OWNERS OF 125 YZ YAMAHA
I am busy compiling a report on the amount of failures that have occurred on the Yamaha 125 YZ.
When a failure occurs, the piston ring locating pin moves in towards the piston crown allowing the ring to rotate towards the transfer and exhaust ports. When this happens the ring ends protrude into the ports with the end result a badly damaged piston and barrel.
After numerous inquiries directed at Yamaha Distributor in Pinetown as to the reasons for these failures, answers received are as follows:
- most of the failures have occurred whilst operating the bikes on sandy motocross tracks or on fast enduro sections.
Yamaha maintains that in these conditions, the fuel mixtures are being run on the lean side causing excessively high combustion temperatures being placed on the piston crown with the end result that the ring-locating pin moves in and the failures occur.
With the above in mind I have asked myself the following:
(a) Why would Yamaha with their vast experience have the locating pin hole drilled deeper than required
(b) Are the pistons supplied by Yamaha being received from a vendor with poor manufacturing qualities.
(c) Why have these failures occurred during most of the 2001 year? (On bikes fitted with the 36mm carb and on the 2001 model fitted with the 38mm carb)
(d) Prior to 2001, failures of this kind did not occur.
(e) I have evidence where these failures have occurred, that the carb jetting has been run on the rich side.
(f) Finally, why has Yamaha radically changed the piston and barrel porting configurations on the 2002 models? No such changes during period 1996 to 2001.
I believe that Yamaha are well aware of the problems relating to these failures but still refuse to admit to their shortcomings.
I would appreciate it if you could forward any information relating to the above failures stating the following:
(1) State the track surface type – hard or sandy?
(2) Was standard exhaust used?
(3) What were the jet settings
(4) Model / year of bike
(5) Type of barrel used ( A / B /C )
(6) State the town where failure occurred
(7) Weather conditions and date
All information can be forwarded to my E-mail address as follows : colinj@muchasphalt.co.za
I am busy compiling a report on the amount of failures that have occurred on the Yamaha 125 YZ.
When a failure occurs, the piston ring locating pin moves in towards the piston crown allowing the ring to rotate towards the transfer and exhaust ports. When this happens the ring ends protrude into the ports with the end result a badly damaged piston and barrel.
After numerous inquiries directed at Yamaha Distributor in Pinetown as to the reasons for these failures, answers received are as follows:
- most of the failures have occurred whilst operating the bikes on sandy motocross tracks or on fast enduro sections.
Yamaha maintains that in these conditions, the fuel mixtures are being run on the lean side causing excessively high combustion temperatures being placed on the piston crown with the end result that the ring-locating pin moves in and the failures occur.
With the above in mind I have asked myself the following:
(a) Why would Yamaha with their vast experience have the locating pin hole drilled deeper than required
(b) Are the pistons supplied by Yamaha being received from a vendor with poor manufacturing qualities.
(c) Why have these failures occurred during most of the 2001 year? (On bikes fitted with the 36mm carb and on the 2001 model fitted with the 38mm carb)
(d) Prior to 2001, failures of this kind did not occur.
(e) I have evidence where these failures have occurred, that the carb jetting has been run on the rich side.
(f) Finally, why has Yamaha radically changed the piston and barrel porting configurations on the 2002 models? No such changes during period 1996 to 2001.
I believe that Yamaha are well aware of the problems relating to these failures but still refuse to admit to their shortcomings.
I would appreciate it if you could forward any information relating to the above failures stating the following:
(1) State the track surface type – hard or sandy?
(2) Was standard exhaust used?
(3) What were the jet settings
(4) Model / year of bike
(5) Type of barrel used ( A / B /C )
(6) State the town where failure occurred
(7) Weather conditions and date
All information can be forwarded to my E-mail address as follows : colinj@muchasphalt.co.za
