why would anyone build a 2.7 rather then 2.8?

[Ant]

Hmm, I know what I'm doing tomorrow.....

that M52 crank has slumbered in its box for to long

M20B20 wrongness kicking about somewhere too.

[maxfield]

Hmm, I know what I'm doing tomorrow.....

that M52 crank has slumbered in its box for to long

M20B20 wrongness kicking about somewhere too.

Will this have a turbo strapped to it

[Ant]

now, who would do such a deed ?

TBH no, I'll do a build for N/A , might be sweet for the Malacite touring, and frees up an M50 for me

[ed325i]

Nice one Ant. I am waiting for my crank to be delivered

[DanThe]

that M52 crank has slumbered in its box for to long

Mines been in hibernation it hasnt moved for so long, its been stood on the kitchen worktop for the last 3 months

[toby]

now, who would do such a deed ?

TBH no, I'll do a build for N/A , might be sweet for the Malacite touring, and frees up an M50 for me

Do it mate then you can keep an eye on it for R&D refinements

[gorgeee]

think ill be going down the 2.8 route too

[Andyboy]

The 2.8 conversion is nothing new - I did one about 5 years ago and the first one I know of was a conversion on an E36 320i in 1994. The 328i had just come out and the owner couldn't afford one so we bought a kit of parts from BMW - crank, rods and pistons. These were Nikasil pistons with the iron skirts and we used an iron 320i block bored from 80 to 84mm. It's said you can't use these pistons in an iron block, but we did and it worked! The 320i head was used and the piston tops machined to clear the valves.

There are 2 or 3 2.8 cranks. The first one has bigger webs that won't clear the bottoms of the early 2.5 M20 pistons but will clear later ones (i,e plastic bumper 8.8CR slugs). The second one will but I've no idea when they changed and BMW don't list it. It was probably a production change and if you orde4r a new crank, you get the one with smaller webs. The third crank is the M52 TU twin vanos. This one has a TDC trigger wheel bolted to the rearmost crank web. It can be unbolted and thrown away if you want, and it fits an M20 block fine.

The 2.7 Eta thing is still valid because the cranks are still about for not much money. But look on Ebay and you will find shagged 2.8 M52 units where the block threads have gone and thus the block is scrap. The beauty of the 2.8 is a) no block machining b) They are getting more common for peanuts and c) you've got 100 cc extra and capacity means power.

The last M52 2.8 I bought was a complete engine from a 2000 m/y 728i. Ebay, £80 with the head removed and cams missing. Best of all, just 10'000 miles from new and mint.

2.8 crank, 130mm Eta/320i rods, 325i pistons and the pistons come right to the top of the block. Give the block a 5 thou shave to clean it up (which you would do anyway) and it's perfect. at 84/84 it's also perfectly square.

[liam012]

ideally you want the smaller webbed crank with the pre facelift high comp pistons?
is that correst? does the tu also allow for high comp pistons?

[Andyboy]

No because the compression will be too high unless you use 98 fuel I built one with early pistons and the cr is about 10.7:1 or something. Later pistons are fine and any crank will do for those.

[Ant]

the tu double vanos crank doesn't fit M20 blocks.

the centre webs catch on the inside of the block casting- no issue just relieve a bit....

biggy is, the later short skirt pistons on 130mm rods will still contact the crank counterweights, and there's nothing to be machined away to make the required clearance.

The OE B28 pistons are slipper style and actually pass through the counterweights to get around ths issue

My guess is the counterweights were "combined" to allow room for the trigger wheel to move internally and as a result all got 13% bigger(ish)

[BMracing]

There are 2 or 3 2.8 cranks. The first one has bigger webs that won't clear the bottoms of the early 2.5 M20 pistons but will clear later ones (i,e plastic bumper 8.8CR slugs).

Being a metal bumpered tech 1 sport, does that mean I have the higher compression pistons? I heard or read somewhere that they changed these in '86? Mine is Sep '87.

Max

[Ant]

Check the engine number dude

should read 84 6E for high CR bottom end, 84 6K for lower Cr mill

lower LHS of block, either base of dipstick casting or approx 150mm further back( normally late 6K )

HTH

[BMracing]

Cool, i'll have a ganders.

