KR-1S.co.uk Forum

Mitaka pistons have a similar sized cut-out and people don't seem to have a problem with those. The same goes for 3mas running mitakas too.

I know what you mean though lozza

Dan

Mmm... My TZ pistons don't have that problem and I have fitted buttons in the piston pin holes this year to stop the short circuiting Lawrence mentions.

I have been led to believe that Aprilia do likewise on their Motors?

mj43 wrote: I have been led to believe that Aprilia do likewise on their Motors?

But short circuiting is not the main reason

what do you mean by " short circuiting"

Rocket wrote:what do you mean by " short circuiting"

the cutaways in the DT125 piston are so big, that when they are at the level of the boost/transfer ports they create a bridge between them. That way there is a direct connection between the exhaust and the cranckase when there isn't supposed to be one

I'm just trying a pair of Wossener KDX pistons, I've cut the skirts slightly to match bottom of the barrels / original pistons.

The lube holes aren't quite in the right place though so they open to the exhaust port briefely!




Look ok otherwise so I'm going to try them

Rocket wrote:what do you mean by " short circuiting"

Mark as Jan says the indents on the side of some pistons can allow gas from the transfer and the KIPS port to mix or escape.

The problem is not confined to just the piston indents, even if you have a piston with no indent in front of the piston pin, the piston pin hole sits across the KIPS and Front Transfer port. From memory a 'short circuit' occurs for 12mm of piston travel - 25% of the stroke.

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"Made many cheap and cheerful pin plugs from balsa and JB Weld, much to Frits' dismay Worst that can happen is it falls out and gets burnt and disappears into the exhaust. A kart motor that got a slight bit of deto showed no residual traces of the plugs. "

http://www.kiwibiker.co.nz/forums/showt ... er/page424

the above Kiwibiker thread is a mix of fact and fiction - but there is discussion of gudgeon pin plugs around page 424 - you need a login to see their photos though

I've just got my engine running with kdx pistons in. not ridden it yet but started up ok. A bit fluffy off idle but that could be carburation.

Professor wrote:
The lube holes aren't quite in the right place though so they open to the exhaust port briefely!

they should be in exact the same location

has your exhaust port been widened ?

KR-1R wrote:.
.
"Made many cheap and cheerful pin plugs from balsa and JB Weld, much to Frits' dismay Worst that can happen is it falls out and gets burnt and disappears into the exhaust. A kart motor that got a slight bit of deto showed no residual traces of the plugs. "

http://www.kiwibiker.co.nz/forums/showt ... er/page424

the above Kiwibiker thread is a mix of fact and fiction - but there is discussion of gudgeon pin plugs around page 424 - you need a login to see their photos though

Certainly has taken a life of it's own, like a black hole it's sucking in every 2T enthusiast in the world.

Professor wrote:

picture on the forum of a KR1 cylindre. you can see clearly the side of your port doesn't go straight down, so it must have been widened bye someone who didn't know what he was doing

They are KR1S barrels, origanaly tuned to stage 3 by stan stevens and I havent changed any thing drasticly on porting since buying the bike. The holes in the wossoner KDX piston are diffinatly slightly different postion compared to genuine kr1s. Maybe useful to have genuine kdx piston to compare?

Seems to be running in ok.

here is all the information on the KDX Woessner piston's :

viewtopic.php?t=7562

still : your exhaustports are too wide I recon

I do have some spare kr1s barrels that are fairly standard I think so I'll have a look at them to compare

Anyone else been using the kdx pistons for long?