Two Piece Crankshaft

Calling for rain the next few days (raining now) so no hay cutting for a while.
Behind on mechanic work so figured I'd finally pull the engine off of my 4000SU to replace the crankshaft that broke.





350 hours since it was completely overhauled, crank was turned .010 on the mains and .020 on the rods.
Previous owner has stumped the oil pan and broke the oil pump off.

You can see the large fillet radius on the replacement crank



Notice the smaller radius on the crank that had been turned



Even though the machine shop ground the crank wrong I'm going to have to eat the whole cost to replace the crank.
Said it had been too long.

I'll be posting this it the ford section also.

I had a 1977 F250 with a 2 piece drive shaft and a 2 piece crankshaft. The drive shaft was designed that way.

I saw one in an F150 with a 302 engine where the crankshaft had broken off so clean in front of the #2 main bearing it looked like someone cut it with a chop saw.

I would agree, radius too tight.

I would have the line bore on the block checked. True enough that is a short radius but doubt that it caused the break, like I said my money is on line bore.

I had a Ford 6000 diesel that made 2 2 piece crankshafts.

Just curious,How did the machine shop grind the crank wrong. I used to grind crankshafts so i was just wondering.

I have always wondered if a rolled fillet crank was really stronger or just impossible to screw up on a regrind.
it is really a pain to dress the radius the sides and the face of a grinding stone to grind a large radius crank and is expensive. But is necassary for the strength . It is also why a quality regind is expensive and almost impossible to have done any more.Paul

(quoted from post at 18:55:41 05/28/18) Just curious,How did the machine shop grind the crank wrong. I used to grind crankshafts so i was just wondering.

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If you've ground both gas and diesel cranks you should be aware of the need the dress the larger radius into the edges of the grinding wheel for diesel cranks.

My neighbor worked at a automotive machine shop, he would dress the grinding wheel check it with radius gauges before grinding cranks with large radiuses.

What surprised me was they ground every journal that way, that grinder had to be throwing some serious sparks while it was grinding the radius out of the crank.

jm, I agree.

The front main web, cap, bolts, all had too take a severe beating when the crank let go. Could even be some cracks.

Hi I have a fordson super major diesel I picked up from a guy cheap here do that with a 200 hour rebuild on it wasn't running quite right when I got
it . Dad was using it cutting grass after I changed the timing and put a head gasket in it. He came back in the house and said it was making the most
funny sounding knock he'd ever heard. When I looked the crank pulley with a considerable amount of end float was a good clue to the problem.

When I got it apart it had the wrong crank radius, I took another used crank to get re machined at the Very experienced tractor /diesel truck machine
shop. He took one look at the old crank and said he knew exactly which automotive shop ground the fillets to the smaller gas spec, he had seen lots of
them the place had done wrong on customers jobs over a few years . It was 1 employee that did them all from what he said, and none lasted more than 3-
400 hours, the customers weren't to happy. That good shop closed when the owner retired. I asked him who I could trust to replace him, he said nobody
really round here. When he quit I quit doing tractor motor rebuilds to. I don't want to put my name on somebody elses junk motor shop work !.
Regards Robert

Some crankshafts have rolled fillets to relieve stress. Examples: 4.2 L Buick V6s and all turbo V6 Buicks.

It is clearly stated in the Buick shop manual that such crankshafts must be replaced rather than reground.

Not sure what Ford service procedures are but grinding away the rolled fillets creates stress risers that WILL cause crankshaft failure.

Dean

I will second or third, LOL, getting the block lined bored. The broken crankshaft might have caused issues in the line bore of the block.

Are fords prone to broken cranks ? I have a 2715e with a
broken crank as well

This is the crankshaft from my Massey Ferguson 2135 industrial with the Continental gas engine. It was re-ground .030 - .030 with absolutely no radius at all.

I had a 1961 G12 Matchless M/C (650cc twin) that the crank snapped about like that first one. I realized I had problems when the oil pump siezed up from all the metal in it.

Not normally but some ACs are.

Dean

(quoted from post at 22:53:55 05/28/18) I will second or third, LOL, getting the block lined bored. The broken crankshaft might have caused issues in the line bore of the block.

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Line bore is fine, main web is ok, no damage to cap or bolts.
Slight abnormal wear on the front main bearings, no visible difference between the #1 rod bearing and the others.



Main bearings on the left are from the front main and show some abnormal wear on the outer edges compared the #3 main bearings on the right.
If the replacement crank was .010 under I'd reuse these bearings, but it's standard so new bearings where needed.

What we don't know is when the crank broke, the first indicator was 4 months after the rebuild when running the decaker in the poultry barns, the warning light blinked on and back off a couple of times when the engine was idled down.


The oil light would blink when the engine was idled at random times over the next few years and I suspected a possible defective sending unit. These engines Never have oil pressure issues or crank problems.

While tedding hay at low rpm's the warning light blinked a few times so I decided to connect a mechanical gauge just to confirm the sending unit was going bad.
Oil pressure was lower than it should be at idle so I left the gauge connected to monitor the oil pressure.
Cold pressure was 75 psi, after the engine had warmed up pressure dropped to 40 psi at operating speed and 20 psi at idle, again lower than it should have been but not alarmingly low.
Next time we ran the decker is when we knew for sure there was a problem, this machine works the tractor hard and after a while oil pressure dropped to 25 psi at operating speed and 10 psi at idle.

When I drained the oil and dropped the pan to look for a problem I was totally shocked to find the crank broke.
We put over 300 hours on the engine from the first time the warning light blinked until I dropped the pan to find a broken crank.
Since everything in the engine was in excellent condition other than the crank I can only suspect the crank had been broke the whole time.

(quoted from post at 23:43:01 05/28/18) Are fords prone to broken cranks ? I have a 2715e with a
broken crank as well

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Some of the early Ford 4 cylinder diesel cranks were prone to breaking but the 65/up tractor engines don't have crank problems unless something else caused it.

I had never heard of a 2715e until you posted, had to look it up, appears to be a bit of an oddball in the tractor world.