Need help!

[abxcontracting]

Piston locked up

Newer to engine building. Have a problem with the piston keep getting stuck a minute or two after idling.. here’s what I have done to the predator 212.
Dynocam cm grind cam
Arc ultra light billet flywheel
Arc billet rod 6254
Chromoly rods
Stock piston
Stock rockers
Billet side cover
26lb springs
Mikuni 24mm flatside carb

So recently I added the 24mm carb and the billet side cover. Since adding them is when the problem started with the piston getting stuck and not being able pull the pull start or anything. Drained oil took it apart checked everything, used mallet And block and freed piston. Everything looked fine. Everything moved freely. Put back together filled with 10w30 oil to spec, started. Idled for a min or two. Have a hair of throttle and stalled and locked up again. Prior to having the side cover and new carb it idled and ran.

 

[itsid]

Either you have a weird thermal expansion issue or are hydrolocking the piston due to an overflowing carb.

Before anything else:
post a pic of your carb installed, maybe we see something you didn't yet

Then replace the carb with the original one for a test,
start the engine and see if it does the same thing after a few minutes.

if it does, the billet side cover might be out of specs,
to be sure, remount the original side cover and the Mikuni and try again to verify.

if it didn't the carb is causing the issue.

Quicktest:
a hydro lock can be turned over by removing the spark plug and slowly rotating the crank by hand
(don't yank on the starter but gently pull )

'sid

PS just recently someone had a clearance issue with a DynoCam and a billet con rod;
check your rcon rod and cam for wearmarks the next time you open the crankcase,
since if it's the same problem in a milder version you are slowly eating away your con rod,
being the weaker of the two.

 

[abxcontracting]

Thanks itsid I’ll try that when I get home today. As for removing the spark plug and rotating the crank. I tried that the first time it locked up and it wouldn’t budge either way. Had to hit piston with mallet and block to free it

 

[mckutzy]

Hopefully you havent bunged anything up... check the cam and conrod....