Possible rebuild of an S54 in an E86 Z4M Coupe

[grannyknot]

Hi guys,
Hopping I can ask some advice from the engine builders here.
The car is an E86 Z4M coupe, 91,000mi on the S54 B32 engine, just bought the car last Oct. with almost no history. It appears to have been well cared for but I would like to start from a known baseline so will be replacing all wearable items.
The engine pulls well and sounds healthy, the compression numbers are good so I'm not worried about the pistons and rings. I don't know if it uses oil yet as I haven't driven the car much.
However, I don't know anything about the condition of the conrod and main bearings so I think they need to be replaced.
I have also purchased all of the timing components to be replaced, water pump, thermostat, etc.

So here is the question, since I'm in there anyway, should I just have the cylinders and rings done as well or just leave well enough alone? I hate the thought of messing around with such good numbers.
I have rebuilt many engines before including an S54 from a 2001 M3 with spun conrod bearing so I'm comfortable with whatever I find.
Thanks

[maupineda]

Leave the pistons and rings alone, a bad Job there would leave you in a worse place. Rod bearings and wearable items you feel like changing and your are good to go

[cobra]

I wouldn't consider any of the routine maintenance items to include pistons and rings as a "while you're in there" since the head shouldn't have to come off...

These engines don't typically burn oil. I would just replace the 100k mile stuff and drive it.

[grannyknot]

Thanks guys, that's what I was thinking too but needed to hear it from someone else.

[bigjae46]

I haven’t ever heard of an S54 having main bearing issues. All of the mains I’ve pulled from S54s look like dull silver with some spotting.

Same thing with rings. Haven’t seen or heard or a piston ring going bad.


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[grannyknot]

Just to close off this thread, here are the pics of the conrod and main bearings when it was torn down, not bad shape at all but it was worth checking.

[bigjae46]

Just to close off this thread, here are the pics of the conrod and main bearings when it was torn down, not bad shape at all but it was worth checking.

The mains look typical of what I've seen. Did you use all yellow main bearing shells?

[grannyknot]

The mains look typical of what I've seen. Did you use all yellow main bearing shells?

Good question, they weren't BMW, I'll have to have a look at the order.

[tlow98]

The mains look typical of what I've seen. Did you use all yellow main bearing shells?

Interesting that you mention that. I know BMW says to start with yellows, measure and assess/change from there.

Then Lang says they start with green and adjust in either direction from there.

Not a lot of knowledge has been printed out here on the webs with personal experience. What are your thoughts on this?

my crank had a lot of green markings, and then it was pretty hard to tell the difference between the white/yellow markings with the oil patina over time.

[grannyknot]

Glyco main bearings is what I used, the clearance for all of them was about .030mm so right in the middle of the tolerance.
The side bearings on the # 6 main were pretty tight so had to shave a bit off to get the axial end play just right, 600 then 800 grit wet on a granite flat.

[maupineda]

Glyco main bearings is what I used, the clearance for all of them was about .030mm so right in the middle of the tolerance.
The side bearings on the # 6 main were pretty tight so had to shave a bit off to get the axial end play just right, 600 then 800 grit wet on a granite flat.

Was your engine burning oil or making noises? why did you have to rebuild it?

[digger]

I don’t get why you tear down basically the entire engine for no reason. Rod bearings yes but the rest only if there is evidence to do so or if you doing a serious high performance build

[grannyknot]

Was your engine burning oil or making noises? why did you have to rebuild it?

I got zero history with the car when I bought it last year with 91,000 mi on the clock, the compression was excellent but I had to see what was going on with the bearings so just decided to overhaul everything in the engine except the pistons and rings. Now that it's been torn down down I can see that it was very lightly used, had lots of oil changes, very clean inside and not much wear.

[tlow98]

I got zero history with the car when I bought it last year with 91,000 mi on the clock, the compression was excellent but I had to see what was going on with the bearings so just decided to overhaul everything in the engine except the pistons and rings. Now that it's been torn down down I can see that it was very lightly used, had lots of oil changes, very clean inside and not much wear.

The auto-obsessed person in me loves this.

[grannyknot]

I don’t get why you tear down basically the entire engine for no reason. Rod bearings yes but the rest only if there is evidence to do so or if you doing a serious high performance build

If you look at tearing down and rebuilding an engine as a difficult, arduous task then I can see why you might say that but for me it is great fun. I like knowing every component is in the best possible condition. I've torn the car down to the last bolt at the moment while I refinish every surface, replace every bushing, bearing, gasket and seal.
The car was in excellent condition but considering its age and mileage it is a perfect time to refresh everything while parts are still available.