Rebuild or not: used BMW engine?

[xvxax]

I am going to toss this question out here despite the fact that not many of you are very familiar with BMWs.

I recently bought a stock 2.5l m50b25TU out of a 1994 325ic with 86,000 miles on it to return my car to STX, an autocross class I don't get absolutely dominated in. My hope is to run in that class next year (when not in the STi) and eventually move up to DSP or SM again long term. My donor motor was mated to a 5 speed, but it was basically driven around 2-3,000 miles a year in Florida until it was moved to PA for 4 months and totaled. The motor has probably lived a very gentle life.

Let's assume the compression is fine because the motor comes with a 15,000 mile warranty, I will verify this, but I basically want to put this motor in my car and never touch it again. What kind of things are must do while the engine is out for a car that will see about 90% track time? Oil pump nut kit, oil baffle, water pump, valve cover gasket, rear main seal, will all be done, but should I pull the head and put a head gasket and studs in it because it's so easy? Should I deck the head while it's off? Replace the weak early e36 valve retainers? Replace the crank bearings? Am I forgetting anything else obvious? Basically this build could cost anywhere from $200-1,500. I'm not sure where to draw the line because everything is so much easier with the engine on the stand. Time is basically no issue, I have until March to put the engine in. I just don't want to throw a bunch of money into this motor unless I need to. What say ye?

[D_Eclipse9916]

NEVER take a head off that is already sealing properly. I would say replace the rod bearings and hell the main bearings if your feeling ambitious (although very rarely you have to worry about mains till over 200k miles of hard use). I dont know how expensive M50s are but if it was less than $1200, I wouldnt even bother with the retainers, unless its a huge issue that the car HAS to make events. I say run it how it is. If it were an S52/S54 because of the expense of the original motor I would do the retainers (which of course dont have issues in those cars).

Ive learned through fellow bmw guys, fellow friends, and personal experience that its much harder to get a headgasket to seal nearly as well as the original one did and to last as long without decking both the head/block. And most average machine shops cant even get it as straight as the factory, nor is there a way to torque the head like the factory does it.

[JustinG]

Jesus....a triple tap!

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[.RJ]

^ what he said. I'd probably just replace the clutch and water pump, and only replace what is leaking. Otherwise, leave it all alone... i.e. if the rear main isnt leaking, dont touch it.

[D_Eclipse9916]

dayum, dont know what happened there.

[xvxax]

I meant rod bearings. My fault. I probably won't touch the crank bearings, but I'll check the wear on the crank when I pull the pan, probably this weekend.
The motor was less than $1,200, but I would be bummed to drop a valve in at any time because:
1. I would lose the motor.
2. I wouldn't be able to get home without a trailer, which I may not have next year.

I think a lot of people forget that the 325s were plagued with the same crappy retainers that the m3 got, but I still don't hear about as many 325s losing retainers on track cars. I don't know why that is. RRT has a tool to pressurize the cylinder so they can replace the valve retainers with the head still attached. Might just have the retainers replaced by them... for $100 per hour.

Were the people who had issues with HG issues replacing worn out parts? Like a HG that had failed? Were they using the original head or a spare? Why don't replace the rear main seal? Curious what the situation was.

The rubber in the rear main seal is 17 years old. Seems silly not to unless I'm missing something.

I think I've been talked off the ledge on a full build. Probably just do basic maintenance, check the rod bearings, etc. Even with the cheap motor, my budget has already passed $3,000 for an almost legal STX build, so I may continue to live my life 60 seconds at a time.. Don't let anyone tell you cars are cheap.

[CaptainHenreh]

RRT has a tool to pressurize the cylinder so they can replace the valve retainers with the head still attached. Might just have the retainers replaced by them... for $100 per hour.

Don't need this. You can put a soft rope in the cylinder, and rotate the crankshaft so that the rope holds up the valves.

[.RJ]

You can use the attachments from a compression tester (assuming you have an air compressor) to hold up the valves. Or soft rope.

There's no harm in replacing the seals, assuming you have whatever tools you need to put the seal in straight and in the right place. It can be easy to get wrong on some motors, if specialty tool is required to R&R and you dont have it.

[D_Eclipse9916]

I think a lot of people forget that the 325s were plagued with the same crappy retainers that the m3 got, but I still don't hear about as many 325s losing retainers on track cars. I don't know why that is. RRT has a tool to pressurize the cylinder so they can replace the valve retainers with the head still attached. Might just have the retainers replaced by them... for $100 per hour..

...M3s only had crappy retainers on the 95s. And even then, ive heard very little (especially in an autox environment) about problems like that. People on the forums tend to bitch and complain and find wayyyy more problems then there are.

I wont say it wont happen, but for me I wouldnt waste the time and money with a $1200 motor that are known for being dead reliable on track anyway. That said, valve seals arent a bad one to replace, rod bearings, and if your doing valve seals, you might as well do the retainers. DO NOT take off the head.

[.RJ]

Valve seals are also easy to damage on install.

I never had any problems removing honda heads, but apples and oranges, and I never took one off that I didnt have to.