Something isn't right...engine rebuild

[catech11]

1989 325i

My first rebuild, bought the car and it came with a spare motor. Ended up using the crank from the spare because a bearing had spun in the original. I didn't think to check the crank throw on the new one because i thought it was from an I engine as well.

I went to put the head on and it does not fit, my only explanation is that it is an "e" crank with the longer throw. The pistons are a little over 4mm above the block at TDC...

Advice?

[Todd Black 88]

Did you use the original I rods with the new crank, or the rods from the other motor the crank came from?

Sounds like you have the 2.7 l eta crank and the 135mm I rods and pistons.

[reelizmpro]

You didn't think to double check the parts you were installing were correct so now you have to pull the crank.

Or they decked the block too much.

[catech11]

they are I pistons and rods, bought them from cabriolet.

I checked several times to make sure the spare motor was from an I car, and from what i found it was just a pre 88 I model. Either i was wrong, or it was a stroker motor

[Todd Black 88]

Do you have a pic of the pistons that were attached to that spare motor crank?

We're they flat?

[catech11]

nope not flat, here is a pic

[catech11]

Here is previous post of mine with more info on the spare block http://www.r3vlimited.com/board/showthread.php?t=327708

[reelizmpro]

Those pictures aren't very helpful. It could have been a super ETA engine which would explain a lot.

[catech11]

and how would i find out if thats the case? What pictures would be helpful?

Edit: I think your right its a super eta, was researching up on this and it does have single valve springs, sounds like the answer.

From what i've read i can just get a set of shorter eta rods and make this set up work? Is this the most beneficial way to go?

[MR 325]

If you do in fact have Super Eta pistons you can use them with an Eta (or Super Eta) crank and rods.

[cunninglinguist]

Why not measure the throw of the crank?

[catech11]

I will measure the throw of the crank, just need to take everything apart again.

I know the answer is probably no, since the bolts stretch but can i reuse the rod cap bolts, i have torqued them down but never run the engine?

[MR 325]

I personally would not.

[catech11]

From what I've read if I use a set of eta rods with the current set up the cr will drop to a level not good for performance.

If I have this 81mm crank and the super eta engine, can I combine them to make a better performing engine, or is it a better route to just get a 76mm crank and use my I rods and pistons

[redlightpete]

If you use the eta crank and rods, and the I pistons, the piston will be 2 mm lower than the stock I motor. The 6 mm increase in stroke raises the piston 3 mm, and the 5 mm shorter rod lowers it 5 mm, so the net change is 2 mm lower. If you cut down the block 2 mm, the piston is now at the stock I motor height, but since you've increased the stroke (and swept area) by 8%, the compression will be 8% higher. 8.8 + 8% is 9.5.

If you have super eta pistons, you could use those, but you'll have the stock super eta compression which is 8.5(?), so cutting down the block to use the I pistons is nicer. The only advantage to the super eta pistons is that you can bolt it all together in your driveway without any machining. But, you have to take the pistons and rods out anyway, so...