GM VORTEC 7400 Timing Gear & Chain Set

[overlander64]

Today, my mechanic gave me the bad news that my '99 Suburban (ordered new in 1998 and delivered to me April 22, 1998) is going to require its first rather costly motor repair. Based on a very thorough inspection, he has advised replacing the timing chain and gear set (the motor has 180,000 miles with about 65% towing) before beginning my towing season.

My quandry is whether to go with the GM replacement, or if one of the "stronger" after market sets may be advisable. I don't intend to upgrade trailers any time in the near future (the Overlander is just the right size for my longest outings while the Minuet is perfect for weekenders). Given the durability of the OEM I am leaning toward the factory as I am budgeting for a new Good Wrench motor at about 300,000 miles -- but I also want to be sure that I am not likely to be repeating this process prior to the projected new motor at 300,000 miles.

Any opinions about which would be the better choice -- GM Replacement part or "stronger" after market set? I have scheduled the replacement for the first week of June so I do have some lead time to make the decision.

Kevin

[wkerfoot]

Kevin,

What is the estimated cost of the two alternatives and what is your mechanics estimate of the relative lives?

Bill

[ROBERTSUNRUS]

Hi, Kevin. Why are you replacing the timing set in the first place? Plastic gear/sprocket broken and engine not running. Ignition timing erratic, due to loose chain. Low compression on all cylinders due to jumped timing chain. Making noise due to worn out sprockets and chain. If you got 180,000 miles on the original chain and sprockets, you did well. Use the same type again. We, at the dealer, used to replace timing sets anywhere from 75,000 miles to just over 100,000 miles; Anything more than that could be a waste of time and money. An old mechanic's saying is "The deeper you dig the more you find." How is the rest of your engine? Will you still have a loose chain due to worn out cam or main bearings? You may be perfectly fine replacing the timing set; Or you may be opening a can of worms.

[scottanlily]

hello over 64,
I work on many of these engines ,the vortec big block like yours and the 5.7
engines as well as the latest 5.3 6.0 engines. The company that owns these trucks have put 250 000 miles on them .Never have i replaced a timing chain
on any of them . The GM chain sets are very durable and do not have any
real failures like the old GM v-8 chains had years ago with the nylon ( crap )
timing gear for the camshaft .Out of 10 1 tons ,250 000 or more big blocks
and small blocks no timing chains done ,other repairs ,but no chain jobs.
I would have your mechanic stick with the factory GM parts for sure.

Scott of scottanlily

[john hd]

kevin

go with factory parts. might as well change the water pump while you are in there.

also ask you mechanic to check all the idlers on the sepentine belt as well.

they are all relatively inexpensive parts.

john

[Silvertwinkie]

I'm with Scott on this. There should be a clear reason why you are replacing the timing chain. We've had GM vehicles for decades, since the early 60s. Every single engine (all small block and big block engines) have gone several hundred thousand miles and not one has ever needed a timing chain replaced, since the early 60's when my immediate family first started buying GMs. Granted by 15-20 years and a few hundred thousand miles, there was not much of the body left being here in the rust belt, but that's for another thread.

Belts, yes, without question, but the chain? I'm also with Scott in asking the compression questions. All 8 have bad compression? Could also be head gaskets (also not cheap, but less than a timing chain swap), piston rings or worse, severe scuffing of the cyl walls. Replacing the chain is not a small task and frankly, the cost of the chain and labor might be close to what a new crate engine would be (less labor). I'd look at what an engine swap might cost before committing to changing out the chain. If you do this, you could get 200 to 300k out of a new engine for the money vs. maybe another 150k with a possible timing chain replacement. If you are burning any oil, to me the answer may be a lot more simple.

If in fact you choose to proceed with a timing chain replacement, I'm with John, go OEM. You are not doing any type of drag strip or extreme duty, high RPM stuff. The cost difference between the OEM and 3rd party may be an issue, but for sure, if you have the dealer place a non-OEM into the engine, they will walk away from any issues that come up, if any. At least if something went wrong, you can easily fall back on the statement, hey, I brought it in for service, I had you, a factory authorized shop put in a factory part and the engine did (enter your favorite problem here). In this case, you'd have some leverage on your side.

[steelbird312]

Kevin,
Please reread Scott of Scottnlilly's post.
I, too, mess with mechanics for fun. He is not just saying all this for fun. What caused you to or why did you ask your mechanic to find this solution in the first place? Was it just a preseason checkup? Was there a specific problem?
How did you do your maintenance during it's prior life? What kind of use did you put it through? Unless it was hard use, I too, would be inclined to believe it is a non-problem. For this diagnosis to be made, he must have some good electronic tuneup stuff to 'see' the slack in the chain causing timing problems.
Unless your mechanic is the dealer, go to your dealer for a second opinion. If it was a dealer elling you to start with, find a very reputable shop with the ability to hook it up for tests to 'see' the problem as it runs and is put through a few paces.

Now, IF INDEED it needs the above, and if you are the least bit mechanically inclined, you can do this yourself. My gosh, if finances are a problem, paying a mechanic to do it is a large expenditure. Many thousands of engines are built or repaired every day, and I see no reason that you would have been put into the few people that were specifically set apart to not have the ability to do it!
Simple. You have the internet. Educate yourself on how-to, and then do it.
Good luck,........but if I were a betting person, I would bet you really don't need a timing gear and chain.
If you were to, buy Delco, or one of the high performance units. Do not buy the 'cheap stuff' to save money. Now that would be a bad plan.

