LS - 1st and 2nd Gen (1990-2000) Discussion topics related to the 1990 - 2000 Lexus LS400

LS400 Crankshaft stripped threads

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Old 11-14-19, 03:15 PM
  #16  
e30antonio
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Real quick: Does anyone have an objection to using this tap?



Last edited by e30antonio; 11-14-19 at 08:31 PM.
Old 11-14-19, 05:01 PM
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Looks good to me. At least hold it next to the crank bolt to make sure the threads are the right pitch.

And as I mentioned in my earlier post, you need to make sure that when it starts cutting threads in the mangled section, that it is synched with the remaining good threads beyond that mangled section. If this is not done, you may end up causing further problems.

And if you have a micrometer or calipers, measure the outer diameter of the tap and the bolt, making sure they're both close to 18 mm.

Also, it had not occurred to me, but seeing it say spark plug on the packaging there, made me realize that M18-1.5 is a standard thread size for spark plugs. I actually have that specific tap already, since I have the following tool:

Lisle 20200 Thread Chaser

Amazon Amazon

Which I've only actually used on the M14-1.25 side, which is a much more common spark plug hole size.

That tool is called a chaser, and if you look at it, you can see it's not designed to cut as carefully as the tap you bought, so yours will do better. But for others that may one day have less mangled threads they want to clean up, this common tool should do it, limited to the first few threads.

Last edited by oldskewel; 11-14-19 at 05:09 PM.
Old 11-14-19, 07:37 PM
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e30antonio
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Originally Posted by oldskewel
Looks good to me. At least hold it next to the crank bolt to make sure the threads are the right pitch.

And as I mentioned in my earlier post, you need to make sure that when it starts cutting threads in the mangled section, that it is synched with the remaining good threads beyond that mangled section. If this is not done, you may end up causing further problems.
Thank you. The threads have the same pitch. I'll confirm the diameter. The biggest thing that confuses me is how the heck the threads are supposed to perfectly match up?
Old 11-14-19, 09:40 PM
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oldskewel
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Originally Posted by e30antonio
Thank you. The threads have the same pitch. I'll confirm the diameter. The biggest thing that confuses me is how the heck the threads are supposed to perfectly match up?
On the matching up thing - good that you understand the issue. That's the first step. Hopefully clear that if the new threads you cut in that mangled section are not exactly aligned / synched / matched up with the remaining good threads, the bolt will not go in right.

I can't tell from the photo just what that mangled section looks like, but my thought was that if the very tip of the tap can fit past that section, and the shallow grooves in the tapered section can start to align with the first remaining thread, then that will let things work. But if the mangled section sticks out too much to allow that, it won't work. It seems like the sort of thing that may or may not work, and you won't be able to know until you try it. So if it were me, I'd give it a try carefully and see if the threads are going to be synched. It will only cut a little at first as you turn it in there, so you'll be able to tell if it's going.

If you put the tap in and it seems to lock in on the first remaining thread, before real cutting begins, you will be good to go. But if you put it in and can, for example, appear to start threads cutting at any location across the full 360*, then there is no alignment, so it won't work.

If that's the case, you'd need to trim down the mangled section a little first. And if you're going to do that, maybe you could just trim it all down so there is no mangled section left, and there is no need to tap. As I mentioned above, losing about 2 threads out of 20 is not going to cause any problems at all. A drill bit (18mm or ~11/16+) should let you trim off the mangled section. Go slowly of course, if you do this.
Old 11-23-19, 03:19 PM
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e30antonio
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Default One problem solved, now for another...

Great news everyone. I was able to use that m18 tap along with a tap handle that supports my 3/8 inch drive tap to redo the crank threads.



However, I have another setback that I am stumped on. The timing belt seems too small to fit over both cam gears (I counted 210 ± 1 teeth). The new and old belt definitely look the same size, but I cannot get it to line up on the passenger side ("right cam") cam gear. It looks off by .75 or 1 tooth; I have marked the points where I parked the gears before taking off the old belt.

I have the "CR" mark lined up with the dimple on the crank sprocket and the driver side "L CAM" lined up with the camshaft notch.

Loosening the idler and tensioner pullies has no effect! It seems to be strictly a problem with slack between the right cam, water pump, and left cam ONLY



Last edited by e30antonio; 11-23-19 at 03:22 PM.
Old 11-23-19, 06:30 PM
  #21  
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Good progress.

On the belt - it should be pretty easy. Carefully compare the old vs. new belt, tooth by tooth. They must have the exact same number of teeth. And of course, hopefully you marked the old belt with white-out, transferred those marks to the new belt, etc.
Old 11-25-19, 09:17 AM
  #22  
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good work getting the threads cleaned up.

as for the belt, it's tight but it will line up!
be patient and I hope you didn't already pull the pin to release the tensioner.
try this: remove the belt and only install it half way onto all the pulleys, not all the way seated as you have in the pic. this may relieve some tension and line things up a bit easier, then you can push in all the way once the markings line up.

to confirm if you line it all up properly is to rotate the engine by hand 2 revolutions and the markings should line up again (markings on the pulleys to the head/block, not the markings on the belt).

also another word of advise: I see lots of oil below the crank. this tells me that the front main seal is compromised. I would certainly take time to replace it now to avoid further leaking.
Old 11-26-19, 03:09 PM
  #23  
e30antonio
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Originally Posted by timmy0tool
good work getting the threads cleaned up.

try this: remove the belt and only install it half way onto all the pulleys, not all the way seated as you have in the pic. this may relieve some tension and line things up a bit easier, then you can push in all the way once the markings line up.

to confirm if you line it all up properly is to rotate the engine by hand 2 revolutions and the markings should line up again (markings on the pulleys to the head/block, not the markings on the belt).

also another word of advise: I see lots of oil below the crank. this tells me that the front main seal is compromised. I would certainly take time to replace it now to avoid further leaking.
Good advise, and good observation there about the crank seal. I'll see what I can do.
Old 12-13-19, 03:02 PM
  #24  
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Okay, this timing belt does not fit. No matter what I try, there's always one pulley left that the belt will not be able to slide onto. For example it seems like if the belt could be 1/4" longer, it'd slide on snugly. Any advise?
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