engine spec question

[dano0]

been offered a 525e crank with 323 conrods and 325 pistons
and have also been told this will produce a 2.7engine with no need to skim the block . firstly is this true and how would i no what im buying is what im really getting
so what i would like to no is where are the part numbers for these parts and what are they
many thanks danny

[chu346]

http://www.e30zone.net/e30zonewiki/inde ... ding_a_2.7

[dano0]

Yes I did read this but I can't see what I'm asking for please show me

[chu346]

Using 325i pistons with a 325i head. This is the best way of doing it but requires a complete engine strip down.

Doing this, the pistons of course match the head. Compression ratios will be 9.4:1 using post 9/87 (plastic bumper) 8.8:1 CR pistons and 10.4:1 using the early pre 9/87 (steel bumper) 9.75:1 CR pistons. Why the higher CR in a 2.7? Because it has an extra 49.8cc of fuel/air mixture to compress.

To keep the con rod angle correct, BMW made the 325i conrods 5mm longer. So if you fitted a 2.7 81mm crank into a 325i block (basically the same as the Eta block), the pistons would stick out of the top of the bore by 3mm. To get around this, you need to use 130mm Eta/2 litre rods. Then the pistons don't come to the top of the bore - about 2mm short in fact. It is no good guessing how much to take off the block face because early Eta blocks were very slightly taller (we are talking half a mm maybe) so you need to fit a 325i piston and 130mm rod to the Eta crank and block, take it to a machine shop and get it measured up properly to get an exact figure. It will not cost any more, and it will be bang on.

1.5 - 2mm is just a ballpark figure.

The next problem is that with @2mm off the block, the crank and the cam are now 2mm closer together which will mean the cam timing will be wrong. For this you will need a vernier (adjustable) cam pulley to adjust the cam timing, particularly if you are using an aftermarket cam. Early 325i pistons (9.75:1) have deep skirts and need 12mm machining off the skirts because they will foul the Eta crank webs. Later pistons clear fine though.

How's that?

[dano0]

Yes I no that butwhat I'm ask ing is if I use eta crank and 323 conrods and 325 pistons what will I get as I'm told I'll get 2.7 with no block decking required and does any body have any part numbers or casting numbers I could check to no what I'm getting is what I need

[chu346]

You will need to deck the block.

Check on here for part numbers http://www.realoem.com/bmw/select.do

I'll leave the donkey work for you.
The crank from a '85 525e not 528e
Rods '85 323i
There are two types of pistons for the 325i so check for years '86+'89

[DanThe]

If you want a useable compression ratio you will have to get the block machined down. Because you have been told you dont need to do this I would be wary about what you are being sold, as chu has linked the engine building guide its plain to see what needs doing, for those with engine building knowledge it is anyway.

[dano0]

ok so i have got some part numbers off the crank and rods
the rods are numbered 1265301
the crank is numbered 1267637
i have put these numbers in to real oem but they don't come up with any thing
sorry if this seams trivial but i just want to make sure i have all the right parts before i start
i also have a 2ltr bottom end that i will get bored out to match my pistons and will be using a 2.5ltr head

all help and advise is appreciated

[chu346]

In that case steer clear then.

If your using a 2.5 head you'll need 2.5 pistons and the shorter 320/323/325e rods

[dano0]

well i have had a chat with bmw and am told that the part numbers on real oem relate to sets not individual parts

so please has any one got any casting numbers from a eta crank and 323 con rods

as this would be helpful to every one and may be add these numbers to the 2.7 build guide and also add that 323 rods could also be used

any help will be gratefully received

[mongomushroom]

you've probably got the answer to this already but if you look for hub81 or h81 stamped on one of the crank webs you know you've the correct size crank. I have a 525e crank which is in the workshop now getting measured up. I'll be getting it back in a couple of days hopefully and can check out any other numbers for you if you like. Think theres a part number stamped on the end. Can you not just measure the rods?

iain

[dano0]

cheers yea there is h81 on the crank.
where do you measure the rods from end to end or center to center .

[mongomushroom]

alright mate
rod centre to centre should be 130mm. i've got a rod in my hand right now and its got 1265 30 stamped on it whether thats a part number or not i couldn't say and my rod could be from a different engine to yours. What I've been told is that if you leave the block unskimmed your compression ratio will be very low and no good for a naturally aspirated engine. I was given a quote of £90 +vat for skimming a block plus you would need vernier pulley aswell

[dano0]

ill measure the rods tomorrow i have a 2ltr block im going to use so i can get it board out to my piston specs then i can build the block up and see how much i need to skim off the top

cheers for the reply bud

[mongomushroom]

rebore sounds expensive. I've seen 325 blocks for about £70 before on ebay. I'm no expert on this but not heard of someone boreing out a 320 block for 2.7. You can use your 320 rods if them other ones are no good

good luck mate