Something isn't right...engine rebuild

[catech11]

removed the crank and measured it today, looks like it is in fact an 81mm crank

[MR 325]

This thread should not continue until you KNOW what parts you have.

[redlightpete]

Yeah read about doing exactly that on e30zone, not looking to shave the block because that would mess up the cam timing.

Im just going to trade it out for a regular 75mm i crank.

The timing could be easily fixed with an offset cam sprocket pin or an adjustable cam gear.

[catech11]

Yeah read about doing exactly that on e30zone, not looking to shave the block because that would mess up the cam timing.

Im just going to trade it out for a regular 75mm i crank.

[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...

[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

[MR 325]

I personally would not.

[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?

[cunninglinguist]

Why not measure the throw of the crank?

[MR 325]

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

[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?

[reelizmpro]

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

[catech11]

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

[catech11]

nope not flat, here is a pic

[Todd Black 88]

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

We're they flat?