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Review: 

EMOT Racing's TZ pistons.

10 to 15 years ago TZ250 owners began to find it hard to buy pistons for their quarter litre machines, stocks were running out … fast. By the time 2003 had arrived they were almost impossible to locate, save for those people who had hoarded a few over the years and decided to sell them now.

1973 to 1980 TZ250s were becoming a novelty at race meetings, with 250 LCs filling the majority of grid positions. EMOT Racing's research dept. cleverly worked out that an Italian TM piston could be satisfactorily substituted for the virtually unobtainable OEM Yamaha item.

Picture: The TM piston which can easily be substituted for a TZ250 item with minor modification, email EMOT Racing for details.

With the popularity of the TZ350 in Forgotten Era type racing classes today it is not hard to imagine that this critical supply situation could raise it’s ugly head for 350cc TZ owners in years to come. This is where quality after-market pistons like EMOT Racing'’s Italian made “GOL” units can be called upon to fill the void and keep TZ350s out on the track. 

Picture: EMOT Racing's TZ350 piston.

EMOT Racing'’s Martijn Stehouwer had spoken of the success and reliability he had been enjoying from the GOL pistons for months before sending a pair over from The Netherlands for tz350.com to review recently, and we are very impressed !

The GOL piston is a very well made, strong looking unit, even sturdier looking than the original Yamaha 328 item. It is essentially a copy of the ART brand TZ350C/D piston with the following improvements:

• 0.5mm thicker skirts.
• 2.5mm thicker wrist (gudgeon) pin bosses.
• Dual, internal wrist pin boss supporting webs. The stock Yamaha item has just one each side.
• 2.5mm lubrication holes in the underside of the wrist pin bosses to lubricate the wrist pin if necessary.
• Piston ring locating pin is installed horizontally inside the groove to reduce the risk of it dislodging from the piston crown at high rpm.
• Piston crown is buffed to help reduce carbon buildup.

Along with the above, the following differences exist as well:

• The inlet skirt length of a stock TZ350C/D piston is 59mm and the exhaust skirt 62mm. With the GOL piston the lengths are identical at 62mm, leaving scope to “play” with inlet timing through the custom machining of the skirt as required.

Picture: Compare the "behind the scenes"  look of the stock Yamaha TZ350C/D piston with that of the GOL item!

• The piston ring groove is machined 1mm closer to the piston crown than the stock Yamaha piston.
• The ring groove accepts GOL, Yamaha or Wiseco rings. (Wiseco of course only when running Nikasil lined cylinders.)

Of course, with the extra aluminium all over the place, the GOL piston is slightly heavier than the Yamaha item, but what you get in return for the weight is strength, though it is quite easy to remove 8 to 10 grams through some careful grinding of the inlet skirts. These pistons look almost indestructible!

Martijn clarifies the situation with his comments: "We wanted to create a strong basis with room for everyone's own individual changes."  (Mission accomplished!)

The piston kits (one piston with a chrome ring) cost €98.00 for European purchases and €82.35 (no VAT) for overseas buyers, though depending on your local taxation laws there might be some sort of import duty applied by your Customs dept.

The reviewed pair of pistons are now installed in the tz350.com TZ350F ready for our next race.  

Stay tuned !

For more detail of  EMOT Racing's aftermarket TZ250 and 350 pistons email Martijn direct at:                      stehouwer@emot.nl

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03/23/08 07:15 AM +1000    

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