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Alright guys and gals, I can really use some help here.

Judy did a rebuild on the topend of my '92 FXDC.

Brand new cylinders, pistons, rings, valves, springs, cam, lifters, etc..

Before completing assembly, I would stop every so often and make sure everything would move freely along the way.
After full assembly, I go to crank the bike and nothing. The engine wouldn't even spin.
I take it all apart again, thinking that maybe a lifter got jammed and wouldn't allow the cam to spin, so I remove the cam and lifters and spin the engine by hand again.. EUREKA! IT WORKED! Put everything carefully back together.. Now it won't spin again.

Now, once again I take everything apart and work my way back. This time I have everything assembled except the heads. I spin the engine by hand so I can see the pistons moving and it spins easily with no binding.

I torque the heads on (to service manual specs) and it no longer spins again. Take the heads off... It spins.

What am I missing here?
Why would the engine not spin if the heads are bolted on and spin when they are not?

This is my first time doing my own rebuild to this extent.
I've followed the service manual word for word. I'm at a loss and could really use some help.
 

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did it spin a bit then stop at a valve or just solid no spin...u use stock pushrods? ... in right placement?..or adj's...crack by hand also only... not with starter...if you have adj pushrods yo can pull em off and see to spin...maybe a stuck valve down per guide...did you flatten the cyl bases also....so the b-gaskets will last?
 

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did it spin a bit then stop at a valve or just solid no spin...u use stock pushrods? ... in right placement?..or adj's...crack by hand also only... not with starter...if you have adj pushrods yo can pull em off and see to spin...maybe a stuck valve down per guide...did you flatten the cyl bases also....so the b-gaskets will last?
No spin whatsoever.
I'm using adjustable pushrods but, the pushrods are not installed at the moment.

I simply have the head bolted to the jug. If I remove the head, engine spins easily. I bolt the head back on, it does not move at all. I'm completely puzzled by this. I just cannot understand what changes when having the head on or off. I've narrowed it down to the front cylinder. The rear is fully assembled with the head on, rockers and pushrods installed.

What do you mean by flattening the bases?
 

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If you are trying to crank the engine over with heads installed, spark plugs in and no pushrods installed,it isn't going to spin.In the most simple terms.........You have to let air in and out.
 

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If you are trying to crank the engine over with heads installed, spark plugs in and no pushrods installed,it isn't going to spin.In the most simple terms.........You have to let air in and out.
The plugs are out when I have the head installed. Except for the first time when I had it fully assembled after the rebuild.

At that time, I had it complete and wanted to give a few cranks to make sure everything had proper lubrication before adding fuel and firing. I did use assembly lube on everything that could possibly move.
When I was ready, I hit the starter button and it just did nothing, as if it were seized. It never even cranked on the initial push of the button.
That's when I started working backwards until the crank would spin freely. At one point, it did spin with both heads on and the plugs out. After it did that, I went to spin it again and nothing. It just seemed like it "seized" again.

As you mentioned, "air in, air out" was one of my first thoughts. The new cylinders and pistons are Vtwin Mfg and claim to be 10:1 compression. I figured the slightly higher compression was the culprit but, unless I'm looking at it wrong, I don't see that being the issue since it doesn't change with the plugs out.

Maybe I'm wrong.. Which is why I'm here to plead for help to you guys.

Should I just complete the assembly (again), add some fuel and see where she goes?
 

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Is your battery good? Load test will verify.Good battery cables? Starter good? Pistons not too tight in the bore? Can you turn it over with the rear wheel while off the ground and in 5th.gear?
 

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Is your battery good? Load test will verify.Good battery cables? Starter good? Pistons not too tight in the bore? Can you turn it over with the rear wheel while off the ground and in 5th.gear?
Battery is good. Tested with a load tester and left it on a charger over night to be sure.

I did jack the rear wheel up and rotated in 5th gear just fine when the head was off. I wanted to be sure there was no binding. It looks perfect. I put the head back on while the rear wheel was still raised, torqued everything down, grabbed the rear wheel.. Now it won't move again. That's the only difference from the time it spins until the time it doesn't. Head off/head on.

I'm already bald or else I'd be ripping my hair out.
 

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Several things could bind it up. All things that should be checked before and during assembly. And i will assume you did not have the pushrods in when it bound up.

What was the deck clearance on the piston head at TDC with the jugs preloaded to the case?

If the pistons have domes, are they in the correct jugs?

When you started out, what was the piston clearance in the jug, with the jugs in plates?

And just because these jugs never ran on that motor, if the jugs are notched (oem are not) are the jugs in the correct spigots and is the skirt clearance enough to prevent flywheel interference?

And last, make sure the studs are tight in the case with the stop ring flush to the case.
 

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Seems like you have a piston to cylinder fit problem that shows up when the head is torqued or the piston is hitting the head at TDC.
 

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Did you have cylinders bored with bore plates. EVO cylinders need to be bored under compression or the can go out of round once the are under compression. Sounds like you have a cylinder binding with the piston once it goes under compression.

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