Stupid LS Engine Question, Where's TDC?

michaelsmiller · **Posted:** Mon Jan 02, 2017 9:15 pm

Back in the days when I was an auto mechanic, things were much simpler. Please answer this simple question. How do you tell if an LS engine is at TDC on cylinder #1? In the cave man days, engines had what is referred to as timing marks on the harmonic balancer. If the timing mark lined up with the pointer on the block and distributor rotor was also pointing at cylinder 1, you were at TDC. I can't find any marks that logically show TDC on the bock or the crank pulley. What I have done so far is rotate the rear tires to turn over the engine and check to see if both rockers on cylinder 1 will wiggle. Dumb answer to your question, " I rotate the tires because the steering rack crosses in front of the crank pulley making it impossible to get a wrench on it." Knowing the firing order and the fact that a V8 fires every 90 deg, I can figure out which cylinder's valves should be closed and which open. The closed valve can be wiggled. I think that I have it plus or minus 20 deg's. I have to tell you that spark plug for #1 cylinder is behind the alternator bracket and blocked by the exhaust manifold. One can't stick ones finger into the plug hole. Putting a spark put into #1 is a Hellen Keller experience. I have a boroscope type device, but when I let go of it to turn the back tire, it moves. All that I can see is the cylinder wall. GM can't be expecting people to do what I did. Please tell me that there is a simple and more logical way to do this. On the Miata, I just stick a dowel rod into the spark plug hole, a little more logical.

Chad Culbertson · **Posted:** Tue Jan 03, 2017 12:55 pm

I've owned a car with a LS but can't answer this since I never had a need to do any work related to timing.

I have to imagine a google search should bring up a good amount of info on this though given how many of these motors are out there.

michaelsmiller · **Posted:** Tue Jan 03, 2017 2:05 pm

There's a lot of crap on the internet as well as Corvette forums. I am replacing the rocker bearings because they are a known weak link in the LS engine family, especially when running at high RPM for extended periods. A few people have told me that my Z06 with 105K miles is running on borrowed time in regards to the rockers. GM rocker arms are excellent, they just have a habit of spraying the inside of your engine with many needle bearings. I did the valve observations as described above, I'll tell you if I bent any pushrods when I get it all back together. Putting new plugs looks twice as hard as getting them out. That was hard.

If one wants an accurate TDC on an assembled car with an LS, one has to get a piston stop and put it in the #1 spark plug hole, rotate the engine clockwise with your hands until it stops, mark the pulley, then rotate CCW, mark the pulley, TDC is then half way between the marks on the pulley. What would it have cost GM to put a mark on the front cover and the pulley? Cheap Inconsiderate BASTARDS!!! :stick:

It seems that there is no easy way to get TDC on a GM LS engine. I guess close is all that you can ask for.

Chad Culbertson · **Posted:** Tue Jan 03, 2017 2:10 pm

Man, that sounds troublesome, the LS3 in the Camaro was quite easy in regards to spark plugs, maybe it was just a package thing on corvettes since they had less room under the hood. I did long tubes and pulled the plugs out for that and everything was quite easy.

Richard Casto · **Posted:** Tue Jan 03, 2017 9:13 pm

michaelsmiller wrote:

What would it have cost GM to put a mark on the front cover and the pulley? Cheap Inconsiderate BASTARDS!!! :stick:

It seems that there is no easy way to get TDC on a GM LS engine. I guess close is all that you can ask for.

It seems that at least once a week we have the obligatory "German engineering suck" thread that is like a moth to flame for VK! Is this supposed to be the moment someone says that BMW marks their crank pulley for TDC (I assume they do.

Honda does!)

Richard

DickRasmussen · **Posted:** Wed Jan 04, 2017 10:15 am

michaelsmiller wrote:

There's a lot of crap on the internet as well as Corvette forums. I am replacing the rocker bearings because they are a known weak link in the LS engine family, especially when running at high RPM for extended periods. A few people have told me that my Z06 with 105K miles is running on borrowed time in regards to the rockers. GM rocker arms are excellent, they just have a habit of spraying the inside of your engine with many needle bearings. I did the valve observations as described above, I'll tell you if I bent any pushrods when I get it all back together. Putting new plugs looks twice as hard as getting them out. That was hard.

If one wants an accurate TDC on an assembled car with an LS, one has to get a piston stop and put it in the #1 spark plug hole, rotate the engine clockwise with your hands until it stops, mark the pulley, then rotate CCW, mark the pulley, TDC is then half way between the marks on the pulley. What would it have cost GM to put a mark on the front cover and the pulley? Cheap Inconsiderate BASTARDS!!! :stick:

It seems that there is no easy way to get TDC on a GM LS engine. I guess close is all that you can ask for.

Are these the engines that also have "drop a valve" concerns? If so you might contact Sam Strano regarding his "head interchange" program and at the same time ask about the TDC issue.

Chuck Branscomb · **Posted:** Wed Jan 04, 2017 2:10 pm

Richard Casto wrote:

michaelsmiller wrote:

What would it have cost GM to put a mark on the front cover and the pulley? Cheap Inconsiderate BASTARDS!!! :stick:

It seems that there is no easy way to get TDC on a GM LS engine. I guess close is all that you can ask for.

It seems that at least once a week we have the obligatory "German engineering suck" thread that is like a moth to flame for VK! Is this supposed to be the moment someone says that BMW marks their crank pulley for TDC (I assume they do.

