stefan

This was caused by debris (plug coil?) not detonation. Detonation is finer and more equally spread over the entire piston.

I had that as well, no need to change the parts. If you want to, you can use some 1500 sandpaper and carefully sand the top of the piston and the button.
Place the sand paper on a flat glas surface (mirror) and slightly rub the piston over it with equal pressure. Don't over do it.

You can put the button with an old plug mounted in a drill, run it at low speed and hold the sandpaper against the pitted surface.

You don't have to sand it completely smooth, just take the coarse stuff off.

You might wanna check your rear bearing as well for missing balls or part of a ball.

RayJ

I would definately change the bearings on the motor with the pitting on the top of the piston. It looks like it was made from a piece of metal that probably came from a ball bearing breaking apart. I broken coil from a plug usually gets ejected from the exhaust port before doing that much damage, and a broken plug coil usually ends up scouring the side of the piston.

keavze

bearing failure?

what could have caused that? mine had about 2 gallons only...

M7H

Bearings can last anywhere between 1-4 gallons or sometimes even more but also less....

Bearing failure can be everything between a small damage on 1 of it's little balls, and total failure....

Always listen good to your engine when on idle, you can hear a bearing which is damaged really good... but you need experience to know exactly what sound you are looking for...
It sounds "raw" instead of "smooth"...

keavze

bingo! guys...

found my rear bearing givng the problem.
will any other parts be affected? (before i change to new bearings and other parts start to fail; or maybe totally ditch the engine?)

xspower

iTrader: (4)

No need to replace the engine if the only problem is the bearings. You can clean up the piston and as long as there are no scratches that are on the side and the fit is still good you can use it. Then either sand and polish the combustion chamber so it is polished and smooth and no pitting or marks or simply replace the combustion chamber. The combustion chamber has to be smooth and free of defects it will make the engine run or slow it down. It is shaped to help with the burn. So for a set of bearings and combustion chamber you should be ok. As long as there is nothing else wrong.

RayJ

Take a good look at the inside of the sleeve. Make sure there are no scratches on the sleeve. Especially near the sealing point of the compression stroke. Also look at the side of the piston crown.....most picco's have a only afew mm's where the fit of the piston and sleeve really seal for compression. If your planning on reusing this set definately do a compression test with it. Rebuild the engine completely. Place afew drops of after run oil in the exhaust port and move the piston up and down in the cylinder to distribute the oil. Rotate the piston to almost TDC and look inside the exhaust port. If the engine starts to lose compression and you see air bubbles leaking from the compression your piston and sleeve are likely on its way out.

keavze

xs and rayj,

there are scratches on the sides of the piston and sleeve (sleeve scratches are very mild though).

did a 'compression test' and yes i could see bubbles. guess it's a goner?!?

if there's a 'compression leak'; how will it affect tuning? can't idle?

xspower

iTrader: (4)

If they are scratch's and not scuffed then I would say that it may be too late. They normally have some marks but the scratch's are no good. And that is not good. Normal to see some bubbles only a slight bit though as the piston moves up to the sealing point though.Can you take a clear pic so we can actually see how many? Can you also feel the scratch with your nail? Xacto? If so then I would have to say yes no good.

RayJ

The taper of the side of the piston is ground with a precision grinding machine. It's measured in ten thousanths of an inch or smaller. Coupled with the finely ground sleeve these tolerances determine whether an engines is a rocket or just okay. This fit is critical to a number of factors: 1) the actual compression under engine usage at operating temperature 2) the amount of friction between the piston and sleeve during engine operation.

Scratches on the inside of the sleeve or side of the piston(Especially at the top of the piston) will negatively effect performance. An engine that can't hold compression under operating temperature will not hold a consistant idle, and be very hard to tune at race temps. This depend on the damage of course.

The other factor to consider when reusing this piston and sleeve set is conrod damage and wrist pin damage. It's hard to know whether or not this had occurred. Just imagine an engine turning at 30,000 rpm and having a piece of metal being slammed into the top of a piston because the head clearance is now compromised with a foreign object? Is there wrist pin damage from over stresses? Don't really know.

keavze

well...i can feel those scratches with my fingernails!
guess it's time for another new engine.

not worth to rebuild with new bearings and p/s.

stefan

I was at the Nuremberg Toy Fair today and had a long talk with Daniele about the new .12 EVO 4 engine.

It is going to be a completely new engine. Here are the features:

- New crankcase that re-positions the sleeve --> which changes the timing of the sleeve towards higher rpm's. the new case also has the two "ears" for the short header springs.
-New crankshaft with slightly different timing and a 4mm crank pin
-New conrod which is beefier arounf the lower journal, due to the smaller crank pin. The rod is also made of a new alloy which makes it much more durable.
-New lightweight cooling head.

The engine should be available by mid-March

keavze

are the front and rear bearings of the .12 evo2 and evo3 same?
what are the sizes?

jameslow

iTrader: (1)

is the idm evo 3 carb same as the idm evo 4 carb? Thanks!

RayJ

Good to see them addressing the issues. Now shims will no longer needed to be placed under the sleeve for higher rpms. The rod situation is also a big plus!

I wish they would drill whole patterns for the engine mounting holes that are similar to Novarossi's. I would consider running these engines again if they would fit properly in my NT1.