rod bearing replacement question's?

[custom e30]

i have a 1988 325i convertible with the m20b25 2.5L, my questions

1. what causes dry start?

2. after it kept dry starting, the engine began to knock, now i am attempting to replace rod bearings only by removing oil pan and going from there, so my question is do i have to check the gap or can i just follow the torgue spec?

3. where can i find a after market high flow oil pump for a decent price?

note. engine is knocking really bad, any damage that would prevent bearing from fix be problem?

note, i removed the b2.5L head and replaced it with a b2.7L head, is this a problem

i have searched forum for hours andno luck. thanks...

[lennon]

replacing the b25 head with b27 head is bad but wouldn't cause knock. why did you do that?

[nando]

I bet it's knocking because your pistons are smashing into the head...

[custom e30]

well i needed a head gasket swap, it was my first time and i learned the hard way to make sure to set the timing of the block and not to forget to time the head, when i tightened head down it bent the valve and broke the rocker, i paid 50 bucks for head out of the yard, im about to fix head and port after i fix bearing...

[custom e30]

i need to know much as possible, i cant screw this up

[nando]

well I would pull the head and make sure that isn't your problem.

the eta head has a much smaller combustion chamber. The pistons are also shaped different - they are flat. the B25 pistons are domed and are meant to come up into the chamber. My gut feeling is the B25 pistons are hitting the B27 head. It could sound like rod knock, or it could actually cause rod knock as the force has to go somewhere.

[custom e30]

what about the pump, is there a better option then stock? also is the pump most likely the reason of the dry start?

[SpecM]

what about the pump, is there a better option then stock? also is the pump most likely the reason of the dry start?

dude you're not listining

the head you put on the car is the problem. Even IF (big IF) the pistons aren't touching the valves, you just created an engine with like a 13:1 compression ratio (guess at the number, really), so at the very least you are hearing pre-detonation (spark knock).

the pump is probably fine, many 200,000+ mile m20s have good oil pumps. there aren't any "better" ones that I have heard of. and ALL cars have "dry starts" to some degree, it is inevitable in car that is turned off for more than an hour. Get a good oem (mahle) filter, it will help with the oil pressure issue a good bit.

[kishg]

you don't need a high flow pump. you do need the right head though :)

[custom e30]

ok im buying everything now to do that.... if/when i change my rod bearings, do i need to use plastic gauge or can i just do the turque spec out of the book,

[jlevie]

Ideally you'd use a micrometer to measure each bearing at several points and compare those measurements to the wear limits for the crank shaft. If the engine spun a bearing or one failed from lack of lubrication the crank needs to be removed and polished even if still within spec. And if one of the rod bearings went it is almost certain that there will be damage to the mains. Meaning that they should also be replaced.

[custom e30]

ok so you know what my problem is from reading above,

so i started the car and started to drive around the block to get it to the ramps in the back of the house,

all the sudden i heard a noise sounding like the engine has marbles in it, and then it just died and i rolled to a stop,

i tryed restarting the car but it sounds like motor is locked, but if i wait 10 minutes and then try, the engine will role over 1 time and stop, then if i try to start again it gives the idea that its locked again, what i mean is the started hits and stops and the motor doesnt crank at all.

any ideas on whats going on?

[SpecM]

any ideas on whats going on?

really dude?

re-read the thread

[Adrian_Visser]

I have an idea.


You toasted your engine.



/end

[custom e30]

ok so whats toasted? cuz thats not helping, im all set to replace rod bearing and swap original head back in, is that a waste of time now