Motor rebuild

#1

Okay guys I have not started a thread in a while because the car is pretty much sorted out at the moment. I did however come across a pretty sweet deal which I am picking up Sunday:cheer: . I am getting two complete blocks, and a rebuilt head maybe 2 heads:P . The motor in my car is strong, but I need to sort out a couple minor oil leaks, and I don’t know how many miles are on it. My plan is to rebuild one of these motors and swap it into my car so I don’t suffer any down time with the car. My question is what all do you guys think needs to be replaced while I have it on the motor stand. Both blocks came out in known good running condition. Do you think I could just replace all gaskets on the block, and bolt on the head and put it in the car, or should I completly rebuild the block while I have the chance.

TIA

Greg

#2

Greg - I am sure others with weigh in, but we just had the same questions a few months ago. At the advice of our local BMW/e30 guru, Dave Pallister, if the bottom end does not have any knocks suggesting bearing problems, just get a full gasket set, rebuild the head (cost us $250), and put it back together. I would consider putting in a crank scraper (Carr), which we did, if you have it on the engine stand. I can’t imagine doing this while the engine is in the car. It requires a lot of filing, fitting, to get it right. Remove the screen on the oil pump and flush it out. Consider having the injectors cleaned (cruzinperformance.com - Rich). They are a pain to replace with the intake manifold on. Also consider new clutch, pressure place, TO bearing. Best of luck.
Ed

#3

Good stuff. I’m thinking about recycling an old motor too. It would be fun to do this while keeping the current engine in the car. In addition to the things mentioned above, I’d like to overhaul the bottom end – cylinder bore, pistons/rings/rods, align hone the mains, etc.

Aside from acquiring a donor car with engine, anyone know where I can find a used M20B25?

#4

^ where are you?

I would love to rebuild the whole bottom end also, but I have priced out the parts needed to completely rebuild the bottom end with a re-bore, and new pistons, and I think I am going to try and reuse the pistons. Only problem is the block I have is from a car that broke a timing belt, were valves hit pistons.

Can I reuse these pistons?

#5

You’ll have to pull the head and physically check the pistons.

As a point of reference, I fully rebuilt my head and swapped it onto a 180K bottom end with new main bearings and put down 150rwhp and 155 rwtq.

#6

The head is already off. you can see where the valves hit pistons, but they look fine. I can probably clean them up and reuse them. What do you think?

#7

I don’t think I would use those pistons without having them Magnafluxed. Of course, you may as well get new ones for that kind of effort. :unsure:

I live near Gaithersburg, MD, if anyone knows where I can find a complete motor in decent condition (ie, not frozen not cracked

#8

Scotty wrote:

[quote]I don’t think I would use those pistons without having them Magnafluxed. Of course, you may as well get new ones for that kind of effort. :unsure:

I live near Gaithersburg, MD, if anyone knows where I can find a complete motor in decent condition (ie, not frozen not cracked[/quote]

your probably right just trying to pinch pennies. I haven’t put it on the engine stand yet, but I hope to get it up there this weekend and tear it apart. I will definitely have the pistons checked out, but I will probably replace them. This will be my first motor build so I will have to learn as I go.

#9
#10

JP - just curious. How did you do your bearings? Did you have the motor in the car? From what I understand there are different color codes for bearing sizes? Did you mic the journals to get a reading and then order them from BMW?
I assume you did not resurface the crankshaft?
Thanks, Ed

#11

The previous owner of the motor did it. He had it out of the car. We’ll see how long it lasts. . . . but for only $200 for the complete motor I couldn’t pass it up.

#12

For what its worth I did mine in the car, bought it with a bad head gasket so I had the head rebuilt and while I had everything apart pulled the pan and popped the pistons out, new rings and bearings (main and rod), and a new oil pump. I had a 240k motor and the bearings were into the copper (so I was happy I took the extra steps), I ordered std sized replacements, 25k of street driving and 10 hpde’s last year and no problems.

Once you have the head off there isn’t much else to do to get the pistons out, you can get the mains with the crank in as well, just have to slip them around once you have all the caps off