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T-Series Idle drop when the clutch is in

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William

Darth Vader
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So, I drove around in the B for a while today, the first time I've done any real driving in it for a while (moving back in with my parents has some advantages, one being easy access to the MG!).

Anyway, something I noticed was that whenever I put the clutch in, the idle speed would drop down, quite drastically. A couple times, when the engine was still cold, it stalled it. This is not a new behavior for this car, and ISTR that my old Midget would do this as well, but why does it do this?

-Wm.
 
It might be time to check your throw out bearing. The throw out bearing on these MGs is carbon faced, so it adds a fair amount of friction to the engine/clutch interface when you push the clutch in. With a good throw out bearing the RPMs shouldn't drop too much, I think I noticed maybe a 50 RPM drop when the clutch was pushed in on my '76 B.

The only time I had the engine stall when pushing in the clutch was when the bearing needed replacement.
 
If the throwout bearing is not he culprit, check the end play of the crank shaft. If there is excessive wear on the thrust bearings on the center journal, it will allow the crank shaft to move too far forward when the clutch is depressed, which will drop the idle significantly.
Cheers,
 
I've a feeling that the car stalls because it's out of tune-it stalls in neutral till it's good and warm. The idle speed's kind of high anyway.

The throwout bearing might be the culprit, although the whole clutch is a fairly recent item, and shouldn't be all that worn. Clutch and gears all work as they're supposed to.

Crank endplay was within spec, I think. The engine runs very well (except the out of tune carbs, of course!)

-Wm.
 
Well, I took the car out again today, and it was much cooler than yesterday. Idle drop seems to be in the "normal" range Nunyas mentioned. Sometimes it didn't appear to drop much at all. I'm satisfied to put this down to user error.

Thanks for the replies, guys!

-Wm.
 
I've not seen an MGB engine with thurst bearing wear to call significant enough to stall the engine. T/O bearings can wear to th' nubs and cause a lot of dramatic noise and pedal "bounce", I can see the metal surround perhaps causing it to stall... tho I've seen the metal "collars" torn into by the three tabs on the center of the PP. Only obvious "symptom" was a bit of "chattering" and early engagement. This particular malady is weird to me. Only thing I can imagine is with age and not being run regularly the rearmost thrust bearings have deteriorated?
 
DrEntropy said:
I've not seen an MGB engine with thurst bearing wear to call significant enough to stall the engine. T/O bearings can wear to th' nubs and cause a lot of dramatic noise and pedal "bounce", I can see the metal surround perhaps causing it to stall... tho I've seen the metal "collars" torn into by the three tabs on the center of the PP. Only obvious "symptom" was a bit of "chattering" and early engagement. This particular malady is weird to me. Only thing I can imagine is with age and not being run regularly the rearmost thrust bearings have deteriorated?
Click to expand...

(shrugs) I dunno, Doc. The idle's always fluctuated a bit on this car. Sometimes it'll just start falling while sitting at the lights, and putting it in will usually cause a slight drop in revs-but my Miata does the same thing. (watch, my Miata will be in the shop next. Just you wait!)I wondered because this was the first time it dropped down and stalled whenever I put the clutch in to engage first from a stop. And, it only did it a few times yesterday, before the engine had warmed all the way through. And it didn't do it at all today.

Now, I remember my old Midget 1500 doing this occasionally as well, both before and after the clutch and box were renewed. That car was definitely not in the best of shape, but hadn't suffered the thrust washer problems the Triumph engine suffered from.

I'm doubtful that the thrust bearings have deteriorated due to lack of use, unless they can go bad over the course of a month or so-we used the car regularly until about Thanksgiving (when the first snows hit), and it got run a few times over the winter when salt was low and the roads dry. I mean, each time the durned thing just started right up (a factoid I never fail to mention to the doofs on another forum who claim all old cars are unreliable)! I could see T/O bearing problems, since they do tend to wear quick, but agian everything works just the same as usual.

Can I just claim it was Gremlins?

-Wm.
 
Sure.

I use: "stray neutrino bombardment" as my excuse with stuff like this. :laugh:
 
Hey, that's right up there with what I heard on a 440(believe, it was a later 12 cyl Modena mobile. When the timing belt broke and one bank of heads got bent.

The tech stated it was caused by "timing belt dust" clogging the belt gears......
 
Modena Faerie Dust!! :laugh:

WOOHOO!!

THAT'S what that was lyin' in the dizzy caps on that boxer Testa Rosa I worked on! All I had to do was clean it out and put new roll pins in the cam locators and th' thing was fine again.

I love magic.
 
meant to say valves in one head, but you got it Doc. Ain't excuses grand sometimes?

I have more than once stopped, did a doubletake with a "Huh"?

After hearing an excuse...................

And what's fun is when they try to elaborate.
 
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