Lagondaforum » Engine » V12 torque loss

Owen Eather	Jan 19, 2011 4:28 am
Subject: V12 torque loss Any suggetsions on a sudden loss of torque from the V12. It has been going like a train up to10 days ago. Two "incidents" were some auto electrical work on trafficators that, I thought, may have affected the power supply to the fuel pumps (new SUs) and a detailer who might have knocked something on the SU carbs when polishing the engine cam covers. Engine starts ok and idles well, with no sign of missing on stationary revving to about 1000-1500 rpm. Occaisonal backfire when driving. Absolutely dies on hills (and it had been especially strong up a 3 in 1 grade near my home). Tappet noise a little more than normal when cold. It is almost as if two or three cylinders go out on throttle application under load. Have to keep revs at about 1500, at least, when changing gear. In the past it would pull strongly from 1000. Now pulls, intermitently, on straight and level, but in lapses. My mechanic pulled a lot of wooly debris from the air cleaner and this, somewhat, improved the problem. If anyone can steer me to possible causes, i would be most grateful.

Owen Eather

Jan 19, 2011 4:28 am

Subject: V12 torque loss

Any suggetsions on a sudden loss of torque from the V12. It has been going like a train up to10 days ago. Two "incidents" were some auto electrical work on trafficators that, I thought, may have affected the power supply to the fuel pumps (new SUs) and a detailer who might have knocked something on the SU carbs when polishing the engine cam covers.

Engine starts ok and idles well, with no sign of missing on stationary revving to about 1000-1500 rpm. Occaisonal backfire when driving. Absolutely dies on hills (and it had been especially strong up a 3 in 1 grade near my home). Tappet noise a little more than normal when cold. It is almost as if two or three cylinders go out on throttle application under load.

Have to keep revs at about 1500, at least, when changing gear. In the past it would pull strongly from 1000. Now pulls, intermitently, on straight and level, but in lapses.

My mechanic pulled a lot of wooly debris from the air cleaner and this, somewhat, improved the problem.

If anyone can steer me to possible causes, i would be most grateful.

Peter S30	Jan 19, 2011 8:30 am
Subject: Re: V12 torque loss I would remove the air cleaner to see if the SU carburettor pistons are moving freely. You can test moving the piston up with your finger (engine not running) and it should go back smoothly without sticking. I had a piston sticking sometimes. Then I loosened the 2 screws slightly which are holding the bell, positioned the bell so that the pistons move freely and fixed the screws again. Check again after fixing. The suction chamber (bell) mounting is very delicate, if it has been moved by the polisher the pistons may stick. The other potential problem is if a piston has a bit to much play it needs good oiling otherwise the suction when opening the throttle is not enough to pull it up (air leak). I have this on one of my carbs. As yours was fine before I think it is more likely the sticking described above. Another thing to do might be cleaning the fuel filter. In my car it is the original one with a big number of metal plates creating the small channels for the filtration. It was full of debris. Ignition timing has not changed ?

Peter S30

Jan 19, 2011 8:30 am

Subject: Re: V12 torque loss

I would remove the air cleaner to see if the SU carburettor pistons are moving freely. You can test moving the piston up with your finger (engine not running) and it should go back smoothly without sticking. I had a piston sticking sometimes. Then I loosened the 2 screws slightly which are holding the bell, positioned the bell so that the pistons move freely and fixed the screws again. Check again after fixing. The suction chamber (bell) mounting is very delicate, if it has been moved by the polisher the pistons may stick.

The other potential problem is if a piston has a bit to much play it needs good oiling otherwise the suction when opening the throttle is not enough to pull it up (air leak). I have this on one of my carbs. As yours was fine before I think it is more likely the sticking described above.

Another thing to do might be cleaning the fuel filter. In my car it is the original one with a big number of metal plates creating the small channels for the filtration. It was full of debris.

Ignition timing has not changed ?

h14	Jan 19, 2011 8:07 pm
Subject: Re: V12 torque loss I had similar with mine after the annual winter decarbonizing & burnt exhaust valve replacement (hopefully no longer now the engine has had its long overdue rebuild) one year. Turned out I'd overlooked connecting one of the distributor LT leads...so yes, it was running very happily on one bank...but down on power (surprise surprise). Daft, but it might just be worth checking.

h14

Jan 19, 2011 8:07 pm

Subject: Re: V12 torque loss

I had similar with mine after the annual winter decarbonizing & burnt exhaust valve replacement (hopefully no longer now the engine has had its long overdue rebuild) one year. Turned out I'd overlooked connecting one of the distributor LT leads...so yes, it was running very happily on one bank...but down on power (surprise surprise). Daft, but it might just be worth checking.

Colin M34	Jan 20, 2011 11:23 am
Subject: Re: V12 torque loss Hello Owen If you had the engine cam covers polished, presumably the distributors had to be removed. Did the correct distributor go back to each bank? David Hine had this problem and found that the distributors on each bank rotate in different directions, so the automatic advance/retard is reversed. This means that as the engine speeds up, the ignition is RETARDED – not ADVANCED! There was much amusement at the Northern Lagonda Factory when this problem and solution was discovered. Not being a V12 owner means I can only pass this information on –though it’s worth checking! Colin M34

Colin M34

Jan 20, 2011 11:23 am

Subject: Re: V12 torque loss

Hello Owen

If you had the engine cam covers polished, presumably the distributors had to be removed. Did the correct distributor go back to each bank?

David Hine had this problem and found that the distributors on each bank rotate in different directions, so the automatic advance/retard is reversed. This means that as the engine speeds up, the ignition is RETARDED – not ADVANCED!

There was much amusement at the Northern Lagonda Factory when this problem and solution was discovered. Not being a V12 owner means I can only pass this information on –though it’s worth checking!

Colin M34

Owen Eather	Jan 27, 2011 8:45 am
Subject: Re: V12 torque loss To all who have given sterling support in your replies - thank you. All will be distilled and employed in the "fix". Mark Whitehead suggested I check the exhaust manifold temperature to see if all cylinders were running. Yesterday I took the tip and tested the ex. manifold temp. Right hand bank was cold as a wet mullet, the left sizzling hot ( and I have the blister to prove it). So, the right hand bank is out to lunch. Now we know what and where, my genius mechanic will look for why ( I think it is spark, but we will see - I have been wrong before). Jim Whitehrad offered, as did H 14, that the engine still pulls on one bank. Absolutely right; except for hills, the V 12 is quite tractable, although sluggish, on the straight and level - wonder what other V 12 engine would perform so manfully. Will advise on progress.

Owen Eather

Jan 27, 2011 8:45 am

Subject: Re: V12 torque loss

To all who have given sterling support in your replies - thank you. All will be distilled and employed in the "fix". Mark Whitehead suggested I check the exhaust manifold temperature to see if all cylinders were running. Yesterday I took the tip and tested the ex. manifold temp. Right hand bank was cold as a wet mullet, the left sizzling hot ( and I have the blister to prove it). So, the right hand bank is out to lunch. Now we know what and where, my genius mechanic will look for why ( I think it is spark, but we will see - I have been wrong before).

Jim Whitehrad offered, as did H 14, that the engine still pulls on one bank. Absolutely right; except for hills, the V 12 is quite tractable, although sluggish, on the straight and level - wonder what other V 12 engine would perform so manfully. Will advise on progress.