Worn out cylinder in my WR450F :(

[Hurky]

Hello, I've just opened the top-end for checking everything against measurements and tolerances like shown in the workbook and found that the cylinder is not in the condition I liked it to be to be honest; The bike has 5645Km with 252 hrs and a bought it second hand so I cannot be 100% sure about the hrs or kms...

I've measured cylinder and piston with a precise micrometer getting the following results (all in milimeters):

Maximum cylinder measure (measured 6 times X and Y like shown in the book): 95,04 (should be 95,00-95,01 so it is off )

Minimum cylinder measure: 95,03

Ovalization: 0,01 (maximum 0,05)

Conicity: 0,01 (maximum 0,05)

Piston diameter at 8mm from skirt: 94,98 (specified is 94,965 - 94,980)

Clearance piston/cylinder 95,04-94,98= 0,06 (Standard is 0,020 - 0,045 with service limit of 0,1 so it is ok)

The rings are also within the tolerances.

First ring gap: 0,40 (standard 0,20 - 0,30 with limit 0,55)

Second ring gap: 0,70 (standard 0,35 - 0,50 with limit 0,85)

Here some fotos of the cylinder and piston:

What do you think ? Is it normal having this signs of wornout in the cylinder with only 5600 Km ??? The measures are all within the tolerances and should not give any problems leaving it untouched but the cylinder is off and the nikasil is not in it best shape, you cannot see the marks of the honing in the longitudinal axis at all and there ARE some vertical scratches that you CAN feel with the nail... I think the correct thing is to replate or going for an exchange cylinder, what do you think ?

Thanks and best regards from Spain.

[Stealth13]

Hello, I've just opened the top-end for checking everything against measurements and tolerances like shown in the workbook and found that the cylinder is not in the condition I liked it to be to be honest; The bike has 5645Km with 252 hrs and a bought it second hand so I cannot be 100% sure about the hrs or kms...

I've measured cylinder and piston with a precise micrometer getting the following results (all in milimeters):

Maximum cylinder measure (measured 6 times X and Y like shown in the book): 95,04 (should be 95,00-95,01 so it is off )

Minimum cylinder measure: 95,03

Ovalization: 0,01 (maximum 0,05)

Conicity: 0,01 (maximum 0,05)

Piston diameter at 8mm from skirt: 94,98 (specified is 94,965 - 94,980)

Clearance piston/cylinder 95,04-94,98= 0,06 (Standard is 0,020 - 0,045 with service limit of 0,1 so it is ok)

The rings are also within the tolerances.

First ring gap: 0,40 (standard 0,20 - 0,30 with limit 0,55)

Second ring gap: 0,70 (standard 0,35 - 0,50 with limit 0,85)

Here some fotos of the cylinder and piston:

What do you think ? Is it normal having this signs of wornout in the cylinder with only 5600 Km ??? The measures are all within the tolerances and should not give any problems leaving it untouched but the cylinder is off and the nikasil is not in it best shape, you cannot see the marks of the honing in the longitudinal axis at all and there ARE some vertical scratches that you CAN feel with the nail... I think the correct thing is to replate or going for an exchange cylinder, what do you think ?

Thanks and best regards from Spain.

was it not running properly? Mine has over 5500 and runs fine, I see lots over 10000 without taking apart the engine...

[Hurky]

It was running good !, but I want to inspect the state before failures happen.....

[GuyGraham]

I've measured cylinder and piston with a precise micrometer getting the following results (all in milimeters):

Maximum cylinder measure (measured 6 times X and Y like shown in the book): 95,04 (should be 95,00-95,01 so it is off )

95.00 - 95.01 is for cylinder when new, so that you can fit any piston with any cylinder and the clearance is within spec

As you see, it has some wear, but your still under the 0.1mm piston to cylinder clearance so you are good to go in that respect

your cylinder does show some signs of scoring, so as its off the bike now you might as well get it replated then you aint gotta worry

5K is quite low for cylinder wear like that on a plated bore

Cylinder wear/damage is usually caused by dirt bypassing the airfilter & getting into the cylinder

Edited July 1, 2012 by GuyGraham

[Just_a_trail_rider]

that cylinder looks pretty darn good to me. I would give it a very light and quick hit with a hone. Then put a new piston and rings in it.

