Snapping noise at 180 from TDC during manual engine turn By davescootissues (Read 442 times)

[davescootissues]

Hello-

I hope I am posting in the right section.

I recently have purchased a 44mm crank, because the threads on my old crank were bad. I have rebuilt 4 different 139qmb's and am wondering if I might have done something wrong, while installing the 44mm crank and 47mm big bore rebuild kit.  It has 69mm valves and the correct rocker arms.  I have set the valve lash at .004.  I am having trouble getting it started and I know the carburetor is good, but that isn't even what I'm concerned about.  I usually turn the motor a few dozen times by hand to help spread the oil around the new engine.  This time I am hearing a snapping noise at 180 degrees from TDC when I slowly turn the motor.  It almost sounds like a valve problem, but I can't figure out why that would happen.  I have 4 base gaskets to make up the space difference from the previous 39mm crank to the new 44mm crank.  The noise makes me afraid if I do get the engine started it will just be ruined.

Please let me know if anyone has an idea of what may be wrong.

Thank You

[jjoshua20213]

Take the head off and rotate the engine to see if it makes the same noise. If it does its not the valves. If it don't then you can pin point the problem in the head area.

[cyborg]

Valve could be sticking open and the snap you hear is it closing

[Alleyoop]

Take off the valve cover and turn it over by hand and you will know if it's the VALVES. You sure you put the cam in right and aligned it when at TDC before you adjusted the valves? That snapping at 180% sure sounds like the rockers or rocker is coming off the high spot and snapping down on the low part of the lobe.
Alleyoop

[jerryscript]

If you don't hear the noise with the head off, put some modeling clay on top of the piston, turn it by hand, then check to see if the piston is hitting a valve, the clay will be pressed thru at one spot if so, if you don't see any of the piston thru the clay, its something else.

[jct842]

Has any one tried to buy modeling clay in the last few years? I tried to find some to use to protect an area next to a weld last winter and all I could find was play dough! It did do what I wanted though.

[JoeyBee]

It's sad when you have to order something online and wait 2 days to get such a simple item. Modeling clay used to be a common place item, but now unheard of by many. Times are changing.

Now you have to get it on Amazon.


www.amazon.com/gp/aw/d/B00FR7TQTC/ref=mp_s_a_1_2?qid=1437542747&sr=8-2&pi=AC_SX200_QL40&keywords=modeling+clay&dpPl=1&dpID=51hJFXPtk6L&ref=plSrch

[jerryscript]

Jul 21, 2015 21:56:10 GMT -6 jct842 said:

Has any one tried to buy modeling clay in the last few years? I tried to find some to use to protect an area next to a weld last winter and all I could find was play dough! It did do what I wanted though.

Here in Vegas we have several shops that carry all sorts of clays, mostly for firing your creations in their kilns, but modeling clays as well.