MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Sluggish engine - timing chain??

Interesting problem I'm having, which I suspect may be timing-related.

Now, after much help from others on this BBS, my engine appears to be running better with a rebuild distributor. I now decided to get after a few overdue items, like fixing the leaking rear hubs and changing the engine oil. I proceeded with that work, which, given I have about 1-2 hrs/week to work on this car, took several weeks to get done. When I was finished and went to start the car, the battery seemed very weak - indeed, it was dead. 4 years old, seemed about right for a new one. So, new battery installed but engine seems VERY sluggish to turn over (about 1 rev per second). Thoroughly checked the ignition circuit - battery to switch, switch to starter, engine to firewall ground, chassis to battery. All good, including a direct battery->starter test, as well as removing and bench-testing the starter. Everything is fine, including the new battery.

So, next I removed the spark plugs to see if (too much) compression might be a problem. Indeed, when all 4 plugs were removed, and hit the starter, the engine spun freely. When I put one plug in and spun the engine, it spun freely except on the one piston with the plug in, where it "heaved" to push through it. Same thing successively with each plug.

Normally, the engine cranks over reasonably well when the battery is charged. So, what has changed? Other than an oil change, beats me.

Could a jumped timing chain be a possible cause of this problem?
Glenn (Ohio)

Glenn,

Check the engine earth cable (left engine mount) as well, when there is a faulty connection there the starter won't receive enough power to spin it freely.

If you drive your car regularly and maintain the batteries properly, they should last quite a bit longer then 4 years.

Hope this helps!
Regards, Koen
Struijk Koen

Glenn,

How well does the engine spin with all the plugs installed but with the ignition OFF? If it spins over at good speed with ignition off but not with ignition on then I'd look at a timing issue. If a plug fires on the upstroke due to some very advanced timing it puts a strain on the starter and it slows down considerably.

Dave
David Ahrendt

Glenn,
Cam and/or ignition timing shouldn't slow starting rpm. In fact the opposite should be true- correct cam timing maximizes cylinder pressures. Unless your motor is newly rebuilt, internal friction shouldn't be an issue. Advanced ignition will kick back, not spin slower.

Check the front starter bush. If this is worn, the motor will turn slower. Turn your lights on and try the starter. If they don't dim, then the circuit has too much resistance. By connecting directly to the starter, you've tested for issues outside the starter but a bad connection/hung brush inside could be the culprit. Can you replace with the fabled "known good component?"

Hope this helps,
Bill
Bill Eastman

Glenn,
I think "front" is a poor description. The bush that wears is the one closest to the drive, not by the brushes. It is actually the "back" bush in the car.

Have fun,
Bill
Bill Eastman

This thread was discussed between 13/08/2006 and 16/08/2006

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.