I got 8K miles out of my original piston and rings. It was old and tired, but it ran just fine.

It would take a lot of dirt to score your cylinder. A more likely reason for the wear on the piston and cylinder is worn out rings. The rings allow the piston to float in the cylinder, never touching the walls. Once the rings are worn, the piston rocks in the cylinder and makes contact with the side of the cylinder.

That cylinder wall is significally harder and tougher than the piston or rings. I would hit it lightly with a hone and check the clearances again. BUt, it looks like a good cylinder to me.

[kawi380]

Yep, :looks a little worn but not to where I would replace it. Like mouricedorris said hone and piston and rings.

[Hurky]

Thanks for all your replys ...

I thought in giving it a hone and putting a new piston in, that was my plan before opening... But I've talk with an friend about the honing and he think that to remove the scratches the honing will eat 0,04 or 0,05mm , and knowing that I was already in the 0,06mm I would be over spec until honed. Well I can hone it only very little to give it a crisscross pattern without trying to hone-out the scratches completly....

The normal procedure after a honing is going to the next oversize letter piston, but here happens a strange thing;

My used piston measured 94,98 (specified is 94,965 - 94,980), I find it very strange that my used piston measure the maximum diameter permitted and it is showing some wear in the skirt. Even more stranger is that all after-market pistons I searched for start with letter A being smaller, if I remember right letter A normally is 94,95, B,C and D are +0,01 so the biggest letter D will end up being 95,98 (Wössner for ex.) or 95,97 (Prox for ex that start with a 94,94mm letter A) So, how is it possible that an oversize letter piston is equal or smaller than my original and used piston ??? If that was not the case I simply opted to hone it and put a bigger letter oversize to maintain the correct clearance.

As of worn rings , there are in specs at least in gap measure, it could have been dirt in the airfilter or possible be using an stainless oil filter ?

Mmh, I don't really know at this point what I will do, I've looked at the Cylinder Works BigBore kits and like the idea of having everything new plus trying the 480cc

Only doing a very light hone and mounting the same piston is also possible and very lowcost, maybe some new rings and thats it.... mmmh....

[GuyGraham]

that cylinder looks pretty darn good to me.

This bit don't look good

As regards honing

don't hone with a 3 legged sprung hone with stones on it - it will take too much metal off as you have already stated

It justs wants a de-glaze, if that is all you are gonna do

it needs to be a ballhone like this

Ball Hone. dont use any thing else labeled as a hone for this.

Edited July 2, 2012 by GuyGraham

[Hurky]

Thanks again.

Finally I'll opt for an new cylinder kit from Cylinder Works, and as the bigbore doesn´t cost much more I'll go for a 479cc bore with a 98mm Forged piston (that comes with the kit).

I'll check the valves and stems and change the oil seals of them at least, the crankshaft looks and feels very good from the rod bearing so I suppose it's ok, the only thing I noticed is a very very small amount of tolerance in the crankshaft axle bearing, I mean, if I try moving the flywheel in every axis I feel a little movement and very low click sound (but as I said, very little). Talked with my friend the machinist and he think that's ok and pretty normal, a little tolerance should be there in the bearings.

So, what do YOU meen ? (he's not an motor mechanics), should I split the cases only to change the two main bearing of the crankshaft or is it indeed normal to feel a little bit of tolerance there ?

Regards !

[MaxPower]

was your previous bike a KX85?These bikes dont wear like high revving 2 strokes. There are bikes that have gone thousands of miles with original main bearings and pistons. What year is your bike?If you have a 05 to 05 you may want to install the oil nozzle like Rs25 had showed us. I just ordered one for my bike to install

[Hurky]

It's an 2008 aluminum frame WR450F, bought second hand and now has the mileage and hours stated in my first post. Is people said me the used cylinder may be cause of dirt, I suppose the crank and bearings are still good enough for the big bore... It least I hope so hehe...

[Hurky]

Not a KX but all my previous bikes was 2T, my last one a GasGas 250EC with the 300cc KIT.....