Sachs Wristpin Needle Cage L/R Play

[KJDonovan]

I have a question for the folks building Sachs engines.  I don't do too many of these and came across something I need some advice on.

This weekend I was putting together a Sachs 125/6B using a 55MM piston and 15X19X19.5 needle cage I got Al and noticed distance between the inside of the bosses on the aftermarket piston are about 2.2MM further apart than the stock piston.  With this extra distance between the bosses on the piston, I am concerned that the needle cage could run to the left or right and I could potentially end up with the rod running on the shoulder of the bearing resulting in a bearing failure.  I asked Al Buehner about it and said that he has sold lots of these pistons and no one has brought this up before, so I figured I would ask here.

Am I overthinking this or should I be looking for a wider (21MM or 21.5MM) needle cage so I don't run the risk of the rod running on the shoulder of the bearing?  I also thought about loosely shimming (1MM each side) the needle cage to keep it on center.  I know other brands call for this (Montesa, Bultaco, etc) but think it would probably be a smarter move to use a wider needle cage.  Anyone run into this before or have any recommendations?

The photograph below shows the difference between the old and new piston.


Thanks,

Kevin

[gooddirt]

Run far away from the cage on the left make a pinkie ring or something.

[KJDonovan]

Larry,

Thanks for the response, what do you recommend I use?  I spoke with the folks at Wiseco today and they do not make a wider needle cage with the same ID and OD so I was thinking of using that one with some copper shims.  I am open for recommendations, I know you build a lot more Sachs engines than I do.

Thanks,

Kevin

[gooddirt]

Is it the plain white box piston you have or  Al's wiseco?

[KJDonovan]

Larry,

It's the plain white box 55MM I got from Al.  The needle cage on the left is Wiseco, I also got it from Al.

Thanks,

Kevin

[gooddirt]

Plain box piston has or should come with its own pin and cage spec'ed for that piston.
 If for sure its Wiseco /Japan  jobber they are ok....

[KJDonovan]

It came with the wrist pin and rings, but no needle cage, I purchased that separately from Al.  I am assuming you are familiar with these "plain white box" pistons. Are the needle cages that should come with these good or 3rd world quality? Sounds like I need to circle back with Al.  Thanks for the responses, sincerely appreciated. Last thing I want to happen is have this one detonate first race.

Thanks,

Kevin

[gooddirt]

no racy racy ..3rd global village

[brian kirby]

This exact bearing was discussed several years ago, '07 or '08 I think. We had several cages break with the expected result. The width of the bearing is not the problem, the poor quality of the bearing is.

Go to a KTM or any Japanese dealership and order an OEM (not aftermarket) wrist pin bearing for any modern 125, it is the same size as the Sachs bearing. As LG said, that bearing is garbage and is a ruined engine waiting to happen.

Brian

[firstturn]

Listen to Brian on this one as we did have some failures and his Uncle (Earnie Phillips) went into great detail on the failure.....and he is a Engineer.

Ron Carbaugh

[KJDonovan]

Guys, thank you for the advice.  I picked up the OEM KTM bearing this morning.  The photo below shows all 3 left to right, Wiseco, OEM KTM and Sachs.  Design wise, the original Sachs looks to be the best of the bunch, but that particular one has seen better days.  While I have not had any issues with Wiseco parts in the past,  I will go with the KTM to head off any issues down the road.



Thanks,

Kevin

[Daniel P. McEntee]

If you are still concerned about the extra end play, check with some one local that rebuilds and services crank shafts. They will probably have a good selection of thin shim washers to use on the wrist pin bearing to help keep it located. The technical term for the shim washers is machine bushings, I think. I don't think you want the fit too close, and .020" clearance would be acceptable because there isn't any load that way. Good luck with the project.
  Type at you later and HAPPY HOLIDAYS!
    Dan McEntee

[gooddirt]

The plain box cast piston was based on a copy of the forged Wiseco from back in the day, which is wider in the pin support area as well. The pin for this piston is longer and uses the smaller cage too. I think Jake F has some OEM pistons.

[KJDonovan]

Daniel,

That's my plan, I will stop by the machine shop and get a couple 1MM shims/bushings to keep the bearing centered so the rod is not running on the shoulder of the bearing.

Larry,

Already got a piston for this one, but next time I talk with Jake I will see what he still has.  I have a the bones for a few other 125's here I need to get done at some point.

Thanks,

Kevin

[gooddirt]

Might hit the head dome which mine did. That was the first sign it's not for race motor's and I pulled it.