Targets of Opportunity:  (inspections)  (plus +  the related, 1 cylinder is low deal)

You are here for any reason, service, Tbelt swap, failed compression. etc.

With valve cover off: 
   (blow the spark wells  out on the 16v, before doing this or get sand grit in to the engine.)

Make sure the 16v cam cap bolts are not loose?  89 inch lbs, some books have this stated wrong, it's INCH LB's NOT FOOT ! As one GM book states. (ouch)
The 8v has Phillips screws on the rocker rails that like to come loose , rumor has it Suzuki started staking them , at some time later (?) in production. I use loctite
Check all head bolts are at spec  torque., (all the ones you can reach)  52 foot/lbs. (if you find 1 loose , do not skip checking them all. The bolts are not TTY
Roll the engine by hand , makes sure the cam lobes lift all the same height. looking for flattened lobes. ( spark plugs removed make this easy)
Look at each cam lobe for extreme wear.? Polishing patterns are ok.
Look at each valve spring, to see if a coil is cracked or broken?
Look at each valves keeper , none missing? or stuck 1/2 way in?
Look for metal shavings about the area.? or green or orange AF coolant floating about, ,or for oil that looks like Chocolate Mousse.
Look at the  rocker followers , they  have spring clips (16v does)  and none of these missing or broken or half missing.

With the Timing belt cover  off: (for any reasons)

Make  sure that large 17mm bolt in the center of the crank pulley has  94ft/lbs , of torque, the TSB covers that new torque, all G16 engine. (a deep wall socket is needed)
If said bolt was loose, discovered below <   50 ft/lbs ?, then make sure the key, on this crank snout cog is not sheared or worse?
Worn  timing belt, split , shredded,  or slipped, (do sneak a peek check.) USE GATES BELTS.
idler loose? or its index missing or broken off, in the tension slider device. (under roller wheel tension device)
Loose cam wheel bolt.?  46ft/lbs
Leaking oil seals cam or crank.
Roll the crank , with the starter motor, spark plugs out), and watch the belt to see if it tries to walk off the cog wheels. It must not.
If motor don't run or runs bad, make sure the false key slot in the cam sprocket were not used, (there up to 2, marked  "I" ,that  must not be used.)
80 PSI compression on all 4 jugs is the classic , TBELT  slip, it was never serviced at 60,000 miles or owner didn't use a GATES belt.

Got  on JUG (cylinder) way low say #2 is  35PSI, during a compression test.
I use a leak down tester, and listen to where the leak is going.
If I had low compression on say #2 and 3 jugs, that be classic bad head gasket, between the 2 cylinders
But the targets of opportunity are , in this case are...
VC off. (valve cover.)

On the bad jug, pretend #2 compression (WOT) is very low:  (only it)
  1.  Lash wrong? not at spec .but actually too tight or negative lash (means always open valve, a tad) no 60k service  done!
  2.  Rocker damage on #2 (view it) (fell out and drifting about?) It will look different than the others if bad. The 16v has odd rocker springs that can and do break.
  3. Cam lobe flat ? #2 (view it)  You can check lift at anytime, just roll the engine over. are they all  equal. Intakes for intake, etc..
  4. Valves sticking open? flex them. feel them go thump(seats hitting ) I use a large hammer, #2 at TDC firing ) and push the valves open with a hammer handle.
  5. A broken valve spring.  or missing valve stem keepers?
  6.  Head gasket blown out, to side on #2 (left or right side)
  7.  Head bolts loose, not at 50 lbs.  a bad sign, can be head warped, or someone used a freak'n , China gasket last time , buy a FELPROŽ and WIN.
  8. Burned valves seats. and/ or valves. During a leak down test, you can hear the valve hiss, (ear at intake port) or even by hand turning over motor.
  9. I can pull the 02 bung, put a small hose there and hear the #2 exh valve leak air. hisssssss. turning motor by hand (sparkplug in) or with leakdown gauge attached.
  10.  Ring land damage , seen on top of piston or worse. or see ring fragments in edge of piston, bad rings, Signs of Detonation? (looks like hammer hits) U
  11. A cracked piston. A bore scope helps here, they cost $99  or can rent them in some autostores...
  12. Scored cylinder walls. Leak down fails see walk test. (bore scoped)
  13. Cracked cylinder walls. Rad. pressure leak down test fails.(bore scope, or special technique with cylinder leak down, walking piston down from firing stroke)
  14. Cracked head. Rad. leak down fails or worse cracks. (the head shop does a head leak down  first, in the machine shop)
  15. A warped head,  (over heated) (needs to be heat relaxed first, then milled.)
A dead EGR system overheats exhaust valves, and they burn., or lash never checked at the 60k mile mark. 

During the cylinder leak down test you see 15% leakage, At TDC, then walk the piston down with a breaker bar at 17mm crank bolt, fighting the pressure.
Near the bottom the exh opens,  but before that the leak rate is 15% all the way down, if not , bad cylinders. Watch the cam lobes to see when exh starts to move.