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  #1  
Old October 14th, 2012, 03:32
knever3 knever3 is offline
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New flexplate, NO START

Specs first,

1987 Jeep Comanche had 4.0L 2wd ba-10/5

Installed aw-4 trans, 242 case and all under hood wiring and fuse box from 1990 XJ. Ran fine until I noticed the flex plate knock. Thought it was a rod bearing so I decided to install my stroker motor. '96 block and head, kept all the renix stuff including the flywheel from the last motor, which was from the '90 donor.

After noticing the noise was on the new motor I removed the flex plate and ordered a new one for an '87 Comanche. I noticed that the windows in the outer ring were in different locations than the old one I pulled. Sure enough, installed it and the timing is so far off it won't start. Ordered one for the '90 XJ and it turned out to be the same part.

So here's the update today. I went to Advance to get yet another flexplate for a '90 XJ/MJ. It was sealed and when I opened it up to compare it was exactly the same as the first three I saw. I took some comparison pictures for you all to noodle on.

Old one with the crack, reason for the whole debacle.



Old one vs. new one.



New one sitting on top of the old one indexed with the crank bolt pattern.













As you can see what I was talking about the timing windows are "off" between the two.

Here's some pics of the CPS.








I bought a flexplate from Crown, I even checked the box to make sure. The same result. The windows are in the wrong spot. I guess I should put it back in and just adjust the dist untill the timing is correct. That is really crazy since the dist is supposed to be set to TDC 0 degrees and the computer is supposed to adjust the timing according to the knock sensor and such.

Picture of all three, my original on the bottom, Advance Auto's ATP/Dorman, and the Crown is on the top. The flexplates do have different holes drilled in them in some locations most likely for balancing.



Back to square one...


Thoughts?
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  #2  
Old October 14th, 2012, 05:31
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beastlydumass beastlydumass is offline
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Re: New flexplate, NO START

is there and kind of id marking on the oem plate? the plate should match what ever year crank ur running thats how the timing is set rite
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  #3  
Old October 14th, 2012, 05:41
knever3 knever3 is offline
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Re: New flexplate, NO START

There's no markings on the flexplate, I was already running the '90 XJ flexplate on my '96 stroker until I noticed it was cracked. It's a 12CW crank but that shoudn't matter since I am using the Renix distributor and computer. the timing was good before I removed the flexplate. Parts stores say from '87-'90 is the same part and I have looked at the '91 part and it's way different.
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Old October 14th, 2012, 09:32
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Re: New flexplate, NO START

I know they made a high altitude version that had a special CPS (IIRC). Makes me wonder if the flex plate was also different, or if they switch from a special CPS to a special flex plate at some point? Perhaps the old plate is the odd ball? Of course it could just be a boat load of China junk plates that are off spec.

Seems you are already aware of the 90 versus 91 difference.

I wonder if the old 90 plate was a factory defect? If so I would test the CPS for proper signal voltage, verify you do have spark, in spite of the plate difference, then look at possibly setting the dizzy off one tooth to match the plate. For all you know the old 90 plate may be the odd ball and the dizzy may be set to match the odd plate?
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Old October 14th, 2012, 10:47
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Re: New flexplate, NO START

since all three plates are from different places then it seems either the oe plate is odd ball like mike said or the year differance is the problem. if u can can ahold of a 96 and verify that then u mite have a challange on ur hands to get a custom or redo the hole timing system
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Old October 14th, 2012, 12:08
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Re: New flexplate, NO START

Quote:
Originally Posted by beastlydumass View Post
since all three plates are from different places then it seems either the oe plate is odd ball like mike said or the year differance is the problem. if u can can ahold of a 96 and verify that then u mite have a challange on ur hands to get a custom or redo the hole timing system
They may all be buying from the same import source.
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  #7  
Old October 15th, 2012, 06:25
knever3 knever3 is offline
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Re: New flexplate, NO START

No soloutions yet, I really don't want to have someone try to weld it to make it work.
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Old October 15th, 2012, 13:04
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Re: New flexplate, NO START

don't believe there was ever a high altitude flexplate, the difference was made up in the CPS alone.

however, I have heard of other issues surrounding RENIX replacement flexplates, including badly offcenter or out of round conditions, so I suspect that whoever is actually making the flexplates for almost every brand just really sucks at it. Not sure what to do about it, since nearly any one you buy is going to come from them.
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Old October 15th, 2012, 13:44
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Re: New flexplate, NO START

You do know that the spacing on the bolts that go into the crankshaft are spaced slightly different, right? This keeps the flex plate oriented with the crank. They are close but you shouldn't be able to put it on but one way.
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Old October 15th, 2012, 14:10
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Re: New flexplate, NO START

Quote:
Originally Posted by old_man View Post
You do know that the spacing on the bolts that go into the crankshaft are spaced slightly different, right? This keeps the flex plate oriented with the crank. They are close but you shouldn't be able to put it on but one way.
Given this, and the original pictures... is there any rotation where the bolt holes and the windows line up?

I'm confused. The only thing I could think would be that your original was some kind of oddity, either high altitude or a specific model with different timing for emissions like a lot of CA cars?
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  #11  
Old October 15th, 2012, 15:02
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Re: New flexplate, NO START

Quote:
Originally Posted by old_man View Post
You do know that the spacing on the bolts that go into the crankshaft are spaced slightly different, right? This keeps the flex plate oriented with the crank. They are close but you shouldn't be able to put it on but one way.
counting the small holes between the big holes all the way around would answer that question, if the number of smaller holes between each of the big holes is all the same then orientation of the flywheel on the crank wouldn't matter.
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Old October 15th, 2012, 16:20
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Re: New flexplate, NO START

I beg to differ. The sequence repeats three times around the rim (4 stroke = each plug fires every other revolution). The orientation and thus the time in which the large hole goes by the sensor actually sets the time at which the plug fires. It is very important that the flex plate gets installed in the correct orientation.

I bet you can rotate the two plates to a point where the holes line up.
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  #13  
Old October 15th, 2012, 16:48
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Re: New flexplate, NO START

You could try this place they make their own. I'd give them a call and explain your problem and see what they say.

http://www.atp-inc.com/
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