Trying to replace broken timing belt. Trying to set #1 cyl. to TDC manually. no compression reading on 1 &4, readings on 2 & 3. What could cause this?? HELP!!

why not read the service manual and not guess.
so you are timing the cam
ours has 2.0L and 2.8L not 1.6L
so what country is this? the books are by country first, then year,
and model and year.
the timing belt (cog belt)
some engines time at TDC #1 firing,
other cars do #4 (with odd cam bias forces)
what this car does IDK but there are SOHC , And DOHC, and 8v and 16valve heads, and the 2 kinds, are not the same
you said magic word cam locks so is the DOHC dual cam head. sure
but our 16v is chain drive. so...
so I have no data on it. 1.6L

google finds this.

https://pmmonline.co.uk/technical/timing-belt-replacement-volkswagen-golf-1-6l-16v/


so is TDC #1 firing (compression) not exhaust stroke TDC.
the settings.

lacking relic manual 32 years old and ago.
all you can do is google it or buy one used on ebay
or google endlessly or like above 1 seconds work.

I do not know if this engine is interference type, and is first thing to learn before tool box open !
google finds

16 valve diesel Interference!

You are at the wrong stroke on the 4 stroke engine. You have to be at TDC on the COMPRESSION stroke. You are at inlet or exhaust stoke TDC :>)

I need some clarification. Did you replace the belt because it broke? If so you may need to replace the head. The problem is if the belt breaks when your moving it usually damages the head and thus needs to be replaced.

you need to do a compression test on all cylinders. All cylinders should have about the same amount of compression with a minimum of 120 psi.
if there is a major drop of compression in a cylinder that means there is a malfunction in that cylinder(bad valve, broken rings, etc
if there is a major drop in compression between 2 cylinders then that means you have a bad head gasket.
if all cylinders read 0psi then you have a broken timing belt
If all cylinders read about the same then you need to check the timing and make sure the cam(s) and crank shaft are still at top dead center (TDC)

There is no manual adjustment for timing, this is done digitally by using a VAG 1552 scan tool or equivalent. Now if timing mark is all you need just to serve your curiosity then there are a couple.

Set engine to TDC for cylinder #1 by turning the crankshaft until timing mark on flywheel or torque converter aligns with marks on the transmission case.

• Manual Transmission

Confirm that engine is set to TDC for cyl #1 by checking that the timing mark on the flywheel lines up with notch at inspection hole on manual trans.

• Automatic Transmission

Confirm that engine is set to TDC for cyl #1 by checking that the timing mark on torque coverter lines up with the edge of the inspection hole on automatic transmission.

Remove upper toothed belt cover. Once removed, you will see the letters O.T. with an arrow on the upper rear toothed belt guard. Check that mark on camshaft pulley is aligned with mark on toothed belt guard. This brings camshaft to TDC for cyl. #1.

It is unlikely that a belt has skipped a cog, but if that happens your engine will run very rough or not operate at all. You might have other issue in the air metering sensors (MAF) which doesn't take account of temperature. That means whether the engine is cold or holt it will always run rough and definitely activate an MIL.

The rotor should be pointing at the No. 1 plug wire on the compression stoke. Thats as to say, turn the engine over by hand or wrench until you fill compressing from the #1 cyl. by holding your finger on it while manually rotating the engine. ( may need asst) When you feel the compression that means your coming up on TDC ( top dead center) of the compression stoke. Now turning the engine the same direction align the timing marks on the harmonic bal. to TDC 0 degree's. Lift off the distributer cap and the rotor should be pointing at the wire that goes to the number 1 plug.

timing belt may have jumped a couple of teeth.bring #1 cyl. to tdc and check timing marks on crank and camshaft gears.perform a cylinder leak down test with the radiator cap off to see if the head gasket is blown into a water passage.

Put the engine at TDC compression stroke , Thats when the valves are both closed on No 1 cyl and the piston is on its compression stroke .then align all cam and crank marks. set dizzy on No 1 cylinder (rotor pointing at #1 plug wire) . rotate engine 2 revolutions and recheck all marks. Fire away

It might have a damaged valves caused by slipped timing belt making the piston and valves banged each other. That is why the compressions are low. Big job.

The easiest way to test this is to carry out a compression test. This test will determine if any valves are bent. The test is very easy to carry out. 1.obtain a compression tester. 2. remove all spark plugs. 3. screw tester into spark plug hole. 4. with your foot on the accelarator, crank engine. 5. read the tester reading and write it down. eg. cyl 1 175psi cyl.2 170psi etc. if you have a bent valve one cylinder will be very low compared to the rest.