Connecting Rod Cap Nuts

[Ken Windom]

I need advice on what to do about cap nuts on the connecting rods for my '51 8N side mount. I took the engine components to the local auto machine shop and had everything evaluated. The result was that the sleeves needed replacing (along with pistons, rings, etc.) and the crankshaft needed grinding to remove several rather badly scored areas. They ground the main journals by .010" and the rod journals by .020". I bought new bearings of the the proper sizes and checked the clearance with Plastigage. I used the original nuts and torqued them according to the values given in the FO-4 manual. Everything checked out OK. The original nuts were backed by pal nuts, and the manual says not to reuse them. None of the vendors I normally use lists new pal nuts, so I searched the archives to see what others have done. The archives indicated that the early N's used castle nuts and cotter pins, but this had been abandoned because of the fear a cotter pin would break off. They were replaced by a different nut and lock (pal) nuts. Most people seemed not to like the pal nuts, either (the mechanic at the local auto machine shop said he did not know of anyone who used them, or where to find any). What I got from the archives sounded like new nuts should be used and held in place with red Loctite. I ordered new nuts from nnalert, which lists them as NOS. They arrived (castle nuts) and I installed them using the same torque values held them in place with red Loctite. But, now the crankshaft would not budge, no matter how hard I tried. I backed off the nuts, and it turns fine. It seems like the castle nuts are too tight when torqued to the values listed in the manual. Does this make sense? Should I use the old nuts with red Loctite? Or should I try to find new nuts that are not castelated and use them? I know how critical it is to get this part of the tractor's engine right, so would just like some confirmation on the correct way to handle this. Thanks - Ken

 

[nor cal rosie]

Pal nuts s/b avail from egge.com (Egge Machine). Can't imagine how a nut could affect bearing fit. Would suspect a cap is on backwards or something like that.

 

[Kruse]

As you tighten each connecting rod up, give the crank a spin. Does one rod do it, or are they all too tight? Find the problem and then fix it. Like posted, if Plastiguage showed the proper clearance, it's probably a rotated cap.

 

[TheOldHokie]

(quoted from post at 15:30:50 07/28/09) I need advice on what to do about cap nuts on the connecting rods for my '51 8N side mount. I took the engine components to the local auto machine shop and had everything evaluated. The result was that the sleeves needed replacing (along with pistons, rings, etc.) and the crankshaft needed grinding to remove several rather badly scored areas. They ground the main journals by .010" and the rod journals by .020". I bought new bearings of the the proper sizes and checked the clearance with Plastigage. I used the original nuts and torqued them according to the values given in the FO-4 manual. Everything checked out OK. The original nuts were backed by pal nuts, and the manual says not to reuse them. None of the vendors I normally use lists new pal nuts, so I searched the archives to see what others have done. The archives indicated that the early N's used castle nuts and cotter pins, but this had been abandoned because of the fear a cotter pin would break off. They were replaced by a different nut and lock (pal) nuts. Most people seemed not to like the pal nuts, either (the mechanic at the local auto machine shop said he did not know of anyone who used them, or where to find any). What I got from the archives sounded like new nuts should be used and held in place with red Loctite. I ordered new nuts from nnalert, which lists them as NOS. They arrived (castle nuts) and I installed them using the same torque values held them in place with red Loctite. But, now the crankshaft would not budge, no matter how hard I tried. I backed off the nuts, and it turns fine. It seems like the castle nuts are too tight when torqued to the values listed in the manual. Does this make sense? Should I use the old nuts with red Loctite? Or should I try to find new nuts that are not castelated and use them? I know how critical it is to get this part of the tractor's engine right, so would just like some confirmation on the correct way to handle this. Thanks - Ken

The nuts you used have nothing to do with the problem - look elsewhere for the cause of your binding. How did you plastigage the rod bearing clearances? You need to install the caps and torque them down to get a plastigage reading. If the plastigage says you have the proper clearances and the crank won't turn something is fishy in Denmark. If backing off on the nuts allows the crank to turn your plastigage reasults are suspect.

TOH

 

[trucker40]

I cant think of any way a nut could ever cause a crank not to turn if you were torqueing it.Castle nuts,regular nuts,pal nuts cant stop the crank from turning if its got the right clearance between the bearing and crank and installed right.If you start taking it apart,take a cap off,see if the tangs are on the same side,and while its off see if it will move.It could be a cap on backwards but also the caps are machined to the rod,so they can not be switched.They also should have numbers on the rod and cap and they have to be the same like 1 on the rod and 1 on the cap and on the same side.You need to check that and plastiguage it like somebody else said.Also the tangs must be on the side of the motor they are supposed to be on and the mark on the piston goes to the front almost always on any motor.

 

[ZANE]

The nuts have nothing to do with the crank locking up.

Are you sure you have the rod caps mated with the rods they each came off?????

They can't be scrambled. Got to go on their own personal rods.

Zane

 

[Bob]

I certainly HOPE you have match-marked the caps and rods and kept each cap in it's own rod and in the original orientation.

AND, I certainly hope you had the machine shop check the rods for size and straightness, install and fit new bushings and resize the "big end" as needed.

If not, it's a darned sad state of affairs of a rebuild!

 

[Ken Windom]

Thanks for all the replies. As most of you suspected, it was operator error I apparently turned the cap for the #1 rod around when I put it back on after checking the plastigage. I would have sworn in court that I double checked that, but guess I had a senior moment at the wrong time. It's back together now, and turns over fine.

 

[TheOldHokie]

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[Ken Windom]

Ain't it the truth! I GO POGO!!!

Heard a radio ad for some credit outfit claiming to be the "Lone Arranger" and thought about Walt Kelly's depiction of LBJ in Pogo. I still can't see a picture of a hyena without thinking of Agnew.