Loss of compression with out starting the vehicle.

[McoupeRS4EVO]

ok so I decided I've put enough into this hobby and decided I would try to make some of it back.. So I got a few used evo's of Ebay(rs4) and I got one with Primo compression. and the only problem was the noob had the idle set screw all the way out. So I ran this engine in my truck.. and it was fine.. I sold a car.. so i put this mill into it.

Upon doing this. I started it.. and it was giving me low low low speeds..Like I could not go above 5km an hour. I removed the body(lambo Countach) with minimal ventilation.. There is holes cut but I didnt want to completly butcher the body. and I started it and I got normal response.. My TX batteries died. So I left it on the back burner. (after the last time started, I checked compression when it reached room temperature and it was fine. I gave the car to the new owner.. and left it with him for one day. He doesn't have fuel or a plug ignitor. So he didnt start it.. but he said something was up with the alignment, so I checked it out.. and upon doing that I discovered the motor does not have any compression what so ever.. When I used it, it was always ran with a filter.. and he didnt start it.. so what do you think this sudden loss of compression could be cause by?

 

[Candyman]

I would first do a few usual checks. See if the glow plug was loosened. Check the head bolts. If they are loose or developed a significant leak, you'll lose your compression. If they are tight and sealed and you're still getting a leak, pop the glow plug out and put a couple drops of after-run oil into the cylinder. Put the plug back in and see if you have good compression again. It may be that the pinch really is shot, but when there's fluid in the cylinder it seals just enough to give a reasonable feeling of compression.

 

[Plaidfish]

after you run it do you ALWAYS pull hte piston to Bottom Dead Center (BDC)??? If not that will ruin the compression, the older the engine is the faster this will ruin it....

 

[olds97_lss]

It may be that the pinch really is shot, but when there's fluid in the cylinder it seals just enough to give a reasonable feeling of compression.

I was thinking this same thing... when dry, you don't have any type of "seal" inside the engine other than the pinch between the piston/sleeve. When wet (fuel/aro), you get a seal. Once the engine warms up, I doubt there would be any compression again at all regardless if it's dry or not.

 

[McoupeRS4EVO]

thanks guys.. I forgot about this thread... I checked all sorts of leaks and fixed a leak at the carb but still no luck. Its wierd when the muffler is off. I have compression. when its on.. theres nothing no sound whatsoever.with the muffler off theres the pop and a the sucking sound. so I'm lost...
and actually thanks plaid.. I never knew about returning the piston to BDC.

So quite possibly this could have been the problem.

I ordered a sleeve for it.. But Ill do a few more things before I change it.

 

[Plaidfish]

you can just get it pinched as long as the piston & sleeve are in good condition...cost about 25 bucks to send it to rayracing or OSrocket....I like ray's work but just like engines it's a prefference thing.....run that into the ground but be preparred to buy a new mill next itme.....I have to really trust someone to buy a used mill...or it has to be a really good deal even if the mill is blown......I got lucky and bought a really nice P5 off one of the members here last year and I've run almost 9 gallons on it myself.....that's rare to find a used mill in good condition and a cheap....usually there is a reason someone is dumping something too cheap