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MG MGB Technical - Starter Engages, Then Slips and Spins...


Hi Everyone...

I just found this BBS and it looks very active, so I have a question:

Then I try to start the engine of my 1964 mgb roadster, the starter motor engages for only about 1 second, then disengages and spins until I release the starter switch.

What could this be?

Thanks!
JN Newton

I have not had the need to remove the starter on my MGB but have had this problem several times over the past 30 years with old american cars. In the US we call the part of the starter that slides to make contact to the flywheel the Bendix. I think Bendix was originally a brand name. Looking at page 168 of a haynes MGB manual shows an asembly similar to the US Bendix. There are many styles but the problem or solution is usually similar.

When the starter motor is engaged the bendix slides our from the force of the turning shaft, moving with the screwed sleve (figure 9 & 11).

When I have had problems such as you discribe, I have found a few solutions or causes. You do have to pull the starter.

1. Look at the teath on the gear that enguages the flywheel. They may be worn badly causing the gear to slip off as soon as the flywheel starts to move.

2. Look at the springs. They may be weak or broken.

3. How clean is the asembly? If it is gumed up badly the sprocket asembly may not be sliding all the way into position.

4. Look fo abnormal ware, Slopy bushings etc.


Hope this helps.

Don




Don


Thanks Don...

I yanked the starter this afternoon.

I want to try replacing the main spring and pinion spring on the starter. Also, the retaining clip and washer seem worn, so I want to replace those too.

I checked at LMC (www.victoriabritish.com) and Moss motors (www.mossmotors.com) but they are both out of stock of these items.

Here is an image of the parts:

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29057

I am looking for parts #3, #4, and #5 in the image.

Does anyone know of a source for these parts?

Thanks!
JN Newton

What I would try is to wire brush and clean/polish the worm screw and it's recesses. Lube only with dry graphite, reassemble and test. The sympton that you're describing is common to the early bendix starter (even when in perfect working order!) although sounds like yours is "to that point" where it needs maintenance. Good luck

Paul
Paul Hanley

Haven't seen those parts generally available for years. But unless the big spring is broken, none of this is your problem. Inside the sleeve with the gear on it is a spiral spline. Turn the gear while holding the shaft still, it should move forward, then return when you let go. If it does there is nothing wrong with the drive.
If I understand you correctly - the starter turns the engine briefly, then kicks out - the usual cause is a cylinder with very poor compression, usually a burned or stuck valve. What happens is that one cylinder fires, but the next has no compression and doesn't fire, so the engine turns fast enough to disengage the starter, but then can't compress the third cylinder enough to fire. Pull all the plugs and do a compression test.
FRM
FR Millmore

Another thing you might try once back in the car and if the symptoms continue, is to put the car in 4th gear and roll the car along the floor a foot or two. This will move the flywheel from its usual stoping point. IF the starter is in perfect working order AND syptoms persist, then its worn teeth on the flywheel. (flywheel stops at the same point every time--or at the same 180's--I forget--same difference for your issue)

How are the gear teeth on the bendix? Do they look worn and battered or crisp and slightly rounded?

FRM, my starter just spins sometimes after brief engagement too--not often--but sometimes. Compression 175 accross the four. I've noticed other's early cars do the same. fwiw

Paul
'64B

Paul Hanley

Paul,
Interesting, does it actually turn the engine before "slipping"? Certainly if anthing kicks it out, it will not re-engage until it is stopped and restarted. The design of the spiral should force the gear into mesh once it is engaged enough to turn the engine, but maybe it can "hang" briefly on the chamfer of the teeth, if they have some wear on them. That early B starter drive is a bit of an oddball for Lucas, and my experience with them was when they (and me) were a lot younger!
FRM
FR Millmore

FRM,yes it engages and the engine turns for a second or two and then the bendix kicks out--just as Mr. Newton describes. What's different on my end it that it happens once every 25 starts. I do have a new flywheel installed. I've always chalked it up as a quirky aspect of the car's fine engineering. As I've said--I'm not alone--at car shows that I've attended, so many of the early cars seem to take a turn of two, making that all too familiar whirly-zing sound when the bendix disengages prematurly.

BTW, I've wondered for a good while, why the bendix itself is long, long unavailable yet, one can buy a whole new starter unit. (The presumption is the new unit would come with a new bendix.)

Why can't we just buy the bendix?????
Paul Hanley

When I had a '66 B I found that the early type of starter would wear the teeth on the flywheel ring. Has this worn to the extent that it does not engage properly.

The other problem used to be the bendix coming off the end of the shaft.
David Witham

There are starter rebuilders in most citys. Try checking with one of them, you might well be able to have the Bendix replaced for a reasonable sum.
The Bendix is designed to 'kick' the starter teeth out of the ring gear teeth when the engine rpm exceedes the starter rpm. A slow or dragging starter can also display the symptoms you describe. Check all your electrical connections to the starter and the engine ground as well.
Bill Young

OOps, not engine rpm, but relative gear speed between the bendix gear and the ring gear on the flywheel.
Bill Young

Because if they sold you the drive, starter sales would drop like a rock - the starter itself is rarely at fault! And I've seen "rebuilt" starters with very used drives.
I guess that this design showed problems and that's why they went to the pre-engaged starters. I never could figure out why they changed to this spring thing from the "basic" inertia drive used on most other Lucas starters in the first place.
Paul's recommendation on cleaning is right on, though I have found that dry graphite does not protect from rust on cars not used frequently, especially when subject to damp storage. I've gone back to using a bit of very light oil, contrary to all recommendations (including my own), and it seems best overall. Rounded off flywheel teeth or pinion teeth may contribute to the trouble, and I've seen a number of ring gears installed backwards. The chamfer on the ring gear teeth is there to let the pinion get into the ring gear; if backwards it tends to bounce off. After enough tries it will round off the teeth.
FRM
FR Millmore


Thank you all for your help!

I took the starter to bits (is that the right way to say it even through I'm a Yank?) and cleaned the bendix. I also pulled all the springs to stretch them out.

I also had to repair the two thick washers with the double "D" holes in them because they were wobbled and the holes were rounded out, causing the outside washer to slip partially off the end snap ring. I welded the inside of the flats on the holes and ground them off and filed them to repair the double "D" shape.

I put it all back together, and it is much better now...but it still will occassionally slip and spin, but not like it did before!

So I guess it will need a new starter later at some point, but even though it has been sitting since 1998 when my dad passed away, the motor fired right up with hardly any effort!
Jim Newton

This thread was discussed between 05/09/2005 and 11/09/2005

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