Strength of the 2.7 vs 2.5 bottomend?

[nando]

maybe a few ten thousanths, but not a few tenths of an inch

the people I've talked to about BMW cranks (like Jim from MM) warned that even polishing too deeply could take out the hardened layer, so I really doubt grinding to an oversized spec would leave anything behind.

[Hallen]

grinding down BMW cranks is not worth it at all

you will have to have the journals nitride hardened again, which isn't cheap. and then having to deal with oversized bearings and other nonsense.

it's far easier and cheaper to find another crank in good shape.

I would agree... unless your crank is already ground down.

Also, the hardening goes down a couple of 10ths so you aren't going to need to do the nitride hardening again unless you want to. Why else would they even offer oversized bearings? The factory couldn't expect people to reharden the crank. If there is something in the manual that I missed, which is altogether possible, I'll be more than happy to be corrected here. Knowing BMW, if the crank had to be rehardened, they wouldn't even give specs; they'd just tell you to buy a new crank.

[nando]

grinding down BMW cranks is not worth it at all

you will have to have the journals nitride hardened again, which isn't cheap. and then having to deal with oversized bearings and other nonsense.

it's far easier and cheaper to find another crank in good shape.

[Hallen]

If the crank shaft doesn't have score marks, you need to measure each journal to check for wear before fitting new bearings. That is several measurements with a micrometer around and across each journal. If worn, the crank can be re-ground and over sized bearings used.

Exactly. Make sure the oil passages are clear.

There are three different bearing sizes that you can use. The cranks can be ground down to two undersizes. If you do that, I would suggest aiming for the lower end of the size for whichever undersize you end up doing. A little loose on the bearing (within spec) is better than tight.

You'll find the double oversize bearings for the rod journal a biotch to find in a complete set though. If you have to buy them separately, they run about $240 where a kit with all the bearings runs about $50 for the standard and single oversize. I guess not a lot of people go with the double size. A used crank will run you anywhere between 100 and 250 depending on condition, etc.

[StereoInstaller1]

I turn my 2.7 crank past 7000rpm on a daily basis

being junkyard engines they may have already been dead when you got them, or very well near it. crank/rod bearing problems are pretty uncommon on the M20.

I was thinking the same thing. A quick survey would show just how reliable the M20 bottom end is.

I think the OP just has bad luck!

[nando]

I turn my 2.7 crank past 7000rpm on a daily basis

being junkyard engines they may have already been dead when you got them, or very well near it. crank/rod bearing problems are pretty uncommon on the M20.

[jlevie]

If the crank shaft doesn't have score marks, you need to measure each journal to check for wear before fitting new bearings. That is several measurements with a micrometer around and across each journal. If worn, the crank can be re-ground and over sized bearings used.

[Chuckcruzin1986]

I think this is the best advice

I would have at least done the piston rings and rod bearings while the engine's out. When the block was on my stand, front/ rear main seals;piston rings/rod bearings were done in like an hour?? Bad idea to put in a motor that you have no idea of. Could have at least pulled the oil pan and check if there were any play in the rods...

Justin

I am going to tear down one of the engines and build it as you have recommended. No more installing used engines.
Thanks
Chuck

[416stroker]

Whats up with all of the new retards. That ask questions and get there answers and feel the need to be smart ass pricks? ITs your driving 2.7 are tough my 2.7i took a beating
and it was a juckyard shortblock

[slo325i]

I blew two 2.7 engines in 2 weeks! Is it bad luck or should I be running 2.5 bottomends. I have not taken them apart but they both had over 200,000 miles and it was not the timing belt (new) but it seems like the main bearings.

The real question is: Strength of the 2.7 vs the 2.5...are they the same main bearings etc.???

Ideas?

Thanks
Chuck

I would have at least done the piston rings and rod bearings while the engine's out. When the block was on my stand, front/ rear main seals;piston rings/rod bearings were done in like an hour?? Bad idea to put in a motor that you have no idea of. Could have at least pulled the oil pan and check if there were any play in the rods...

Justin

[Chuckcruzin1986]

Learning to drive.......please help

I am ready to learn how to drive. Would someone step forward and guide me as to what to do? Should I keep the revs under 2000? Warm the engine for 2 hours before bringing above 2000? Maybe if I had an automatic trans it would help. Maybe I should hire a driver. Change the oil every 1000 miles? Remove my synthetic oil?
Ideas please?



Thanks,
Chuck

[slow e30]

Yeah, its not the engines dude, its you. learn to drive the car.

[mikegar]

5kwatson needs to learn how to drive too cause his shit blew up too...

[5KWattson]

you need to learn how to drive...

+2

[Jordan325iC]

You're just unlucky. There is no information at all that suggests that 2.7 bottom ends are any weaker than 2.5 bottom ends.