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XR100 piston ring end gap .086 WTH???

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Hello again. This time I have disassembled another engine I purchased for $75 and inspected everything. I got to measure the piston ring end gap per the Honda service manual which gives a service limit of .02 for the first two rings. HOWEVER...Mine are at a whopping .086 which I find extremely hard to believe they were worn that much. The engine was smoking pretty badly and had plenty of oil coming out of the exhaust, but still had 150psi compression.  So I went and checked another bad cylinder I have with a wiseco 53.5 piston and the ring end gaps were just as bad.  So does anyone know if the service manual is correct for end gaps and if so have you seen a ring be 4x the limit on a running engine?  Take a look at the attached picture for referance.  That is the stock bore cylinder.

Photo on 3-26-17 at 10.31 AM.jpg

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Looks like another case of the wrong ring size for the bore size.   If stock bore is 53mm, and your cylinder is bored to 53.50,  std 53mm rings will have excessive end gap like that.  Do the rings have any numbers on them ............ and numbers on top of piston?  Always need correct ring size to go with bore size!:thumbsup:

Old School Al

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1 minute ago, Old School Al said:

Looks like another case of the wrong ring size for the bore size.   If stock bore is 53mm, and your cylinder is bored to 53.50,  std 53mm rings will have excessive end gap like that.  Do the rings have any numbers on them ............ and numbers on top of piston?  Always need correct ring size to go with bore size!:thumbsup:

Old School Al

Al,

  I have two cylinders and pistons.  The one in question is a stock bore and stock piston that has the .086 ring gap.  Uncertain if its ever been rebuilt before but with a stock piston I'm leaning towards no.  The second cylinder that i measured is an overbore with a wiseco 53.5mm that i used just as a reference to see if those rings were as far out as the stock bore cylinder (which they were).  does this make sense?

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1 minute ago, komodo said:

Al,

  I have two cylinders and pistons.  The one in question is a stock bore and stock piston that has the .086 ring gap.  Uncertain if its ever been rebuilt before but with a stock piston I'm leaning towards no.  The second cylinder that i measured is an overbore with a wiseco 53.5mm that i used just as a reference to see if those rings were as far out as the stock bore cylinder (which they were).  does this make sense?

also the piston has a 436 stamped on the side.  I measured the cylinder bore with snap gauges and vernier calipers last night at 53.06mm with a service limit of 53.1mm

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28 minutes ago, komodo said:

also the piston has a 436 stamped on the side.  I measured the cylinder bore with snap gauges and vernier calipers last night at 53.06mm with a service limit of 53.1mm

On your stock bore cyl sounds like the rings are out of something else with a smaller bore.  And the Wiseco has the wrong size rings for the bore.  Are there marking on the rings showing size............?

Old School Al

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50 minutes ago, Old School Al said:

On your stock bore cyl sounds like the rings are out of something else with a smaller bore.  And the Wiseco has the wrong size rings for the bore.  Are there marking on the rings showing size............?

Old School Al

the stock rings do not seem to have any markings on the with the exception of the middle ring which i think i can make out a faint 7R on one side.  does that mean anything?  base on the current bore can i get away with just new rings?

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39 minutes ago, komodo said:

the stock rings do not seem to have any markings on the with the exception of the middle ring which i think i can make out a faint 7R on one side.  does that mean anything?  base on the current bore can i get away with just new rings?

The 7R doesn't help us.  Depends on the condition of the bore.

Old School Al

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so that was the only marking i could see.  is it possible this may only need a new set of rings?  the bore seems to be within tolerance

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2 hours ago, komodo said:

so that was the only marking i could see.  is it possible this may only need a new set of rings?  the bore seems to be within tolerance

If the bore is ok the correct ring set may very well take care of the problem.

Old School Al

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