how do i know when my engine is shot?? - RC Groups
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Jun 16, 2007, 05:11 PM
Registered User

how do i know when my engine is shot??

How do i know when my engine is blown up or shot..? i have a trx 2.5R
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Jun 17, 2007, 01:49 PM
Most tof the time it's when the compression is gone compared to new.

The engine will fire, but flame out when hot, stop idling, bad power.

Turn the flywheel slowly, if the compression bleeds down quickly when cold it may be worn out.

There are lots of things that can be wrong, but this is the most common thing if nothing catastrophic has happened like overheating or air cleaner falling off.
Jun 21, 2007, 08:18 PM
Registered User
turn the flywheel over, if there is no compression its done.

Nitro Guru?
Jun 22, 2007, 02:17 PM
Registered User
thanks guys
Jun 29, 2007, 12:49 AM
over user
Stevo Revo's Avatar

Ring her up

Got a good trick for you. If you don't want to buy a new piston and sleeve if your motor is toast, listen up. This is probably a 8 on a scale from 1 to 10 in difficulty, but it has worked for me. I didn't invent this trick and I only have about 10 tanks of fuel since performing it, but others swear by it.

First begin by dissasembiling your motor. The cause of your low compression is caused by a worn out piston. And what you are going to do is make it tight again. You need to find or purchace a high quality tubing cutter, such as a plumber would use. What you are going to do is put an oil ring at the top of your piston, about halfway between the top of the piston and the boost port hole, or about a 1/16th from the top.

This serves two purposes. One is to create a void at the top of the piston for oil to collect in, (longevity) and reason #2 is as you use the tubing cutter to put a shallow groove you are displacing material that increases the diameter of your piston arounud the groove. You must be very delicate in making sure that the groove tracks straight around the first lap so you begin where you started. Then at that point give her just a few light turns as you slightly tighten the cutter. A good trick to use if you can't turn the piston in the cutter by hand is to re install the con rod and use a pin of some sort to put in the other end of the rod for leverage. Remember you are trying to groove the piston, not cut the top off. Once you are satisfied, take a shapening stone (400 grit or finer) apply some light oil (wd40 or whatever), and LIGHTLY roll and drag the diameter of the piston on it. Now clean it and test fit it to your sleeve. It should start and go about halfway up. You want it tight but not so tight that you can't assemble it! If too loose, repeat ringing process, If too tight, repeat stoning process.

Once you are satisfied with the fit, you need to fit it just a little more. Assemble the engine, leaving off the end plate and leaving out the glow plug. Re install your engine's flywheel. You are going to use the retaining nut to hand-turn over the engine. Make sure that you put plenty of lube down the glow plug hole. Using a socket wrench turn over the engine a few dozen times. The first few times the engine will be very tight. If you are uneasy about this, and you think it is way too tight, dissassemble and repeat stoning process. It will turn very hard but it will go. Lube is the key. You are trying to form the aluminum to match the bore. Add lube as you are turning it over and over, don't be afraid of too much. Once you can turn it over by hand relatively freely with socket wrench, its time to get out your drill and work it some more. Use the drill and a socket to drive the motor while almost continually pouring lube down the cylinder. This proccess shouldn't take more than a minute at 1000rpm. Stop frequently to check that it's not getting too loose. You want to get the motor free enough that once completely reassembled, that it won't be to tight to run. You still want to feel a pretty good resistance at the top of the stroke when you turn it by hand (not with the drill or wrench) with the plug out, but not so much that you cannot turn it over by hand.

You will see a dirtyness to the lube you have been putting in your engine, that is just minute particles of aluminum wearing away as you work it in.

Once you are satisfied with the fit of your piston and sleeve, dissassemble one more time, clean everything and put her back together for the last time, Just remember to give her a light lube before you close her up.

Re install engine in vehicle and go through the engine manufactures break in process.

I have just recently done this, and the motor runs like a champ. Good idle and good power.

This is not an exact science, but the worst thing you can can do is have to replace your worn out piston and sleeve anyway. So if you're sure your motor is toast, give it a try. It's the only way you learn.
Jun 29, 2007, 06:45 AM
Registered User
thanks, do yo uhave a revo??
Jun 29, 2007, 09:30 AM
That is called "pinching" the sleeve, resizing the sleeve to regain compression. It's very popular, although on cheaper engines where the cost of the piston/sleeve isn't much it is much better to simply replace them. WELL worth doing on a $300 italian motor, but on an engine where the piston/liner costs $35, just replacing the parts saves time and money.

It is Just as easy to pinch a sleeve Out of round, I've seen that happen too, it's not a panacea.

There are outfits that will pinch your piston/sleeve for about $20, the reputable modifiers do good jobs.

Always keep in mind that there is a point where simply replacing the engine is a better option. OS makes replacement engines for most RTR's for under $100 that far outperform the stock engines.
Jun 29, 2007, 11:03 PM
over user
Stevo Revo's Avatar
Yes you can get a new motor for $100. Yes you can get a new piston and sleeve for $35 to $50. You can do whatever you like. If the trick doesn't work for you all you invested is your time. If it does you get a fresh motor for free. Whether you do or not is your choice, there are millions of people out there will millions of opinions, you are the only one that can decide what's best for you.

Good luck.


No I don't own a Revo. I own a RC10 gt. My buddy calls me Stevo Revo when he wants to go out and bash. He's the one with the Revo.
Apr 23, 2012, 09:47 AM
Registered User

oil grove in piston

bro i just came across your thread, i have had a few engines put aside because of piston wear, why did i not see this before, worked your magic on two so far, runs like a beast, i put it in lean it to the max and my boys have a time bashing them, the two have shared a gallon of fuel so far and the compression is still fantastic, great fix, thank you

and this is not called pinching, pinching is resizing the sleeve not the piston
Last edited by ratballs; Apr 23, 2012 at 09:50 AM. Reason: addition

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