main bearing cap screws

[FergFord]

Broke a main bearing cap screw this morning. It looks like a non-original part and possibly a softer bolt. Does anyone know where I can find replacments? Would any of those from the Ford N's fit? Or can one substitute standard grade 8 bolts.

 

[Anonymous-0]

Which tractor, which engine?

Gerald J.

 

[FergFord]

TO-20 Z120 engine.

Sorry for the lack of details. A little discouraged this morning. Obviously.

 

[Anonymous-0]

A MF dealer might have the parts or be able to get them. There is a place that specializes in Continental engine parts. I don't have a link for them in this computer. Located near Chicago.

My MF-135 parts book shows for the Z-134 that is fairly closely related to your Z-120 that the main cap bolts are 1/2x2-1/2 NC hex head (MF part number 21 215A) except are 6-1/2" long (MF part number 1 750 131 M1) at the oil pump. This page shows the washers are special (MF 1 754 683 M1). Those long bolts sound like special and the short ones as common bolts. The Z-145 uses the same parts.

Look at their heads. A grade 5 should have three marks on the head, a grade 8 has 6. I'd think a grade 5 would be better than an 8 in this application because of the shock and vibration. Most of the bolts I've noticed on my MF-135 are grade 5, but I've not been inside the crankcase.

My MF-135-165 I&T manual suggests main bearing cap screw torque of 85-95 ft pounds. For a 1/2 inch bolt that's not a whole lot.

Gerald J.

 

[FergFord]

The cap screws do not appear to have the standard grade markings. The one that broke actually has no markings at all except for a dimple on the head. The others have either a NE #### designation or a Rockford brand symbol. The lengths for your MF-135 are very similar to mine. The issue with standard cap screws are that the heads are thinner and not drilled for the binding wire. I will be trying my local MF dealer, NH dealer and maybe Fastenal if necessary tomorrow. Can really get anything done on a Sunday.

 

[Anonymous-0]

Yes, it could well be they are special machined bolts that are critical to the bearing cap alignment so an ordinary rolled bolt won't do.

McMaster-Carr has bolts with drilled heads but the threads and the shank of the bolt may not line up accurately enough for main bearing bolts. If the hole in the cap just barely clears the bolt shank then its sure that's a critical dimension for aligning the cap.

A dimple in the head may be the center used for lathe turning.

Gerald J.

 

[Anonymous-0]

Bolts aren't made in a lathe. If they are, they aren't any good. All high performance bolts have their threads rolled onto the blank by rolling machines. This squeezes the metal down which makes them last longer in fatigue.

 

[Anonymous-0]

Your neighborhood salvage yard probably saves those kinds of bolts. I see no reason to use less than Gr 8 or the best the original equipment vendor supplied. The higher performance bolts will stretch more before permanent yielding. A bolt works like a spring. You've got to have some stretch or it won't stay tight. There needs to be enough thread engagement to prevent stripping out.
As for why one failed, that could be caused by someone overtorquing it in the past, or it could be a flaw in the material. Used bolts, or the other bolts in your engine might have the same problem waiting to happen. As they say about used bolts (in critical places), try the Navy floatation test. Throw it over the side, if it floats, don't use it. I don't know whether the bolts on this particular engine have a limited life, or if replacement is recommended.

 

[DennisPinOhio]

I just bought parts for my TE 20 at a local Ford tractor dealer. They were very helpful and were familiar with the Ferguson line.
You might try that, if you have one close by.

 

[Anonymous-0]

Depends. If the bolt shank is also the alignment pin, you can't get alignment between that shank and the threads with rolled threads and have to go to cut threads and shank at the same setting, probably screw machine but same effect as a lathe.

Gerald J.

 

[Anonymous-0]

Actually a grade 8 will stretch less and many consider a grade 5 to be a superior bolt for shock loads, considering a grade 8 to be a bit brittle with shock loads.

Gerald J.

 

[gshadel]

Your old cap screws were probably over-torqued by prev. owner. I've had the same thing happen on lug nuts several times, and a few bolts as well. The service manual torque for those bolts is 85-95 ft.lbs, which suggest that is a grade 5 bolt. Grade 8 bolts have torques over 100# for 1/2" bolts. Grade 5 bolts going into cast iron is pretty typical from what I've seen. And yes, head bolts/nuts are grade 5 also. Will grade 8 bolts hurt, or back out? I don't know. Guess the final call is up to you.

George

 

[Lance J.]

Dennis P.- I don't have an MF dealer nearby, but there is a New Holland dealer 1/2 mile from my work place. I wonder if they could help me when I need stuff for my '55 TO-35.

 

[Anonymous-0]

My nearest JD dealer printed off nearly 100 pages of MF-135 parts they could supply a couple years ago.

Gerald J.