Honda does!)

Richard

BMW does, yes. On the S62 for example, there is a mark on the harmonic balancer you match up through a window in the cover, but you do need to use a mirror to see it from above if I recall.

So, the LS engine was designed by Chinese engineers then? (i.e. referring to Mike's earlier rant) :?:

michaelsmiller · **Posted:** Tue Jan 10, 2017 5:45 pm

I think that the best way to describe GM design and production quality is by using the term variable exceptionality. The engine architecture is as sweet as one can get, the quality of individual designs and production practices seem to be left up to individual engineers without acountability. There is very little design and quality consistency from part to part. For example, the valve covers look like they were formed by a 5 year old from play-doe. That explains the plastic engine covers. The block, heads, rockers are beautifully designed and manufactured. GM clutch design shows borderline incompetence. How hard can it be, they haven't changed the design in close to 100 years. Can they design a slide so that the seats don't rock in a Corvette like a short legged stool? The aftermarket sells shims to fix this. The overall architecture of a Corvette is wonderful, it's just poor corporate wide attention to detail. My car has an LS6, I believe that it's the LS7 that has valve drop problems. LS 6's had early valve spring cracking problems due to poor quality control. I believe that at 15 years old, mine is past early life failures. I think that I have all of the GM induced problems fixed with the exception of the rocking seats. I have all of the receipts to show that mine has been a trouble free car. When you track a car, weak links tend to show themselves. I actually got excellent results from Chinese engineers because I had the reputation of being a PITA. It's all about expectations.

Arthur McDonald · **Joined:** Fri Aug 29, 2003 1:54 am **Posts:** 2052

I recall making an emergency repair to a broken (plastic) gas pedal bracket in Dishman's C4 Corvette with a tie wrap. My favorite GM feature was the gray plastic lug nut caps from the 80s and 90s.

Chuck Branscomb · **Posted:** Wed Jan 11, 2017 9:08 am

Arthur McDonald wrote:

I recall making an emergency repair to a broken (plastic) gas pedal bracket in Dishman's C4 Corvette with a tie wrap. My favorite GM feature was the gray plastic lug nut caps from the 80s and 90s.

I don't know. I think GM lying about and covering up the ignition switch fault caused crashes and deaths, lying in court when an internal whistleblower (Kelly) sued the company over it years before the whole thing came to light, etc...that kinds of takes the prize for profound corruption, arrogance and criminality by a car maker.

michaelsmiller · **Posted:** Wed Jan 11, 2017 12:37 pm

My Corvette has that same ignition switch issue, but is not included in any recall because the ignition switch is on the dash board ala Porche. The steering lock has been disabled on my car because of it's inherent reliability problem and I remove the key FOB from my car key when I'm on track because I do not want the engine to shut off unexpectedly exiting hogpen.

Yes Art, my car has the plastic grey lugnut covers. They are also available in black. The C7 seems to be free of most of these GM turds. They still haven't fixed their clutch design. At least the flaws aren't as obvious. Maybe having a female CEO has forced an improved culture on GM. I know that the female executives that I worked with were typically better and smarter than the men that also held the same posts, Rometty excluded. (Am I opening a can of worms here?)

michaelsmiller · **Posted:** Wed Jan 11, 2017 1:05 pm

We (I) have been a little harsh towards GM. Sure there are things that they do that just bugs the crap out of us. On the big picture scale, I have a 15 year old Corvette Z06 with 105K miles on it that is still very fast on the track, handles superbly, and has shown to be reliable. How many cars with this level of performance can make the same claim; Porsche, maybe, Ferrari, no way, Lambo, in your dreams, Viper, probably. Ford GT 500, probably. I could not afford to own any of these cars. I do have to thank the previous owners of my Z06 for taking such good care of it. That's a big part of the reason that it has survived so long. At your next HPDE event see how many C5's are out there and how well they are performing. It acceptable but not preferable to be flawed so long the primary reason for it's existence is well done.

Chuck Branscomb · **Posted:** Wed Jan 11, 2017 9:05 pm

From following the C5 Z06 market since I was hunting for the M3 four years ago, prices are basically unchanged for nice used low mileage C5 Z06s if not firmer by ~10-20%. I saw this on R&T's web site and thought it was interesting: http://www.roadandtrack.com/car-culture/a32169/the-corvettes-that-dont-get-driven-sold-or-bought/. The fact that the theme of this article is now being highlighted likely signals the inverse of what they are stating -- in other words it's time to buy nice, low mileage C5 Z06s for the long term.

The sedan Z06 equivalent from back then, the E39 M5, has been appreciating like crazy (for low mileage, well-kept examples) in the past 4-5 years. One recently sold for $145,000 that had 300 miles on it. Cars with 20k or so miles are selling for well over $60k now. Of course there were only about 1/4 the number of M5s sold versus Z06s sold, so it's a much rarer car. Apparently it's also much easier to find a Z06 owner who hasn't driven his/her car much, taken incredible care of it, treated it like a family member (at least if that article is to be believed).

Straying off that topic a bit, one other car I almost bought back then was a 996 GT3. I had found a 16k mile example with Motons, extra set of high end wheels, and a few other extras a guy had been trying to sell for a few months. The car ended up selling for $52k. Today? The same car with more than twice that mileage is bringing about $70k. The 997 GT3s were going for $70-75k back then, and now four years later most all of them are going for more than $100k. Sheeesh.

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