Cheers mate

[reggid]

Check the engine number dude

should read 84 6E for high CR bottom end, 84 6K for lower Cr mill

lower LHS of block, either base of dipstick casting or approx 150mm further back( normally late 6K )

HTH

don't you mean 25 6k ...... and 25 6E ......

[StuBeeDoo]

Check the engine number dude

should read 84 6E for high CR bottom end, 84 6K for lower Cr mill

lower LHS of block, either base of dipstick casting or approx 150mm further back( normally late 6K )

HTH

don't you mean 25 6k ...... and 25 6E ......

84 as in mm - ie bore size???????

[Andyboy]

Yes, 84 is on the side of the block.

[Andyboy]

the tu double vanos crank doesn't fit M20 blocks.

the centre webs catch on the inside of the block casting- no issue just relieve a bit....

Aaah, are you using a 320i block (bored out) or a proper 84 mm Eta block? The last TU crank I saw in an M20 block was a 2.5 and that fitted okay - but has a shorter stroke of course so wouldn't have any issues.

[gorgeee]

how difficult is it to fit the double vanos crank?
does anyone do the machining thats required as me and my mate are both doing this so may be easier to get the machining done and the spacer made from the same place?

[DanThe]

pm sent regarding crank machining gorgeee

[ed325i]

pic of the spacer

[gorgeee]

thanks for that dan
just hope its all fairly straight forward
now gotta get the heads on ebay as we got 2 complete m52 engines

[Andy325i]

thanks for that dan
just hope its all fairly straight forward
now gotta get the heads on ebay as we got 2 complete m52 engines

Are you buying in bulk?

[gorgeee]

nah just me and a mate both wana carry out this conversion
he has a touring and i want to do this to my sport
i see you have a 24v 2.8 in your e30,we're both not ready to go through as much with wiring and the rest of it

[Andy325i]

Don't be put off by the wiring! Thats the easy bit (at least for OBD I) not sure about OBDII yet but Ste will be able to advise you. You know you want to drop the M52 in. They go very well

Andy

[DanThe]

Twin cams is the way forward

[Turbo-Brown]

Trying to get my head around the crank we all want!

If the pistons weren't an issue because you were having them made to suit, would either the TU or the non-TU crank fit?

And does the TU crank just have a single counterweight per throw or a double as per the say the M20B25 crank?

Cheers!

Alex

[march109]

Alex I'm also reading it seems about 10 mins behind you, from what I can see andyboy reckons the TU crank can be used ;

M52 TU twin vanos. This one has a TDC trigger wheel bolted to the rearmost crank web. It can be unbolted and thrown away if you want, and it fits an M20 block fine.

And from what I can tell Ant reckons it can't withought some machining as well ;

the tu double vanos crank doesn't fit M20 blocks.

the centre webs catch on the inside of the block casting- no issue just relieve a bit....

[Templ8e30]

Trying to get my head around the crank we all want!

If the pistons weren't an issue because you were having them made to suit, would either the TU or the non-TU crank fit?

And does the TU crank just have a single counterweight per throw or a double as per the say the M20B25 crank?

Cheers!

Alex

The TU crank has 2 counterweights per pot, the outer 2 counterweights are smaller than the rest though.

If you use the 325i conrods and custom pistons either crank will work.

The TU crank contacts 3 parts of the M20 block, either side of the oil breather box and the casting for the rear auxiliary shaft bearing, both are easily ground down a couple of mm with a dremel or die grinder as I did.

I have a TU crank here that I'll be selling, Im not going to save up for the next 6 months for a set of custom pistons. Yours for £50 + post if you want it ?!.

Cheers,

Iain T

[HairyScreech]

will the m52 2.8 tu pistons not work then? as that would cure the piston contact problems.

[Turbo-Brown]

PM Sent about the crank

[Templ8e30]

PM replied Alex

Cheers,

Iain T

[JazzMan]

I've starting building a 2.8 and have a question for those that have built one before:

The pistons come up slightly further with the M52B28 crank / M20B20 conrods / M20B25 pistons installed over stock:

Stock TDC


M52 crank TDC


Is this going cause any clearance issues with the head? Should I order a thicker head gasket?

[Ant]

what is the deck to crank c/line measurement Patrick ? ( should be 206mm, or 206.5 on 27E blocks )

the pistons should be 0.5mm lower in the block than the stock B25 crank and rods.

I've assumed you carried the pistons over same for same ?

[reggid]

Ant i think your right to question whether the pistons are the same