New Mitaka pistons - Are they right?

varonos · Post by **varonos** » Sat Sep 24, 2011 11:09 am

Hi guys,
I am rebuilding my KR1S C engine. I just got the barrels replated and I received the pistons. I thought Mitaka is a good options. Although pistons do not have oil holes...as the previous pistons on the bike...Are they right? I do not want to kill the replated barrels...

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Thanks in advance!!!!

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JanBros · Post by **JanBros** » Sat Sep 24, 2011 11:19 pm

here you can find all the data off the piston .it's from a KDX125, but everything that matters is the same, apart that they are +/-5mm shorter.

http://www.megaupload.com/?d=9DJEWXX3 (wait 45sec before you can download the pdf).

certainly don't run it without the lubricating holes !!!

varonos · Post by **varonos** » Sun Sep 25, 2011 12:16 pm

Hi Jan Bros,
Thanks for your comment.
I will send the pistons back to Langcourt tomorrow.

Luders · Post by **Luders** » Sun Sep 25, 2011 7:47 pm

Stan Stephens has sold a lot of his kit to them, including the 300cc conversion stuff for the KR.

How much did they charge you for the barrels?

JanBros · Post by **JanBros** » Sun Sep 25, 2011 8:31 pm

varonos wrote: I will send the pistons back to Langcourt tomorrow.

if it's just the holes, you can drill them yourself.

varonos · Post by **varonos** » Mon Sep 26, 2011 7:20 am

Hi Luders,
They charge about 110 for every barrel. My previous experience says that they do a pretty decent job, service is very quick.
Janbros, I will see if I can send them back and the proper ones otherwise I will drill them...hopefully they will fine..
Thanks

Luders · Post by **Luders** » Mon Sep 26, 2011 9:52 am

That's about the going rate

varonos · Post by **varonos** » Wed Sep 28, 2011 9:38 am

I got the new pistons through the post yesterday. i will post some photos this afternoon...It looks like they are they same pistons - but with 2 holes on each side.
Apparently the mitaka piston box says DT125.....Any ideas? I was trying to find the standard piston dimensions of the KR1S in the forum...but no luck..Anyone can help with a link or the dimensions?
I am going to weigh and measure them at work today and find out...
Thanks in advance for your help!

Howie · Post by **Howie** » Thu Sep 29, 2011 7:10 pm

Apparently the mitaka piston box says DT125.....Any ideas?

This got me thinking

So I went out to my shed where I have a piston for a DT125 & had a measure up.

I knew the Dt125 (not sure about all models but the engine I have is from an early 80's bike) had the same bore & stroke as the Kr1s but I didn't know if the gudgeon pin was the same size or crown height etc etc.

Anyway, they are very similar other than the piston for my Dt125 has a longer skirt & NO holes but they share the same gudgeon pin dimensions & the crown height looks very similar.

Maybe Mitaka do a 'universal' piston kit? To fit several different models.

varonos · Post by **varonos** » Thu Sep 29, 2011 8:31 pm

Finally I got the photos from the pistons. I measured them today...
Here are the results:
Bore: 55.928mm
Stroke: 64if i am right- forgot the paper at work...

Weight:134g

Here are the photos. Any ideas if the ring pegs postions are fine?

Any comments?
Thanks for all your help[/img]

varonos · Post by **varonos** » Thu Sep 29, 2011 8:34 pm

Sorry right photos are here...

JanBros · Post by **JanBros** » Fri Sep 30, 2011 8:46 am

varonos wrote:Finally I got the photos from the pistons. I measured them today...
Here are the results:
Bore: 55.928mm
Stroke: 64if i am right- forgot the paper at work...
Weight:134g

Here are the photos. Any ideas if the ring pegs postions are fine?

with bore I suppose you mean the height of the piston ?

in this topic, you can see where the pins need to be :
viewtopic.php?t=7562

and as I said before : you can use the KDX125-dimensions to check it out : all the important dimensions (compression height, location off the pin's + holes, dome, ...) are all the same.

dave32 · Post by **dave32** » Mon Oct 10, 2011 2:08 pm

Funny you should say about them being similar to the DT125,previous ones i have bought had DT/TZR125 crossed out and Kr1/s wrote instead,these were from Grampian.
aAlso they used to be Jap made by Prox which was stamped inside the skirt,now there Taiwan made.
The ring locating pegs also now seem to be on opposite(upper and lower) side than the Jap ones used to be,which wont make any difference to be fair.
One thing i would do is chamfer the skirt with a decent file and dress it with fine wet/dry.
Also if it came with those dodgy C clips with the tail,chuck em over the hedge and fit some off a 4DP TZ.
The tail will wear over time from the constant rubbing of the gudgeon pin then drop off into the cylinder,they were made fro pistons without extractor slots so there not needed,plus there very weak and can be fitted with no effort.
Funnily enough they used to come with decent clips and RK rings(in a red box),now the rings are an unknown quantity.
Junk the oil control ring aswell as over time they become brittle,on removing one from a 3000 mile set of pistons they just deteriorated in my hand!
Also check the ring end gap and dress the ring ends with an oil stone or similar.
Out of curiosity where did you get the pistons?
my last set(that i wasnt impressed) were from PJ engineering.
and as Janbros said you can drill your own oil holes.
Hope this is of some help.
ATB
Dave

ioannis · Post by **ioannis** » Wed Oct 12, 2011 11:31 am

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dave32 · Post by **dave32** » Thu Oct 13, 2011 10:26 pm