325is engine re-build questions

markdas · 01-10-2012, 04:14 AM

Some general areas I could use anyones advice on......

Im stripping down our 325is engine (this is fitted to an endurance race car) with the intention of re-building with new rings and bearings etc. The compression had dropped from about 190psi per cylinder to 165psi over the course of 6 12-18 hour races but the internals are spotless and so far all seem good with the old bearing shells, piston rings and crank.

I was going to rough up the cylinder glaze a little with a honing stone device for a power drill....how much de-glazing do you suggest? Also, the pistons are pretty clean except for a coating of hard black bulid up on the tops......should I carefully remove this, especially around the valve intrusion areas and would a soak in fuel and a wire brush be okay?

When removing the crankshaft I obvious had to remove the front seal housing (after figuring out the crank nut has to come off)! with that housing is an oil pump drive shaft and another seal.....I can't seem to find that seal listed anywhere in the parts catalogue? can anyone help with that? I have a new crank front and main seal on order, an engine gasket set, rear main seal etc.

Are there any basic checks I can do on the oil pump itself, it seems fine and we are getting 40-50 psi of pressure when running the car (except left handers when is drops - so a baffle kit is going in this time)!

thanks in advance

Mark

markdas · 01-10-2012, 04:24 AM

forgot to add these for interest

markdas · 01-13-2012, 04:40 AM

De-glazed the cylinders last night and started the re-build, I have come up against a problem with the main bearing shells not being the same as the ones that were in there.......got a support help request in with Waynes folks now!

markdas · 01-13-2012, 04:42 AM

The outer two shell halves are the originals that came out.

The one in the middle is the shell that needs to fit into the main bearing cap. The problem is the original shell has two locating tabs and the new ones only have one, wider tab that won't fit into the groove one the bearing cap?

markdas · 01-13-2012, 04:44 AM

Crank removed before de-glazing

HPMotors · HPMotors's Garage

Great Pictures! Looks like a fun job. What series you run your car in SCCA? NASA? We've been running SCCA for a bit, but stopped doing long enduros a few years back. Loads of fun but seemed a bit hard on the cars. We've got a little series here called the Carolina Cup that is only 45 minutes. Really not much longer than our lap races but great fun.

Curious as to the history of the engine. Is this a rebuild off of a previous rebuild or from stock?
What were the bore dimensions? ie, how much wear? You say you used honing stones to break the glaze? Personally, I like to use what I call a dingle berry brush - looks like a small chimney sweep brush with abrasive balls at the ends of the wires. Do this with an up and down motion to get the 45 degree pattern that is needed to get the rings to seat. Wash and flush thoroughly with HOT water and soap/degreaser. VERY important step. Not sure if a stone is the best thing to use? I believe a hone is primarily used to alter bore dimensions slightly. The balls on the brush only touch a small part of the bore at a time, so does a better job of breaking the "glaze".

While I've built many engines over the years, I've never put a bimmer six together - got two 325i engines I'm about to do though. Seems fairly obvious that the bearing shell can't go into the bearing cap. Fairly normal for one bearing to have oil holes/grooves and the other not. Not normal (in my experience) for it to change locating tab styles.

My suggestion would be to take the parts to your trusty performance machine shop and have them magnaflux the crank, polish it and figure out what bearings you need. I think it a must to fully check out the crank - especially since you have it apart anyway! It is probably fine, but with the magnaflux check you will be sure. The polish is more than grins and giggles - will prolong your new bearing life. While I have mikes and calipers, those machine shop guys have the best stuff and do it all the time - always feel better to have someone checking behind me.

Henry

markdas · 01-13-2012, 08:43 AM

We race 24 Hours of Lemons!

Great fun and really hard on the car......we've done 7 races now, only one of them was a complete 24 hours non stop, they are usually 8-9 hours on day 1 and then 6-7 hours on day 2.

We have to do it all on the cheap as the car has to be valued at $500 (not including roll cage, safety gear, brakes, etc).

So no chance of professional crank grinding and polishing, just a good clean up and re-fresh!

markdas · 01-13-2012, 08:46 AM

To my knowledge this is the first time the engine has been apart, there was still some faint signs of the factory hatching.

I used the honing stones (3 of them on sprung arms) on a slow speed for about 15 seconds in each bore.

markdas · 01-19-2012, 06:51 AM

Had a slight delay in the re-build due to ordering main bearing shells for a 1987 engine and this is a 1990. So the bearings have different locating tabs......Pelican service and parts folks came to the rescue though!

So with that sorted I got the crank and pistons re-fitted and next step is to fit a crank scraper/windage plate and sump baffle, which is proving tricky as its fouling on the oil pump!