MGB & GT Forum

I recently tore down my 3 main bearing engine and replaced the main bearings and connecting rod bearings as well as I had the camshaft and crankshaft machined and I have reinstalled and timed them. I also set #1 cylinder at TDC before I installed the cylinder head. Unfortunately prior to reinstalling the head I had loosened off the adjusting screws in the rocker arms. My problem, which may be apparent, is how do I now adjust the valve timing? Using the rule of 9, starting with #1 cylinder at TDC, you would turn the crankshaft until valve # 8 is fully open and then set the gap on rocker # 1, set the gap on rocker #3 when valve #6 is fully open and so on. Each time turning the crankshaft until the opposing valve is fully open. Since I inadvertently loosened off the rocker arm adjusting screws prior to installing the head, how do I determine when the opposing valve is fully open.

I thought that prior to setting the gap on # 1 rocker I could turn the crankshaft clockwise until the pushrod for the opposing valve # 8 is at it's highest point. I could then turn down the opposing adjusting screw, which would compress the valve spring and open the valve. I'm just not sure how far to turn the adjusting screw on the opposing valve prior to setting the gap at .015. The gap would be corrected on the opposing rocker once I set the gap for that valve.
Any thoughts would be greatly appreciated.
Mike

P.S. I hope this makes sense.

I admit to being easily confused.

But are you confusing valve timing with valve clearance? Valve timing is 'adjusted' during assembly by either using a venier cam sprocket (it allows the cam gear to be positioned independently of the cam shaft) or offset keys between the camshaft & its gear. Valve clearance is adjusted at the rocker arms using the 'rule of nines'.

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Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

Consider this:
With #1 piston at TDC with both #1 intake & exhaust valves closed (tappets down) set the valve clearance on both valves.
Rotate the crank 1/2 turn clockwise and set the #3 intake & exhaust valve clearance.
Rotate the crank 1/2 turn clockwise and set the #4 intake & exhaust valve clearance.
Rotate the crank 1/2 turn clockwise and set the #2 intake & exhaust valve clearance.
With any cylinder at TDC on the firing stroke both tappets are on the heel of their cam lobes.

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Be safe out there.
Kenny

All the crank and pistons know is where they are. They don't determine valve timing, the camshaft does. Just time the cam to the crank, then set the distributor drive gear and distributor/ignition timing to where the cam is. HTH

If you are adjusting the valves rather than valve timing, then follow Kenny's post. (-:

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Friends talking around a fire is the history of mankind.



Edited 1 time(s). Last edit at 2014-12-18 09:06 AM by Rod H..

Don't "consider this", do it. If after doing it you are still not sure you can always go back to the rule of 9.

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Si Vis pacem, para bellum

Thank you gentlemen, yes I am referring to valve clearance, sorry. I did time the cam and crankshaft prior to installing the head. Kenny that seems really simple and very doable. Therefore I do not need to use the rule of 9?
Thanks again for your help. Mike

use the "rule of 9" to ensure that you are truly on the back side of the cam when adjusting. Do it when the valves are on TDC firing stroke and you are not on the back side of the cam. Not critical of course but may end up a thou or two off.

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Law of Logical Argument - Anything is possible if you don't know what you are talking about.

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."

"Do it when the valves are on TDC firing stroke and you are not on the back side of the cam."

On the TDC firing stroke both of the tappets are on the heel of that cylinder's cam lobes ("back side of the cam", if they were not a valve would be open when the fuel mixture fired. The heel of the lobes are symmetrical between their closing and opening ramps. This can be demonstrated by setting the TDC valve clearance at zero with dial indicators on the top of both rocker adjusting screws. The cam can then be rotated forward and backwards many degrees before any tappet movement occurs. That large number of available "heel" degrees is why the Rule-of-Nine works.

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Be safe out there.
Kenny

Kenny's method works just fine. However if you're more comfortable with the Rule of 9's, then you can use it with confidence. It doesn't really matter what the valve lash is on any of the valves to start with. Just turn the engine and observe the valves until you see one of the valves fully open. Then adjust its mate using the rule of 9's.

So if number 6 is fully open, then adjust number 3. It doesn't matter at all what the lash is on number 6; all you have to know is that number 6 appears to be fully open. "Eyeball close" is plenty close for number 6 enough since the base circle on the cam lobes are very wide, so if number 6 is reasonably close to being fully open, number 3 will definitely be on its base circle such that you can adjust it with confidence.

With this method, it doesn't matter what the lash is on number 6 to start with, since what you're looking for is the apparent fully open position, and the valve will be as open as far as it's going to get regardless of the lash of number 6 to start with...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

TDC firing stroke the cam is on the side of the lobe not the 'heel'. The clearance may appear to be there, but on many cams the valve will still be tight lash....not 'open' but not fully released to max clearance either. I don't know of anybody who is looking for accurate adjustment on an MGB engine that doesn't use the rule of 9.

my 2 cents.

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Law of Logical Argument - Anything is possible if you don't know what you are talking about.

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."

Thanks again guys, that's great advice!!

Previously posted but worth mentioning again.

With the cam shaft rotating at half crankshaft speed, and with much of each lobe being base circle, you don't halve to position the cam with precision to set valve lash.

A closed valve remains closed (on base circle) for many degrees of crank rotation.


Set #1 or #4 to TDC (mark on pulley) and set lash for half the valves.
Rotate crank 360 degrees to TDC and set the remaining 4 valves.

Knowing which valves to adjust each time is easy. Nothing to remember .... 2 intake and 2 exhaust will be closed. Set those.

An oil change takes more time than setting lash.

The easy fast way and the explanation of duration and why you don't need to be dead on.


it ain't rocket science and takes but minutes.
Don't tighten the valve cover more than just snug or it will leak

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Well there you have it folks. Instead of helping the guy out to understand the rule of nine and doing one valve at a time, the experts offer up a solution where by you can save time and do two....or even four....at once....if you understand duration. It only takes but minutes...so I guess if this is something you do once a week then it is important to save as much time as possible regardless if you understand what you're doing or not.

I say go slow.....if you get it right, you won't be doing it again for a long time.

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Law of Logical Argument - Anything is possible if you don't know what you are talking about.

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."

"I say go slow.....if you get it right, you won't be doing it again for a long time."

If you really want to go slow and be dead in the kitchen accurate try this. The rocker mounted dial indicator slides from valve to valve with the pointed tip thumbscrew indexing into the oil feed hole on the rocker shaft. This unit is especially helpful when setting different valve clearances for intake and exhaust.

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Be safe out there.
Kenny