Pop, then lost most compression won't start now HELP

[StreetDemonCustomCycles]

Okay so I took my old engine that had been sitting under my house for around a month, the engine wouldn't start and I had a spare so I put it on and just left the old one, when recently I decided to see if I could get the other one going. It wouldn't start so I ended up riding WOT down a huge hill choke off to get it started. Finally as I'm approaching the end of the hill it sputters to life, it seemed to blow out the cob webs, anyway it ran pretty well until I start ascending that same hill and I hear a massive pop from the engine but not like a backfire, then most compression was lost. The head gasket was intact and was fine but I replaced anyway, I put new piston rings in as well, still no compression. The engine is a Skyhawk GT2B for reference.

Thanks in advance!

 

[Street Ryderz]

Okay so I took my old engine that had been sitting under my house for around a month, the engine wouldn't start and I had a spare so I put it on and just left the old one, when recently I decided to see if I could get the other one going. It wouldn't start so I ended up riding WOT down a huge hill choke off to get it started. Finally as I'm approaching the end of the hill it sputters to life, it seemed to blow out the cob webs, anyway it ran pretty well until I start ascending that same hill and I hear a massive pop from the engine but not like a backfire, then most compression was lost. The head gasket was intact and was fine but I replaced anyway, I put new piston rings in as well, still no compression. The engine is a Skyhawk GT2B for reference.

Thanks in advance!

The pop could have been anything and since it wasn't really running anyway rip it apart and find the issue.

 

[6blueoval9]

Maybe a crank or clutch seal that popped out...only way to know is to take it apart.

If you're sure your head gasket and ring seal is good and you have no compression the crank and clutch seal is a good place to look.

 

[crassius]

sounds like a crank seal (champagne cork popping) - open both sides and look for oil near the crank

 

[gary55]

So you replaced the head gasket and rings but still no comp. What did the cylinder walls look like. Was the head warped. The clutch seal has nothing to do with compression. The seal behind the bevel gear and the rotor other than minutely have no effect either as far as the cylinder comp. is concerned. I'm guessing you have done a comp. test. What did it read?

 

[StreetDemonCustomCycles]

So you replaced the head gasket and rings but still no comp. What did the cylinder walls look like. Was the head warped. The clutch seal has nothing to do with compression. The seal behind the bevel gear and the rotor other than minutely have no effect either as far as the cylinder comp. is concerned. I'm guessing you have done a comp. test. What did it read?

Thanks all for your fast responses, the clutch seals and crank is all in perfect order, I checked that as well there is only around 70miles (105km) on the engine. The compression test showed 11 PSI. Also no warping or misshaping. The cylinder is unscored, and is clean as a whistle, minor carbon buildup on the top of piston. I checked timing and the Magneto keyway at TDC is at the 1 o'clock position.

 

[Street Ryderz]

Thanks all for your fast responses, the clutch seals and crank is all in perfect order, I checked that as well there is only around 70miles (105km) on the engine. The compression test showed 11 PSI. Also no warping or misshaping. The cylinder is unscored, and is clean as a whistle, minor carbon buildup on the top of piston. I checked timing and the Magneto keyway at TDC is at the 1 o'clock position.

11 p.s.i ? one more than ten? That's f***ed!

 

[StreetDemonCustomCycles]

I know, so how do I fix it lol,

EDIT: I just redid the comp text now I have 23PSI?? This is weirding me out.

 

[Street Ryderz]

I know, so how do I fix it lol

Seems odd you say that the cylinder is good and yet no comp,unless there is a hole in the case,the piston or your exhaust port timming is way to high it really doesn't make sence. What's the bore dia about a 1/2" below the deck?

 

[StreetDemonCustomCycles]

yeah about a Half inch below, no hole in case piston exhaust is all stock standard and works perfectly. I just checked the spark plug threads they are fine and head thread is fine.