924Board.org

Jaspermaertz · Joined: 01 Apr 2023 Posts: 3 Location: Netherlands Bocholtz

Hi
im a rebuilding my engine and i need 1 new piston.
the size on the piston is 87.45. and i cant find one used or new..

can anyone help me?

morghen · Joined: 21 Jan 2005 Posts: 8879 Location: Romania

87.45? that sounds like non standard, you sure its not 86.45?
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Jaspermaertz · Joined: 01 Apr 2023 Posts: 3 Location: Netherlands Bocholtz

Nope its really 87.45

Cedric · Joined: 27 Aug 2004 Posts: 2608 Location: Sweden

Its the third and last oversize according to the spec manual, finding such a pistons wont be easy.
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Karlio · Joined: 17 Nov 2019 Posts: 65 Location: UK

Friesinger motorsport have them in stock, around €600 a piston

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Jaspermaertz · Joined: 01 Apr 2023 Posts: 3 Location: Netherlands Bocholtz

Bought the piston at Friesinger! the piston cost 300 euros ex VAT..

now im looking for a set of pistonrings for the remaining pistons.. 87.45. or could i use 87.5 rings?

Coco_Lev · Joined: 04 May 2020 Posts: 81 Location: France

MikeJinCO · Posted: Fri Apr 21, 2023 11:12 pm Post subject:

I worked for a piston ring company for15 years. There is nothing special about 95% of the piston rings made, a few slight changes to get them to twist, taper faced or barrel faced, etc. Back at the time except for a barrel faced top ring most of the changes were to the second ring to change sealing/scraping characteristics. If you find any ones rings of the proper bore then the only major difference is the thickness and pistons are easily machined for other rings. I believe Mitsubishi makes engines with a bore of similar size for one.

If I recall correctly, the only thing about the 931 ring that was a little different is that the top ring is thinner than was typical at the time, These days it would be a very common or even thick for a modern performance motor. I believe Wiseco has a listing of there rings by bore size and thickness and would be a good place to start.

An alternative is to go to Circle Seal, they make rings by rolling steel rather than machining castings so can produce a set of any size needed. A caution on them tho is that I have heard, very unconfirmed, that their rings are very unhappy if the ring lands are not perfectly parallel. ie worn.

When I was building my race car motor with old 931S2 pistons and a NA head, no 931 rings were available so we just machined the pistons for thicker standard NA rings. Worked fine
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

Karlio · Joined: 17 Nov 2019 Posts: 65 Location: UK

Oversize rings are very rare these days both n/a and turbo. A set of standard turbo rings are as much as the piston you just bought.
Total seal do gap less rings that should fit. totalseal.com
Or as you are in Holland and speak the lingo you could try www.thn.nl and see if they have got some rings.

MikeJinCO · Posted: Sat Apr 22, 2023 8:52 am Post subject:

I just looked up Wiseco . Mitsubishi 4G63 87.50 bore, 1.0,1.2/2.8 thickness.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)