hp18racer

My 1981S Euro I THINK has 85S pistons, two have broken ring lands.

The pistons have a '+' stamped in them. Can anyone help me tell for sure which pistons they are?

I'd be interested in two matching what I've got or even a full set of US pistons if the price is right.

Thanks

Mark Anderson

What is your engine number? What makes you think the pistons are 85?

9146GUY

I have a set (8) of PN 928 103 086 50 pistons 97.50mm
I also have a set (8) of PN 928 103 093 00 pistons 97.50mm
Both sets are new.
PM for more details

GlenL

Late Euro S piston in 98mm
It's the depth of the valve reliefs that's the difference. Yours does look like it may be later

Clean off the tops and there should be more numbers.

US pistons will be lower compression. 928I probably has the right pistons and they'll be 1/2 off this month.

hp18racer

Engine Number:
M 28 / 22
82 F05520

PO indicated engine short block had been replaced at some point.

hp18racer

Thanks for the responses.

hp18racer

Bores look good, I'd like to find pistons the same diameter and avoid the expense of machine work. Block number and piston markings below, just looked at your link GlenL, heading out to the shop to clean more of the piston

Cleaned the top off completely, no more markings found than shown in the pictures.

Hilton

1 is the tolerance group
0884 is August '84, M is Mahle
M28/22 is indeed the later 310hp engine.


Correct piston replacement part is:

928 103 086 14
Piston: MAHLE
97.00mm Tolerance Group 1
82E 6114 onwards (i.e. from late '84 model year)

Just in case, its worth measuring piston diameter just in case yours is an oversize.. first oversize is 97.5mm, second is 98.0mm, in case some time in the engine's past they scratched a bore and went up a size.

hp18racer

My most sincere thanks Hilton!
Got the parts I need on order

GlenL

He nailed it. The manufacturer's code is key.

Track the tolerance groups. They will be stamped on the block and the pistons. Get replacement pistons of the same group and gap the rings.

Broken lands are often due to knocking. Any broken piston rings? I had this problem before and what happened (I think) was that oil blow-by lowers the octane and then there's knocking that breaks rings which means more blow-by and more knocking.

To address this, I got special rings from Total Seal that are designed for turbos and are more durable. They're not gapless rings which is their signature product. Like $20 a ring for just the top rings. The cost-effective approach is to get sets of Goetze rings, toss away the top rings, and use the Total Seal rings.

upstate bob

Total Seal makes good stuff. The sets vary as to which ring is gapless. I put a set in my auto-powered airplane engine. They take a while to break in. -aluminum G10 with steel liners, TO rpm 5300, cruise 4700. suzuki, tough as nails.
79 5 speed, tucked away with a CTEK for the season.