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1997 LS400 Timing belt possibly skipped teeth

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Old 01-19-14, 03:28 PM   #1
dcrobira
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Default 1997 LS400 Timing belt possibly skipped teeth

Hello,
I have a 1997 LS400.

History:
Owned for 2 years. The guy I bought it from said he changed timing belt and other parts, not so sure about that, now… The car overheated a couple times in the past 6 months. Changed thermostat first time, and it got better.

Last week, my son was driving the car, it overheated, then he let it cool down. Later, he was driving down the freeway, and the car lost all power and died. He tried to restart, but it just sputtered a few times and died.

I just pulled off the distributor covers and checked the belt marks for alignment. They do not line-up on the cam gears when the crank is at TDC; they are not in the proper position per the photos I have seen (e.g. not at 1:00 and 11:00 positions); the belt marks change in relation to the marks on the cam gears each time I do a full rotation of the belt using the crank bolt.

I checked compression. Left side all ~180. Right side all ~80. Right side wet, still ~80.

Figure belt jumped and bent valves.

Is it worth it to change the head?
Any estimates on cost?
Steps to do the job?

All advice appreciated.
Thanks,
Bob.
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Old 01-19-14, 04:28 PM   #2
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marks on the belt are just for initial setup, marks on the gears are what you use to check against the crank.


if you have 80psi on the right, your diagnosis is probably right about some bent valves...

whether it is worth it or not depends entirely on the condition of the car. if the car is mint, then yes, it probably is worth it.


How much is it going to cost?

What colour is my house and how much will it cost to paint it red?
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Old 01-19-14, 05:19 PM   #3
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Dont forget to check for piston damage.
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Old 01-19-14, 05:37 PM   #4
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Food for thought:
I don't know this first-hand, but some of the posters here have said that it is cheaper to buy a used 1UZ engine than fix one if it has extensive damage (like piston, valve, etc. from broken timing belt).
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Old 01-19-14, 07:28 PM   #5
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Quote:
Originally Posted by dcrobira View Post
the belt marks change in relation to the marks on the cam gears each time I do a full rotation of the belt using the crank bolt.
marks should should line up with the cam pulleys and cam pulley backing plates on every other rotation of the crank, not every rotation, as this is a 4 stroke engine!
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Old 01-19-14, 08:22 PM   #6
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also, from the evidence you have presented so far, I see nothing definitive about there being damage to valves or pistons here - in fact, this scenario would be less likely than a blown head gasket or a non-destructive timing jump, from your description of overheating and the equal pressures in all cylinders on that bank.
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Old 01-20-14, 10:20 AM   #7
dcrobira
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Guess I will take a closer look at the cam marks before calling pick-n-pull.

I forgot to mention that I got the "P0340 Cam Shaft Position Sensor Bank 1" trouble code.
Is there any other test that will isolate the issue before pulling the head?

Figure I can get my boys to tear down the top end to get some experience, since most teenagers around here barely know how to check air in the tires.

thanks,
Bob
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Old 01-20-14, 11:08 AM   #8
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I would just pull the front end of that motor apart and reset the timing to be correct before pulling the heads off...
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Old 01-20-14, 11:22 AM   #9
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If you are going to get into this I suggest you purchase a new Timing belt to have ready because I believe the old belt is Crap if this happened. And also be really careful about setting up the engine for belt install ! It must be perfectly in proper position during assembly .
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Old 01-20-14, 12:48 PM   #10
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yes, to reiterate what I said earlier, do not assume just yet that this engine in wrecked, first check the timing belt alignment and replace timing belt & tensioner, it may run just fine and then all you have to do then is work on the overheating problem.

there is no need to pull a head on an engine until you have to!

PS - make sure all pulleys, idlers, etc. inside the timing belt case are clean and dry, anything wet or greasy is a problem!

get the Aisin TKT-030 kit of all OEM parts and you get the AISIN Water Pump, KOYO Idler Bearing, NSK Tensioner Bearing, NTN Hydraulic Tensioner, Mitsuboshi Timing Belt - all in one kit of these real Toyota OEM parts for about $200
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Old 01-20-14, 01:40 PM   #11
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Got it….

I kept thinking it was strange how the compression was equally low in all cylinders on that bank. After thinking about LScowboy's comment earlier, I realized how the cam being off a couple teeth could cause that behavior.

Now, I think I might have gotten lucky. I will check it tonite, and replace all parts with the suggested kit when I get it.

Btw, the old belt is oil-soaked, possibly power steering fluid.

I was wondering if the overheating would cause the tensioner to fail (I suspect it was never changed).

Thanks for all the advice/comments. I will keep you posted.
Bob.
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Old 01-20-14, 01:51 PM   #12
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if the timing belt is oil soaked, that's a huge issue, there is no tolerance for any oil whatsoever inside the timing cases, not even a drop! - you must find and fix all oil leaks, coolant leaks, PS fluid leaks - anything entering the timing belt covered area or leaking within it, and inspect the cover gaskets as well

a timing belt has zero tolerance for oil or any other fluid, which will cause it to slip!

overheating could possibly affect the hydraulic fluid of the tensioner, that would be really odd - far more likely would be oil/coolant/fluid inside the timing belt area, or else the tensioner is just worn out or a tensioner or idler bearing seizure or even a water pump issue

I would not even think about pulling a head before that Aisin kit was correctly installed and the car was run and rechecked for leaking inside the case multiple times

some inside the case leak sources are cam and crank seals, failing idler or tensioner or other bearing greases, coolant from water pump leak or other coolant hoses and other coolant carrying sections, etc.

Last edited by LScowboyLS; 01-20-14 at 01:56 PM.
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Old 01-20-14, 11:09 PM   #13
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I checked the cam gear marks against the backplate marks when the crank is at TDC.

RH cam gear mark is 6 teeth before the backplate mark.
LH cam gear mark is 3 teeth before the backplate mark.

This equates to 90º and 45º atdc on the crank.

Will a 90º slip of the timing belt cause valve damage?

Thanks,
Bob
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Old 01-20-14, 11:30 PM   #14
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For what it's worth, I'm Pretty sure if you had damaged valves or pistons, your compression readings would be Significantly lower.

I had an 87 Cressida where the number 5 piston had a hole punched in it from some sort of pre-detonation, and its compression reading was a big fat ZERO.

If the pistons DID crash into the valves, you would be looking at some pretty catatrophic damage to both the internals as well as the head itself, and you would likely be getting nothing at all in those cylinders.
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Old 01-21-14, 05:40 AM   #15
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yes, are you sure you are really at TDC, please explain your methodology for ascertaining TDC so we can make sure you are determining this correctly
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