175 Jugs

[Robert]

I have new piston and rings for my 175 to install. Cranshaft is sound and seal between the cases seems to be doing its job. I just have low compression and 7000 miles on the current piston/ ring set up. In changing them out, what would you recommend in "braking the glaze" on the existing hard chrome bore. Should I not touch it at all? Might consider recoating with Nikasil- any good recommendations out there for a bore refinish. Dont think I need it but definitely will consider it. Thanks  Rob

[B ion St.Bernard]

If chrome is in good shape, you can brake glaze with suitable sand paper. Make sure ring end gaps are correct. Can't use standard pistons with Nikasil. Also Nikasil and differrent pistons will get very expensive.

[OldSwartout]

I have done it both ways - slapped in new pistons and rings without any prep work and at other times have used sandpaper to roughen the surface slightly.  The problem is that you can't really do much to the surface because it is so hard, so I'm not certain it even helps.

Bion - Paul Piskor and I did run standard pistons and rings in nikasil bores for a while on our racers, but have since changed to Wiseco pistons made for a Suzuki RM85 (which requires some modification to cylinders and heads).

Glad to see you on this forum.

[Robert]

What is the issue with the Nikasil replating and different pistons. In speaking to the several plating firms, they ask that I send the pistons with the cylinders and they will fit them perfectly. What am I missing? Other wise, good old sandpaper and new pistons and rings are in store for me.

Thanks  Rob

[OldSwartout]

What is the issue with the Nikasil replating and different pistons. In speaking to the several plating firms, they ask that I send the pistons with the cylinders and they will fit them perfectly. What am I missing? Other wise, good old sandpaper and new pistons and rings are in store for me.

Thanks  Rob

They want the pistons just so they can get the bore size correct to provide the necessary clearance.  There isn't any way they can trust piston measurements sent in by the mechanic vs. measurements made by their machinist; there is just too much possible variation depending on measuring equipment, skill of the operator, temperature at the time of measurement, etc.  Being off by .0005 inch can cause a seizure. Even back in the "old" days of bore jobs, the machine shop always wanted your new piston to use for measurement.

[Robert]

Thanks Karl. One of the previous posts mentioned that if you Nikasil your jugs, you cannot use the standard pistons. Another post mentioned that they were used. Does anyone have personal experience with running the standard pistons with a Nikasil plated bore? How about the good old hard chrome vs. the Nikasil ? Some other Bridgestone sites mention a few places that still do the hard chrome, any recommendations out there?

[OldSwartout]

Both I and Paul have run with standard pistons in nikasil bores.  We switched to Wiseco pistons  and rings because of problems with the standard rings breaking.  That was occuring with the chrome bores, also. I even ran two of the 1mm wide Wiseco rings in the top groove of standard pistons in nikasil bores for a while.  Millenium Technologies that does nikasil also does hard chrome, as do some other suppliers.  My feeling is that the nikasil holds up through a piston seizure better, but otherwise either one is fine. 

We had to switch to nikasil  bores with the Wiseco 1mm thick piston rings as they only have chrome-faced rings available, and you can't run chrome rings on chrome bores.

[Robert]

Thaks Karl for the great info. I'll look uo Millenium. Years back I used a set of the Wiseco pistons for a rebuild. Are there still some available on some shelves? Will the cast iron stock ring work fine with the Nikasil or do I need to change to a chrome faced ring in this case. Thanks

[OldSwartout]

The stock cast iron rings will work fine in the nikasil bores.  However, you could also use the chrome-faced rings from the iron cylinder 90cc bikes with nikasil bores.  They might last longer, but we generally don't put tens of thousands of miles on these old bikes, so it shouldn't matter.

There aren't any Wiseco Bridgestone replacement pistons available anywhere that I'm aware of.  The closest we found was oversize Suzuki RM85 pistons; unfortunately, they require about .0005 more clearance, have .035 less pin to crown height and a flatter crown, requiring mods to the cylinder and head to use them.

Although Wiseco still shows them in their catalog, they don't have any 50mm non-chrome rings available, so we had to go to nikasil to use the Wiseco pistons.