Engine overhaul - Update March 2019
Some of my Links have died for both - so will try to sort those out soon.
I am also slowly converting the newer pages over to a different format - easier for links on a phone etc ( ie bigger link buttons )
After several conversations with a french owner of a 1gm10 - in need of retoration - the following info has come to light ( or at least a glimmer )
Ribparts Marine - DO have oversized piston and rings @ 0.25 - but they are listed under 2gm20 parts - and the no they quote has been superseeded ? - but the part no below provides concrete part listings ( as at dec 2019 ) if searched. They are available still.
All three engines - 1gm10 - 2 20 and 3 gm30 all use the same piston.
There used to be 0.5 oversized listed on Rib Parts under 2gm10 - but no longer. I believe they were in production - so if desperate try any of the links below ( 2019 )
I have a feeling the 0.5mm oversized were essentially a gm20/ 30 part - and as all three use the same part no piston assembly - they do not recommend overboring the 1gm10 to 0.5mm.They do state in the manual it can be rebored 0.25 however. ?
But the 0.5 overbore is a grey area - something must be ok with 0.5mm as Yanmar made a set ! Even in the text in the manual for 2 gm and 3 gm they still say - do not overbore past 0.25 ? So who knows ?
As far as 0.25 oversized is concerned - my old links are dead.
As of Jan 2020 -
Standard part no Piston and rings as stock - 105311-22090
Plus 0.25 Piston and rings set is - 105325-22570
( checked )
bottomlinemarine.com ( uk based ) has OS in stock ( £ 167 ) this is a very thorough parts source fo genuine yanmar parts - and a good part no index.
0.25 OS can be sourced also at
this link ( tested Jan 2020 ) takes you to their current website. Follow the link to 'dedicated parts website'. As said - you need to log in, just user and pass - and it now works in all browsers. Sometimes you have to download a small 'reader' for these type of parts fisches. Its very good - its the actual yanmar parts drawings and listings etc.
and as stated above - Rib Parts marine have them listed under the 2 gm 20 parts fiches - 0.25 OS piston and rings in stock. The part no I quoted under the engine overhaul pages for OS 0.25 is correct. It is common to find oversizes only listed under 2gm20 ! The 1 2 and 3 gm's use the same piston - 75mm diam.
The old links I gave for the Yanmar workshop manual have changed - and for the good ! The new version manual identical to the one I bought from Yanmar is free at manuals.lib.
The index is a little awkward - as its 480 odd pages - it has a page preview, but thats in page no - but the index is in section no/page in section !!!I have modifed the index page with 'notes' - the page no start for the section - which makes it easier. Its only 14 mb pdf - no point zipping it.
The other manual - the older one - is still available, but a different link.
Its chunky at 64 mb - but whats that these days .
here for direct if you want - see above link.