Mitaka piston casting defect

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DougB
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Re: Mitaka piston casting defect

Post by DougB »

Hi Dirk,

I only started to find this problem last week so now I'm trying to get in touch with suppliers and see what they say, I still can't say for certain what has caused it and I'm going to be trying to find out, hopefully with the help of the distributors or Mitaka, but we'll see. All 4 pistons that have been running are badly affected to different degrees, the worst one is so bad the pin rattles in the piston.

I know I'm not going to put Mitakas in any time soon! I've read that a few people have used the Wossner pistons without issue but Janbros has pointed out they do have problems and other than that it looks like YZ125 '89 Wiseco pistons work.

If I hear anything back about this problem I'll let you know.

Cheers, Doug.
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JanBros
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Re: Mitaka piston casting defect

Post by JanBros »

bozbridge wrote: it looks like YZ125 '89 Wiseco pistons work.
don't forget : the deckheight of those is from memory 2mm less !

KDX125 is almost identical to KR1, except it's a bit shorter at the bottom.
viewtopic.php?f=19&t=7562&hilit=kdx125
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dirk
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Re: Mitaka piston casting defect

Post by dirk »

bozbridge wrote:... I'm going to send them all back to the supplier and see if Mitaka can suggest any reason, and have decided when I rebuild I'll probably use Wossner pistons next time.
....
Hi Doug

any news?


I was brave (or crazy) and have installed the new piston (warranty).
Unfortunately, after about 200 -300km the base gasket * slightly leaking.
i have the nuts tightened again (now seems to be sealed).
on the occasion I've looked into the cylinder outlet.
the coating from the pistons (as far as I could see) was virtually non-existent.
far more than the "old" piston after 500km (viewtopic.php?f=19&t=12419).
the piston surface but looked good.
no scratch.
maybe the coating is only a running-in aid?
the cylinder wall was not great either.
on both cylinders right and left of the outlet very light gray stripes could be seen. about 1cm wide and ~ 4cm long (more I could not see).
but did not look squeezing by piston. no scratches.
the engine ran well.

i drive the engine, and look what happens.
i do not feel like every time to build the engine apart.

cheers
Dirk

base gasket *
Kawasaki has new base gaskets.
the new seals look brownish and are made of slightly different material.
KR-1S 1990
RG500 1987
RGV 250 1992
TZR250 (2MA) 1987
DougB
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Re: Mitaka piston casting defect

Post by DougB »

Hi Dirk,

I've spoken to the supplier and I've sent 2 pistons back for them to check. The only definite conclusion we reached is that the expander ring behind the bottom ring should NOT be used, the break up very quickly, the supplier had already had some pistons back that this had happened to and on all 4 of my pistons they have broken up as well.

The black coating doesn't last long but I was told it isn't meant to and will wear off within a few hundred miles as it's mainly to help the pistons to run-in.

When I hear any more regarding the problems around the gudgeon pin and I'll let you know.
DougB
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Re: Mitaka piston casting defect

Post by DougB »

I've had some info back, started a thread in chit-chat about the piston trouble and reply from Mitaka.
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Re: Mitaka piston casting defect

Post by KR-1R »

EGG
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Re: Mitaka piston casting defect

Post by EGG »

The more I read these threads, the more I'm starting to worry a bit about my Mitaka pistons which were installed maybe a year before this thread and I did use those expander rings.

Currently I'm not getting great compression (95psi on one cylinder and 105 on the other when the engine is at 41C). The engine also puts out vast amounts of smoke above 9k RPM. I'd always assumed this smoke was fuel/oil residue in the powervalves getting cleared when they opened.
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