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Discussion Starter #1
Soo dont know it I'm just being paranoid or not but after I give it a good rev or get off hard acceleration, I hear a 1 second metal on metal graze, definitely sounds like within a rotation.

The new top end has 40hrs on it. Vertex piston. I did not get cylinder replated yetas I did post about that earlier in the year. I could see some scoring so could it be this be the issue causing it?
 

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Hmmmm.......metal on metal sound from cylinder?????............
Metal on metal from cylinder.....
Worn cylinder coating when I assembled the motor 40 hours ago...
Hmmm.....40 hours on a worn cylinder in a 2 stroke is an eternity for a piston....did I loctite those power valve actuator gear screws???
I wonder if the power valve is smacking the piston when I chop the throttle and governor tries to snap power valve closed???hmmm...
Sounds like that motor needs a checkup... start with compression test. Remove power valve actuator covers and exhaust pipe and check power valve actuator looseness. Inspect exhaust side of piston while rotating engine slowly and observing piston through the exhaust port. Drain coolant and remove cylinder head for an inspection. Probably best not to run it anymore until trouble is found. Be sure to post pictures and check back as needed
 

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Discussion Starter #4
Hehehe, metal on metal inside cylinder :) what else could there be in there!

I'll have to tear her down and check her out. I know I loctite the power valve gears as the came loose x2. Also what I could in there and recall playsomewhere, due to wear and tear.

Also just remebered that the cylinder port had some chipping on the edges when I took it off when I bought it. I did tell myself replating after this season due to cylinder. Looks like the time came quick!

Thanks guys, always good stuff!
 

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Strip - Check - Replace. In MX we replace the Vertex piston at 40 hours (top riders do it at 12 hours) and rings at 20. So every 20 hours we fully check cylinder, powervalve, squish, conrod, gaskets, that bolts and nuts are tight, any wear we find will be rectified before all goes back together, we clean and polish it all and reassemble, until 20 hours later we do it all again. And still inside those 20 hours we at times have mechanical failures!

One thing we learnt very early is to trust your gut feeling and your hearing. If something feels or sounds different it is! It won't go away and if we do not sort it straight away the cost will only go up!
 

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Your gonna be eggspert at building these 2 bangers freaky,

Like the old sayin goes I spose:
When in doubt, pull it out......... I am taking about the piston and cylinder;)
 

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Discussion Starter #7
Welp, here she is. Same bad looking piston. Lotsa black on this one. Technically it should have been richer because I waterproofed the airbox, and the plug was,/is wet whenever I check it. So the black is blowby?

The powervalve slide seems to be causing the ever so quiet 'skid skid skid' sound when I let go of throttle in high rev scenario?

Sending the cylinder out to powersealusa for replating.

What do you guys think? Is it just bad cylinder? Have bore guage to check the specs.

In the piston pic, the left is previous piston , and right is current. Showing all sides.

The cylinder top cover has knocks and dings from first piston so that's not new. Just showing color, which the black is on exhaust side
 

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I have seen pistons that have seized look better... Your barrel and piston damage is most probably from crap going in through carbi. When you have re-done barrel and you fit a new piston:
  • I recommend new aircleaners as the old ones might be letting dirt in.
  • Also make sure that there is no place that air can get in withouth first going through the aircleaners!
  • Also use grease on the lip where the aircleaner connects to the intake boot to stop dirt creeping under! Also use quality aircleaner oil!!
  • Ask someone with lots of experience how they stop dirt from getting in while they change the aircleaner and ask them to show you! (as that is often when you will get dirt in to the carbi, often with out realising it).
It also looks like the bottom skirt of the power valve has come in contact with the piston... This, I expect, is as result of worn power valve and/or mechanism. If you decide to stay with the old power valve then file/machine the bottom of the skirt so it does not touch the piston!!

