OzVMX Forum

Marque Remarks => Spaniards (Bultaco, Ossa, Montesa etc) => Topic started by: cappra on March 16, 2012, 03:22:15 pm

Title: upper rod bearing side clearance
Post by: cappra on March 16, 2012, 03:22:15 pm

Anyone have an idea what the side clearance should be on the upper rod bearing on a VB 360?
Right now I have a side clearance of around .009" (.229mm) with the shims in place.

Title: Re: upper rod bearing side clearance
Post by: Montynut on March 16, 2012, 06:52:23 pm

I have been working on .6mm L/E clearance on all my Monty engines. All engines have done a full season of racing with that setup. Using the KTM 250/300 L/E bearing. I have found that every piston seems to have a different clearance.

Title: Re: upper rod bearing side clearance
Post by: cappra on March 16, 2012, 08:21:36 pm

Low end is ok. It's the topend bearing endplay that is causing me problems.
(http://www.southwestmontesa.com/bearing.jpg)

Title: Re: upper rod bearing side clearance
Post by: Montynut on March 17, 2012, 12:17:36 am

Jared my rely is about the top end when I mention L/E I mean little end (top end).

Is that a Mahle piston or Italkit?

I have been using the KTM 250/300 top end bearing which is the same size as the original Monty top end bearing. I have been setting up the top end with 0.6mm end float and have not had any problems. That was the clearance in my VF250 top end from the factory so I have been using that value without problem. Just about every new piston that I have fitted required a different set of thrust washers to be made :'(

Title: Re: upper rod bearing side clearance
Post by: cappra on March 17, 2012, 02:44:32 am

I'm not sure who makes the piston. My customer sent it to me with no id.  I think
it's a Tarabusi Enduro unit. For sure not a Mahle or Italkit. Are you making the spacers out
of aluminum or steel?

Title: Re: upper rod bearing side clearance
Post by: Montynut on March 17, 2012, 08:12:20 pm

I had them made them out of steel. Well actually I used (this will really make Ross's day) 'inconal' steel which is the material used in large steam turbine casing bolts which has a very low coefficient of expansion but any high quality steel will do I would think.

I am not sure if Aluminium would do the job but then the piston is aluminium although it is high silicon alloy. As you know the originals are steel. I did not consider anything but steel. I have had several sets made some require a stepped washer while others require a plain washer.

Title: Re: upper rod bearing side clearance
Post by: cappra on March 17, 2012, 08:58:17 pm

I'm also trying to use the KTM bearing which is 18 x 22 x 20.
the book call for the 6660.011 bearing, which is 18 x 22 x 15.
I have been unable to find this size bearing anywhere. Wiseco
also has a 18 x 22 x 19.65 bearing. Like you said, it seems all the
pistons are different. I trying to use the stepped shims now, but am
coming up too tight on the clearance. Maybe some flat shims with the
Wiseco bearing will work better.