Quick Poll - Engine Rebuild

[qjmcrae]

Quick question for the nitro community - When do you guys decide to rebuild an engine vs. tossing it and getting a new one? I have a really old RB 21 I was just going to toss, but just dawned on me I have never really come up with a good answer on this one. Just looking for input.

[spooky]

If you need piston , sleeve, connecting rod and crank bearings, just toss it and get a new one. If it is only the piston and sleeve that needs to be replaced , it would be worth rebuilding.

[qjmcrae]

So, how does one know when you need all, and not just the piston/sleeve? I have only replaced piston/sleeves, and honestly, I have only done that a couple of times (once on this motor, and once on a os 12 cv).

[Tony Newland]

You'll want to measure mainly the crank pin where the rod goes... any more than .03mm out of round and its toast.

Also check the radial movement of the bearings... meaning try to move the crank up and down/side to side, ANY movement, or grittyness and the bearings need replacement. you can easily feel any grittyness by removing the crank and turning the bearings with your finger.

the rod should also not have more than .03mm out of round shape or it needs replacement.

piston and sleeve is easy, with the engine assembled lightly coat the cylinder with oil and with the glow plug installed rotate the engine slowly and watch through the exhaust port for excessive bubbles coming from around the piston and leaking through the exhaust port. Some engines loose their pinch fast but are perfectly sealed up. the balance between pinch and seal is what you want. Pinch is bad and proper breakin eliminates the heat causing, power robbing pinch and forms a seal. Thats what you want. If it bubbles escessively when the gnine is cold it will be a problem to tune when its up to temp.

I think your biggest problem is being able to find the right parts... RB has been a joke for the last few years with a erratic parts supply.

What version is it exactly, I can see if I can locate the correct parts, then you can price it out. Most likely its not going to be economical.