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MGB Running poorly

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Svcmangler

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Hey everyone, so I pulled the engine and did a reseal of all the oil gaskets. While apart I decided to replace the chain tensioner and gears. I lined up the gears so the the dots were a straigth line both at the 1 o’clock position. I have read that the manual says to line the dots up with each other in order to get TDC. Apparently this is incorrect as it put #4 at TDC not #1. I put the engine back in and started it up and it backfires and coughs etc. when I put the timing light on it the timing is way advanced so much so it is completely off the timing marks. I don’t understand what could be wrong. I took it all apart again, and everything look correct. Distributor is at 2 o’clock position and #1 is at TDC. What else could cause this?
 
Firing order is 1-3-4-2 - 180 degrees out? Did you pull the distributor drive gear and maybe replaced it incorrectly? Check out John Twist's video, especially about 3 minutes in:

 
Svcmangler said:
I lined up the gears so the the dots were a straigth line both at the 1 o’clock position. I have read that the manual says to line the dots up with each other in order to get TDC. Apparently this is incorrect as it put #4 at TDC not #1. I
Click to expand...

If, as you seem to state, BOTH dots were at the one o'clock position, the cam is 180° out of time. Pistons one and four are both at TDC at the same time, so cam position determines which pot has valves set to be on compression for firing. If you just mean the distributor rotor is pointing at the number four electrode and you've lined up crank and cam correctly, watch Twist's video.
 
So I decided to take the cover back off and reinspect. Looks like I had the chain out a tooth. Reinstalled being careful to ensure is stayed at TDC and the distributor was also in the correct position. Hopefully once back together all will be good.
the chain does seem to have more slack on the longer side than the side with the tensioner. Is this normal?
 
If the marks line up and some slack is still in the chain's length opposite the tensioner, you may find cam timing to be somewhat retarded. The crank cog pulls on that length of chain. If you take the crank through a couple rotations by hand, recheck the timing mark alignment. You may have some chain wear or "stretch." I'd be fitting a new chain.
 
The shop-manual procedure is correct. You probably had the engine at TDC on the exhaust stroke, when it should have been on the compression, or vice-versa. Dunno about MGBs, but on the 4-cyl TR engines, you set up the valve timing at TDC on the exhaust stroke.

You must always set the timing with the chain taut on the side opposite the tensioner. That's the way it is when the car is running. This is critical!

I agree that it's a good idea to replace the chain when you have the engine apart, if it hasn't been replaced recently. They're usually cheap.
 
If you haven't got a manual, I suggest finding a copy of the Bentley Press "Official MGB Workshop Manual."

This is a scan of the Haynes book, but the procedure is correct:

CamAlignment.jpg


Fig1.17.jpg
 
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