Ok, so I'm in the process of rebuilding my engine. I have been very careful to not mix up my main caps and installed new ACL bearings. I have also plastigaged all 5 mains and all in spec.

Now for the issue, when i tighten the last cap bolt(left side of the engine on the rear) the crankshaft locks. It locks with less than what feels like 10ft-lbs. I am uploading a video to show this condition when i have access to a cable for my phone.

I have tried different caps just to see and the same thing occurs so I think it could be the crank or the block itself. I am still going to try a few different different ideas but has anyone else heard of this happening before?

I really hope I dont have to take this to machine shop or scrap the whole block/crank

 

OK, so upon closer inspection the bearing that goes into the block looks like it may be too long. What i mean by that is that one side is completely flush with the machined surface for the cap but the other side the bearing is overflush what looks like 2 or 3 thousandths.

Is there any chance that you would possibly need to file the ends? that just doesnt seem right.

Another little bit of info is that the area that is binding is the two outer edges of the bearing through all 180 degrees which i think coincides with the theory about needing to shave the ends as it would cause the bearing to bow in that way when torqued.

The same binding occurs with the old bearing in place and no binding when none in place(I know duh, but had to just check everything)

 

You should not file the bearing. Something else is wrong. I'm a little confused with you describing the problem but also saying you checked clearances and they are fine. How did you check clearances if the main cap won't seat and tighten?

 

I know you never want to remove material from the bearing bc if the coating is removed it will eventually eat away and chip. It just send that is what appears wrong is that it is to long.

I never said it doesn't seat, maybe I didn't explain it well. The cap seats fine. The problem comes in when I torque it down. It spins free until around 10 ftlbs of torque. I had tortured all the bolts to 40 to check clearances before I found out that it had this problem but when I did that it was well within spec (all around 0.002"). I also checked and the issue occurs when only that cap is tightened so it's not that the crank is out of alignment.

Btw it all spun freely before disassembled about 2 months ago, I've only cleaned everything since then

 

So you torqued that cap to 40lbft with plastigage and the tolerance is correct but the crank doesn't turn? If I'm understanding, I think the only way that's possible is if the side clearance is too tight. You may need to take it in and have it line bored.

You say it spun freely when it came apart. Is this a rebuild? Machine work has been done? How have the block and caps been stored?

Pictures?

 

Woah woah woah. I just read your initial post again. Explain your process of tightening the bolts.

 

You won't be able to notice .002-.003" of bearing sticking above the block, more than likely
If anything is sticking slightly above, the other side is sticking slightly below.

Double check all the arrows on the main caps face forward.

 

Google "bearing crush".

--Ferdi

 

This is the part that's vexing me...

 

Yea, the way i worded that may have been confusing. I followed the procedure in th manual to tighten the bolts. I just did the torque sequence in steps of 10ft-lb starting at at 20ft-lb.

I know alot of my posts are not worded too well but im just coming of post night shift lol and only have a day a week to work on this as it is a 3 hr drive so progress is a bit slow, so thats why its been so long since it was last together

 

gutted miata- now that you mention it idk why that didnt occur to me about the side clearance, probably bc the night shift recovery haha I will check that next. Also i have all the arrows correct, i dont think you can actually install it backwards and everything line up but i may be wrong.

Also the parts were systematically laid out and cleaned in a parts washer one at a time. All parts are stored inside air conditione/heated shop. Block is on an engine stand. As of right now no machine work was done. This is a rebuild because i had a few serious leaks but im doing some head work(OS EX valves, porting and polishing, deshrouding and blending the combustion chamber

Curly- I'm trying to understand what you are saying. Are just saying it may be sticking on the opposite side of where i plastigauged it? I will check that as well

ftjandra- I forgot about that, I havent worked with journal bearings in a while but i did know about that. I have actually designed bearings before(never had to manufacture them though) for my senior design project last year(I'm a mechanical engineer). I just am a little rusty on that stuff and im used to crankshafts running needle bearings, motocross background.

Joe Perez- me too, it doesnt make sense that it used to spin free and now it doesnt.

 

You could move the caps around to isolate the problem. If the seize problem moves, it's the cap, otherwise it's in the block side.
You could move the bearings around, too.
I'd use old bearings for this test.
Also, make sure the oil galleries are clean.
Was the cap dropped, or stored/stacked under heavy stuff?
And, are you sure the thrust bearing has nothing to do with this?

 

Thrust washer?

 

I thought of thrust bearing too, but I'm pretty sure if it was the thrust bearing it would be hard to turn with no caps and certainly once no3 was tight.

 

This sounds stupid, but, you did wipe the plastigauge off, right?

 

I have cleaned off the platigauge and i have tried moving the caps around and it appears to be on the block side because whatever cap was in the rear position had the problem. I also considered the thrust bearings, ill try the old ones but i would really be surprised if that was the issue because I would think it would affect more than just the one cap.

There are no suggestions i will turn down, i just want to make sure i get this right and i may be overlooking something obvious but ive spent about 3hours trying to sort this out. I will be autocrossing tomorrow but will spend most of the day Monday looking into this issue. Im sure ill figure it out, i just hope it doesnt take too long, i want my miata back lol

 

My point was the caps, they can face forward or backwards. One direction is wrong, one is correct. There are arrows cast into all 5 caps to show correct orientation.

 

How sure are you that all the main caps are facing the right direction and are in order? If they are binding the crank when you put the old bearing in, the only cause is assembly error.

 

I am 100% sure they are facing the right way an 99% sure i put them in the right order. I will take everything out and clean it all again and recheck that nothing could be causing any issues and if i still have the issue I will try and rearrange the orders an if one setup lets it spin free i will plastigage everything again

 

You need to put all 5 caps from THE SAME ENGINE in the correct order and direction. Changing any of these three factors can cause a crank to bind.