Cam timing

[Littlehellraser]

Cam broke on my l20b , put motor in time and install new one . Now I have no compression on #1,2,3 and 10 pounds on #4 . Motor turns free ,and pulled head and checked for bents valves , there are no signs of bent valves , no marks on piston.  I got cam sprocket on #1 just before mark .  I just missing something simple. Motor has about 400 miles on it and it was idling when cam broke right behind #2 cam tower. 

 

[EDM620]

Start with checking the simple things. Valve cover off, turn over engine by hand. Valves opening in the correct sequence? Start with the engine at TDC compression stroke cylinder 1 - Poke a stick into the cylinder through the spark plug hole and verify piston movement relates correctly to valve timing - Compression - (piston going up, both valves closed), Power (piston going down, both valves closed), Exhaust (piston going up, exhaust valve open), Intake (piston going down, intake valve open) strokes. Do this with every cylinder.

 

Odd that a cam broke - shaft snapped? What was the cause? Maybe there is other internal engine damage. Possible the head is warped, again why did the cam break?

[Littlehellraser]

I have a guess why the cam broke, found the bolts on cam tower were lose

And the head bolts on tower were not torque. 

[Littlehellraser]

I bought the motor rebuild my someone I should have ,now is has come back to bite me .

[datzenmike]

Set to TDC compression stroke on #1 using the ignition TDC timing mark on the crankshaft pulley. Take the valve cover off and look at the cam.

 

Sprocket should look like this...

 

While in this position check valve lash on both #1 valves, intake on #2, exhaust on #3. Turn engine exactly ONE revolution. Check valve lash exhaust on #2, intake on #3 and both valves on #4. If no lash valves won't close tight and there is no compression.

 

 

 

 

Cam tower bolts are only 4-6.5 ft lbs or they strip. Before starting it again take all the rockers off and try turning cam by hand. If it won't turn, the cam towers are not in alignment because the head is banana shape. Cam breaking is almost always because the head is warped badly.

 

Never set the head on a surface valve side down, turn it on it's side.

 

L20B cam dowel on the end should be on the #2 sprocket hole and was set this way at the factory. It will run this way but not at best.