WISECO Piston clearance ??

[Mark Annan]

I have a couple of Wiseco pistons for Sachs 125 motors.  What is the recommended clearance to set them up?  I seem to recall they like a little more clearance than the factory Sachs pistons.  Any input would be greatly appreciated.

Mark

 

[Larry Perkins]

Mark, we set our Sachs racers up at .0035-.004 but break them in well before racing.  Main thing is to not let the bike get too hot the first tank of gas.

 

[Doug Wilford]

A 125 at .004 is ready for a rebore, maybe on the 400s'  Normal set up for 125 is .002 I like to set them a little under even as tight as .0015.  The Wiseco will work fine at .002

 

[Larry Perkins]

I "Respectfully" disagree.  I believe I would lock up a 125 racing it with a Wiseco piston at that clearance in MX.  For trail and woods maybe okay.  The Sachs manual says .00532 to .00537.  I am talking thousandths of an inch not mm.  Maybe that is the difference between our thoughts?

 

[john durrill]

Mark,
 We were talking to Bobby Lucas about the set up on Wiseco Pistons last month.
He is of the opinion that the cam grinding on the piston was done wrong. If you assemble the Top end and run the engine through 20 or so times . disassembel it and use 600 grit wet dry on the wear spots ( high  spots ). you can use the .002 or .0025 piston clearance. You should break it in as well ( about 4 or 5 tanks of gas ).
We found that the rings were softer than stock so we had to check them  and replace them more often.
Bobby said they gave good service if you removed the high spots.
 .004 set up could lead to a broken piston skirt in a short time.
John

 

[Larry Perkins]

I would agree with a KTM motor and a Mahle piston.  I bet Bobby was talking KTM and not Sachs.  I never(knock on wood) broke the skirt in a Sachs motor that I raced.  Not in The Day or current.  I don't think you would see that till .009 to .010 and even then under revs.

 

[Bob]

Here's what Wiseco recommends. It is an instruction book that came with a vintage Hodaka Wiseco piston.

http://users.erols.com/dynobob/wiseco_1.jpg

Bob

 

[john durrill]

Larry,
 Hope I have your luck * GRIN *
 I have had to bore and replaced pistons in Hodaka , Yamaha ,and Sachs alloy cylinders due to cracked pistons. They ran between .005 and .006 clearance when we checked them.
 The alloy cylinder Sachs had a bigger and taller intake port than the iron barrel . That could have been the culprit.
 Rule of thumb for piston clearance is .001 per inch of bore unless you have hard , high silcone content pistons.
Most NOS pistons fall into that class anymore.
I know we had a bad time with the Hodakas and Wiseco pistons. We finaly quit useing them unless the customer requested one.
Found out from A Wiesco rep ( Last month ) the same thing Bobby suspected about the cam grinding. They use the same alloy today with better rings and a different profile on the pistons they sell now.
 Set a piston up at .004 and by brake in its at 4.5. Any dirt or water and its in the .005 range. Thats my reason for the shortly on piston failure
John

 

[Mark Annan]

Thanks for the input guys.  I knew I would get some good feedback here.  I think I will set it up hte Wiseco's at .002" and then "adjust" the high spots.  

I have several of the early Penton service manuals and a Sachs factory service book (1974).  Piston clearance specs are not mentioned in them.  The Penton book does detail how to rebalance the crankshaft/rod assembly. The only clearance specs I have seen in print are packaged with the Wiseco pistons or in the Cylmer Sachs book.  The Cylmer book calls for .0047" to .0057"  (depending on overbore size) piston clearance on a new piston, and a max of .008" on a used.  It also specifies a max of .008" taper or out of round.
 
Just about every Sachs motor I have been inside (admittedly just a few) has had cracks in the piston skirt.  I assume they all had lead a rough life.  They all had over .008" clearance.  One had .018".  That piston was shattered, I pulled it apart with my fingers.  I just got an .080" ( 2 mm !! ) oversize Wiseco piston for a Sachs 125.  That thing has such thick skirts that I don't think I could crack it with a hammer.  Definitely will need to balance the crank with that one.

While on the subject of clearances, what is the acceptable radial clearance for the rod big end?  and how do you determine it with out disassembling the crank?  What is the specs for the side clearance?  I have been told that if you can feel any movement when you try to twist the rod (rotate it perpendicular) on the big end bearing it is no good.  Any input??

Thanks again,  Mark

 

[Larry Perkins]

I was taught that if there was any up and down play to the rod at the up or down stroke that it was replacement time.  But what do I know all my Sachs motors should have blown long ago.  I am sure glad the one that I won on in the Astrodome back in The Day didn't.  Oh well I am just lucky.

 

[john durrill]

Mark,
 hear is a cut and past from a question a few months back. this is what o found when i did some checking on rod side clearance. I'm with larry you should not be able to detect any up and down play. I tried useing a B crank tha had less than .001 for Andres ride and when assembled i could hear the clearance when the engine was running.
 It would not  have survived the mountains we rode in that run.
Any way hears the info we got from a shop that does a lot of two stroke cranks.
 gary,
sorry to be so long in getting back to you.
side clearanc on the NOS crank for my 125 was .015. Talked to a shop that does a lot of crank rebuilding and they said thats about right for a rule of thumb on most 125 to 200 cranks. wear limit should be somewhere in the .025 to .028 range. thats in Inches. you can use a feeler gauge to check it.
John



Edited by - John Durrill on 05/17/2002  11:19:56 AM