Building m20b25 to m20b28

[JC1974]

Have question if someone here can help me please? Have problem with weights on conrods. Pistons and "fingers" weight : 4x480g 2x478g conrods:4x606g 1x608g 1x604g have also one more kit conrods from other engine but those are totally different weights. Question is can i use one conrod which weight are 608g then i will have this situation : Pistons 4x480g 2x478g conrods 4x606g 2x608g and totally balance will be right are this opinion are correct? Ty all for any info.

[JC1974]

I mean to use one conrod from other engine.

[reggid]

grind 2g off the bottom of 608g rod and good to go. 2g is close enough

[JC1974]

Got more problems,pistons i have (3set off them) not fits seams i have 73,93 high but needs to be 63,63 grrr anyone knows where i can get those? Ø83,98 H63,63

[Gavt]

Low comp pistons fit fine and clear the lobes of the crank high compression pistons need the skirt trimmed off at a machine shop. The high comp give slightly better power due to the higher compression but has more issues with detonation with poor fuels and piston to valve clearance with big cams. All relatively easy to sort out if your machinist is any good with pistons

[Gavt]

And to answere you last post if you want the low comp ones eBay would be your best bet
I have a set of 320 con rods I'd sell if you need these

[Gavt]

Just realised you have these (conrods) as stated in your first post.

[reggid]

machine the piston skirts to clear

[ross_jsy]

Also keep in mind there are 2 types of b28 crank, one with larger counterweights. Even with skimming the pistons they won't clear (ask me how I know )

[jmc330i]

Also keep in mind there are 2 types of b28 crank, one with larger counterweights. Even with skimming the pistons they won't clear (ask me how I know )

Go on then, how do you know?
You could have the counterweights machined?

[reggid]

ive seen some yanks (they dont have the small counterweight cranks) just machine the low comp slugs until they fit, if you start to cut into the pin boss youve probably gone too far IMO though im sure some choose to run it anyway. yes you can machine crank and rebalance

[JC1974]

Can i get some answer wat cranck it's correct to use then?

[JC1974]

I'm using bmw nc38 1432277 cranck

[reggid]

http://www.e30zone.net/e30zonewiki/inde ... ding_a_2.8

my understanding this is the visual difference

[JC1974]

Seams I have wrong crankshaft ,how much i need to take of in mm from counterweights?

[reggid]

modify skirt as much as safe to do so then measure how much you need to remove

[JC1974]

Seams its 2mm to much but if I take of 3mm then think it's not save to engine go high rpm with it think to take of 5mm then it's safe . But better to ask who have done it before and know wat is best

[reggid]

you probably want about 2mm minimum clearance when all is said and done.

[JC1974]

Yup and ty for all info.

[JC1974]

2242898 are this crankshaft really from m52???

[ross_jsy]

Also keep in mind there are 2 types of b28 crank, one with larger counterweights. Even with skimming the pistons they won't clear (ask me how I know )

Go on then, how do you know?
You could have the counterweights machined?

I could have done, although machinework like that has to be done off island which is added hassle. But then an m30 came up so I stuck that in instead. Still got all the bits to build an m20b28 sitting in the back passage so maybe one day...