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MG MGA - Valve Adjustments

We just got a rebuilt head in from a machine shop and ran into a problem with adjusting the 8th valve which is an exhaust valve. Its always the last one. We followed the manual and the adjustments were going good setting all the proper gaps until #8. If we unscrew the adjusting screw all the way it still isnt enough to allow the feeler gauge in to set the gap. The other 7 valves adjusted perfectly. Im a little concerned that the 8th valve has no gap. What Im wondering is could this be normal or do we have a wrong valve possibly installed on the valve job work. The rocker arms appear to have very minimal wear so I dont think that could be part of our problem and the push rods look fine where they meet the rocker arms. Im afraid to start it to try adjusting the valves with it running with no gap on #8.
Thanks
Jeff

Are you sure that you have the cam in the right position to do the adjustment on that cylinder?
dominic clancy

Jeff:
first check what Dominic suggests. Follow "the rule of nine" EG if you want to adjust #8 rotate engine (I like to use the crank w/o spark plugs) until # 1 is all the way down (open). To adjust #7 rotate until #2 is all the way open, and so on.
If you're adjusting correctly I would check the usual suspects: Is the #8 adjuster correct, rocker the same? How about pushrod-too long?
If all checks ok you may have to pull the head again and check length of valve stem or condition of the seat.
It absolutely needs a gap, however.
Good luck-hope its something simple
John
John

Were doing exactly as your suggesting. The rule of nine with the spark plugs out and turning the crank by hand. The number 8 adjuster and rocker arm are the same as before. The pushrods are the same as before as well. All we had done was a valve job with new valve guides and springs and a resurfacing. We left the pushrods in the block and they should be in the same positions. I'm assuming if a pushrod is switched it wouldnt matter since they are the same length. We pulled the rocker arm assembly off for the valve work and didnt disassemble it. When we got the head back we simply refitted it and re-torqued the nuts. I guess we could take it back off and try again. If that doesnt work I guess we could pull the # 8 exhaust valve and compare stem length to another cylinders exhaust valve.
Thanks.Jeff
Jeff

Jeff,
The pushrods fit into a small dish in the lifters. A pushrod will often stick slightly when you pull up on it pulling the lifter up with it. You may have inadvertantly pulled the #8 lifter out of it's seat during the head removal. The lifters may be accessed through the tappet covers on the side of the engine without removing the head.
Bill
Bill Boorse

Easiest first:

1. Make sure that the top of the pushrod is properly seated on the rocker arm ball. I seem to recall having this happen many years ago.

2. Pull the rocker assembly off and lay a straight edge along the top of the valve stems. They should all be about the same relative height. If # 8 is higher than the others then.

3. Pull the head and compare how the valves are seated in the head. If #8 appears to be set in deeper, you may have to renew the valve seat and/or replace the valve is it has been ground in too far.

Chances are the machine shop put in the wrong valve.
Good luck!
Don
D. R. Carlberg

Bill:
That would make sense. If the push rod doesn't go down all the way the rocker arm on the other side wouldnt go up to give the gap. We did pull out a push rod or two to check their condition. Maybe good ol' #8 was one of the push rods we looked at. What does the bottom of the lifter(tappet) fit into? We should be able to pull the rocker arm assembly off and lay a straight edge across the push rods and see if #8 is riding a little high.
Thanks,Jeff
Jeff

Jeff,

The bottom of the tappet goes into a hole cast into the block. Checking that the tappet is in its correct position is clearly the first thing I'd check. Second check, as mentioned above is to verify that the other end of the pushrod is correctly seated on the rocker. Good luck

Paul
Paul Hanley

Jeff,
Don's suggestion is a good way to check the valves. Each lifter fits into a hole which supports it over the camshaft. If the lifter is removed from the bore of the hole it may not drop back in properly.
Bill
Bill Boorse

If the lifter was "sucked" out when the pushrod was removed, why would the lifter even move. It seems to me if that happen when the engine is turned over that rocker will not move.... without even having to take the tappet cover off.
JEFF BECKER

A very good idea re: the lifter seating. If the rod is moving up and down as you attempt to adjust the gaps then the lifter probably is down in its hole. I would examine it directly to be sure its all the way down.
Its been awhile since I've been in there. Is it possible (like on Triumph motorcycles) for the pushrod to be off its seat on the lifter thus having it stand up higher-thus closing the valve gap?
John
John

Jeff B,
Jeff has never said that the #8 rocker moves, only that he cant get a gap. If the #8 rocker is moving up and down then you are correct that the lifter must be in it's bore. It may just be, as John says, that the pushrod is not in the lifter properly.
Bill
Bill Boorse

Bill

Jeff said that he set all the valve gaps up by the book and the 8th valve was the last to be done. Assuming he did No1 first he would have set No8 valve fully open, suggesting that the rocker arm and valve were seen to move.

Steve
Steve Gyles

The # 8 pushrod does move up and down as we hand turn the crank. D.R.'s suggestion about putting a straight edge along the top of the valve stems pin pointed the problem. The # 8 valve is defintly sitting up higher. Now we need to pull the head back off to see if #8 appears to set in alot lower. If its doesn't appear to be sitting alot lower we'll pull the valve and compare the stem length to another exhaust valve.
Thanks, Jeff
Jeff

Possibly a total red herring, but is it just possible you have got a 1500/1600 mk1 exhaust valve (1.28" valve head diameter) in a 1600 mk2 head (1.34" valve head diameter) hole?

Steve
Steve Gyles

Steve,
I stand corrected.
Bill
Bill Boorse

This thread was discussed between 23/05/2005 and 24/05/2005

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