2018 Aprilia RS4 50 Euro 4 Upgrade Project

[toratora]

I don't think I've ever seen a cylinder look like that—the only thing I can think of is that you were running it without water, which is very dangerous. The photos do show what looks to be scoring to me, but it is always hard to tell from photos. Still it looks to me like it was run way too hot.

At this point I would pull the top end. Clean all the parts. Replace the wrist pin bearing (they don't do well with heat), and if the wrist pin shows any wear at all I'd replace it too. The piston clips would probably also be good to replace, and I might even consider putting in a new ring. After everything is clean then check the ring gap, and adjust it if necessary. And this is of great importance: Do not run it without water again!

[kaldis12]

So first, ypu should pull the clutch in always, but okay it would stall.

So,
From 80kms its should look like about as new.
The wall looks to oily and scratched( altough its not scratch, just you see that way) if your nail doesnt get catched by the "scratch then its good. But that pattern on the wall makes me really think that the ring will go to the trash very soon. They could be faulty. You should check the ring gap. If you leave it like this, believe me it wont end pretty good.

For the stalling, you should check the exhaust smoke color. But if the ring is really that tight, it could cause issues.

As far you dont know the ring gap, I should start it up again.
The "scratches" could be because of too tight rings or too hot cylinder.

[Berkeley]

ok will do as per the above.

There are no score marks. when I cleaned it and ran my finger around it felt smooth. The first run there was no water just to get the bike going this was around the 60 deg mark then stopped.On the second run in test I did fill it with water , but from the reservoir as I said earlier that didn't fill the radiator, so yeah that one definitely ran hot.

The first run bumping it it smoked for the first 30 seconds but after it didnt for all of the time that ive been running it. the only signs were a bit yesterday when i pulled into the garage and tried to idle it again.

With the cylinder looking that that should i just cut my losses and buy a new head?? or ok to keep this one and clean it.. if so whats the best way to clean the cylinder walls?
cheers

[kaldis12]

It seems that the micro scratches in the cylinder to keep the oil in there has gone from that scoring sorta stuff. So you should hone it up just to be sure. Buy new rings, change the piston wrist needle bearing, change the circlips. At least if the piston is in good condition if no then I would say buy a piston kit. You get it with rings and circlips. But for the cylinder I would hone it up immediatly.

As for the cylinder you should run your fingers through the ports if you feel any sharp edges.

[toratora]

Don't hone nikasil. It will ruin it! You can use a green pad, but don't be aggressive with it. Simple Green should take most of that stuff off. It's possible that the running without water caused some issues. It will be really difficult to pinpoint where things got ugly. Starting with clean parts should help figure things out. Again, ring gap, air leak, etc. those sorts of things could have contributed to it too. The great thing is your attitude to hang in there, and work through it. That's the proper way to be with these things. Just be methodical, one step at a time. Things may get weird, but eventually you'll get through it.

[kaldis12]

Yeah sorry not sure how they call it in english. In hungarian we call it "hónoltatás". They "scratching" back the micro scratches into the cylinder like in the factory for better oiling. Not sure how it is in english. We do it in every nicasil cylinder what looks like above. They (I will just call it scratching) scratch it again and voila just like new.

[jkv357]

Is the cylinder for sure Nikasil plated?

I'd want to measure the bore and the piston to confirm the piston-to-cylinder clearance is correct before gapping and installing a new ring.

If it is Nikasil plated you need to be gentle when cleaning, if not I'd have it honed (have them measure the cylinder and piston at the same time).

Something was not right.

[kaldis12]

Yes its for sure nicasil plated. If you look at it you can tell it. I said, its not honing but they scratch back the microscratches. I dont know how they call it. But that helps a lot in these cases.

[Berkeley]

Hey tora and guys.. Never give up!!! whoop whoop I've found the problem and it was the piston ring. ( relief)

I did a great job of completely f'in it up trying to get it in when it wouldn't go. At the top end there wasn't much damage so didn't look like such a problem but at the bottom loads of tiny vertical score marks, The piston ring was misshapen and where it stuck out on one side you can see where it was worn. The ports look ok but on the top or bottom theres some rubbing so not perfect. The piston ring however is a right mess and must have let oil get into the ports making it a nightmare to start on electric, and not be able to idle ( well I hope this is the case). I don't know if the cylinder is any good and may just bite the bullet, and get another top end kit for it.

Here are some pretty pictures.

I cleaned up the spark plug before I did the last run and it still looked clean
.

The top of the head was cleaned but you can see some signs of oil at the front end
.

Ouch! .

top end
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Bottom end. You can see the top side of the port worn.
.

The whitespecs were from a kitchen towel I just wiped it.
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The beautiful Piston.
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This is where the ring protruded and warn.
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Wrist Pin .

Deformed Piston ring .

Small end bearing ( or has another name), anyway will replace it.

[kaldis12]

So now you got the problem. Now you have 2 choice. 1st is to buy a new kit. The 2nd would be that you send the top to someone who can remake these small microscratches like metrakit does in the facility. Buy a new piston kit and bearing. In price I would say that the 1st would be the best coice. After a nicasil cylinder got anything scratches or marks even i wouldnt trust it. If you re "hone" it(the microscratches, so dont be confused, i didnt mean milling up the bore.) Its just not the same. So i would change it to a brand new.