Binding engine 535i

[jjdickm]

I am rebuilding my engine and my number 3 piston is binding for some reason. The bearings are fine. I have not checked the clearances on the piston rings yet. They were the same rings. I didn't replace them I am just trying to make the engine run so I can drive the car. But this damn piston is binding. Its probably the rings. Any advice is appreciated. im just getting tired of assembling this engine. I have put together about ten m30 engines and have not had this in the past.Thanks in advance.

[Barney Paull-Edwards]

If all the other pistons do not bind them check that you have any stepped rings in the right way round and that all rings are 60' apart. Not sure what the BMW ring gap is but if you are re-using old ones then that should not be a problem,cleaned the lands thoroughly?

[632 Regal]

pull #3 back out and inspect it, somethings obviously wrong.

[jjdickm]

I was just looking at it and there is a small tab on the side of my rod that is actually hitting the block. I don't have these on my other m30? I don't know why they are there or why they are hitting the block. I think bmw cut machining costs and decided not to have the tabs taken off from the cast. wtf? I am going to switch out the rod with another one I have to see if that does it.

[Bin_jammin]

I was just looking at it and there is a small tab on the side of my rod that is actually hitting the block. I don't have these on my other m30? I don't know why they are there or why they are hitting the block. I think bmw cut machining costs and decided not to have the tabs taken off from the cast. wtf? I am going to switch out the rod with another one I have to see if that does it.

You're going to replace one rod out of a set with a different one? I'd sooner think about clearancing the block than swapping in what might very well be an odd weight rod.

[jjdickm]

I am going to change them all out.

[Ross]

Interesting rebuild there, using the old rings and bearings. I think it's safe to assume the same rods too. ? If they cleared the block before then they ought to clear it now.
Are the rods installed correctly or perhaps flipped around?

[jjdickm]

I thought that might have been the case but its not. I replaced the bearings so they are actually not too long ago on my last build and didn't have any binding problems then. I check all the rings and they are the correct gaps as well so that is why I am reusing them.

[jjdickm]

I went with standard bearing does anyone thing an over sized bearing would be better for the main bearings?

[jjdickm]

I can now rotate the engine it just feels so tight. its hard to rotate it.

[Ross]

Doesn't sound right. Just a short block you should easily turn one hand.

[Bin_jammin]

I went with standard bearing does anyone thing an over sized bearing would be better for the main bearings?


Going to reply to two of your posts here in one shot. First of all, oversized bearings are for when you've had the crank turned. This cuts material off the crank bearing journals, thus making them smaller in diameter, requiring bigger bearings to fill the space vacated by the material removed. If you put oversized bearings in an engine without cutting the crank, it will not rotate, and you will have a LOT of trouble on your hands.

Second, you have a problem with your crank being hard to turn. I'm going to assume you have the plugs out of the engine and you're not fighting the compression. If that's the case, go back to square one.

If you don't have the plugs in, the first question is: "Have you plastiguaged the engine?" Plastiguage is a strip that you place under the bearing caps, then torque the caps down. The plastiguage has markings on it to tell you how much clearance you have on each bearing cap. After torquing the caps to spec, remove them and inspect the plastiguage. If the strips tell you you don't have enough clearance, you may need to either order a different size bearing, or open up the clearances on your bearings with some super-fine sandpaper.

[jjdickm]

I guess I should recheck the bearing clearances.

[jjdickm]

I have plasiguage but I haven't used it on this engine it will be my next step.

[jjdickm]

what should the clearances be?

[Ferret]

I guess I should recheck the bearing clearances.

You've not accidentally got a piece of crap/grit underneath one of the bearing shells have you? Or... crossed one of the bearing shells over from another con rod?

[Bin_jammin]

what should the clearances be?

Honestly, I don't know what BMW specs their bearing clearances to, but I'd be willing to guess somewhere in the neighborhood of .050 or so. Don't go by me though, contact your local service department, or get the Bentley's manual or something.

[jjdickm]

not that I know of. I clean every thing before it goes in. I am going to pull th crank out today after measuring it with the plastiguage So I will double check.