Replaced the stocker with a wiseco.The Cyl was honed with a flex hone,all the rings are assembled correct,timing is right.I put a dab of oil on the piston skirt as RHC advised.I shimmed all valves on the loose side except for the exhaust valve that is connected to the auto-decompression mechanism,I left it on the tight side.I put valvoline mineral 20w-50 oil in it for break in,I will change it to fs 10w-50 oil after break in.

Kicked the bike for 25 times without any oil in the engine,seemed to have less compression than the stock one did.Filled the engine with oil and kicked another 25 times,compression got better,problably because the oil helped the rings to seal.Dont get me wrong,the engine still got compression,just not as much as it used to.

Could this be because a forged piston uses larger tolerances when cold than cast ones?

The Wiseco tollerances are loose but it will still have good compression installed propely.

The 20w50 is way to thick man. I doubt this is your problem but a good 10w40 is fine.

I would suspect the cam timing if the head/valves/valve seats are fine. If it's off one tooth it can do exactly what you describe.

No. The wiseco pistons use very tight tolerance lately. Were you able to check the ring gap? That's what makes compression. How does it run? I won't get into a debate over dry or lubed rebuilds, but I always rebuild with assembly lube.

get a compression gauge and check it. No way to tell if you are really out of acceptable range without knowing.

I agree that 20w-50 is to thick when cold,it was the only mineral oil I could find.The later number indicates its viscosity when hot,you want to use xx-50w oil,especially when using a high compression piston in hot weather.You can visually see the difference when taking the valve cover off.

All forged pistons have larger clearance compared to cast when cold because it expands a lot more.I measured the ring clearance,it was a bit smaller than the used oem ring but still within the specifications.
The cam timing is 100% on.

I shimmed the left exhaust valve(auto-decompression) from the loose side to the tight side,that should lift the valve a bit moore and flow a bit more when starting,and making the engine easier to crank over.Just my theory.

The bike still got good compression,it just feels like it had more before.Maybe im just paranoid.I will start the bike tomorrow and see how it runs.

the wiseco pistons used to have more clearance but not lately. Have you measured the piston to cyl clearance on one? Most are around .001-.002 and thats it. My wiseco was about .0017 or so.

Actually the first number in an oil weight is the grade when hot and the second is when it is cold, think about it- when oil gets hot it thins out, thats why you always run the engine to normal temps. before changing oil. That allows the now thinned oil to flow down into the lower case, where the drain plug is.

"The actual viscosity grade of a lubricant is determined by the Society of Automotive Engineers, for example SAE-15W40 for a multigrade oil and SAE-40 for a monograde oil. The first number (15W) refers to the viscosity grade at low temperatures (W from winter), whereas the second number (40) refers to the viscosity grade at high temperature."

The Service manual specs:0,020-0,042mm.The clearance stated on the wiseco box is 0,051,and thats somewhat what I measured on my wiseco setup.The clearance on forged pistons is much larger on the piston crown than at the bottom of the piston skirt.The piston crown gets a lot hotter than the skirt,the higher the temperature the more clearance the forged one will need when cold,thats why the clearance difference is more noticable on the crown.

I think im making myself crazy about nothing.Will fire her up tomorrow,warm up,shut down,check the compression,and if good then:ride:

When you set the clearance, if you were boring it, on a borable cyl that is, you measure at the bottom of the skirt. That's what you set the clearance by, not the dome. I will agree that forged pistons have more clearance on the dome than cast pistons.

Yep,the clearance is measured at the bottom of the skirt.

Went riding today.Started on second kick,no unusual noises so I started riding.Did some full throttle acceleration on 4 gear and started riding.I stopped after a while and heard some ticking noise on idle,I messed with the chain tensioner and the noise dissappeared.Continued riding and the noise came back.My friends yz450f made the same sound,but I dont remember hearing it before I did the top end.

The engine was still easy to crank.However it didnt burn oil like with the oem,started as good as always and made great power.I will take the valve cover off tonight to check that everything is ok.

The only problem i had that I thought the stock junkchain would work for one more ride.It stretched so much that the chain would even fit the rear sprocket and locked up.Hopefully it didnt harm the countershaft bearing.All this on 3h.Ive got a new rk x-ring chain to put on,but it needs a spacer to fit.

http://www.thumperta...achmentid=49319

Got the valve cover off,all valve clearances are ok,timing is on.Took the igntion cover plugs out to check the timing and found the oem piston circlip behind the big plug.I have absolutely no idea how it got there.Still,I dont think its the source of the noice,I think it has something to do with the chain tensioner.

MCL said:

YIKES piston cir-clips floating around inside your engine is NOT cool. I hope your sure it is the original removed from you're old piston. If not, the wrist pin will contact the cylinder wall.......

The OEM chain tensioner is auto, if you collapsed it all they way in before installation once you release it, its set. The timing chain could be worn, I like to replace the chain at top end time.

Yeah I know.It must be the old circlip,there is absolutely no way for it to get where i found it.I still have a hard time to understand how it got there.I bought the bike new this summer,it has only 4h on it.I replaced the piston because of the wrist pin issue.

I took the auto cam tensioner apart only to discover that the service manual has no information about it.I have no idea how much spring tension it should have,quess I need a new chain tensioner,preferably a manual one.

Tip of the day,dont disassemble the chain tensioner!

MCL said:

Yeah you don't want to do that.

With the guts removed drill and tap the end out to accept an 8mm bolt. Get a long 8 mm bolt (3 inch) and install with a lock nut and sealing washer into the tensioner body. The tensioner is now manual. If it sweats a bit use some PST on the threads.

The piston cir-clip can jump into the LS case when you remove it, down the chain tower.

Well,Im hoping that ape has a manual cam tensioner for the kx450f,otherwise I will problably order a new oem.

Yes it can get from the head to the ls case,but I found the circlip behind the bigger timing plug on the left case.There is absolutely now way it could get there.

MCL said:

I think your wrong about that.Didn't you find it there.

I found it behind the big timing plug on the left case.Its a separate little chamber where the end of the balancer shaft is turning,it is isolated from the left case with a oil seal.

Anyways,the dealer wants 105(150usd)euro for a new auto tensioner,I think I rather light myself on fire and run through a meth lab.I dont seem to find a manual tensioner for the big kawi.

MCL said:

I told you how to make yours manual......