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Dear Peter,

I just finished reading your work on First Five and seems you do know a lot about BMW's.

I just finished (with my Mechanic Aldo who is extremely capable) rebuilding the upper side of the engine changed the guides,seals and valves all from Walloth in Germany, still have to change the rockers and shafts there.

The cyl have a minimal play but will try next to rebuild the lower part of the engine. Aldo (Mechanic) wants me to get him new pistons +0.50 and the rest of the shells for piston and crank +0.20 and start from there. Another option would be to leave the same pistons and fill the cylinders locally at a very good machine shop.

I take it that for my engine I will have to look for parts from the E3 E9 sharing I believe the very same 2500 engine. Otherwise and except for the injectors all my parts come from the 1975 530 US version...

What would you suggest?

I'll chime in here as I've been thru a number of M30 engines over the years.

BMW crankshafts are very rugged and hard, they rarely require regrinding, and it's not something I would do unless there is damage, it's not something you do just because you are doing the engine. An oil pump or maybe oil pump gears, yes, but the cranks hold up very well.

Pistons and the block. I have seen both blocks and pistons with significant wear requiring boring and or new or replacement pistons. I've also seen many with very high miles and modest wear that I've reused. I'll have to try and think in metric as we usually use inches for clearance here, but I'll give it a go. Stock, piston clearance should be around .0015" or .038MM. But I've put together engines with more like .006-.007" or .18MM with no problems at all. Quiet, long lasting engines.

I don't recall what your specifics and regulatory requirements are, but you can put a 2.8 crankshaft and pistons in what was a 2.5 engine without any modifications other than just installing them.

Thanks for your input.

Would it be better to fill the block to make the current pistons with regular rings fit the best tolerance?
Or would it be better to go find new pistons with an extra 0.50 + diameter to fit into actual cylinders ?

I would have to look around for a new set of pistons 0.50 + probably from an E3 or E9 with a 2500 engine. Didn't know the 2800 cylinders could be used but rather stay with original configuration.

I understand the crankshaft is still ok only the shells at 0.20+ with eventual machine refitting are ok.

New cylinders with 0.50 + are hard to find and very expensive.

What would you suggest?

Thanks!

Would the work on a 525 E12 M30?


link:

http://cgi.ebay.com/ebaymotors/ws/eBayI ... K:MEWAX:IT

No, those would not work on a 2500 engine, they are for a 2.8 which has a longer stroke so they would be about 4MM too low below the deck which would give you a very, very low compression ratio, I'm not even positive it would run. Don't forget if you want to stay at 2.5, you can use E28 pistons too, there was a 525i that was a 2.5 M30 engine they used until production stopped in 87 or so. I think they would be slightly higher compression probably 9.3:1 instead of 9:1, but I'm not sure on that. And being E28 they might be easier to find. Don't confuse the 525i with the 525e, which was the M20 small 6, nothing interchanges with them.

Found the following: (If this is what you mean) but this would complicate things even more...

S 1968 - 1981 2800CS

528I

Bavarian
MaxSil™ Pistons / 2nd oversize / 86.47mm (+0.50) Bore Clearance 0.0015" Wrist Pin Standard


Link:

http://store.bimmerworld.com/maxsil-rep ... p1129.aspx

Same thing, it's a 2.8 piston and it won't work with a 2.5 crank. Not unless you get a 2.8/3.0 crank to put in it, and yes, then the combination will work.

The following are strokes for M30 engines
2.5=71.6MM
2.8=80MM
3.0=80MM
3.3=86MM
3.5, early=84MM
3.5, later=86MM

The rods are all the same so you need to match pistons with the correct crankshafts.

And since the pistons are very expensive I wanted to double ck with you.

Found the following parts that are actually the pistons for the E9 2500 Coup Euro

And for the E3 Sedan 2500 Euro and US

But I can not find the listed for the 1974 E12 525

01 MAHLE PISTON 86,47MM (+0,50)
6 08/1968 02/1977
11251261989



I will also need the:


BEARING SHELL 47,750MM(+0,25) X

11241258430


And the:


BEARING SHELL RED 59,75MM(+0,25) X

11211261043

(They show them "red" and "blue" in the BMW catalog and I do NOT know the difference, do you?


Do you think they fit my car?

the new pistons for my car are:

MAHLE PISTON 86,47MM(+0,50) 6 08/1976 11251263432

and that the size fits perfect just the top was changed a bit for better combustion.

What's your opinion?

I would hate to make that investment and find out they didn't work...

Best

The piston I believe will work, the combustion chamber stayed the same from the start of M30's until the M30B35 engine in the late 80's. Pistons for an E34 might not work, but I think by then they were using M20s for 2.5L engines.

On bearings, I have seen red/blue listed in the factory literature, but I've always bought aftermarket in the nominal size and had no problems. It's good that BMW offers and referrences the small differences in standard sizes, but it's not really necessary. On the other hand, I'm also of the opinion that it's rare that one can build an engine as good as the original factory one. They use good quality parts, all of them, and often match things closer than we can. And everything is new. Moving to the third hand, the engine I built for the E28 I used to have was all used parts, a crank with well over 100K miles or 200KM on it with just new standard bearings, slightly used pistons, assorted ages of other parts and I put 175K miles (280KM) on it when I sold it and it was still in good shape. I sometimes had to add half a quart of oil between changes. A long winded way of saying don't get hung up on things being perfect.

Thanks Mike, you are correcto!

sorry late to this party but Mike W is the person I would ask those question of.