'88 325is M30 street car-->S54 -->S50 -->M54 Enduro Race car

[MR 325]

Good call on replacing those bearings!

[wazzu70]

Yikes on the bearing. Glad you decided to replace them!

Engine bay looks good too!

[gills]

wow, very good call. The fact that the rod caps are practically staring at you in the face with the pan off and on an engine stand, it'd be stupid to overlook them. I'll be sure to do them now.

[The Dark Side of Will]

Well, thanks to Nando for suggesting I replaced my rod bearings. I was not going to do it, considering my engine has relatively low mileage (under 70k). But this was the rod side of #6

All the way down to copper! Caught that one just in time.

Do S54's run high oil temps, or not get enough oil to the rod bearings? Why do they (and S85's and S65's) chew up their rod bearings so quickly?

I'm aware that the reversal loads at the top of the stroke at 8200 RPM are pretty phenomenal, but BMW also knows this and should be able to make sure those bearings get enough oil.

[nando]

High rpm and the rod jourbnals are a little on the small side.

[The Dark Side of Will]

NASCAR R07's (and Hondas for that matter) run Honda journals to 9,000 RPM.

[nando]

they're usually square or undersquare, the S54 is oversquare. and the S54 rod/stroke ratio is pretty low.

[tinkerputzer]

Wow nice catch. Are s54 main bearings 180° or 360° oil groove?

[nando]

Its the rod bearings that usually go bad

[tinkerputzer]

Yes i'm aware lol. Was just curious since the main bearings feed the rod bearings.

[The Dark Side of Will]

they're usually square or undersquare, the S54 is oversquare. and the S54 rod/stroke ratio is pretty low.

S54's 87x91, right? So it's undersquare.
Hondas have "bad" rod ratios also, and they aren't as famous for chewing rod bearings... at least not that I've heard.

EDIT: Higher rod ratios would certainly help, though.

[wazzu70]

S54 bearings are pretty skinny for the loads they see at high RPM.

[LJ851]

The rod ratio shouldn't affect the cap side of the rod bearing.

S54's 87x91, right? So it's undersquare.
Hondas have "bad" rod ratios also, and they aren't as famous for chewing rod bearings... at least not that I've heard.

You haven't even seen the cap side rod bearing ?

There is one aspect affecting bearing life left unmentioned and that is piston/rod weight.

[The Dark Side of Will]

Woops... misread the post and was thinking it was the cap side. My bad.

[blunttech]

Jonathon... Rod bearings and rod bolts came in at 430pm Friday Ill ship Monday am