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MG TD TF 1500 - When she's hot she's temperamental

My 51 TD that is. When first started the car idles at about 950 rpm. When I come to a stop and depress the clutch the idle stays at 950. But when the engine gets to 75-80 degrees C and I come to a stop with the clutch depressed the idle drops to 300-200 or stalls. If I let the clutch out (in neutral) the idle returns to 950. The engine is a stock XPAG TD2. To recap:

Below 75 C clutch pedal down 950 RPM
Above 75 C clutch pedal down 300-200 RPM or stalls.

Any ideas?

Thanks

Tim
TD12524
TD26711
Timothy Burchfield

Depress the clutch slowly after warmup and note when the rpms drop... it is at the last fraction of an inch? Could be pressure plate ran out of travel hot and you're pressing flywheel and crank hard against engine thrust bearing. Adjusting clutch to a little more clearance may solve it.
JIM N

If the car has been converted to rod clutch from cable it may need a clutch stop post fitted to stop overthrow.
If still cable the stop should be set by the cable stop nut Fig E:2 in WSM
Ray TF 2884
Ray Lee

Thanks gentlemen for the input. I have checked the obvious things and still have the problem. i should have added additional information to my original post. I changed out the gear box for an identical one and that's when the problem started. I didn't have the stalling issues befor the gearbox change so i don't think the crank or flywheel in the problem. i used the same throw out bearing and clutch and pressure plate which had 150 miles on them. the TB looked perfect, no pitting or scorch marks. When I depress the clutch there is no noise like grinding or metal on metal interference. The fall off in RPM starts immediately when I depress the clutch pedal more than an inch. I'm leaning toward the linkage (since I have no idea otherwise). i plan on removing and inspecting it tomorrow. If I find anything of note I'll report back .

Tim

cross posted to MG Experience
Timothy Burchfield

OK, this is nuts. While I was waiting for some MG Guru to tell me what was wrong with the TD I decided to re curve a spare distributor and reinstall my pertronix II EI module. I had switched it over to my 53 TD. I pulled the distributor from the 51 and put in the re curved one with the EI. Lo and behold the large drop in idle disappeared. Now when I push in the clutch pedal the RPMs drop about 150. I have no idea why the EI would change the RPM issues with the depressed clutch pedal. If anyone has any ideas I'd be glad to hear them. But right now I'm a happy (and relieved) camper.

Tim

cross posted to MG Experience
Timothy Burchfield

the only thing to do that is earthing, EI systems are very sensitive to voltage drop.
Check all your earths and straps.
Ray
Ray Lee

You may have a better ground after removing and reinstalling the distributor, but yeah it's strange.
Steve Simmons

Ray, Steve and Jim, the thing is that the problem occurred with the points in the distributor. It went away when I installed the EI. I didn't change the ground wire but it could be that putting in a new distributor made the ground better as Steve said. I'm afraid to investigate further since the car is running so well mow.

Regards and thanks

Tim
Timothy Burchfield

OK, maybe this is it. Timing! If I set the timing at 20 degrees advanced at 2,000 RPMs I have no stalling issue. A few degrees above or below 20 degrees advance at 2K RPM and the engine stalls when the clutch pedal is depressed at 900 RPM. Perhaps the friction from the pressure plate or crankshaft thrust bearings is such that if the engine isn't operating at it optimum it will not overcome that friction.

Tim
Timothy Burchfield

Tim,
Did you by any chance just get the engine rebuilt with a new crank?
JIM N


Tim, I believe you have a distributer mechanical advance that is very sensitive to RPM changes around the 900 RPM range. When your clutch is depressed it is normal for rpm to fall off a little at idle, however, it is not normal for your ignition timing to abruptly change which I believe is what's happening with your car.

Recommend you inspect the mechanical advance mechanism(springs, weights etc.) Further consider sending it to Jeff at Advance Distributors for an advance re-curve and tell him what your experiencing.
Richard Cameron

Jim, 300 miles on it but with the original crank.

Richard, I'm running a Pertronix Ignitor II not points. As someone advised on another forum I checked the timing when the clutch pedal is depressed and there was no noticeable movement of the timing mark. So I don't thing the timing is changing with the clutch pedal movement. I have a SUN Distributor machine and the advance on the distributor is very steady with no jumps in the advance curve. BTW, Jeff doesn't like EIs (understandable from a business stand point). Thanks.

Regards

Tim
Timothy Burchfield

I asked about the new crank as I recall the new thrust bearings are wider than original to account for wear on a used crank but could be tight on a new one. I don't see that note on Moss at the moment.

I just fit a new set of main bearings with a new crank and had a lot of trimmming to do on the rear inserts as they locked the crank up. Then when I installed the rod inserts- locked up tight again. Found a set of NOS Vandervell rod inserts and problem solved. Wished I could've found some old Vandervell mains.
JIM N

Jim, When I rebuilt my engine I used bearings from Moss. I think it is possible that the clearance for the crank thrust bearings may be tight. I honestly can't remember if I checked them or if I did, if they were in specs. I do know that with all the bearings installed the engine rotated freely. Perhaps when the engine isn't running at its peak the friction of the crank against the thrust bearings at operating temperature slows the engine down excessively. That doesn't happen when the engine is first started. It is running so well now that I am going to leave it alone. Thanks for your input.

Regards

Tim
Timothy Burchfield

The bearings do come wide and are meant to be custom fit to each car.
Steve Simmons

This thread was discussed between 10/05/2018 and 16/05/2018

MG TD TF 1500 index

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