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MG MGA - Rebuilt engine missing

My MGA1500 engine was rebuilt in October 2013 and it failed on my first long road trip last summer. A new crankshaft was installed with new bearings in the fall of 2014. I have about 420 miles on the repaired-rebuild and the engine is missing badly. I have had the distributor rebuilt and the carburetors overhauled. When I inspected the motor I notice moisture around the number 2 and 4 spark plugs and a noticeable 'air bubbling' from the #4 plug thread. What could be causing this problem and would you bring this back to the same mechanic at this point? I'm very disheartened at this point and looking for the best way to get my car back in proper order and enjoying it again. Any thoughts are welcome on this. Steve Lofaro
Stephen Lofaro

Try a compression test. (Uses a small handheld device which screws into the plug hole). Should be able to hire or borrow one. Possible head gasket failure here.
Any white "mayonnaise" showing on the dipstick?

Matthew.
M Magilton

Was the cylinder head checked for cracks, during the rebuild process?
...CR
C.R. Tyrell

Stephen, a bit more history would be useful -
How was the engine running before the failure?
What was the mode of failure - did the crank break or what?
When did it start missing, and exactly when does it miss - on tickover, under load, high revs etc.
If you have air bubbling from #4 plug hole that could be a bad thread or a loose plug, but what do you mean by air bubbling? Air is a gas.
Did the same mechanic do the repair as did the original rebuild?
Give us more to go on!

Art Pearse

Stephen:
The wet and bubbling plugs may not be related to the rough running issue. 1st just try to tighten the plugs to see if they are not seated on the gasket.
Then check your valve adjustment and go over the distributor points, condenser, timing rotor, cap, and wiring, including making sure the firing order hasn't been changed. Good luck and report back with what you find!

Brian W.
ZBMan

Hello All, Well apart from all the things I did there is a reason the last thing is what fixes the problem...

The same mechanic did the repair of engine in the fall of 2014 as he did the rebuild back in summer of 2013. The crankshaft had burned through #3 and #4 bearings with #3 taking the worst of it. He installed a new crankshaft last fall. He sent me off with instructions when he finished it in January to return at 500 miles to have the motor re-torqued, but even before that I needed to go see him because the car just sounded wrong...tappy and kind of hollow. So, he adjusted the points and valves about a month back and I was around 365 miles along and it was running nicely. Then last Wednesday (a week ago) I was going to run the car out to the beach for a couple of days and it just sounded and ran terribly...missing and kind of 'backfiring' and it was tough to distinguish but I realized it was mostly when I tried to accelerate or give it power. The mechanic was full up in his shop and he suggested some things for me to try and sort it out...pulling one plug at a time, checking the plugs for fouling, etc. He suggested changing the condenser, and I did...no fix. I even drained the gas tank thinking it might be bad gas. Coincidentally, the battery drained the other night after my antics and I had to replace it...so that was new. It turned out I got the car into his shop on Wed this week, and when he changed the points...and that fixed it. I guess he used the points from last year when he finished the rebuild of the rebuild. What makes points crap out that fast? (And I am wondering why he didn't suggest the points from the beginning?)

I want to thank my friends here who posted on this issue...and perhaps we learn a bit more...I know I did.


Stephen Lofaro

Stephen, assuming you have a standard points set up, the problem might be that your coil has too low resistance. The primary winding should be in the region of 3.5 ohms. Some coils are only half that and they need a series resistor.
Art Pearse

Also - to be fair to your mechanic, he was probably on the right track with the condenser being the fault
The condenser limits sparking burns on the points and if it's faulty the points get burnt
He got you to replace the condenser but the points had probably already suffered damage ,which he replaced and all is well
My 32cents worth is that the condenser caused it
willy
William Revit

The '53 coil in my TD caused it to run lousy and eventually die once it got hot. And it did get very hot, a tell-tale sign.

.....
MAndrus

Art, Can you explain the proper way for me to test the coil with my meter? It's a Lucas Sport Coil...I'd like to check the resistance as you mentioned. Installing a resistor is a bit beyond my skill level because I don't know what type or where to install it. I mean...I could have the mechanic do it but the recent repair history has been less than stellar.

Willy, Your point is well taken...pun intended!

I ran the car up to Queen's English car show in Northridge, CA this morning and it ran nicely in the morning air just under 190 degrees F. On the way back the temp ran up near boiling going up the grades but quickly lowered back down to near 190 on the downhill. Seems like this motor has been running hotter than my previous motor...and I have had the radiator cleaned and tested for this rebuild. Is this normal range? Thoughts?

I'm also hearing some tin can type of sound through some RPM's especially on throttle and it's annoying me as all get out. At even throttle and downhill it sounds much more 'on song'. Mechanic adjusted valves on Wednesday to .016 when he also torqued the head for the 500 mile check. Is this simply going to be a characteristic of my 'new' motor? Wondering...

Stephen
Stephen Lofaro

Stephen, select the lowest resistance of the ohms setting.
Turn it on, short the meter leads to check it reads zero.
Then with the ign OFF, connect the meter directly across the two LT terminals on the coil. Polarity don't matter.
To be ultra sure, you might want to check the voltage to ground at both of the coil terminals before you do this - should be zero. (this is to protect the meter, ask me how I know!)
Art Pearse

Stephen
Two points
1-If your engine has a tingly sound under load and it's getting hot maybe the ignition timing is too far advanced - get your engine man to take it for a spin and check the noise- and check the timing before you do some damage ALSO - The thermostat could be the wrong one A lot of people have fitted too hot a thermostat and have heating trouble- From memory I think it is supposed to be 160-165deg F---70-75degC
2- To check coil resistance it is good practice to eliminate any outside influences--When measuring resistance there should be no voltage at all -Make sure the ignition is turned OFF
Best to disconnect all the wiring off at least one of the small coil connections, Then measure the resistance across the two small terminals--
Approx specs should be, -keeping in mind they vary a bit between brands--but as a guide--

3 ohms -- Normal straight 12volt coil with balast resistance built in.--normal MGA coil

1.5 ohms - 12volt coil which needs an external resistor

0.7 ohm -- 12 volt coil for electronic trgger ignition

cheers
willy
William Revit

Yes, as Willy suggests, it sounds like 'pinking' and that can cause over heating. It just needs the timing backed off a degree or two. This can be done by trial and error or get your man to dynamically time it. The standard setting is 3500rpm and 32 degrees of advance with the distributor vacuum disconnected.

After adjusting you may need to alter your idle running which will likely have dropped down slightly.

Steve
Steve Gyles

Steve,

Your issues sounds similar to an experience I had a couple of years ago. When the under-hood temps got too high, the car would start missing. Then on a long, hot trip I was getting some light missing at highway speed, and also began getting a tinny sound like I ran over some sheet metal.

Once she cooled down all was ok again. I suspected the Lucas Sport Coil since I had already had one fail under warranty. The coil was getting pretty hot.

On the return leg the coil gave up. Pulled out an ancient spare and made it home.

The cause of the overheating coil appears to have been ancient spark plug wires. I think that with the coil miss-firing I was dumping unburned gas into the exhaust were it would ignite. Not as a backfire, but as the tinny, running over metal sound.

New plug wires and a solid core coil (as opposed to oil filled) has solved the problem.

John

John Backman

This thread was discussed between 20/04/2015 and 27/04/2015

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