Picked up a seized engine E70 (N55)

[BergA]

Unfortunately I didn't find a smoking gun. The oil passages were perfectly clear, and the two neighbor bearings look "fine."

One potential hijink is that the parts fiche doesn't show individual connecting rods for sale -- only in sets of 6. And it's $611. So somehow I need to find a source for a single connecting rod.

[Scott ZHP]

That crank does not look happy to me; it's blued from heat. Are those ridges in the 6/7 mains?

Maybe oil was added after the bearing cooked? I hate that these new engines lack a damn dipstick.

[Brian425]

I think both may be fixable. Have the crank measured and then magnafluxed to see if it is salvageable. You should be able to resize the rods.

You seem to have the knowledge, so I doubt I am telling you anything new. Not like the Fords and Chevys where you can find Eagle rods and cranks for little $$ to build a fun motor.


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[BergA]

Originally Posted by Brian425

I think both may be fixable. Have the crank measured and then magnafluxed to see if it is salvageable. You should be able to resize the rods.

Hi Brian, can you tell me more about resizing rods? I'm pretty confident the crank can be restored. A shop near my house commonly welds/grinds/polished damaged crank journals. Of course, buying a new crank for $500 isn't ridiculous either.

However if the rod is worn too large, I don't think it can be repaired? Can they weld additional material inside? The fiche doesn't show any oversize bearings available, so it would need to be honed to original diameter (50.00) in order to keep the correct gap. I'll try measuring it with a caliper tonight for a rough idea.

[Brian425]

They take the cap off the rod and grind the cap and rod where they meet. This makes the big end of the rod a slightly smaller diameter. They then hone the rod to make the diameter correct and make it perfectly round again.

Your machine shop will know how to do it.

I would spend some time to figure why the bearing spun. I doubt they over-revved the motor (they have a rev limiter). You did not show all the bearings; but, I would expect oil starvation from low oil to show wear on all or most of the bearings. (Clevite has a good guide to read bearing wear.) I would suspect that it was a combination of piss poor maintenance, beating on the truck while it was cold.

I would check the piling system and put in a new oil pump.

Good luck. I have built 30-40 Chevys and Fords; but, never a BMW.


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[BergA]

Thanks for the info. One hesitation I have for that process is these connecting rods were originally fracture-split rather than machined. As such there are no dowels to create alignment. So unless the machine shop installs dowels, there's no way to re-align the top and bottom after machining.

I just contacted a gentleman on eBay who's selling a crankshaft. Fortunately he thinks he has connecting rods too, so I can likely buy from him.

[Brian425]

Ah, like the modular Fords. So, yes, they are junk.

Sorry about that.


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[BergA]

The final solution is going to come down to how to deal with the scored crankshaft. The choices are:
-Send mine to a machine shop to have it ground & polished. They would probably weld/grind/polish just the bad journal, then polish all others.
-Buy a used one online. There's one on eBay for $500, and I'd have it polished before assembly
-Buy a complete brand new "package deal" from BMW which includes a crank and all bearings.

First cut below. This is my best "apples to apples" comparison and certainly doesn't include all the parts I need. If I do piston rings it will be $600 onto each option.

[Scott ZHP]

If this were mine, I'd probably go for option #3 and try to negotiate a better price. Unless you are already getting the parts at, or near cost. It's easy to spend someone else's money.

You're looking at a $500 delta between brand new and best case iffy option. I'd want a firm quote/opinion from the machinist about either of the other crank options.

What's the history on the eBay crank? And does it come with specs from the machinist?

I guess it all depends on what your plan is for the X5; are you planning to sell it, or keep it?

[Brian425]

I would add $50 for magnafluxing the old crank or a used crank. No reason to take a chance on the crank being cracked for so little $$.

Personally, I would let the results of the machine shops testing of the original crank guide me. In either case, I would build.

One thing I disagree with is going with a used oil pump. For me, it is just not worth the savings.


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