How bad/not bad is my nitro engine?

[ZED32]

So I freed up my stuck nitro engine. (OS Max CZ .12 i think) Noticed that the piston rod was very loose on the crankshaft and has A LOT of play. The bottom of the piston rod also hits the inside of the block. Should there be a bushing where there is currently just a big gap?

[RC10th]

Yeah, that's not good, the bushing is gone. What do the bearings feel like and what does the combustion chamber in the cylinder head look like? Also is there any scoring on the piston/liner?

A new rod should be easy to find, but it depends on the condition of the rest of the motor.

[ZED32]

Yeah, that's not good, the bushing is gone. What do the bearings feel like and what does the combustion chamber in the cylinder head look like? Also is there any scoring on the piston/liner?

A new rod should be easy to find, but it depends on the condition of the rest of the motor.

Yikes. Begs the question, where did it go?! The head looks fine, although I dont really know what a good one looks like. It's just a little dirty and needs a new glow plug. Nothing outwardly bad. The bearings are... gritty. Not seized, but definitely need to be replaced. The piston liner looks really good, no scoring, but I cant get it out. Its completely stuck in the block and even hitting the thing with a blowtorch has failed. The engine is currently sitting in denatured alcohol to see if that does, well anything.

[RC10th]

The cylinder head combustion chamber should be nice and smooth, if it's pitted or grainy then it's no good.

Bearings and rod should be easy to find and replace. To remove the liner stick a zip tie in the exhaust port and turn the crank to push the liner up. If it's really stuck you may have to heat the case slightly with a heat gun.

[ZED32]

The cylinder head combustion chamber should be nice and smooth, if it's pitted or grainy then it's no good.

Bearings and rod should be easy to find and replace. To remove the liner stick a zip tie in the exhaust port and turn the crank to push the liner up. If it's really stuck you may have to heat the case slightly with a heat gun.

So this isnt good, is it. Is there a way to refinish the head?

Got the piston and liner out too. I cant see or feel any score marks in the liner. The piston, on the other hand, has this huge mark in it. I am assuming that is not great either?

[RC10th]

The head doesnt look great but is probably OK, but man that thing must have been hot if the anodizing is that discolored.

But no, that piston doesn't look good. In the correct orientation how far up the liner can you push the piston?

You may be missing the Teflon wrist pin caps too.


If you can't push it all the way to the top maybe replace the rod and see if it runs.

[Lowgear]

The bearings are... gritty. Not seized, but definitely need to be replaced.

If you decide to replace the bearings, watch some videos on YouTube as there's a technique to it using heat to expand the case. Also possibly freezing the new bearings to aid in reassembly.

[ZED32]

The head doesnt look great but is probably OK, but man that thing must have been hot if the anodizing is that discolored.

But no, that piston doesn't look good. In the correct orientation how far up the liner can you push the piston?

You may be missing the Teflon wrist pin caps too.


If you can't push it all the way to the top maybe replace the rod and see if it runs.

The piston does not come out of the top of the sleeve. Stops just before. It was almost certainly getting too hot. The cooling fins in the head were completely filled with mud when I got it, the person who previously owned it didnt take very good care of it and I wouldn't be surprised if the tune was way too lean. I'll probably get a new rod and send it. Might as well.