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MG MGB Technical - GT Lacks power

For years I have been trying to figure out why my GT has no 'get up & go". The engine runs ok, idles fine, cruises ok, but it has no 'off the line' power and seems to struggle to get to 4000 rpm. The dizzy is schlemmerized, carbs rebuilt, engine rebuilt, etc. I was going through the archives looking at others with the same problem and someone stated that if the timing chain was off by one tooth the car would run but lack power. Anyone know if this is true? I was told by others that if it was off by a tooth it would run really crappy and I would know there was a problem for sure. I checked TDC and the valve positions and they looked ok. Is there a more exact way to check that the chain is on correctly? Will a B run ok with a tooth off? Thanks for any advice or experience with this problem.
Samuel Sullivan

Only really by removing the engine front cover and checking the dimples in the gears, otherwise you need a degree wheel and an understanding of exactly what the valve timing specs mean.

There can be very many reasons why an engine won't pull the skin off a rice-pudding, and going through a full check and setup of valve clearances, ignition and carb settings would normally be the first thing to do.
Paul Hunt 2010

Yes thanks Paul all the above has been done. Looking for a way to check for a chain positioning problem without removing the front cover.
Samuel Sullivan

Sam.
It will run one tooth off.
Check for obstruction in the exhaust system. Partially blocked muffler and pipe will do that.
It is also possible that your timing mark on the vibration damper is moved.Check it's mark with # 1 plug removed and slowly turm engine till piston is at top dead center. You can rock the negine in gear with all plugs removed to do this check with a wire in the plug hole to use for a depth gauge.
You can also advance the distributer by had to achieve the fastest idle. then check for power . Listen for a preignition knock and if so slightly retard timing. This will show you if your TDC mark is off.
Does the engine seem to run hot? This also could indicate cam timing is off.
Sandy
SANDY SANDERS

It will run and it will act exactly as you describe. In fact, it will run just fine a few teeth off, but will be even more like you describe. We had a 6 cyl Healey years ago that was absolutely perfect, but had no power at all despite perfect starting and idle, ran fine if you could get it moving. Turned out to have a sheared key in the crank, and cam timing was about 60 degrees late; this was the result of having the crank nut not tightened correctly, and welded in place to keep it from falling out!

The procedure for quick check is in the shop manual, very easy assuming a stock cam. AM I THE ONLY PERSON WHO STILL READS THE BOOK? If not a stock cam, you need to have the timing figures and enough understanding to figure the difference, but it will not be much with most street cams.

(slightly edited for clarity)
(with #4 inlet full open)adjust cold clearance on #1 inlet to .021
Turn the engine until #1 inlet is just opening (ie clearance goes away)
Engine should now have pointer aligned to TDC mark. (#1 cylinder will be at valve "rock", #4 will be at TDC firing position.)
(most commonly, the TDC mark will be past the pointer by about 1 1/4" [depends on damper size] or 18 deg for one tooth late)

Note:
Timing marks on sprockets are always suspect, frequently wrong, notably but not exclusively on repro bits. MG B series especially may have A series sprockets fitted, which have marks in different position.
Visual alignment of the marks at assembly is often not correct, even if the marks are correct.
Timing marks on damper and cover may also be out.
Half a tooth or 9 deg makes a very noticeable difference for those familiar with how the thing should run, and I have taken factory assembled engines apart that are this far out.
I always set them up with a degree wheel on assembly for these reasons.

FRM
Fletcher R Millmore

You can check the cam by using a cylinder stop ( old plug with a bolt in ) to get true TDC. Then a dial gauge on a valve. You can download a degree wheel.


http://www.thegsresources.com/files/degree_wheel.pdf
c cummins

This thread was discussed on 02/07/2010

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