MGB 1980 MGB Timing Issue

[kyreb1862]

I have read that the 18v engines rarely jump timing but I think it may have happened to me. The car had been running, not great but running. I had noticed that the timing was erratiic. I would set the timing at 10 degress come back to it a few minutes later and it would be on 20 degrees or maybe even somewhere on the ATDC side. When I would line up the marker on the damper with the pointer it would always point to No# 1. Yesterday while the car was running it suddenly backfired and quit. I tried to start it and it would buck the starter like it was badly out of time. This morning I checked the timing by putting the engine on TDC. Now I understand why the engine was bucking the starter. The rotor now points at #3 plug on TDC. All the ignition components are new or rebuilt. The distributor has been rebuilt and converted to mechanical advance to work with a 45 DCOE. The plugs, plug wires, cap, rotor and coil have all been replaced along with the ignition module in the CEI box. Any informed guesses as to what might have happened, or what I can check, or is a partial tear down inevitable?



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[JPSmit]

Not sure about the tdc but the timing drifting like that seems to me that the dizzy isn't tight enough.

 

[kyreb1862]

Actually I was also concerned about the dizzy being loose so I had snugged it up and it didn't help any thing. The engine was rebuilt at 45K and has 60k on it now. I think the biggest problem is that it was stored for 15+ years previous to my buying it. The car was a one owner till I bought it.

 

[DrEntropy]

The timing chain in there would be making alarming noises if it were loose enough to "jump" teeth, IMO. But if you're confident the dizzy is properly installed, in good condition and engaged with the drive dog, the timing cover is the next place to go. Bit of a pain as you'll need to get the engine off the mounts by about six inches and well braced.

 

[kyreb1862]

The distributor was rebuilt by Jeff Schlemmer so I am confident of its quality. The distributor is bolted down and engaged with the drive dog. Looks like the timing chain cover is the next place to go. I was thinking maybe the tensioner was gummed up from so many years of sitting. I am stumped.Wish me luck.

 

[DrEntropy]

Well, at least we're here. If th' tensioner is an issue the cover will have "whitness marks".