worn drive belt slipping could be it , cutting grass and dragging heavy logs up a slope are entirely different. remove the belt guard and detail check , all areas. pulleys , spring tension , rusted areas . it could be as simple as a worn belt . hope you find it , pete 

[gwest_ca-(File Mod) 11,479]

You may still have a damper on the drive belt idler pulley. As the drive belt wears the idler pulley needs to come back farther to keep the belt tight. The damper in the red circle may need to be adjusted back to allow the idler more travel.

The damper may be an air shock with a small hole in the end that gets plugged with dust and dirt. You can wash it out and place back in service.

 

Garry

[Ed Kennell 41,959]

Thanks Garry.    The pin I refer to is item 17 in Garry's above dwg.

[Dennis C. 142]

Thank you ball for your suggestions. Yesterday I did order a new belt and idler pulley as it does squeal when engaging. Once all the parts arrive I will check all the items you mentioned. Hopefully I will find a cure.

[ebinmaine 72,669]

1 hour ago, Dennis C. said:

squeal when engaging

There's a hint. 

 

 

[peter lena 9,271]

I agree with the squealing issue , my own experience, is to detail lubricate every movement / frictional point . when it moves without any effort it works as it should , pete

[Lee1977 7,206]

Might be that cylinder that they attached to the clutch idler not complete releasing,  I don't what year they started putting them on.  It was already removed on my 312-8 when I got it.

[Dennis C. 142]

On 10/3/2020 at 8:09 AM, Ed Kennell said:

This tells me there is no problem with the engine.

The engine torque is not getting the power to the ground.  This could be due to belt slippage caused by a bad belt, dirty engine or transmission pulleys, bad idler pulley, or weak idler pulley spring.       Power can also be lost in a loose axle hub with a sheared key in the hub or the transmission pulley.

There is also a 1/8" roll pin fastening the clutch lever to the cross shaft to the idler pulley. This pin can shear and cause the lever to slip and not transfer the spring load to the idler pulley.

 

If the belt is slipping for any length of time, there should smoke and smell from the burning belt.         I would look for a loose hub first, then the sheared key in the cross shaft lever.

I pulled off all the guards and inspected all the pulleys, pins, clutch spring; all good and there is no dampener on my clutch. Belt is  fairly new and the idler pulley is new as well. While the rear wheels were off, I depressed the clutch, transmission in neutral and started the engine. When I slowly released the clutch the squealing and some rattling started but it appears to be coming from the transmission. After several revolutions the noise subsided..  So I removed the idler, belt, engaged the transmission and turned the input pulley by hand.  The pulley turns  more than a quarter of a revolution before the axles turn. Rotating the input pulley forward and back and there is   a lot of play. I'm thinking all my issues are with the transmission as It was full of a milky water/oil mixture which I have already addressed. A rebuild of the trans is my guess but not within my mechanical abilities. Does anyone still repair these transmissions?

[The Tuul Crib 7,339]

Yes. These can be rebuilt very easily!

There are instructional videos that 

go thru step by step how to dismantle

and reassemble . You can get the bearings(if needed) and seals as well 

[953 nut 59,969]

With a bit if help from the people on this site you can rebuild your transmission, Below is a thread from @stevasaurus, he is the go-to guy on transmissions around here.

 

[Dennis C. 142]

Unfortunately I do not have a place to work or tools necessary to take on a transmission rebuild. If there was a member close by I could take the trans to I would gladly pay for a rebuild this winter.

[Ed Kennell 41,959]

2 hours ago, Dennis C. said:

  The pulley turns  more than a quarter of a revolution before the axles turn. 

Are you sure the pulley or a hub is not slipping on the shaft or axle?   This is typical if there is a sheared key.

I keep going back to your statement that the engine maintains RPM but the tractor slows down under load.   

A sheared key on the input shaft or an axle would slip more under load, but I do not believe it is possible for a geared transmission to slip internally.  

The bearings and or gears would have to be worn so badly to allow the gears to disengage, I would think the transmission would lock up.

[Dennis C. 142]

13 minutes ago, Ed Kennell said:

Are you sure the pulley or a hub is not slipping on the shaft or axle?   This is typical if there is a sheared key.

I keep going back to your statement that the engine maintains RPM but the tractor slows down under load.   

A sheared key on the input shaft or an axle would slip more under load, but I do not believe it is possible for a geared transmission to slip internally.  

The bearings and or gears would have to be worn so badly to allow the gears to disengage, I would think the transmission would lock up.

Input pulley is locked tightly on the shaft and keyway is fine.  I did notice the first time I mowed with the tractor that there is gear lag in the transmission from loading and unloading. Like going over uneven ground. Like i said,if I could find a member in CT that could rebuild the trans i would gladly pay for the work. Once it clears up today I will put the tractor back together and try gain. New belt should be here by noon. Nothing wrong with the original belt or idler.

[Ed Kennell 41,959]

If you don't have the means to do a rebuild, it may be time to look for a replacement within driving distance.  There are a lot of these transmissions around.

[Lee1977 7,206]

What gear was the transmission in when you got the quarter turn. There will be some lag as the transmission have a lot of gearing In third gear high the engine has to turn 24.6 times before rear wheel turns once.

The trans mission pulley has to turn 15,1 time before wheel turns once in third gear high.. I have never checked how much lag is there. I'm not sure that there is anything wrong in the transmission.

I would put on a new clutch spring as the bely may br slipping with a heavy load, My 312 is a 1988 or 1989 I put on a new belt and clutch spring last year,  I orded my spring form RCPW I think it was around $10.

 

Edited October 6, 2020 by Lee1977

[The Tuul Crib 7,339]

4 hours ago, 953 nut said:

With a bit if help from the people on this site you can rebuild your transmission, Below is a thread from @stevasaurus, he is the go-to guy on transmissions around here.

 

[Dennis C. 142]

New belt and idler. No more noise and tractor seems to climb up the small hill better. See what happens with another load of wood. Thanks for all the help. great group of people here.

[Rob R 973]

Do the simple stuff first if belt and pulley good either put a stiffer or new spring on the idler or shorten the existing on a few links.....  I simply added an additional spring on the pedal and it has worked perfectly for the past year. Purchase spring (pair) at Tractor supply for a couple of $.

 

Edited October 22, 2020 by Rob R