Low compression

Good morning.

The engine is timed to number one cylinder compression stroke on top dead center.

The fact that it may be timed on the wrong cylinder may mean you have damaged the valves since it is an interference engine.

GM does not specify if this engine is an interference engine or not.

To be safe, always observe the following precautions.

If cylinder head is installed on the cylinder block:
- Do not turn the crankshaft or camshaft if the timing belt/chain is not installed or if the camshaft timing has not been confirmed to be correct.
- Do not rotate engine backwards.
- If a broken or "jumped" timing belt/chain is suspected, do not use the starter to crank the engine.
- If a "catch" is felt when rotating the engine by hand, do not attempt force the engine to rotate past the "catch".

If cylinder head is removed (overhead cam engines):
- Do not set cylinder head on a flat surface with combustion chamber down.

When re-installing a cylinder head:
- Confirm that the crankshaft and camshaft gears align with their respective timing marks or confirm that all shafts are set to TDC for cylinder number one before placing the cylinder head onto the cylinder block.

If the timing chain/belt has broken of "jumped time" with the engine running, always check for bent valves by pressurizing each cylinder with air with its valves in the closed position.

I also attached the alignment of the gears as needed.

Roy