* BOJ fails to add stimulus, sending yen to 18-month peak
* Investors, traders wonder if BOJ unable or unwilling to do more
* Entire global stimulus experiment increasingly in doubt
By Wayne Cole
SYDNEY, April 29 (Reuters) - The Bank of Japan's shock decision this week not to provide additional stimulus to the struggling Japanese economy has prompted some investors and traders to bet that policy makers are out of bullets, clearing the path for further gains in the yen.
After BOJ Governor Haruhiko Kuroda on Thursday dashed expectations of more easing, the yen has been on a tear. It yen spiked 2.6 percent to 108.11 against the U.S. dollar straight after the decision to post its biggest daily gain in more than five years and pushed on to an 18-month peak of 107.075 per dollar on Friday. A stronger yen is punishing Japanese exporters and left the Nikkei share index down 5 percent for the week.
Kuroda has been at the forefront of Japan's efforts to escape the debilitating drag of deflation, launching massive asset buying campaigns before taking interest rates negative earlier this year.
For him to pause on policy, even if only to gauge the impact of past easing, alarmed markets addicted to ever-more aggressive and exotic stimulus measures from the world's boldest central bank.
"The sneaking doubt here is that perhaps we're witnessing the end of the great monetary easing experiment and that's obviously a very dangerous path for the BOJ," says Frederic Neumann, HSBC's co-head Of Asian economic research in Hong Kong.
"The pressure will only grow for the BOJ to do more," he adds. "Without any further action, it is fairly likely that the yen would continue its upward trajectory and equities will continue to be under pressure."
Kuroda did on Thursday leave the door open for more stimulus, stressing there were no limits to what monetary policy can do to address strong risks to the outlook.
"There's absolutely no change to our stance of aiming to achieve 2 percent inflation at the earliest date possible, and to do whatever it takes to achieve this," he told a news conference. "If needed, we can deepen negative rates much more."
The BOJ cut its inflation forecasts in a quarterly review of its projections, also on Thursday. And it again pushed back the timing for hitting its 2 percent price target, by six months, saying it may not happen until March 2018 at the latest.
The yen's resurgence was also an echo of the euro's reaction in March when European Central Bank Governor Mario Draghi said that further cuts in interest rates would not be needed.