By the way, look at Silvertwinkie's signature....amateurs built the ark...I'll bet they could replace a timing chain if necessary.

[john hd]

i have changed a couple of timing chains on some of my prior vehicles, two trucks and one impala.

i did it primarily because of erratic timing, lousy idle and fuel economy.

all of them were of the plastic type, replaced them with steel oem components.

i think kevin can get this work done for a fraction of the cost of a crate engine.

john

[overlander64]

Greetings All!

The background on this diagnosis included:

• Service Engine Soon Light illuminates in January.
• Idle is noticeably rough, and the motor stumbles periodically upon accelleration.
• Clicking or rattling from front of engine at or near idle.

The diagnostic operations included:

• Code returned by on-board computer indicated crankshaft/camshaft position sensor error.
• Timing was inconsistent and was difficult to set to factory standard.
• Pulled distributor and bench-tested with the device passing all tests.
• Road tested with portable diagnostic computer with the report being evidence of slightly irratic timing.

It has only been about 10,000 miles since the motor had its major tune-up in preparation for the trip to Salem, OR last summer. The process included new plugs, PCV valve, EGR valve, plug wires, serpentine belt, hoses (including all emissions hoses), both fuel filters, cleaning of fuel injectors with two being replaced, and setting timing parameters.

I had noted a decrease in fuel economy, but had passed that off to the fact that I have switched from premium 92/93 octane to regular 89 octane for my solo travels last summer, and the Suburban sits idle far more of the time than ever before. The drop has been a fairly consistent 1.5 to 2.0 MPG in my Interstate travels (my new job is only two blocks form home so I don't have to drive to work).

The estaimate to replace the timing chain and gear set with GM factory components is between $900 and $1,100. The water pump was replaced with a new GM pump at 122,000 miles when it began leaking. The pully and tensioners were replaced when the truck was prepared for last summer's journey. The truck has been serviced by either one of two long-time GM dealers -- Pioneer Motors in Lancaster, WI or COAD Chevrolet-Cadillac-Pontiac-Buick in Anna, IL every 3,000 miles utilizing the severe service maintenance schedule. There is no evidence of oil burning, and compression and leak-down tests return well within the normal ranges for this engine. I am not opposed to replacing the timing chain in advance of failure as only my Oldsmobile escaped without related motor damage when the timing chain failed.

The recommendation was to replace the timing chain set before taking off with either of the trailers. I had been suspicious of the timing chain for about the last four months as the motor has been displaying symptoms similar to those that my '84 Toronado had for about 6,000 miles prior to the failure of its timing chain.

Since my late summer plans include a trip to Breckenridge, Colorado, I wanted to be sure that the Suburban was up to the task. The timing chain issue was the only critical issue found -- the temperamental electronic transfer case controls are going into failure mode again, but I am through with repairing that device.

I guess that you could say that I am ready to err on the side of caution after having timing chains fail on my '84 Oldsmobile (189,000 miles) <307 V8>, my '84 Eldorado (69,000 miles) <4.1 Liter V8>, and my father's '94 S-10 Blazer (124,000 miles) <4.2 V6>.

Kevin

[Silvertwinkie]

Sounds to me like you've done your homework...I'm totally floored by all the timing chains you've replaced. One or two maybe, but you've replaced a fleet of them it seems.

Keep us posted if it gets any better after the repair.

[john hd]

kevin

i was going to ask you if it was setting off the check engine light due to the position sensor error.

looks like you answered the question.

if it were mine i would have it changed, skip the water pump as you have already done that.

the transfer case switch is made by lucas, (not renound for reliable electrical parts, ask anyone with a british car or bike. their trademark is "the prince of darkness" if that is any indication!) i have been through one due to faulty wave soldering on the back of the panel. the components are fine, it is the assembly that is sub standard. you might try taking one of the failed units to an electrical repair person and have them resolder the back of the circuit board manually. can't hurt to give it a try.

john

[scottanlily]

I would say the rattle in the front of the engine is definately a cause for
concern and investigation .you can check your CMP (cam position) on a scan tool ,it should be 0 degrees .An out of range crank sensor (usually on a chevy astro 4.3)will cause your CMP to be incorrect .The noise is the key .Im
surprised still that its so thrashed ,Very unusual .One thing I have noted
on vortec big blocks is cold piston slap (another whole story).you have done
alot of timing chains though .By the way ,where the heck are you getting 93
octane fuel ???? One other thing ,the timing never changes unless somthing is wrong ,no adjustment is needed ,and you need a scan tool to set the base adjustment after a repair is performed like a timing chain .Have your
mechanic check the distributor and the drive gear for excessive damage or wear ,the distributor is plastic and can be worn severly as well as the gear
which means the camshaft dist drive gear also is trashed ,do this before comitting to the timing chain job as a new engine may be the best thing to do .

Scott of scottanlily

[overlander63]

Originally Posted by scottanlily

By the way ,where the heck are you getting 93
octane fuel ????
Scott of scottanlily

Scott, we can get 93 octane gas at any Amoco/BP station. Probably not the case in California, tho.

[Silvertwinkie]

Yes 93 octane is availible at almost every gas station around here. One or two places have 94 octane and one I believe has one blend slightly higher they say is "racing" gas.