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MGB receeding valves?????

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bgtrn

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Recently adjusted valves and found #8 was completely closed, reset it and 1000 miles later valves got very noisy. Checked and #8 and #4 were completely closed(meaning no clearance). What is going on? Compression is 160 across, vacuum test was perfect, runs strongly but noisy valve train and developed miss at idle and not seem as smooth in revving as last year.
Plugs all a rusty red in color, no smoke at exhaust. Any ideas. Thanks Dennis P
 
Are the valve stems for those valves, when measured from the top of the head, taller than the rest?? If so you could be seeing valve resession going on as the valves and seats are wearing away. If not, then note the adjusters on those valves, did they seem to have moved?? Perhaps the lock nut wasn't tight enough.

The only other things I can think of that might affect the valve train, like a bad pushrod, lifter, cam or rocker, would more likely open the gap rather than close it.
 
If all else looks OK, pull out the lifters and examine them.

May be worn lifter or cam lobe......not uncommon in an MGB.
 
Adjusters were still tight, lifters are from Moss, 10 years old with 8,000 miles. Can side covers be accessed without removing manifolds?
 
Lifters or cam lobe wear would increase the clearance making it "clatter". A lessening gap at the rocker/tappet would indicate valve seat degradation.
 
I'm sorry to question your work, but are you sure you're measuring and adjusting them correctly? I can understand valve seat recession closing up the gap, but if you readjust them, they shouldn't clatter. It sounds more like the gap's closed up because you're not quite on the lowest part of the cam. Then when you readjust, the clearance is too great.
 
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