Cylinder Head gap

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kernel65

kernel65

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I had a valve job done (Frank Diehl in SC, great fella) got a few other things checked out and started putting the head back on. Been reading about installing the cylinder head and saw it mentioned about pulling the cylinder head down or slightly tightening the head against valve pressure. Does this mean the head is not supposed to sit flush on the barrel when you reinstall it?

I cannot get the head to sit flush with the top of the barrel. I've got less than a 1/4" gap, three of the rockers are loose, one exhaust valve is what is holding the head up, and the pistons are at full top stroke. I don't know if I'm at TDC or not, I've rotated the engine over so many times to where the pistons are the top of the stroke I've lost my place, and each time it almost seems like it's a different valve that is holding up the head. Is this where I start tightening bolts or am I still off? I'm trying not to force anything. I know the rods are in the right place up top and pretty sure they are in the guides off the cam, but who knows...

Scott
 
Usually at least one valve is open, so that's why the head doesn't fit flush with the cylinders when assembling. Quarter inch is roughly what I've always seen. Just tighten the bolts and nuts in the order stated in the service manual. Snug first on all then torque in sequence per the manual.
 
Cool. Thanks David. I forgot to mention it's roughly the same height as when I popped it loose taking the head off. I'm just afraid of screwing it up.
 
kernel65 said:
I had a valve job done (Frank Diehl in SC, great fella) got a few other things checked out and started putting the head back on. Been reading about installing the cylinder head and saw it mentioned about pulling the cylinder head down or slightly tightening the head against valve pressure. Does this mean the head is not supposed to sit flush on the barrel when you reinstall it?

I cannot get the head to sit flush with the top of the barrel. I've got less than a 1/4" gap, three of the rockers are loose, one exhaust valve is what is holding the head up, and the pistons are at full top stroke. I don't know if I'm at TDC or not, I've rotated the engine over so many times to where the pistons are the top of the stroke I've lost my place, and each time it almost seems like it's a different valve that is holding up the head. Is this where I start tightening bolts or am I still off? I'm trying not to force anything. I know the rods are in the right place up top and pretty sure they are in the guides off the cam, but who knows...

Scott
Click to expand...
At TDC, 2 valves on one cylinder will be rocking. the other valve will be closed. That is the exhaust valve will be closing while the inlet valve is opening and pretty well equal opening at TDC. If you displace one vale while tightening the head, you can easily remove it rocker shaft and rocker to reset it. Been there Done that.
 
Scott,
How's it going? I always tighten down the 4 bolts right by the spark plugs first to get the rods in place. But make sure as you tighten them down the push rods don't get tight. I keep turning over the engine while tightening and watch the rods through the exhaust ports. Once the head is down, I do the rest. You can always figure out later where the TDC is on which cylinder by looking for both closed valves (loose rods or valve lash).

Dave
 
I always back the tappets right off before re-fitting the head in order to keep things as level as possible, but there's still a gap.
 
B+Bogus said:
I always back the tappets right off before re-fitting the head in order to keep things as level as possible, but there's still a gap.
Click to expand...

Yep i also do that BB.. +1
 
I re-fitted my head on Sunday. Make sure that the pushrods are seated as you tighten the centre bolt, once the rocker balls are in the pushrod cups use a strong elastic band to hold each in place as you move on to the next &/or tighten the centre bolt (loop onto the rocker studs). Keep checking as you tighten, I drafted my son in to turn the engine as I ran the bolt down & kept checking every pushrod/valve. Then pull down the other 4 head bolts, add the under-cylinder nuts & torque by the book.

A 'clicking' on rotation as the centre bolt is tightened indicates that at least one pushrod us not correctly located, a Commando engine will run surprisingly well with a misplaced pushrod (it will however make a horrible random clank which is very noticeable at tickover - see the thread Heading for Bellvue).

Good Luck,

Mike
 
Thanks all for the info. Nothing I read really said anything about starting out with a certain amount of gap in the head and barrel so that clears things up. I'll give it a go while turning the engine over as I start putting the bolts back.

Scott
 
As Mike Sullivan said, getting them damn pushrods in the damn sockets is the has gotten me on almost every occation of setting the head. Seem to never fail, once I tink I have them all and start tightening, one will surely be laying off.

Take it slow and check again and again and again.

After that, I bring the had down with the central bolt and 4 bolts along the spark plugs, still checking pushrod seatings. Then torque per spec.
 
As mick hemmings said pop a bolt below the head when you set it on the barrels , with your elastic bands on the rockers , set the rods then take the bolt out and they should sit perfect. That's if your eyesight can see in the head.
J
 
I think perhaps part of the difficulty might be due to people concentrating too much on tightening x number of bolts squarely when the greater part of their attention ought be focussed on seating the pushrods?
Tightening the #1 bolt alone will pull the head down squarely to the gasket face. Once done, if the pushrods are correctly located then the other fasteners can be added, however, if at any point a pushrod moves out of position (as they do :wink: ) there is only one bolt to deal with.
 
L.A.B has it right the first bolt pulls the head down but you got to keep a eye on your push rods to make sure they are sitting in possition when you do it, if you read your manual right this is how its is done, after it is down and the push rods are all good then you put the rest of the bolts in then tighten them in the right order, so easy.

Ashley
 
As described by L.A.B. cylinder head went down with the single middle bolt, the rest went in per the manual without issue. Ying (Mike) came over and checked my work, double checked valve clearance and after some coaxing it started up.

After start up it still had some white smoke. Guess it was residual oil in the pipe but it cleared after a few miles of riding and now I start the retorque/valve clearance game...

Thanks all for the help.

Scott
 
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