questions on rod\piston play

[mudronin]

please excuse the lack of proper grammer, but i was wondering if anyone could tell me if there should be any play in the crank<bottom of rod> bearing and wrist pin bearing?

also on kips should it move freely when turned by hand?

the bike:
1995 kdx 200 supposedly fresh topend with new nikasil and piston. the piston has LOTS of space in the cylinder and it has been sleeved rather than coated.
the cylinder has scoring in the front around the exaust port and scratches in the back. this doesnt seem like a fresh motor.
i did ride it before purchase and it seemed ok except the common rattle. after about 30 ride time at home my curiosity got the best of me and off came the top end. ill be happy to link pics and a short vid of the movement.


thanks

 

[ridejunky]

No up and down play on crank bearing. A very small amount of side shake when tdc measured at top of rod ok. Wrist pin should have no play. Kips should have no bind but
freely is relative.

 

[mudronin]

freely: without a tight spot during cycle.

posting a video link of crank side movement shortly.

 

[ridejunky]

Then freely it is!! :)

 

[mudronin]

Update

ok i cant post video link yet because i need to get my post count up:)

anyway, i tracked down the part number for the piston and it shows to be a STD replacement [part#711M06600] size. now i am beginning to feel a bit foolish and i am VERY glad i didnt call the PO to gripe!

the reason i took the thing apart in the first place was the knocking. i got the trusty stethiscope and narrowed it down to the topend. i know the kdx is somewhat noisey but this seemed extreme. think ill send the cylinder off to FRP and have it ported and recoated/honed to stock then i think a bottom end job....since i already have it out. i also noticed some oil on the balancer as i rotated it so looks like maybe a leaky seal.

 

[mudronin]

update#2

ok.....

After further inspection of my new toy, I found a boldly stamped "C" on the cylinder. Since I am fairly new to 2 stroke work, doesnt this indicate the overbore? e.g. std, b,c

I measured across the bore at the top of the cylinder and was surprised to find it at just over 66mm and although with the rings inserted and true leveled with the top of the cylinder using a depth mic, there are no gaps between the ring and cylinder wall. I do etching and engraving and have a light table, so this is an easy thing for me to check.

I realize that the cylinder will be slightly larger below the ring line, which is why I measured at the top for the starting bore size. with the piston in {minus rings} using a metric feeler gauge, the piston to cylinder clearance at the top of the cylinder is .076mm while the center portion of the cylinder is.178mm . While I'm here I will also mention that closer inspection of the piston pin, the bearing portion was shiney and smooth but the outside seemed to have 'spun' in the piston though I cant verify any wear due to lack of proper micrometer. So... it seems this was a 'C' size then resleeved to standard but with no nikasil. Looks like its off to frp...but I will email Jeff first to see if he can check my piston for servicability while he has it there.

While that is happening I will have a very good local race shop split my case and replace all bearings seals and pin.

Full list of parts involved:

bike $1300
fmf rev pipe $207
bearing/seal kit $56
twin air filter $30
gasket set $39
boyesen power reeds $32+shipping
main and pilot {155/45} $13
cylinder porting $185
boring if needed $65
re-nikasil $165
dunlop 952 {f/r} $101
chain/sprokets $79 {steel front aluminum rear gold xring pkg.}
hotrods kit $89
engine split pin/rod install ~quoted "about 80 bucks"

man when i do it that way this is costing me a ton! But can you really put a price on fun? :laugh:

 

[glad2ride]

Hi. Sorry to hear of your troubles. You may want to buy a service manual. You are measuring in the wrong place. Normally, a bore gauge is used to measure the cylinder inner diameter, then a micrometer to measure the piston. Subtract the piston measurement from the cylinder measurement to get the gap measurement.

"Standard" is not really some OEM measurement. The cylinders and pistons are "A", "B", "C", etc. It's a .01mm difference. Check the Pro-X site for differences.

The big end bearing has a side play specification.

Several people have complained of KIPS (power valve) parts making a rattling sound.

Good luck with your new bike.

 

[mudronin]

hey thanks for the response but i do have a manual and what i was mainly checking for is uneven wear. i did use a mic to measure the bore {spring loaded inside dia. tool then mic'd with a caliperand the crank end play i also used a metric feeler gauge.

really heads up to make sure its done proper and again thank you! i checked the pro-x site for the list and i will measure my wiesco to make sure it is still up to snuff.