R65 (R65LS) Piston

[Sejati]

Does anyone can advise whether this is original piston for BMW R65 (R65LS in my case) ?
It has flat top, marking embossed RW inside.

If it is not, than I need to look for the original, either new or secondhand.

Thank God, the cylinder Nikasil lining is in good condition.

[tunnelrider]

Hi Sejati,
That looks like one well used, beat up piston!  I'm not sure if it's the original but I doubt any R65's with Nikasil cylinders came OEM with flat top pistons.  I think the one you have is a Mahle piston, who manufacture pistons and Nikasil cylinders, by the 'm' insignia embossed on the inside of the piston crown, but I'm pretty sure any R65LS will have come originally with curved, convex crown pistons, probably from Mahle also.

You'll have to measure the inside diameter of your cylinders to ensure a replacement set of pistons will fit, while ideally not having more than 0.080mm piston / cylinder clearance.  OEM pistons came in three sizes, A, B and C, ranging from 81.955mm to 81.985mm.  The piston will have the size stamped on the crown, the cylinders also have a size stamped somewhere (can't recall where now tho sorry).  I recommend buying a replacement pistons as a matched pair preferably, otherwise vibration from different weights could be a problem.  Any pair of R65 pistons that fit will do, the key thing is to get the right rings for Nikasil cylinders.  Check the ring end gap before installing them, you may have to alter it depending on whether you end up with different size pistons from the cylinders (they also come in three sizes).

[georgesgiralt]

Hello
IMHO your piston is for a 1979 R65 with iron lined cylinders or for a highly detuned R65 ...
If you clean the crown you should see the markings and you can confirm (or not) my saying.
Hope this helps

[Sejati]

The only readable letter on the crown is something like “0.50”...
Not sure what that means. As below photo.

[wilcom]

Her's a pic of  a set of 1981 pistons and barrels from my spare's shelf. Maybe yours is from an 79 or 80 or as was mentioned , one of the "detuned tax bikes" pistonsftp://

[Sejati]

You'll have to measure the inside diameter of your cylinders to ensure a replacement set of pistons will fit, while ideally not having more than 0.080mm piston / cylinder clearance.  OEM pistons came in three sizes, A, B and C, ranging from 81.955mm to 81.985mm.  The piston will have the size stamped on the crown, the cylinders also have a size stamped somewhere (can't recall where now tho sorry).  I recommend buying a replacement pistons as a matched pair preferably, otherwise vibration from different weights could be a problem.  Any pair of R65 pistons that fit will do, the key thing is to get the right rings for Nikasil cylinders.  Check the ring end gap before installing them, you may have to alter it depending on whether you end up with different size pistons from the cylinders (they also come in three sizes).

To measure Inside Diameter of cylinder, is it in the TDC or BDC position ?
I see in Motorworks.co.uk for example, for Nikasil cylinder, there is only one option piston of size, and ring. But for iron cylinder there  are couple of sizes. Cmiiw.

All that I can find making on cylinder are :
6.5
B 2 9 (2 being on top of 9)
82ZN4W2
R
Mahle

[Sejati]

Her's a pic of  a set of 1981 pistons and barrels from my spare's shelf. Maybe yours is from an 79 or 80 or as was mentioned , one of the "detuned tax bikes" pistonsftp://

Yeah... obviously mine has been swapped by some irresponsible owner/mechanic... the bike from 1982.

Could you advise all the embossed marking written on your spare cylinder ?

[wilcom]

Her's a pic of  a set of 1981 pistons and barrels from my spare's shelf. Maybe yours is from an 79 or 80 or as was mentioned , one of the "detuned tax bikes" pistonsftp://

Could you advise all the embossed marking written on your spare cylinder ?

I'll get them down this afternoon, The pic was from an ebay sale history, I have never opened the box. The spare cyclinders and pistons weres from a trusted seller and no need to look in side until now

[wilcom]

I had a spare moment b4 leaving so let me shoot these pics to you

3 markings on the cylinder   

1st is........... 06 [size=18]A[/size] 19

2nd is .......... 6.5 (six dot five)

3rd is ............82ZN4W2

pics are poor but show where the markings are on the cylinder

[tunnelrider]

To measure Inside Diameter of cylinder, is it in the TDC or BDC position ?
I see in Motorworks.co.uk for example, for Nikasil cylinder, there is only one option piston of size, and ring. But for iron cylinder there  are couple of sizes. Cmiiw.

