What size pistons to order? - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• What size pistons to order? by myke_w on 13 Nov, 2005 18:02
• I have a block that I know needs bored, but not sure how to go about decising what size pistons. Should I send it to the shop and tell them to try  20 over, then if that doesn't work try 40 etc? Or should I just go buy the biggest ones I can find? Not sure how to go about this.. Any help is appreciated.
• #1 by 935racer on 13 Nov, 2005 18:11
• Is the block badly scored? Oversized pistons usually cost the same,when you get the pistons send one to the machine shop so they can bore to fit. Also replace your rod bushing/bearings as well they will need the wrist pin and the piston for that.
• #2 by myke_w on 14 Nov, 2005 06:19
• I understand that they cost the same, but i have no idae what ones to order...
  I dont want to get 20 over and then have it bee too small and not be able to return them, see my point?
  I also want to take the least material out, in the interest of leaving enough meat to do this again, if needed down the road... So How do I tell what I need?
• #3 by myke_w on 14 Nov, 2005 06:19
• I understand that they cost the same, but i have no idae what ones to order...
  I dont want to get 20 over and then have it bee too small and not be able to return them, see my point?
  I also want to take the least material out, in the interest of leaving enough meat to do this again, if needed down the road... So How do I tell what I need?
• #4 by QuickTD on 14 Nov, 2005 06:30
• The normal practice would be to measure the bores with an inside micrometer at the most worn area, usually just below the "ridge". You can then order pistons large enough to clean up the wear. 0.020" will pretty much clean up any engine that was previously running and didn't suffer a catastrophic failure. If something bad happened and deeply scored the block you may need to go bigger.
• #5 by fspGTD on 14 Nov, 2005 11:04
• AFAIK, manufacturing tolerances for piston diameters should be pretty tight for new vw diesel pistons, given how critical of a dimension it is.  So I don't see why you couldn't defer your decision about what bore size to use until after the boring is completed.  The diameters of new pistons should be checked, but the pistons themselves are not needed for boring or honing AFAIK (except just to check that they have the proper diameter.)
  
  But, I don't rebuild engines for a living, so I'd check with the machinist you plan on using to be sure.  A vw diesel experienced machinist might be able to get new pistons cheaper than you can anyway, especially if they buy from their engine parts supplier frequently and in bulk.  So, I'd select a good machinist first (preferably with vw diesel experience), and talk to them about your situatuation.
  
  Maybe do a little research on pricing for various brands and overbore diameters of aftermarket pistons to see if they are competitive.  I heard a rumor that .040" are the most commonly available & cheapest available VW 1.6 liter Diesel pistons nowadays.  (I can't remember if that was for naturally aspirated only, turbo only, or both.)
• #6 by myke_w on 14 Nov, 2005 12:40
• Cool, thanks.
  I can get them for 66 a piece before shipping with rings in any oversize. I found a good shop that prefers to bore the first oversize, then check and so on, they call me and tell me what size to order, easy enough. Will definitely be doing new intermediate shaft bearkings as they are allegedly responsible for low oil pressure in these motors. 3 angle valve job and block work, including polishing crank will not be over 300 which is in my opinion, a steal. basically translates into a new bottom end for under 600, when they are being sold as remans for well over that.
  I'll update as I get more info and thanks again
• #7 by fatmobile on 15 Nov, 2005 00:29
• Getting new rod bushings pressed in and reamed too?
   $300 include balancing the rods and pistons?
• #8 by myke_w on 22 Nov, 2005 10:40
• New bushings will be pressed in. Got pistons in the 40 over size for 66 bucks each brand new kolbenschmit brand (oem). Shop I found can even cut the head with the inserts, which I know is super rare... now that I've been thriugh this onec I know where to go get the job done. Anybody in ohio that needs help I can hook you up.
• #9 by Jeff@TheQuadShop on 22 Dec, 2005 18:17
• Hey Myke, I'm in KY and need to rebuild my 1.9 TD. Can that shop do them too?
• #10 by myke_w on 22 Dec, 2005 18:33
• Yes, for sure, what all do you need done? They are a full service shop, my motor came out very well. They don't need thier hand held, hand them the parts, the spec sheet and give them some time and they do the magic.
• #11 by Jeff@TheQuadShop on 22 Dec, 2005 18:40
• I have one bad cylinder thats reading 200psi and the others are in the low 400's. So I guess that means I'll probally need a complete short block rebuild. I just had the head milled and gasket replaced so its good.
  Do you know if they have had experience with the 1.9's? I would also like the crank modified for the TDI pulley.