M20 B25 build......

[OnMy2ndE30]

I am sure this has been covered before, but I am having issues trying to find someone who has done a similar job before like this.

I have an 87 325i vert that i "think" has a slight rod knock. The valves clatter loudly even after I adjusted them, and there is minor sludge build up in the head. I have a friend who has a b25 lower end that came out of his track car that the timing belt snapped on. He is selling it to me for $50. He says it spins freely and wasn't damaged when the belt snapped. I was thinking about sourcing a used head from pick n pull out of a wrecked 325i and having it checked. I should be able to get all the parts, ie short block, head, timing belt, water pump, and gasket kit for around $200-$250 and put it all together myself. I am curious though.....the short block still has the cross hatching in the cylinders and none of them are scored. It has been in his storage shed for a few months. I am wanting to know if I tear it down to have the block hot tanked, can I re-use the crank and bearings as long as they aren't damaged? Installing new main and rod bearings is kind of intimidating to me and if there aren't any issues with the engine visually when I tear it down, should I theoretically be able to reuse everything?

[deutschman]

If you tare it down replace the parts. If you are good enough to take apart and put back together a head the you should be able to do main and rod bearings as well. Just take your time, do not rush ANYTHING, use lots of pictures, and have the right tools. Oh and work clean and organized. You should be fine.
You will kick your self in the ass later if the bearings go bad and you could have just replaced them while you were at it.

[jlevie]

Do not have an M20 block hot tanked. That will destroy the intermediate shaft bearings. They can be replaced, but not easily.

If you disassemble the block, have the cylinder crosshatch honed and use new bearings and rings. The crank must be measured and bearing bought that are the correct size for the journals. You also must check and adjust the ring gaps. If you don't feel up to doing this the right, leave the block alone. Just clean it and put the new head on.

[deutschman]

do not have an m20 block hot tanked. That will destroy the intermediate shaft bearings. They can be replaced, but not easily.

If you disassemble the block, have the cylinder crosshatch honed and use new bearings and rings. The crank must be measured and bearing bought that are the correct size for the journals. You also must check and adjust the ring gaps. If you don't feel up to doing this the right, leave the block alone. Just clean it and put the new head on.

+1

[OnMy2ndE30]

Thanks for the advice guys. I do appreciate it. Would there be any issues if I took the caps off the main and rod journals just to put some assembly lube on them to avoid a dry start condition? I know you all are probably beating your heads against a wall asking WHY????? I am not that comfortable messing with precision components like replacing the bearings and to have the short block rebuilt is out of my price range.

[nando]

you can easily prime an M20 oil pump with a drill. on the drivers side there's a "cap" where the old distributor drive used to go. pull that off and the oil pump drive gears inside, you can fit a hex shaft into the pump and prime it before you crank the car over.

[jlevie]

Thanks for the advice guys. I do appreciate it. Would there be any issues if I took the caps off the main and rod journals just to put some assembly lube on them to avoid a dry start condition? I know you all are probably beating your heads against a wall asking WHY????? I am not that comfortable messing with precision components like replacing the bearings and to have the short block rebuilt is out of my price range.

This is pretty much an all or nothing proposition. Unless you intend to replace rings (or bearings) there is no point in removing bearing caps. If you do want to replace rings, then you will have to pull the crank to have the block honed. In which case you need new bearings (matched to the journal dimensions).

Either leave it a lone, or do it right.