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Bore measurements and over sized pistons

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Hey guys, curious as to your thoughts on this; I'm doing the top end and am trying to determine if I should replate, or if I can go with an over-sized Piston, so I'm trying to figure out what are acceptable clearances. 

 

Manual says stock piston is 66.35 mm (2.6121995 in) and standard bore range is listed as 66.400 mm - 66.415 mm (2.614168 in - 2.61475855 in)

 

The old piston actual measured 2.611 In, so just a touch below "stock"... can they compress a little? 

 

The bore measured .004 over that = 2.615 in. 

 

Bore = 2.615 in and the far end of the manuals listed range is 2.61475 in. 

 

I found this in YZ forum for piston sizes, and I am guessing it's the same for Suzuki?

 

A - 2.61228 - 2.61240

B - 2.61244 - 2.61256

C - 2.61260 - 2.61272

D - 2.61276 - 2.61287

 

Would you replate, (or do a sleeve)? Or just put a D piston in there? 

 

I'm also a little confused because, typically when I do a top end I check for glazing and look to see how well I can see cross hatching. If I can see it, I clean it up with scotch bright pad and run a B or C piston and call it good, because I have always been told that cross hatching is only a thousandth thick so if you can see it, your in spec. In this case however, I'm 4 thousandth, almost 5 thousandths over and cross hatching looks fine. I only measured because the piston showed signs of blow by and I didn't think I had that many hours on the motor (I'm getting an hour meter this time). 

 

Anyhow, thoughts? 

Edited by Kenpo1

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Well if I have read you numbers correclty, Your bore measures 2.615 and the D piston measures 2.61276 then this would give you 0.00224 clearance or 2.24 thou- Piston to cylinder. or .0568mm. Ideally you would like to use 1 thou per inch of bore size so this would equate to 2.61 thou. If you used a B piston then (2.615 - 2.61244 = 0.0026 or 2.6 thou clearance.

You would really only consider replating if the cylinder was showing signs of exposed aluminium how ever given that it is over the recommended for the manual then you may want to consider it. I like sleeving for a number of reasons that suit me personally but it all depends on what type of riding you are doing. Sleeving allows me to bore out and hone. Good luck with your decision.

How many pistons have you installed so far into this engine and have they been forged or cast? 

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Well if I have read you numbers correclty, Your bore measures 2.615 and the D piston measures 2.61276 then this would give you 0.00224 clearance or 2.24 thou- Piston to cylinder. or .0568mm. Ideally you would like to use 1 thou per inch of bore size so this would equate to 2.61 thou. If you used a B piston then (2.615 - 2.61244 = 0.0026 or 2.6 thou clearance.

You would really only consider replating if the cylinder was showing signs of exposed aluminium how ever given that it is over the recommended for the manual then you may want to consider it. I like sleeving for a number of reasons that suit me personally but it all depends on what type of riding you are doing. Sleeving allows me to bore out and hone. Good luck with your decision.

How many pistons have you installed so far into this engine and have they been forged or cast? 

 

I've only put one piston in the motor. Bought the bike used. I usually run Wiseco but I put in an OEM cast piston because the kit came with the bike. It doesn't have that many hour on it (my trailtech shows 15 hours, but I put that on a few months into the season) so I was surprised to see ring blow by on the piston. That's what prompted the measurement. I don't see any exposed aluminum, in fact, cross hatching doesn't look half bad... 

 

Regardless, I want I tight motor with good ring seal, so I'm thinking I ought to do something. Given the cost of replating and a top end kit, I'm thinking it may be time to send it off to EG for a big bore kit. I've always wanted to try one of those.  :ride:

 

Thanks for your comments. 

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