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Guest Anonymous

Did my machine shop screw up?

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Guest Anonymous

It looks as if they align honed the main caps with the bearing lock tangs on the same side. Caps are matched to their proper location, just turned 180 degrees. If they align honed it this way, will this have screwed things up or make no difference what-so-ever? Just need to flip them around and begin assembly to figure out?

One thing is for sure, I will never take any engine back to these idiots again. They originally told me the turn around would be 3-5 days, but instead had my entire bottom end for 5 weeks. Billed wrong, told it was cleaned but wasn't, given freeze plugs that were wrong. To everyone: NEVER GO TO WATERHOUSE MOTORS OF TACOMA, WA. Should have known better and took it to Autosport Seattle, cause Brad truly is the man.

Ryan

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Guest Anonymous

Then it probably isn't a problem. The only problem I could forsee is the thrust bearing surface between the two caps being uneven if the caps weren't dead center of the studs. Look at #3 and see if you can feel a difference between them. If so then the crank will not spin once it's installed. Check your main journals with a dial bore gauge to make sure the hole is proper.

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Guest Anonymous

Ryan writes: "It looks as if they align honed the main caps with the bearing lock tangs on the same side."

Hold on, are you sure your stuff was not assembled like that when you took it apart?

BMW M10 mains all have the caps fitted "lock to lock" wrt the bearing tang grooves.

'Some old guy' should know that, if he's paid attention to the assembly or RTFM. I don't agree with his idea that it might be OK to fit them backwards (if having align-honed.) Besides the thrust surface concern, the problem is that the caps are made to "register" in one position (fit tightly).

The caps have to register correctly to prevent them from walking and fretting in place. Under certain circumstances, a replacement cap can be fitted, but it's a lot of work to get the correct register (and requires having a large quantity of spare caps to choose from), just not worth it on an M10 when complete cores are so readily available. Even when you have a close match, the work involves moving metal from the block side inward with a blunt tool, and requires an experienced skill level to perform.

Fitting caps backwards would be nearly impossible to get it right.

Mains are fitted lock-to-lock, rod big ends are fitted opposite each other.

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Guest Anonymous

(nt)

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Guest Anonymous

I don't really care how it went together and came apart. Look at it from the bearings perspective. The tang is a locator of the bearing. Since the main bearings are centered on the crank and the tang is the same distance from center on the top or the bottom cap; it really doesn't matter as long as it was align honed. The only problem could be the thrust bearing surface not being flush. One could argue that if the caps are on backwars then they might not be flush either when turned around backwards. If that's true then yes there is a cause of concern because the bearing will be trying to ride in the fillet area of the crank.

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Guest Anonymous

The tang location is just used here as a guide for how the caps are to be fitted, it does not have an impact on the issue at hand, which is the precise fit & alignment of matched caps to their locations in the block.

The main bearing caps are produced to feature a tight "register" fit in their positions in the block, each one in it's own place. This needs to be correct, because the crank whips around quite a bit, it does not stay rigid straight when it's working. This crankforce acts on the caps which need to be tightly supported in the block via proper register, not just the bolt clamp.

Of course there's the need to have the #3 main with the proper thrust face (unlikely it's as good with the cap reversed), and again it's obvious that extra machining can possibly make the main bearing bores correct to size and alignment.

But the key thing is, the loss of register & extra misalignment that results from reversing the caps is two more major strikes against a reversed set.

The register is critical to controlling the crank -- if it's not absolute, the caps will walk & fret in place.

Any time a main bearing bore is re-sized, the cap is cut down a bit to make the hole small enough for the hone to work it to size. This should be done as little as possible, as it effects the register to a small degree.

The amount of metal that would need to be removed to compensate for reversed caps is probably far more than any conscientious machinist or builder would allow. The geometry on a reversed cap is not going to be worth correcting, there'd be lots of extra work to get a very sketchy result at best.

Could it be done.. sure, but why throw good money after bad?

Has it been done .. probably somewhere. But I've been thru many BMW blocks of all states of damage, but never seen this attempted on purpose.

It's hard to see how it could even happen, as this work does require measuring the bores during setup, how could anyone not see the caps were fitted backwards and the holes were way out of shape as a result.

If it matters enough to do the align hone in the first place, why waste the effort on a bad combo?

Just about any block work on an M10 can be recreated on a suitable donor for less effort than saving a butchered lower end.

Ill-fitting caps are not something to compromise on, any experienced engineer/machinist/builder would know that. Just because it might start & run does not prove it was OK to do.

If not, that's a huge red flag that shows you're dealing with hacks, take the work elsewhere unless you don't care about buying crap work from crooks or idiots.

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