FS650 Big End/Small End issues? Sloppy piston!

LemoneyF · Jun 2, 2015

Hi All

The berg has been grounded for months now, ive been so busy lately and it kills me to see it the way it is. Lucky for it though, very soon Ive got some time to put into it to (hopefully!) get it looking and running like new. Three months ago one of the exhaust conical springs broke (318hrs, not bad!) and just now I opened it up to inspect for valve/piston impact. Luckily, it looks fine- the spring broke very close to the seat and the valve wasnt hanging into the chamber much at all.

However Ive noticed a respectable amount of slack in side to side piston movement, as well as radial movement when you grab the valve pockets and twist. Theres maybe 0.5mm of side to side movement, and 1-2 degrees of radial twist. I cant find any info on this and Im keen for some expert insight. What might cause it? Weirdly, there was no alarming noise, compression is still very high, theres no 'clunk' at TDC, and my liner has no strange or serious wear for the length of the bore. Could it even be normal? (accounting for thermal expansion ect)

Im considering installing new piston rings, main bearings, cam chain, DVSK and a bit of other stuff, am I up for a crank rebuild too? I havent yet had time to split the cases and I know this would probably yield the answer straight up, but im interested to hear thoughts first.

2004 FS650e, rebuilt at 11000kms with new mains, crank, piston, valves ect. Conical springs let go at 18000kms, 318hrs.

If my explanation doesnt work I can make a quick video.

Thanks, Rob.

bushmechanic · Jun 2, 2015

front to back movement is normal, the piston is smaller at the top in front and back

side to side movement ... not so much as front to back but still ok, haven't noticed any concerning twist in any of mine

twist comes from little end and big end wear, only one way to find out for sure which one it is.

tourist · Jun 2, 2015

To try to deepen understanding - Does crank axial play manifest in side-to-side play of piston.. ? The rod should never move ON the crank, but can the piston/rod move the crank if the crank can move?

worstinfinland · Jun 2, 2015

The small end pin to piston side-to-side play is about 1cm, so I don't think piston side-to-side play in the liner could say anything about big- or small end issues.

bushmechanic · Jun 2, 2015

tourist said:
To try to deepen understanding - Does crank axial play manifest in side-to-side play of piston.. ? The rod should never move ON the crank, but can the piston/rod move the crank if the crank can move?

no

jmscrttndn · Jun 2, 2015

FWIW, I just replaced my conrod at 100hr. The inner big end surface of the conrod started pitting which caused some issues.

If you are going to tear into the engine, the conrod may be worth doing. From my recent experience, the ConRod kit was cheapest from Munn Racing (get the deal for his site thru KTMtalk.com)... and it was $150 CAD to do the labour.

bushmechanic · Jun 2, 2015

600 thanks LOL

that was an easy one tourist, 2 letters and a smiley face

tourist · Jun 2, 2015

LemoneyF · Jun 3, 2015

Yeah thanks guys, WorstinFinland that didnt even occur to me and is a sound explanation. jmscrttndn with your conrod pitting did you replace the conrod as well as the big and small end bearings? Munn racing lists the conrod repair kit at $430US, did this include the conrod itself? someone told me it was just bearings, which is a frightening thought.

jmscrttndn · Jun 3, 2015

LemoneyF said:
Yeah thanks guys, WorstinFinland that didnt even occur to me and is a sound explanation. jmscrttndn with your conrod pitting did you replace the conrod as well as the big and small end bearings? Munn racing lists the conrod repair kit at $430US, did this include the conrod itself? someone told me it was just bearings, which is a frightening thought.

I certainly didn't pay $430USD... it was probably around $300USD. Not sure if the pricing increased in the last month or what... again, be sure to get the 25% discount thru KTMtalk.

It was $372 USD before discount.

Be VERY specific when explaining how you want it shippied. He shipped my first package perfectly... but totally screwed up my second one.

Conrod repair kit comes with new conrod, new big end bearing, new big end pin, and a new little end bearing (plain bearing, looks like a bushing). You may want to get yourself a new little end pin too (again, with the level of effort of splitting the cases, you may as well do it right).

Taffy · Jun 4, 2015

the Husabergs are poor on the little end on the bikes up to 2004. ALL the engine sizes are like it. i do a half price little end bush.

that rod is $415 here. but post is very cheap and you won't get any import duty fees by the time I'm done!

Taffy

bushmechanic · Jun 5, 2015

Hes in OZ there is no import duty up to $1000

james its an 04 ... different rod.

lemony for a cheaper option try orangeberg for the rod kit, his contact details in my signature

jmscrttndn · Jun 5, 2015

bushmechanic said:
james its an 04 ... different rod.

My bad. Funny how the prices fluctuate. For example, the 450 rod is much more $$ than the 650 rod (if I remember correctly).

Also, The rod kit specifically said made in Italy. There are a few Italian rod makers I have seen online. This gives me hope for being able to acquire hard-to-find parts into the future... go straight to the source in Italy. Hopefully my rod holds up for 200 hrs so that the Bike will be at the end of its life and I won't have to worry about another rebuild.

FS650 Big End/Small End issues? Sloppy piston!

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