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Just doing my first piston change on my 2004 EXC 400.  Head and cylinder off, I can move the con rod from side to side a centimetre or two, affectively moving side to side on the big end.  Is this normal/ok or should there be no lateral moment?Video here 

 

Thanks, Dan.

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That looks like a tad much but idk if i'd be worried, as long as there is no up and down play you should be good to go. Up and down and you need a rebuild! 

I'll let others Q in though

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Older ktm's have an issue known as crank spread, where the crank is trying to separate. The crank then begins to bind on the main bearing killing horse power.  Many places have reverted to welding the crank pin.

Your vid it looks excessive , but you'd need the service manual for the actual measurements.

The latest cranks, only allow for about .5mm side to side and about 1.1 mm axial as an example

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Absolutely no up/down at all allowed 

It's difficult to hold and move up/down only so try it several times to be sure

Edited by gitenby
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Spud has the key, get the service manual and follow the steps for checking the crank. There will be allowed limits for play and you can measure and compare against the allowed values.  

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Thanks for the replies guys.    Whilst I'm here how does the piston and cylinder look to you guys?

The marks on the sleeve are imperceptible to touch, cant feel any grooves/scratches with my finger nail).  I cant feel any variation in the cylinder where you see the marks. It's more targeted polishing :) than gouges and theses no lip at all at the top of the cylinder when the rings top out which I believe is a good sign?

Presumably I do need to change that piston? not looking good on the skirts

I can borrow a bore gauge and measure front to back, side t side of the cylinder - would that indicate if OK or not?

 

Another bit I'd happily take advice on is state of the valves/heard - should I clean this up, get valves ground and seats re-cut?

All this was working perfectly fine by the way.  I'm doing a bit of restore on the old girl, haven't changed the piston in a few thousand miles so thought it time to.

Thanks, Dan.

 

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How much money do you want to spend?  If you put it back together with that cylinder it will run, but that could definitely use replating and a new piston.  You can ask the machine shop if it can be honed, but I don't know how much honing they can do on a plated cylinder.  The head can be cleaned up to remove the carbon.  Soft scrub and hot water, etc.. just dry and oil it immediately after.  To check the valves, put something thin like carburetor cleaner, ether, etc.. in the intake ports and exhaust ports, then flip the head over and see if any leaked past the valves.  If nothing leaked then they are still sealing OK.  Might as well replace the valve stem seals while you're in there, though you'll have to remove the valve springs to do that.  If you want to be very thorough then probably send the head out and have it checked.  Measuring the valve seats, stems, guides, etc.. requires tools that most people don't have sitting around.  Then again, on an older bike like that, I would personally just do the leak test, maybe install some new valve stem seals and leave it at that.   You can spend silly  money making the engine like-new again, but is it worth it?  Do check the crank though, before you do anything else.  If it's out of spec then start adding up all the parts and decide if a bike that old is worth all the cash, or if it's better to just trade it now or ride it as-is as long as it runs.  

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19 hours ago, floydstar said:

Thanks for the replies guys.    Whilst I'm here how does the piston and cylinder look to you guys?

The marks on the sleeve are imperceptible to touch, cant feel any grooves/scratches with my finger nail).  I cant feel any variation in the cylinder where you see the marks. It's more targeted polishing :) than gouges and theses no lip at all at the top of the cylinder when the rings top out which I believe is a good sign?

Presumably I do need to change that piston? not looking good on the skirts

I can borrow a bore gauge and measure front to back, side t side of the cylinder - would that indicate if OK or not?

 

Your cylinder looks great! cross hatch still under the polish. Still have it checked for out of round and in spec for new piston.

You can wash soap & water and very lightly use green scotch bright and follow cross hatch pattern instead of hone  Follow the service manual for specs crank/cylinder/head and you will be in great shape for least amount of money.

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6 hours ago, gitenby said:

Your cylinder looks great! cross hatch still under the polish. Still have it checked for out of round and in spec for new piston.

You can wash soap & water and very lightly use green scotch bright and follow cross hatch pattern instead of hone  Follow the service manual for specs crank/cylinder/head and you will be in great shape for least amount of money.

Agreed. Cylinder is fine. Piston a bit iffy. New rings and call it good will get you by for quite a while. It's impossible to tell on the valves from the picture. 

Old school way to test. Pour some gasoline on the head and see if it leaks past the valves. If so, time for a valve job. 

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Call me picky, but those polished grooves on the cylinder give me the willies. At least measure it up to make sure the cylinder is still round.  If those are wear marks then I would personally consider having it plated or honed, if it fits your budget.  If they are aluminum deposits from the piston, then you might be able to clean them out with some acid which will dissolve the aluminum but leave the plating alone.  

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Ive seen pistons with the Teflon very smoothly worn, you have gouges, the question did that recently begin due to the bottom end?

IMo its important to find if the bottom end is in good shape.

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I agree, those groves don't look good at all.  Was there an overheat or lubrication issue at some point, or maybe some sand got in there, etc? 

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4 hours ago, sirthumpalot said:

I agree, those groves don't look good at all.  Was there an overheat or lubrication issue at some point, or maybe some sand got in there, etc? 

You're seriously worried over that slight scuffing? Are you forgetting that's a Teflon coating? 

Measure the bore and the piston, it should still be well within spec. Clean the bore, replace the rings if the end gap is too wide and go ride (scuff the bore slightly if he replaces the rings). My guess is he'll have another 200 hours or so unless he's using it as a motocross bike or other hard racing.

I've seen much worse than that still within spec and holding perfect compression. 

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Yes they do bother me. ;)  If it were a newer bike and my personal bike, I would absolutely fix that.  But I do concede that it will likely run for some time like that, and being an older bike it is worth considering the cost vs. the payoff.  

edit -->But it is definitely worth finding the cause before putting it back together.  If something else is failing, then now is a great time to catch it before there's a more significant problem. 

Edited by sirthumpalot
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 Thanks for all the replies, much appreciated. I took it to my local bike shop/service centre today and they agreed they didn't look too bad and it measured true but they said they could rehone it within tolerance of a new piston for £35  Plus the price of the vertex piston I was going to buy and install anyway.

 Seems like win-win and some peace of mind but not a lot of cash 

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3 hours ago, floydstar said:

 Thanks for all the replies, much appreciated. I took it to my local bike shop/service centre today and they agreed they didn't look too bad and it measured true but they said they could rehone it within tolerance of a new piston for £35  Plus the price of the vertex piston I was going to buy and install anyway.

 Seems like win-win and some peace of mind but not a lot of cash 

That's a good deal. I'd do that myself. 

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