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2t piston advice?

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Hi guys,

 

I made a quick check through the exhaust and found some marks.

I can feel a small hairline mark with my finger. Couldn't feel anything on the "segment".

The other side of the cylinder looks just fine.

Piston has only 5 hours.

What would you do?

Cr250 07 used for trail riding.

DSC_1302.JPG

DSC_1304.JPG

 

I've added pics as attachment through the app let's see if it works.

 

Sent from my D6633 using ThumperTalk mobile app

 

 

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The mark is only on the upper part, like 2 cm starting from top, and compression is still ok I guess but I did not make a real pressure test.

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Also my cylinder was milled and I'm wondering if it could be the result of the job done.
I know the holes depth are not a reliable aspect, but I remember that I thought one side had slightly more depth than the other. Do not remember wich one though.


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Salut lephil, just to be clear on terms used:

-cylinder 'milled' as is : voulant dire alésé ? (re-bored)

-was it re-plated  (Nikasil replaqué ?) perhaps exhaust bridge area not clearanced enough

-does the piston have oil hole on the exhaust side ?    (le piston a t'il des trous de lubrification côté échappement?)

-dirt/debris getting past the air filter ? (check inside the rubber intake boot)

-do you engine compression brake a lot ? (freine/ralentir avec la compression du moteur)

Edited by mlatour

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Honda pistons alot of times do not come with bridge holes drilled.  If your on the gas it will be a problem 

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If that is the ring I'm seeing on the piston in the first pic, you have some trouble ahead of you. Stop riding it. Pull the head, and cylinder, and take a good look at the piston with it out of the engine. I'm not liking what I'm seeing at all.

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Hi guys, thanks for your feedback and sorry for not beeing able to follow up more quickly.

First, i'll add some elements to the descriptin then answer to all other questions asked.

The bike was stored for a year. it runs on 3% + premix with high quality oil that leaves a coating on everything for a long time. The area is only sandy and heavy dusty conditions desert like.

The last 2 times I used the bike:

first: my plastic water bottle broke in my backpack while on the single track and flooded the air box, it stoped the motor. (air filter was dirty at the time a DT1 + a sock)
I stopped, put the bike on the rear wheel immediatly, tried to start it a couple times then changed the plug. Bike started again and I got back home rather quickly (10 minutes ride)

Back at home I drained the oil, and put some fresh one in. I saw a very limited amount of water inside.

Second : last day, to prep it for storage, I kept the bike running while cutting gaz tank flow (Yes I know...bad method). The motor revved up High and I couldn't kill it with the kill switch so I finally killed it with the clutch. It must have revs like crazy for 20 sec maybe 30? not sure.

 

Now to answer all your questions:

When I say milled cylinder I'm talking about camP mod.

Cylinder and piston are stock. This is the first and only piston of the bike's life that was still perfect. (checked and measured carefully 10 hours ago or so.)

The piston does not have oil hole on the exhaust side.

I checked inside the rubber boot / carb / reeds and couldn't see anything, it was clean clean clean.

My compression doesn't seem to have changed. (not measured, just an impression)

 

On the first pic you can see 3 vertical scratches on each side of the piston

I've checked again and it looks like I have 3 or 4 other vertical scratches on the cylinder on the other side of the piston. Looks really superficial.

 

My guess for now is that for some reason, some sand went in.

 

Of course I could put it apart to inspect but what then? Pics show clearly what I can see.

Is a new nikasil in order for that? Not sure at all. A new piston? not sure either.

A new ring wouldn't hurt, but if the compression is good?

The thing is, I got one week left of riding and then I'm going back home. I really can't decide what's the optimal way to go right now.

 

What I think is very strange is that the marks are only on the upper part of the Piston.

Edited by lephil

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1 hour ago, lephil said:

Second : last day, to prep it for storage, I kept the bike running while cutting gaz tank flow (Yes I know...bad method). The motor revved up High and I couldn't kill it with the kill switch so I finally killed it with the clutch. It must have revs like crazy for 20 sec maybe 30? not sure.

Do you have any water in the radiator?

Sounds like the motor overheated while running the fuel down.

That's the only way a motor continues to run-on w/o any fuel and spark.

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radiator fluid has been changed recently.

After inspection I think I may have had a bad contact on my kill swith button

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So you ran the bike lean by shutting off the gas. Since it reved out of control you definitely had a minor seizure. You need to replace the piston and have a good look at that exhaust bridge.

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ok, what are the indicators of the minor seazure? all I see is superficial...

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If you can feel those scratches with a fingernail, (pretty sure you will) I would not call them superficial.

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Yeah I can.
Ok better to be on the safe side,I'll take it apart and check it out.
If cylinder has the same deep marks as the piston do you think it need a nikasil or it can wait?

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Yeah I can.
Ok better to be on the safe side,I'll take it apart and check it out.
If cylinder has the same deep marks as the piston do you think it need a nikasil or it can wait?

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Recoat it or but a new oem cylinder.

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