125/6b Engine Experts / rebuilders

[BrianTaylor]

Need help from the experts here : I have a 125/6b engine that needs a new piston and ring set . I received a new piston set but when I look in the intake port I see the anti rotation pins of both the top and bottom ring . I would describe them as the top ring pin in the 6 O'clock position and the bottom  pin in the 7 O'clock postion from the exhaust port. I have an old piston from Wiesco that has the position in the 4Oclock and 8 O'clock positions which means the gaps are not in the intake port . I called Al B. today and asked for the correct piston he said he had one 0686 207 026 but he said the same thing that the pins would be in the port at 6 Oclock  and 7 Oclock and he didnt think that was correct and maybe ask some experts ..... any ideas [?] what is the correct number for a 2nd oversize [?] is that ring going to hang in the port ? [?]..... this goes against any other bikes I have done [^]..... thks for your time Brian T.

Brian Taylor

[Doug Wilford]

Brian;   If your pins are in the exhaust port,  I would say the piston is in backwards, normally the pins are nearer to the intake at about 2 and 10 looking from the top. 0686 207 016 1st over 54.5 0686 207-017 2nd over 55.5 There are lots of 54 mm pistons out there from different mfg. Sachs used Mahle 90 percent of the time.

[BrianTaylor]

Doug let me ask you this ...when you put a piston in do you have any concerns with the ring gaps being in the intake port on a 125 6b ? thks Brian

Brian Taylor

[firstturn]

Brian, Doug will be on vacation for a while.

Ron Carbaugh

[john durrill]

Brian.
 if you have the right Piston . the ring ends will not be in any port. just make sure you have the Sachs piston for the cylinder you are useing. iron barrel pistons have the ring retaining pins in a different place from the alloy barrel pistons.
 Hope this is some help.
John D.

[BrianTaylor]

Ron and John thks for reply.... it looks like I have been sent a piston for a iron barrel not the 6b engine. BT

Brian Taylor

[Kip Kern]

Brian

The NOS pistons for the Aluminum Cylinder have raised grooves up parallel to the rings.  The NOS cast iron cylinder pistons have smooth sides on the pistons.

[imported_n/a]

Kip and John,

I have compared the ring pin locations in the iron barrel pistons and the aluminum barrel pistons.  I eyeballed both pistons with an aluminum barrel in my hands.  As long as the pin position doesn't end up in either a transfer port or the intake port, is it okay to use the older pistons in the aluminum barrels?

Glenn

[firstturn]

Glenn,
  Pistons are pistons when it comes to working in a cylinder.  If the piston ring pins are not located in any port your OK.  Next you look at piston pin placement(always compare to piston coming out) compared to top of the piston and skirt length.  If I have confused anyone I'm sorry, but you have to remember that in the old days I kept a lot of off brand (Hondas) running using Suzuki pistons (every year Honda ran out of pistons on new CRs.

Ron Carbaugh

[Kip Kern]

Glenn   I have to agree with Ron.  If you look at some Wiseco or Tarabusi pistons, they  look like older Sachs/Mahle.  The 152cc conversion used either a Wiseco or Yamaha piston in them so as long as everything lines up properly, it should work OK.

[imported_n/a]

Thanks, Kip.

I bring this up because there from time to time are pistons on E-Bay for the iron barrel Sachs that sell for peanuts or don't sell at all.  Maybe there isn't much demand for them, but if they could be safely used for later cylinders, maybe we all can save a little money and use them, if later pistons are that much more $$.

Glenn

[imported_n/a]

Guys,

Over the weekend I pulled out my box of pistons and made a more detailed examination to try to come up with an answer to this.

I first looked at a 0686 207 008 55.5mm iron barrel piston.  The ring pins are about 5:00 and 7:00, if the arrow on the piston crown is pointed correctly toward the exhaust port, the arrow being 12:00.  When fitting the piston to an aluminum cylinder, the pins pass to the intake side of the transfer ports.  However, a difference I noted when comparing this piston to a 0686 207 026, the rings on the 008 piston are positioned about 2mm lower on the piston.  The wrist pins look to be in the same place.  Also, the 026 piston has the new ring placement for the top ring at 6:00, which would tell us that it does not travel far enough down in the stroke to hang out into the intake port.  The same holds true for iron barrel 100 pistons, 0686 208 007, compared to 0686 208 117 for the aluminum barrel.

Also, the Wisecos I have, the 100 and 125 series, the one-ring pistons have their pin placement at 6:00.  The two-ring pistons are 6:00 and 7:00, like the aluminum barrel pistons.  

Brian, I would install the piston on the rod, arrow toward exhaust, rings on the piston, and then carefully install the barrel all the way down.  Again, carefully move the piston to bottom dead center and see if there is any bottom ring showing, and if so, if the ring pin is visible.  I think if you don't see the ring pin, you could run the piston without fear of hanging it up.  I don't know if there were any taper differences in the way the pistons were machined.  I would think not.  

Good luck.  If you decide to run with this setup, let us know.  I have iron barrel pistons in 49.0mm, 49.5mm, 55.0mm and 55.5mm sizes, with cylinders at 48.0mm and 54.25mm and not needing a rebore yet.  I intend to try to use them when the time comes.

Glenn

[BrianTaylor]

:)Glenn you were bang on....I assembled the cylinder tonight stuck my face down the intake port  and low and behold the Rings do not even enter into the intake port at BDC... WHOOOOOOOHOO Glenn you saved me a lot of money as I was going to sheepishly return this unit I was sent and I was prepared to buy another one which with out your diligence of checking it for me and emailing back  would have thought been wrong again.... You know I thought this post was kind of a stupid question but I also learned that it was not and I truly had it answered by an expert ..... Thanks again Glenn ... Brian Taylor

Brian Taylor

[imported_n/a]

Brian,

It's great your engine can go back together now.  Let us know if you have any problems.  

What was the part number on the piston you have?

I'm glad the information was helpful.

Glenn

[BrianTaylor]

:D:D Engine went together perfectly tonight ... Glenn the piston I got was a Sachs part 0686 207 026  it is stamped 54.43 2 ring top L ring bottom rect ring ... I make it out to be the 2 nd oversize......... now my next one ( its stuck solid and been soaking in marinade ) :)Brian T.....2 75 Rokons and 2 74 Six days

Brian Taylor