Marvel Schebler TSX tractor carb rebuild

[Steve]

Ok, buttoned her back up enough to run and started it. The valve train seems to run smoother, however the miss is still there. I put fresh gas and a whole can of seafoam in it, gonna let it run awhile and see if any improvement.

Do you have an IR camera to see if one of the exhaust ports is cooler than the others?

 

[FergusonTO35]

Nope, don't have nunna that fancy stuff. I 'spose compression and leakdown testing is next.

 

[Steve]

Nope, don't have nunna that fancy stuff. I 'spose compression and leakdown testing is next.

Well if you need to borrow it I can put it in a box and send it your way.

 

[FergusonTO35]

Dude, you rock! How would I go using that?

Just got done mowing the front yard. The valve adjustment and Seafoam did seem to help. Performance wise, it never missed a beat. The sputter is still there, maybe a little less frequent than it was. I am still planning to check compression and leak down.

 

[Steve]

It's easy! You just point it at things like you would a non contact thermometer but it gives you an image of the heat.

 

[FergusonTO35]

Went ahead and ordered an OTC leak down tester. This is the first time I've needed one since I was a tech, the dealership always provided one. It should be here early next month.

 

[Larry B]

You can always try the redneck engine test. Make a sparkplug adapter that hooks to an air compressor and turn engine till a piston is at TDC with valves closed. Block engine from turning and apply around 100PSI to the cylinder and listen at the exhaust pipe and carb for air leaks. Suprisingly accurate to find leaky valves.

 

[FergusonTO35]

May just have to do that!

 

[FergusonTO35]

The Little Brown Santa Claus dropped off a new OTC leakdown tester, and Steve has graciously sent me his IR camera to use. Hopefully I can get back into it here soon. The MF 2706 is currently handling the mowing duties. Yes, the 2018 tractor is a backup to the 1955 model!

 

[FergusonTO35]

Snuck away from the couch-office for a bit and did a compression test, here are the results:

Cyl. 1 2 3 4
Dry 135 143 140 135
Wet 140 150 150 140

I think that is pretty good for a 66 year old 7.5 to 1 compression engine. Next up I'll do the leak down test. Spark plugs are nice and crusty, although I think the carb is rather rich right now.

 

[Larry B]

How hard do you run the tractor? Many times folks mistake too cold heat range plugs as engine running rich. The plugs need to run about 1000F degrees to operate in the self cleaning range. Depending on how hard you run the tractor can determine what plug you need to use. My 184 LoBoy likes the D18Y if i run it hard mowing grass. If i use it to just pull a trailer around the yard i need to use D21 plugs. The D18Y is a mid range plug so if not working the tractor hard may need the D21 plug. If the thermostat is stuck open it can cause engine to not reach proper operating temperature and cause plugs to carbon foul also.

 

[FergusonTO35]

Thanks very much. I mostly use it for finish mowing in the summer. Until this year, the D18Y plugs always stayed pretty clean. I'm thinking that the valves are now leaking so much that I'm not getting a good fuel burn. Planning to do the leak down test soon. Question about that: it's been a long time since I used one of these things. Do I have to set my air compressor to produce a specific PSI or will the adjustment knob on the gauge take care of that?

 

[Steve]

Thanks very much. I mostly use it for finish mowing in the summer. Until this year, the D18Y plugs always stayed pretty clean. I'm thinking that the valves are now leaking so much that I'm not getting a good fuel burn. Planning to do the leak down test soon. Question about that: it's been a long time since I used one of these things. Do I have to set my air compressor to produce a specific PSI or will the adjustment knob on the gauge take care of that?

Compressor at normal line pressure. Cylinder at tdc compression stroke. First gauge is regulated pressure entering cylinder. Second gauge is pressure able to be maintained by the cylinder.

If the first gauge is 100 psi and the second gauge is 75psi, the total leakage is 25%. Not good.

The closer the second gauge reads to the first gauge the better the seal.

 

[FergusonTO35]

Thanks bro.

 

[FergusonTO35]

Ok, did the leakdown test today and looks like it's time for a valve job, if I did this correctly! I did the test according to firing order, with the distributor rotor pointing at the terminal for the cylinder being tested. Number one cylinder was also lined up with TDC on the flywheel.

Cylinder no. 1 3 4 2
Inlet PSI 80 80 80 80
Cylinder PSI 26 34 30 32

Line PSI on my compressor is 120 PSI, don't know if that would make any kind of difference. Air is escaping through the valve cover breather tube (just an open tube) and air cleaner. So, looks like valves, seats, and guides at a minimum. I ran the plow through the garden a couple of times afterwards, it's amazing how well it still runs with such huge leaks.

 

[Steve]

If you're gonna tear the head off and rebuild it you may as well do an in frame rebuild while your there. Pistons and sleeves and a set of bearings can't be too much for it?

 

[FergusonTO35]

I'm thinking about it. Cylinder head stuff is about $150.00 total. Inframe kit minus gaskets is around $400.00. Given that compression and valve leakage is roughly the same on all cylinders I think the valve gear is just plum wore out.

 

[Steve]

I'm thinking about it. Cylinder head stuff is about $150.00 total. Inframe kit minus gaskets is around $400.00. Given that compression and valve leakage is roughly the same on all cylinders I think the valve gear is just plum wore out.

It is but only freshing up the head is like giving an 80 year old woman a face lift. Still worn out underneath. (Shivers uncontrollably after the thought of that...)

 

[Larry B]

If you are going to pull the head mighas well pull the pan and plastiguage the rods and mains.

 

[FergusonTO35]

It is but only freshing up the head is like giving an 80 year old woman a face lift. Still worn out underneath. (Shivers uncontrollably after the thought of that...)

Hey now, some folks are into that!