Technical Big nut too tight?

[LiteRye]

I just tightened down my big crank nut to 108ft/lbs. after doing so, if I try to move the pulley by hand it won’t turn. Is this normal? I have the pistons, barrels and head installed.

 

[the hobbler]

I just tightened down my big crank nut to 108ft/lbs. after doing so, if I try to move the pulley by hand it won’t turn. Is this normal? I have the pistons, barrels and head installed.

No Ryan, that is NOT correct---something is amiss. If you still have the sump off, check the clearance between the bearing and the crankshaft at the TIMING-CHAIN end---you should have at least 10thou clearance (measure with a feeler gauge). It sounds as if something is too 'thick' or has 'nipped-up' against something it shouldn't. Even with the barrels, pistons and head installed (and plugs OUT) you should still be able to turn the engine over.

 

[bugsymike]

No Ryan, that is NOT correct---something is amiss. If you still have the sump off, check the clearance between the bearing and the crankshaft at the TIMING-CHAIN end---you should have at least 10thou clearance (measure with a feeler gauge). It sounds as if something is too 'thick' or has 'nipped-up' against something it shouldn't. Even with the barrels, pistons and head installed (and plugs OUT) you should still be able to turn the engine over.

At each stage of assembling a engine, check everything is free and working smoothly as it should. Hopefully it is something simple like a stepped washer the wrong way around or as the hobbler has suggested. These sort of things could lock the engine solid. If it moves a little in each direction it can be valve timing wrong so valves hit the piston. Also I have seen angled con rods the wrong way around hitting the side of the engine block. Rebuilding engines is a skilled job, however a careful DIY with close attention and photos of every step of the way if necessary, can certainly make a very good job of it.
Equally I have seen alleged professionals make mistakes.

 

[jolly500]

Hi.
I've just had that problem with mine. Although I have a 650 engine this might be relevant.
I had to replace my main pulley and used one from a 500, which when tightened up, also 'locked' and wouldn't turn.
After investigating, I found that although the pulleys look identical, they aren't. The flange behind the pulley is a different length by about a millimeter or so which is just enough to bind the pulley against the timing gear cover. Fixed mine by having a spacer made to push the pulley further out by a mm or so.
The 500 pulley was from an early engine, and as has been reiterated often on this forum, there are many small differences between the 'N' engine and later ones so this might not be relevant to your problem if you are using your original pulley?
Regards
Steve

 

[LiteRye]

Thanks for all the responses. Frist, I’m going to pull the plugs and see if that gives her enough to move.

My car is a bit of a mismatch of various years so it’s impossible to tell what’s original and what’s not. It’s a 650 motor that has 500 tinware and a dynamo. This is the pulley that came off the engine when it came out of the car.

 

[fiat500]

Have you had the crankshaft out of the engine?

 

[Toshi 975]

My money is on the big spacer washer that goes inside the front main bearing cavity behind the piston ring type even bigger sealing ring. The smaller washer spacer has an internal chamfer on one side which must face the main bearing. Put it the wrong way round and the crank will lock up when you tighten the big nut.

 

[LiteRye]

Yes crank was out. The engine and pistons rotated freely before I bolted down the big nut. Just pulled off pulley and it spins freely again. Can anyone tell me if this is the appropriate pulley for a 650? Google seems to indicate that is it but I wanted to check with the experts. Is there some sort of spacer that is supposed to go between the main bearing metal “ gasket” and timing chain sprocket or between the sprocket and the oil thrower / big nut washer?

 

[LiteRye]

My money is on the big spacer washer that goes inside the front main bearing cavity behind the piston ring type even bigger sealing ring. The smaller washer spacer has an internal chamfer on one side which must face the main bearing. Put it the wrong way round and the crank will lock up when you tighten the big nut.

I have a feeling this may be it. I followed the Haynes but maybe in taking things off and on I flipped it

 

[fiat500]

Yes crank was out. The engine and pistons rotated freely before I bolted down the big nut. Just pulled off pulley and it spins freely again. Can anyone tell me if this is the appropriate pulley for a 650? Google seems to indicate that is it but I wanted to check with the experts. Is there some sort of spacer that is supposed to go between the main bearing metal “ gasket” and timing chain sprocket or between the sprocket and the oil thrower / big nut washer?

