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1999 Oldsmobile Alero, 2.4 litre 4 cylinder engine.  Engine fires right up and sounds good at the tailpipe but sounds like a bag of hammers under the timing chain cover.  I have had one mechanic tell me that it might only need a replacement of timing chain and tensioners because the engine will run with some slippage of the timing chain.  I have another mechanic telling me to just figure the engine is damaged and go straight to replacing the engine.  I was told growing up that an interference engine would destroy the valves very quickly if the timing chain has broken but my car is running.  The mechanic that said to replace the engine said he could tell that because of how much the engine was rocking.  I need any opinions of whether it is worth pursuing that the timing chain and tensioners may be the only problem or whether it is likely the engine valves are destroyed even though the engines starts and runs and why it wouldn't be worth the time to at least pull the cover and look at the timing chain?  

you might want to read this article..

http://www.enginebuildermag.com/Article/2485/rebuilding_the_gm_quad_4.aspx

this is an update to that article

http://www.enginebuildermag.com/Article/2426/updating_gmx2019s_quad_4_engine.aspx

http://www.quad4forums.com/forums/

here is an image of the 2.4 timing chains.. and guides..

http://econtent.autozone.com:24991/znetrgs/repair_guide_content/en_us/images//0900c152/80/23/af/cd//medium/0900c1528023afcd.gif

some shops will repair motors... when the timing chain goes bad.. others are just parts swappers... it just depends on the shop... i know shops that do both... i know of some shops that i would not let them under my hood to replace the timing chains..  but they do have the ability to replace complete motors..  others that will dig into motors to find the problems and fix them...    a lot of them have worn through the timing chain guides...  read up as much as you can so you can make a proper decision... and know what and why the mechanic is telling you something..  it is your car.. and your check book...

the quad fours also had head gasket problems...    so you might plan on that also... with a valve job.. but then you are half way to a reman motor...  

Did anyone ever suggest to you that it might just be the harmonic balancer.
The 99 did have a harmonic balancer. I have never seen the quad 4 run
without a "miss "if it was even 1 tooth out on either cam.
I have seen a few were the timing chain tensioner were bad and made the
chain  somewhat noisy . This is an hydraulic tensioner, fed by the engine oil.
And leads to a bad varnish build up of the piston Assembly of the tensioner ,
and have been know to stick somewhat on the short side.

Harmonic balancer:
Part:    BK 6005240  
Product Line:   Balkamp  
 
List Price 106.21