Piston ID Help

[jimbojames]

I'm in the middle of a rebuild on an engine I don't know the history of. Having totally disassembled the engine, I have found that it appears to have be rebuilt before. If I understand correctly, stock cylinder bore would be 89 mm. Mine average 89.764. The pistons are Mahle brand and are marked with 89v59. After a quick google search, I can't seem to get a consensus on the correct bore for these cylinders. See attached snip from Mahle catalog PDF, which I think is related. How do I know which part number it is? I can't find the seven digit number anywhere on them.

[TobyB]

I thought at one point a 'third' oversize of 89.75 was available, but I am alone in that belief-

others who know more than I say 'nuh- uh'.

 

I do know that now, you're looking at an 89.97 for a 90mm bore- if they ever were available, they certainly aren't now.

 

It's possible that was a 'factory only' oversize, as I've only ever seen the the 89.22 piston in BMW rebuilds.

 

I think you're going to have to bore it if you want new pistons for it.

 

sorry,

 

t

 

Edited January 1, 2018 by TobyB
mistyped 88.22

[Simeon]

4 minutes ago, TobyB said:

I thought at one point a 'third' oversize of 89.75 was available, but I am alone in that belief-

others who know more than I say 'nuh- uh'.

 

I do know that now, you're looking at an 89.97 for a 90mm bore- if they ever were available, they certainly aren't now.

 

It's possible that was a 'factory only' oversize, as I've only ever seen the the 88.22 piston in BMW rebuilds.

 

I think you're going to have to bore it if you want new pistons for it.

 

sorry,

 

t

 

 

I have a set of the 89.97. These are the only real bargain I have ever bought on eBay. Not for sale though. 

 

[jimbojames]

I probably have to re-bore anyway because they seem badly oval by about 0.03 if my measurements are correct. 

 

Your clean pistons have given me the idea to clean the carbon off and look for markings on the head. 

[Hans]

Keeping in mind that the pistons have to match the head style (121, E12, etc)

[Mike Self]

Most Mahle pistons I've seen have their diameter stamped into the piston crown; clean 'em off real well and you should be able to see it.  

 

mike

[Hans]

Where did yo find the mahle catalogue?

[jimbojames]

8 hours ago, Hans said:

Where did yo find the mahle catalogue?

http://www.mahle-aftermarket.com/na/en/catalogs-and-literature/catalog-pdfs/pistons/index.jsp#mahleoriginalpistoncatalogpi-20-09

[Hans]

Thanks. Maybe my eyesight but I don't see BMW listed. Is that an old link?

[jimbojames]

Sorry, wrong one. Try this: https://www.mahle-aftermarket.com/media/media-global-&-europe/products-and-services/engine_components/classicline_2017_18.pdf

 

Search M10B20 to find the area I referenced.

[jimbojames]

Thanks for the cleaning suggestion. After cleaning off the tops, it's clear they are 89 96 pistons and my bore measurements were wrong. After recalibrating, cylinders are already at ~90 mm (apx). I don't know if I trust my gauge enough to test for ovality, etc so I'm not sure what to do.

[Hans]

You need to use a proper bore gauge, measuring at at least three points down the bore and at 90 deg. as I recall. BMWs work at close tolerances. I would haul the block and the pistons to a reputable machine shop and get some accurate measurements.

[2002Scoob]

Take your pistons/block to a proper machinist and they’ll be able to tell you everything you need to know about If you can use them with the bores or not and how best to move forward.

I just did 89.97 Mahle Pianos in my rebuild, that should be a standard overbore size, I forget which step without checking the manual.

You can see the piston diameter stamped into the top just above the A1.




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[TobyB]

Whoopsie, that's as big as they grow, in the usual materials.

You can certainly have some made bigger, but it's not going to be a stock size.

 

There are several options- the cheapest being to source a different block-

but you now need to decide which direction you want to go, based on how original

you want to keep the car, what your balance of performance vs stock is, etc...

 

t

[2002Scoob]

2 hours ago, TobyB said:

You can certainly have some made bigger, but it's not going to be a stock size.

 

I think you're right, Toby. Anything larger is getting into E30 territory. If I remember correctly isn't the limit like 92-92.5? 

 

Toby is also right in that you should weight the value of the block you have. My original block was still in the car with it's factory bores in-place, but my budget was too thin to do it properly. My solution was to just shell it, buy a spare block with higher comp. pistons for cheap, and start from there. 

 

it of course snowballed into an epic case of scope-creep... but It got me a nicely performing motor in a matter of months for a very respectable amount of money.

 

When the time comes I have no qualms selling it because I'll still have the original block fresh and preserved to do properly. That is, unless I end up throwing in a couple electric motors instead... Which I think I will. And it will just become a nice numbers-matching coffee table.