pistons and rings

[Shinyballs]

We are having problems trying to locate pistons and rings for an '86 K75C. To make it more difficult, the cylinders may have to be bored (waiting for machine shop to get back with a verdict of oval or round). If they need boring, we need oversized pistons and rings.

Is all this available somewhere? Anyone know? If not available, is there a compatible piston from a totally different vehicle?

Thanks
Ray

[The Mighty Gryphon]

See my reply on the other thread.  As far as I know there are no oversize pistons available.

[Duckbubbles]

The cylinders are Nikasil (?) coated aluminum and are not to be bored any at all.  I have heard (in the way back past) of people boring and sleeving the block with steel liners.  Sounds awfully expensive.  If your block is really out of round, worn out, you would be better served to get a used block or whole engine from a wrecking yard.
The stock lining is extremely tough and unless there was some damage will last many 100,000's of miles.

Frank

[frankenduck]

If the engine has gone bad then it is probably easier and cheaper to just get another engine with relatively low miles.

I'd recommend getting an engine built after June 88 with the newer, less smoky, pistons and rings.

[Shinyballs]

The word from the machine shop is that the cylinders are fine, straight and round  . So they just did a ball hone to the cylinders, head resurface, valve seating and new valve seals. So we will have to find out which crank bearings and connecting rod bearings we need. As for the piston rings, I talked to a tech at BMW Motorad and after spending some time on the computer and on the phone, he could not locate rings anywhere. The rings are not available anymore. So we will put the engine block back together with the starter and check the compression. If it's better than it was before, we will just use the old rings. Unless we find an aftermarket, universal set of rings that can be trimmed to fit.

[Duckbubbles]

I am just throwing this out there in case someone else can confirm.

The K75 and K100 share the same bore size.  The pistons are different but I wonder if the ring lands are the same.  Supposedly, Realoem.com lists ring sets for the K100 P/N 11251460994 as still available.  Less than $70 each which is a shock and probably out of date price.  You can check your old rings for wear by inserting them into the cylinder and measuring ring end gap just like fitting new rings.  If the gap exceeds limits (.0098-.0177 in./ .250-.450mm) they are worn out.

Frank

[frankenduck]

I am just throwing this out there in case someone else can confirm.

The K75 and K100 share the same bore size.  The pistons are different but I wonder if the ring lands are the same.  Supposedly, Realoem.com lists ring sets for the K100 P/N 11251460994 as still available.  Less than $70 each which is a shock and probably out of date price.  You can check your old rings for wear by inserting them into the cylinder and measuring ring end gap just like fitting new rings.  If the gap exceeds limits (.0098-.0177 in./ .250-.450mm) they are worn out.

Frank

$74.88

https://shop.maxbmw.com/fiche/PartsSearch.aspx?&searchtype=undefined&parts=11251460994%20

[Shinyballs]

Thanks for that, that is good advice and I'm going to check this out. Since the cylinders had a ball hone done I would prefer new rings.

as for the crank and connecting rod bearings, anyone know how to decifer the tri-color code for their bearings? They have yellow, green and white in either STUFE 0 or STUFE 1.