All that I can find making on cylinder are :
6.5
B 2 9 (2 being on top of 9)
82ZN4W2
R
Mahle

From the markings on your barrel it would seem it's a 'B' size, according to the Clymer manual an inside diameter of 82.005mm to 82.015mm.  I'd check Ebay for R65 pistons for sale and post a msg on the parts for sale board on this helpful forum 'wanted pistons', someone may have some unwanted pistons to help you out.
Nikasil barrels I think are pretty uniform diameter BDC to TDC, if you do measure the inside diameter use the smallest measurement.

Ideally you want to match 'B' barrels with 'B' pistons but considering as you say Motorworks have only one new piston part available for Nikasil barrels, I'd say also most used post 1980 pistons will do the trick, I guess what I can't say right now is the min. clearance needed to fit a piston with new rings, for example if you got a C size piston and new rings.  Motorworks do second hand pistons too if you're ok with the hefty price, and half the price of a single new piston.. maybe ring or email them to see if they have any second hand if their price is ok, there's a reasonable chance they'll have what you need.

Thinking about it now the price of (2nd or new) pistons aren't that much really, they last a very long time (barring any mechanical or maintenance failures ) and they're pretty much the heart of the bike.  Most post '80 airheads are probably still on their OEM pistons.

[Sejati]

Thanks for everyone feedback and advise...

[Tony Smith]

i'd be interested in seeing a photo of the cylinder head that piston was paired with as if the piston/head combo is from one of the reduced power models it will have a very different squish band to the "full power" varieties.

I can confirm that it is NOT a standard "iron bore" piston, they were pretty much the same as the late model nickasil bore items, there is a minor difference in deck height which reflects the higher compression of the 50hp R65 over the original (one of numerous detail changes BMW made).

Long term members will recall that I fitted iron bore barrels to my 1984 engine and posted a picture of an iron bore piston next to a nikasil bore version, locked together using the rings to highlight the greater deck height on the nikasil one.

I ran 6,000 miles on that combo with zero problems aside from whingeing about lack of power - but I took care of that a little while ago.

In any event, that piston of yours is stuffed. Depending om how much you want to spend, either haunt eBay for a useable 2nd hand set or buy a new standard set from 7-rock, or, gasp!, an 860 kit form the same source (but please do have the heads reconditioned and check at least your big and small end bearings before fitting a big bore kit.

[Sejati]

The cylinder photo the same as Wilcom shared above. It has the same part number. I’m pretty sure someone was fooling around using some different piston head. Which might be came from different era of R65. And this is giving me problem of overheating.

Currently I push my luck by ordering 7rock 860cc, hope it will fit okay.

Btw, how to check big and small end bearing ? Are those  the crankshaft bearings ?

[Tony Smith]

Btw, how to check big and small end bearing ? Are those  the crankshaft bearings ?

Your conrod has a great big bearing at one end (crankshaft) and a much smaller one at the piston end - called "big end" and "little end". :-)

To check the little end - insert an oiled piston pin into the little end and try to "rock" it on the end of the conrod - any movement at all requires careful further investigation - interestingly the hardened pin usually wears before the soft bearing so if there is only a small amount of movement it is worth trying a new pin and if there is no discernable movement I would go ahead and reuse the little end.

To check the big end you need an appropriate spline drive socket to remove the conrod bolts so that you can visually inspect the replaceable bearing inserts.

If there is no sign of abnormal/uneven wear you are generally safe to put the rod back together with new bolts and a torque wrench.

But, if the bearings show uneven wear (different colour shade around the bearing is your clue) or the bearing shows lots of metallic particles embedded in it, then the next step is to use a micrometer to measure the crank big end journals to see if they are within specification.

The bad news is that if they are not, then the crank has to come out and the main bearings also checked prior to (hopefully) reassembling with new bearings.

BUT, the BMW bottom end is very tough and very long lived, if the main or big end journals are worn out of spec then a complete rebuild is required and that involves a significant amount of work beyond the scope of most home mechanics (but there are many internet documents that would help you do so if you were keen - it is not difficult, just meticulous).

I would check at least the big end bearings if you are fitting an 860cc kit as the 30% capacity increase is a big ask if anything in the bottom of the engine is not in 1st class order.

[Sejati]

Thanks for the advise Tony.

Will check on the small end bearing.

However, since i dont have tools to open the big end bearing, I was checking by wiggling it. It is tight on top bottom and back and forward movement, but a tiny play on side left and right. Hope this presumably okay.