850 engine repair in process

Background:



Previous owner purchased new in '55. It is a gas engine. Used last summer to brush cut 30 acres, worked great. Sat all winter. Whoever posted that capital I is used in place of numeral 1 is correct.


Started in May and ran for a short while, had to move brush mower. Parked for a few days, I noticed puddle of oil formed on floor below the transmission housing and a drip of oil on the cotter pin. I had already purchased a used oil pan in good condition because the original was dented with no leaks. I also detected oil on the fly wheel when checking the spark timing so, rear main seal needed refresh. When I pulled the rear main bearing block this is what I found:



The first problem is I believe most of you would say that the lip on the crank seal is facing the rear; wrong!!

The second problem is the crank bearing is severely worn.

In response I have taken the engine off the tractor and disassembled. What I found is:



Four piston rings. The shop manual says four rings are for the diesel engine. Is that so? The number one piston is marked with an "M". The other 3 pistons are not marked at all.



The number 3 piston head only has deep pitting which may be caused by detonation.



After decarbonizing all four pistons number 3 is the only one that is pitted. Why? Is it somehow running on a leaner mixture than number 4?

Please comment on why diesel engine pistons are in this gas engine or on anything else you see that I may have missed.

As always, I appreciate any expertise that you bring to this forum.

Be well
Jim

A couple of thoughts;
They can't be diesel pistons.
Same stroke = 3.6in on gas and diesel.
Gas compression ratio = 6.75-1
Diesel = 16-1
Compression ratio was done with different
pin heights - distance from wrist pin to
top of piston. It would be impossible to
run a gasser with 16-1 CR.
I know on the N Series you can get pistons
with either 3 or 4 rings.
Likely could/can on Hundreds too.

At 6.75:1 C/R, it's pretty unlikely that any of the jugs would suffer from detonation. Unless there was a glowing ember in that hole for a long time.

It looks to me like impact damage from some small bit that got in the hole. What does the head on #3 look like? If it's the same, then I guess the piston took most of the beating.

On the other hand, if it was some kind of detonation, that could be the cause of the high bearing wear, but only if it's on the bottom bearing saddle(s). If the top of the saddles look fine, and not the bottom, then you've been pounding that engine pretty bad.

For what it's worth I have a 850 engine torn apart and am selling parts. Here's my Craigslist ad

https://eugene.craigslist.org/grd/d/springfield-ford-850-gasser-tractor/7346929015.html

Thank you for posting nashranch. I'm not certain what to buy yet.

How many piston rings on each piston on that engine?
Did you ever replace the rings? If so who was your source? I'm having trouble finding 4 ring sets.

Thank you for posting UltraDog Mn.

i did some research and I don't believe that the N tractors had a 172 ci engine. It appears that the 8N pistons are 3 3/16 inch diameter while the pistons on my engine are 4 inch.

Mine have three rings. Don't know where you buy 4 ring sets

I found this. Maybe it'll help

https://www.yesterdaystractors.com/RINGSETS_Piston-Ring-Sets_15643.htm

Call Yesterday's Tractor @ 1-800-853-2651

Tripper225, Ultradog didn't say the N tractors had 4 inch pistons, he said you can get 3 or 4 ring pistons for them. I have to agree with Docmirror about the pitting on number 3.

The lip is backwards and should always go towards the oil crank case. That way if pressure builds up in the crank case, the seal gets pushed towards the OD and increases sealing capability. If it were the other way (like in your picture), oil would easily push out past the seal.
One other comment - leave the groove between where the current lip seal is and the bearing empty. That is an oil return groove and allows oil to flow across the bearing and back to sump (note the hole in the bottom of the groove). If that groove is blocked the oil will be dead-headed. The only reason I mention that is there is a video on you-tube where they installed the lip seal and also installed a rope style seal in that groove. Belt and suspenders is not always a good idea. Lol. Good luck.

Thank you for your post Jim L WA.
I followed through on what UltraDog posted. There is indeed 3 ring and 4 ring sets for the the 172 ci engine just as there is 3 and 4 ring sets for the 134 ci engine. The ring set in my tractor engine has 4 rings in the oil ring slot; top, bottom, and ID backers and the oil ring and I have not found a duplicate for these rings so I may have to get new pistons and rings.

Thank you docmirror for your post. Your comment made me dig a little deeper into this engine

I have collected more data:

1 cylinder 3 has the largest diameter from ring wear and it has .003 taper.

2 Cylinder 3 had the lowest compression (95 psi wet and dry) that I found before I worked the engine. I also posted the stats here.

3 Connecting rod 3 was assembled backwards. I checked the photos that I made while disassembling the engine. According to the manual the oil hole is to face the cam side of the engine and it faced opposite.

My theory is that cylinder 3 has been short of good lubrication since the previous owner had that work done. For the 40 years that he has been my neighbor (he bought the tractor in 1955 I moved here in 1980) I did not see him do any hard work with the tractor. He did snow plowing in the winter ( he had a 30 x 50 driveway) and a few acres of hay in the summer ( he stopped haying about 15 years ago). He was partially disabled and would take a joy ride once in a while. Last summer I brush mowed 30 acres and that caused the hotter number 3 cylinder to have detonation. There is no evidence of detonation in the other 3 cylinders.

This engine has good potential to work well after I rebuild it. The crank journals are consistently .01 undersize with no taper and polishing will make the crank ready for reassembly. I will get new sleeves for the crank, connecting rods, and piston pins. I may also get new sleeves for the block and pistons with rings to match.

I have not checked the oil pump yet, I have always had 40 psi pressure or more, but I am going to play it safe. I have pulled the transmission input shaft seal and will replace it while I am in there.

Please let me know if there is other things to check so that I will have the best opportunity for success.

As always your help is greatly appreciated.
Be well
Jim

Thank you docmirror for your post. Your comment made me dig a little deeper into this engine

I have collected more data:

1 cylinder 3 has the largest diameter from ring wear and it has .003 taper.

2 Cylinder 3 had the lowest compression (95 psi wet and dry) that I found before I worked the engine. I also posted the stats here.

3 Connecting rod 3 was assembled backwards. I checked the photos that I made while disassembling the engine. According to the manual the oil hole is to face the cam side of the engine and it faced opposite.

My theory is that cylinder 3 has been short of good lubrication since the previous owner had that work done. For the 40 years that he has been my neighbor (he bought the tractor in 1955 I moved here in 1980) I did not see him do any hard work with the tractor. He did snow plowing in the winter ( he had a 30 x 50 driveway) and a few acres of hay in the summer ( he stopped haying about 15 years ago). He was partially disabled and would take a joy ride once in a while. Last summer I brush mowed 30 acres and that caused the hotter number 3 cylinder to have detonation. There is no evidence of detonation in the other 3 cylinders.

This engine has good potential to work well after I rebuild it. The crank journals are consistently .01 undersize with no taper and polishing will make the crank ready for reassembly. I will get new sleeves for the crank, connecting rods, and piston pins. I may also get new sleeves for the block and pistons with rings to match.

I have not checked the oil pump yet, I have always had 40 psi pressure or more, but I am going to play it safe. I have pulled the transmission input shaft seal and will replace it while I am in there.

Please let me know if there is other things to check so that I will have the best opportunity for success.

As always your help is greatly appreciated.
Be well
Jim