Attached pictures of:
  • How our pistons look like after 40 hours of use (when we replace them) having been screaming in our 125sx.
  • The barrel we replaced in our 2012 125sx after some alloy melted on the top of the piston (wrong CDI so timing was wrong...) You can see where the alloy attached itself to the bore. Apart from that the barrel was OK and we did complete the race meeting and my son won the event! (This barrel had done over 300 hours...)
When you compare these to yours I know what ones I would fit in my motor if I could not get new parts...
92917
92918
 

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Discussion Starter #9 (Edited)
Thanks for feedback axzon! I do have 2 old air filters in rotation and always wondered how long they are good for, hate to throw throw things away :(. Now that you mentioned it, I'm actually suspecting dirt getting in from the spark plug hole. Dirt getscaked to the recessed hole edges. This has always worried me when removing/installing plugs. Ganna have to make a flap to go over the plug boot and completely cover the recessed hole.

I am certain I am not getting dirt in from improper air cleaner removal as I clean very often during complete bike wash (with the twinair cover) and when I'm done, I wipe the oil puddle in the boot. Most times the cleaner is not bad because I don't ride in dusty conditions.

Also will start using kerosene to clean and see how that goes. I use straight LAS powder mixed with water, restaurant degreaser concentrate and dish soap to clean but still takes forever to clean off the bel ray tacky blue stuff. I would rinse, let it soak, scrub filter together, rinse, repeat, repeat repeat.

The powervalve I know had some serious play in it. Any idea which parts are wear parts? I have an idea. I know #5 has tremendous play. Anything else? You'd know?⁰
 

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#5 is the small exhaust valves (x 2) that opens and closes together with the power valve flap (#20). So #5 does not get close to the piston. #20 is the one that has been in contact with your piston (you can see the wear). When you re-assemble (hopefully after purchasing a new power valve #20...) you need to adjust the "home" position (when motor is not running) of #20 so that #20 (power valve) does NOT touch the piston!!
 

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Re air filter cleaning: We replace the airfilters as soon as they show wear (small part of the foam start to break off). As a result we do not use any expensive air cleaner solvent, but just normal petrol. Normally takes a couple of years before the petrol damages the air cleaners. We only use the petrol to remove the air cleaner oil. We then hose down the air cleaner to remove any fuel and most of the dirt. After that we wash the air cleaners in warm water by hand using washing powder. Then we rins them in water in a tab and replace the water until we find no more dirt at the bottom. That normally means 2 - 4 rinses. Hang to dry, apply new air filter oil and you are ready to go!
 

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Discussion Starter #12
Thanks for the great tips!

Powerseals received my cylinder. I'm wondering if I need those chips I have welded. They are not catching on piston as they are going outwards one is cracked but piece I still hanging on. Will the replating be fine against these or cause premature wear?? Should powerseals let me know before they do anything??

Thanks
 

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I had a look at your pictures. If you are a recreational rider and you do not compete then give it a go. But I would buy a new/a good condition used cylinder if it was for our racing.

Did you send a note with the cylinder where you asked the questions. I suspect that if they are prepared to coat the cylinder they would tell you that they can do the work on the cylinder, but there will be no guarantee...

But then again I do not know the company and their ethics.

My recommendation is to contact them when they have the cylinder and have a chat and see what they say before you waste your money.
 

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That is not too bad looking from I can see in pictures. They may simply opt to give that rough edge a kiss with a carbide burr to chamfer the edge. Nothing too dramatic. Your cylinder service should have the final word on this, but it doesn't look too bad from here. Some cylinder uglies and scoring can be fixed by reboring cylinder for a big bore kit. That would be a win win for you.
 

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Discussion Starter #15
Welp, received the cylinder back from Powerseals USA. Called then prior to work regarding the chips and it was no issue, they ground it smooth and looks great! Turnaround time was faster then expected!

Have everything put together, with .75mm gasket resulting in 0mm gap for x dimension, and 50.5mm set for z dimension
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All still spec since last build. She sounds great!
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That's great news to hear.
Glad it worked out well for you
 

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Loking good! Now just make sure no dirt gets in to the cylinder and you will be able to use the cylinder for many piston changes!

Just make sure you set the "home position" for the Power Valve so it DOES NOT touch the piston!!
 
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