I'm having a little trouble with my engine rebuild. The block is an N42 and the head is an E31 with 2mm oversized intake and exhaust valves. I had the engine bored out 0.020" (.5mm) and installed new pistons and rings. The pistons are flat top. When I was installing the head it looked like the metal ring that goes around the piston bore on the headgasket may interfere with the valves.

I have installed the head on the block at TDC. The cam timing mark was exactly where it should be and the bright links on the chain were in the correct position. However, when I try to turn the engine over by hand after roughly a quarter turn it is binding. It is relatively easy to move for a quarter turn (or so) and then all of a sudden it stops dead.

If it's not the ring around the headgasket then it could be the block. So perhaps I should notch the block a little more. I'm thinking the safest bet would be to go with the 2mm gasket and suffer any lost compression (which might be good as I am going to be in the 10.5:1 or 11:1 range). Before I pull the head and have to get another head gasket, I would like to get anyone's input on what else might be going on here.

Thanks for your time.

I'm no expert in this but it could be one of two problems. You may need to notch out an eyebrow on the cylinder(S) or the valves may be hitting the top of the piston, in which case you would need dished out pistons.

I have no idea how you are going to determine which is the problem?

There are a couple of really knowledgable engine builders on this list, I'm sure they will chime in and point out other fixes.

You may need to count the links between the spots on your cam chain setup. An old racer trick is to put a wire from a wiring harness wire (that you have laying around, do not cut from the harness) (most everyone has extra wire sitting around or in tool box) that has been stripped and one wire removed. Place it around one link (this will be the crank starting point) and count 42 links (go to the right counting), place another wire around the 42 link (This is the cam timing spot). Count it again at least three times. After that place it on the engine. After making sure that the 42 links wires line up with the marks on the crank and cam, tighten down the bolts. Again check the links and marks, to be sure all still line up. Then remove the wires from the timing chain. The valves should not hit the piston at all. I had it happen to me. I was one link off and could never get it to start. Jeff Winter, Ralle/Sport in Denver told me about this little trick.

To check for interference in the head/cylinder remove the head and place a thin layer of modeling clay across the surface of a couple of pistons that are rising and near the top of the stroke. Replace the head and torque down. Rotate the crank until you meet resistance and pull the head again. You will see impression in the clay where any interference exist. If you suspect the valve is hitting the cylinder wall a bit of machinist's bluing applyed to the valve will leave a mark where it contacts the lip of the cylinder. Checking the mechanical timing as recommended too.

Thanks for the info. I have heard of the modeling clay idea, but I wasn't sure I felt comfortable putting clay on my piston. I'll probably try this and just be careful.

Jeff,

What exactly are you saying about counting the links? What is the significance of the wire? Is it just so I can keep up with my starting and finishing link? If the links line up correctly the timing should be fine, correct? How would it be one link off? The chain is brand new.

Zack, it's not the timing or the head gasket, I'd say it's the valve touching the piston especially when running a stage 3 cam with bigger lift. I'm afraid you'll have to take the pistons out & get them fly cut if you want to maintain the desired C/R.

Nixcars, I am afraid of the same thing. I think the way that I will go is a 2mm head gasket, rather than fly cutting the pistons. I don't need a performance monster.

Note that this is basically the engine build from the PO. I'm just somewhat stuck with what I have.

Zack, depending on the amount of lift the stg3 cam has & how much you've had taken off the deck & head, even with a 2mm H/G I'm afraid you'll still be in trouble.

Zack you may need to consider other options. I'll start with, dished pistons or different cam. nixcars has suggested fly cutting the pistons, any others?

Different rod combination???

Thanks for the suggestions guys. I was out of town this weekend. I will have the head off again this week. Hopefully I'll get this figured out pretty soon. I'll try to keep you posted on what I end up doing to solve the problem.

Zack,

Did you rule out the gasket first? Is it possible someone sold you a 240 instead of a 280 gasket?

Curious to hear what you find regardless.

Steve