Are they the original main bearings?

 

[LiteRye]

Are they the original main bearings?

Yes

 

[LiteRye]

My money is on the big spacer washer that goes inside the front main bearing cavity behind the piston ring type even bigger sealing ring. The smaller washer spacer has an internal chamfer on one side which must face the main bearing. Put it the wrong way round and the crank will lock up when you tighten the big nut.

So I stripped everything down and checked the washer and the chamfer was facing towards the inner crank. It seems that the crank shaft sealing spacer (bearing gasket?) will not move when pressure is applied. I checked this by installing the timing chain sprocket and pulley without the cover. I guess it’s time to try to replace the sealing spacer and see if that fixes the issue. Hopefully it’s not a main bearing issue

 

[fiat500]

So I stripped everything down and checked the washer and the chamfer was facing towards the inner crank. It seems that the crank shaft sealing spacer (bearing gasket?) will not move when pressure is applied. I checked this by installing the timing chain sprocket and pulley without the cover. I guess it’s time to try to replace the sealing spacer and see if that fixes the issue. Hopefully it’s not a main bearing issue

I asked about that because I think the white-metalled edge acts as the thrust-bearing; on a new one, you can't guarantee that it's the right thickness.Yours is a puzzle.

 

[bugsymike]

Does sound like a crank thrust washer issue as Pete has just mentioned, either slipped on assembly or if new than not to OEM spec. The white metaled side , assembled with plenty of oil should face the moving part of the crank, it's job is to take load/thrust when pressing down the clutch and when correctly assembled you should be able to detect slight forward and back movement if you grab the flywheel . Years ago we had a customer who always started his car with the clutch down, it resulted eventually in the engine seizing as the crank had welded it's self to the engine block, not a Fiat

 

[LiteRye]

I can’t seem to make sense out of it. Could the washer be binding on the crank somehow? This was not an issue before disassembled and the main bearing washers and crank did not change.

 

[fiat500]

Have you read this thread?

Crank too tight?? | FIAT 500 (Classic)

Hi all, I'm busy putting together a 650cc engine for the first time. I had the crank 'main' journals measured as standard. I've installed the crank with new standard main bearings at both ends and it turns perfectly. I've installed the camshaft and the timing gear (including the 2 'spacers')...

www.fiatforum.com

 

[LiteRye]

Have you read this thread?

Crank too tight?? | FIAT 500 (Classic)

Hi all, I'm busy putting together a 650cc engine for the first time. I had the crank 'main' journals measured as standard. I've installed the crank with new standard main bearings at both ends and it turns perfectly. I've installed the camshaft and the timing gear (including the 2 'spacers')...

www.fiatforum.com

Yes. As I assembled the bits without the timing chain cover last evening this does not be the same issue.

 

[Toshi 975]

I assume that the timing chain is assembled correctly with the self tensioners facing out towards you. I once bought an engine that had been rebuilt by Middle Barton Garage from a guy that was very unhappy with it as it would hardly run. When I stripped it down they had installed the timing chain the wrong way around so it was grinding into the main bearing housing.

 

[LiteRye]

I assume that the timing chain is assembled correctly with the self tensioners facing out towards you. I once bought an engine that had been rebuilt by Middle Barton Garage from a guy that was very unhappy with it as it would hardly run. When I stripped it down they had installed the timing chain the wrong way around so it was grinding into the main bearing housing.

The timing chain is correct. I even assembled without the chain and cover and still won’t turn when tightened down. It seems like it’s binding up as soon as there’s pressure as I’m able to get to full torque without the flywheel on and locked.

 

[bugsymike]

The timing chain is correct. I even assembled without the chain and cover and still won’t turn when tightened down. It seems like it’s binding up as soon as there’s pressure as I’m able to get to full torque without the flywheel on and locked.

If you have the sump off and the nut loose with engine turning freely, can you see what moves to pinch together and cause the locking up as you slowly tighten it, to help you pinpoint the direction to the problem.