As you may have seen on other threads, I'm going to be redoing the entire top end of my 2000 4.3 engine. It will have around 150k miles on it when I tear into it. While I'm this far into it... should I :

change the...
timing chain
oil pump, strainer etc
water pump
distributor

anything else that is a known issue or potential problem on these things, or anything that will increase performance or MPG?

Why I ask is, I dont want to pop the damn hood again except for oil changes till the day this thing rusts away!

 

You can check timing chain slack without disassembling anything. More than ~12 degrees slack is excessive and warrants replacement. Chain & gears are not a common problem on these engines. I service several with over 200K and they're still well within spec.

Oil pump: Check oil pressure, that will tell the story about the bearings & the pump. As for the pick up screen, can't tell unless you look at it.

If the water pump is leaking, or ethylene glycol has be used, replace it, and use Dexcool, (ethylene glycol will destroy the seals in the pump).

Distributor: Without expensive diagnostic equipment to check the bushings, might want to replace it with an aluminum housing distributor, along with an AC Delco cap. After installation, check & adjust camshaft retard, (requires capable scan tool).

Intake gaskets: Felpro MS98002T

Injector upgrade: Delphi #FJ10565 (comes with the bracket).

AC Delco 41-993 plugs with a gap of .060"

Are you planning on replacing head gaskets? Typically not a problem on this engine, (unless you cook it). More head gaskets are replaced due to misdiagnosis, than are actually bad. Most of the time it's just the intake gasket leaking, (which is replaced when the head gasket is replaced).

Keep in mind that if you do anything with the timing cover or crankshaft position sensor, you'll need to have the relearn performed, (requires capable scan tool).

 

Thanks Capt. How can I check the timing chain without disassembly?

My oil pressure is 40 at speed, 20 idle.

It has green antifreeze in it right now, that's what was in it when I bought it. You're the only person I've ever heard actually recommend dexcool, I thought it was corrosive and hard on parts? I know the supercharged Buick guys insist on getting it out of their motors for longer life.

My problem is a burnt exhaust valve on #6 cylinder I think. Cylinders 1-5 have 120lbs, #6 is 60lbs. There's no water in the oil, no pressure in the crankcase, no water loss that I can find. So I can only assume it's a burnt valve. Would you agree?

So I'll be pulling the top end off, replacing both head gaskets, surfacing the heads .003", replacing any damaged parts, replacing the intake gasket etc. I'm thinking of port matching the heads and intake, unless you feel it a waste of time.

This engine has never overheated to my knowledge, in fact it runs cool.... in between the 150-200 mark, usually just to the high side of in between the marks.

The only code showing is a misfire on #6 (I replaced the plug when I did the pressure check) and the heater on the O2 sensor.

 

To check timing chain slack: Slowly rotate the crankshaft clockwise, (DO NOT rotate counter clockwise) until the timing marks line up. Remove the distributor cap, have an assistant watch the rotor as you slowly rotate the crankshaft counter clockwise. When the rotor just begins to move, stop rotating the crankshaft. Measure how many degrees the crank moved.

Oil pressure: What RPM did you test it? Was the engine at operating temperature? Did you use a manual gage or the dash gage?

Coolant: There are countless threads on the forum, (and on the internet), discussing the differences, advantages, and disadvantages of each, so I won't go into detail. There is one undeniable fact: Coolant was not the only thing that was redesigned, the water pump seals were also changed. The ethylene glycol contains abrasive additives that will destroy the seals prematurely, guaranteed. Do some research and decide for yourself which coolant to use

Judging from your compression results, you could very well be correct in your diagnosis. Did you perform a cylinder leakage test on each cylinder?

Port matching, (sometimes called "port & polishing") is time consuming but usually worth the effort, if done properly. Keep in mind that when the head is milled, it changes the angle between the lower intake manifold & the cylinder head. Talk with the machine shop about the options available.

The thermostat should begin to open at 195F. Normal operating temp should be very close to 198F, (using a scan tool). Don't rely on the dash gages for coolant temp or oil pressure, they are not known for their accuracy

 

I'm just fixing to replace my timing chain, and gears. Could you please tell me how to perform the Relearn? By the Way, it's a 2000 blazer, 4.3l. W vin., 2wh dr.
Any help, or tips would be greatly appreciated.

 

Welcome to the forum!

Have you checked timing chain slack? You can check it as explained above. Any more than ~12 degrees slack warrants chain and gear replacement.

If the timing cover and/or crankshaft position sensor is moved, removed, or disturbed in any way, the relearn is mandatory. If the timing cover is moved, removed or disturbed, it must be replaced, do not reuse it. If the relearn is not performed, the engine will probably start and run however, the PCM will use crankshaft position sensor data from the previous relearn, which is now inacurate. The crankshaft position sensor relearn can only be performed with a scan tool capable of initiating it, the $500 el cheapo ones can't do it.

 

No Sir; I haven't checked it. The vehicle has 180,000 miles on it. It has been a good one for me, and I'm putting a couple thousand dollars into it to keep it for a few more good years. As far as I know there is nothing wrong at all with the timing chain, but someone told me that it would really make a difference if I were to put in a new one. Would this be a mistake? Could it cause problems if I were to put a new one in it? Thanks for your help.

 

With 180K miles, unless you abused or neglected the engine, I would be amazed if it needs a chain & gear set. I've got one out there with 390K on the original chain, it gets driven daily! It wouldn't hurt anything to replace the chain & gears, (other than your wallet), but it wouldn't gain anything either. Lotta money & work involved: oil pan must be removed, timing cover must be replaced, and it will require the crankshaft position sensor relearn to be performed, (with a high end scan tool). The 4.3L is not an interferance engine. It will not bend valves if the chain lets go or the chain jumps on the sprockets. Easy enough to check the slack, when it gets up around 12 degrees, replace it, or wait until it jumps time

 

Okay. Thank You very much. I will take your advice, and save some time, and money. Thanks.

 

I'm reopening this thread, as I have the Blazer torn apart and everything 'guessed at' is now known.
no burnt valves, the passenger side head was cracked through the intake valve seat. The valley is very cruddy, looks to be a 'quaker state' motor. The cylinder walls look and feel great, as do the piston tops.

My plan as of right now :
purchase 2 rebuilt heads. I'm planning on going with Allied out of Atlanta, who sells heads for $170 each (on ebay, and that price is shipped) with a 1yr warranty.

purchase a top end rebuild gasket kit - intake, heads, VC's etc.

Clean valley and other reachable internals, then pull oil pan and clean it out as well as the bottom of the block.

Replace oil pump with either Melling or Sealed Power.

Any thoughts on brands of parts/etc, or anything else that needs to be attended to while I've got it torn down this far, please advise!

Also - the reason I didnt replace the motor was I could not find a decent one. They all had either a million miles or questionable history, and were RIDICULOUSLY high! I'm not paying $1200 for a motor with 150k miles on it.