Scraping sound when cranking?

[scguy]

So I've got the engine mostly together on my 89 Comanche. Engine setup is 92 HO short block, the 93 HO head (7120), AW4, flexplate, and the starter are all from the same 93 XJ donor.

 

When I crank it over, it makes this scraping sound. It doesn't make it if it's running, only with the starter engaged. I've tried another starter I had lying around, same issue. Flexplate isn't cracked, the bolts are tight, and the teeth are fine. No rub marks anywhere on the flexplate, bellhousing, or starter. Any ideas?

 

[Pete M]

can you watch the flywheel spin while it cranks? 

[scguy]

can you watch the flywheel spin while it cranks? 

Yes, it seems like there's a small variation when turning, but probably no more than 1/16 inch.

[Eagle]

18 minutes ago, scguy said:

24 minutes ago, Pete M said:

can you watch the flywheel spin while it cranks? 

Yes, it seems like there's a small variation when turning, but probably no more than 1/16 inch.

 

Should be zero. Cracked flexplate?

[Pete M]

it certainly sounds like it happens once per revolution and it's identical each time. 

[Jeep Driver]

Yeah, sounds like a bad flex plate or gear ring. 

[scguy]

The flexplate was fine when I installed it, I tourqued it to spec. I reckon I can pull it apart and see.

 

Edit: fine as in not cracked.

[jdog]

Do you have the starter shim in?

Stock 1988 swb 4.0 ax15 np 231.

[scguy]

Do you have the starter shim in?

Stock 1988 swb 4.0 ax15 np 231.

The metal plate between engine and trans? Yes

[eaglescout526]

2.5L starter has the shim

 

4.0L does not

[omega_rugal]

the starter and the flywheel teeth are slighty misaligned

[scguy]

I pulled the transmission, don't see anything rubbing, so I'll be installing a new flexplate.

[Warren Mohler]

Are the dowels engine to trans in place?

[scguy]

Are the dowels engine to trans in place?

Yes

[Eagle]

8 hours ago, scguy said:

The flexplate was fine when I installed it, I tourqued it to spec. I reckon I can pull it apart and see.

 

Edit: fine as in not cracked.

 

The typical crack is hard to see even if you know to look for it. It's usually around the outer diameter of the bolt reinforcing ring.

[Dzimm]

Did the trans slide nicely into the crank?  If you had to use the bolts to cinch up any Gap it's likely not aligned properly.  It should slide right up flush with the block easily.

 

It's surprisingly easy to screw it up if you aren't careful, I learned it the hard way and had a crazy grinding/scraping sound when trying to start.

[scguy]

Yes they mated easily and didn't have to draw them together with the bolts. I bolted them together out of the truck and put the engine/trans/transfer case in as one unit.

[Warren Mohler]

I will assume you used the proper starter bolts. Can't imagine what could be wrong that you would not be able to see, I have replaced a lot of flex plates due to cracks even had one that the entire center was broken and still started without such noise just sound bad running. I would put a dial indicator on and see how far it's out before spending too much $

[scguy]

Here's the flexplate in question. Don't see any cracks, but I'm sure I saw a difference like it was off center when turning it over. Was going to install a new one today, but the parts store lost it, so...

I don't have the original starter bolts, but I have ones of the proper length, thread and grade installed.

[Warren Mohler]

It has been a while since I put one on, if I remember right the lower bolt has a shoulder that may position starter to ring gear. If new flex plate does not  fix problem try to pry  starter away from flex plate and tighten, a few thousands will make a big difference

[omega_rugal]

22 hours ago, scguy said:

but I'm sure I saw a difference like it was off center when turning it over.

 

that, if you can notice it then is too much

[scguy]

So under further inspection, I've found the flexplate has about .015" of play around the crank. The new one does as well. They are the correct flexplate for the application. Unless someone tells me why I shouldn't, I've used feeler gauges to space it evenly and torque it down. I imagine it was off center before, causing the starter gear clearance to change.

[scguy]

Being the cheapskate I am and having blatant disregard for my labor time, I decided to try the old flexplate with proper spacing.

 

Result: same problem.

 

So back apart it came.

 

Managed to pull the trans, remove and install the new flexplate and back together in 45 minutes. Of course, it helps to have no driveshafts in or trans cooler lines hooked up.

 

Result: fixed. Should have done it the first time, but I took a shot at saving $100.

 

Measured the old flexplate then and found discrepancies of at least .060" out of round.

 

 

So this one is solved. Finally.

 

[Pete M]

solved!  doesn't much matter how ya got there as long as success is at the finish line.