XJ81 -94, starter motor rebuild

V12-Engine
#1

Hello, first post here.

Most often I find everything I need on this or other forums and I have hence not joined until now. I really like this forum.

To go straight to the point - I have removed the starter motor (Magneti Marelli M80R) and I plan on rebuilding it. I have searched and read a lot about that topic here on Jag Lovers. I am searching for a rebuild kit if there’s any. (Brushes found, I think - LASX92-93 ?)

I have given a lot of thought about buying a new gear reduction starter and then follow this quite excellent write up. Installing a Gear Reduction Starter

On the other hand, my XJ81 has never been hard to start, I have never felt the need of an upgrade, so to speak.

So, anyone know of a good rebuild kit?
(links in old threads are dead)

Are there any particulars about opening and rebuilding? What might break or fall out etc…

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#2

Since you posted in the v12 forum, I will assume your 1994 car has the 6.0L V12.

If so, and if the XJ12 and the XJS use the same starter, your is a gear reduction starter.
Much of what you’ve found here about the older Lucas starters will not be applicable.

Years ago, I found a remanufactured starter, under a Bosch part number SR9492X and bought it. Trying to rebuild the original starter motor probably would have been more expensive.

#3

Yes, I do, or rather, she does :slight_smile:

Thanks for connecting the dots on the case of gear reduction starters, now a thread on comparing different starters for the V12 makes a lot more sense.

The rebuilt Bosch starters I find cost about $200. Not a prohibiting cost, but maybe rebuilding myself might be cheaper?

#4

That sounds about right. I don’t remember the details, but when I looked, I could not find a kit that will include everything needed.

The brushes are one part that wears, but there are bearings (bushings) and might also need replaced. Components of the solenoid might be pitted/corroded.

I figured that since I will be doing it for the first time, and since replacing the starter on the V12 is not one of the easiest jobs, I’d rather get a professionally rebuilt starter (I know, many will comment that chances are the rebuild was done in a country with cheap labor and may have included just cleaning and painting).

On the flip side, I did not send the original as a core return and still have it somewhere in the basement. If you succeed with your rebuild and are kind enough to share the process with us, I might follow your lead… :-)))

#5

Henrik,

Why don’t you take the starter appart and see what’s wrong?

You can easily modify commercially available brushes to fit.
Bearings you can find in any bearing outlet. Usually the dimensions are printed in the bearings.
Bushings could be harder, but it’s a motor that runs for a few seconds every now and then, so normally they should be fine.

1 Like
#6

Yes, You are right. Found the brushes, see video below.

Well, I will post the process :slight_smile:

I found some useful videos on YouTube

Generic:
DIY: How to Rebuild a Starter Motor - YouTube

Specific:

2 Likes
#7

Good stuff. Thanks for sharing.

#8

So, I have started to take the starter motor apart. Looking good, everything is well greased up, but also very dirty. Keeping a lot of paper and rags around is a good idea.

When pulling out the armature, looking down on the magnets in the case I see one is cracked and the metal sheeting that covers it is damaged. Apparently the armature must’ve done some damage here for reason unknown. There’s really nothing inside except black dust, so no offending piece of metal or what not that may have come in there unless the starter has ground it down. The armature doesn’t look too damaged, except perhaps when it comes to some of the grooves cut into it, see pictures.

So, I guess I better order a new one. This one will probably work if I replace the coals/brushes. The end cap bushing doesn’t seem to be a bad fit, but I don’t have the precision tools to measure it; micrometer and bore-gauge respectively. Anyone who can chime in on the tolerance used here?

The brushes/coals isn’t unevenly worn, the cogs looks to be in nice shape etc… Part of me wants to keep it for spares, other part wants to trade it in when I buy a re-manufactured one.

So, I didn’t get very far with this one, but tell me about anything fun and interesting that lasts :smile:

Thanks for the interest though :slight_smile:

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#9

I will make a wild guess on that “unknown reason” :-)))

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#10

:joy:

I did the idiotic thing and tapped a bit, but it never turned after that. I didn’t cause that damage, but am not without sin.

#11

A few tips: The black dust will be carbon from the brushes. The grooves cut into the armature are for balancing, unlikely to be any damage there. I would get a multimeter and check that the resistance of the coils is consistent. Don’t try to bench test it at full power without securing it very firmly, otherwise the torque will throw it across the room.

#12

Henrik, are you using some type of English translator? Or the auto-spellchecker is on?

Coal and coil are not the same thing :-)))

Regarding the bushings - you are correct, visual inspection is meaningless.

My old starter would work fine when cold, but would be struggling to turn when hot.
I was advised that the brass bushings are likely out of spec (I don’t recall the number, but you are correct that a micrometer will be necessary to determine that).

This was when I decided to go for the Bosch remanufactured unit. Labor rates of the local machine shop made this decision very easy…

#13

That’s a lot of balancing, though.

#14

It does look severe. It would be interesting to see the other side.

#15

Bit of damage in the leftmost groove, certainly looks like it at least.

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The other side

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There’s contact damage where it has ground itself against the cracked magnet.

No, no spell check, just that I read some post on the old forum, from a man from Finland, who said that brushes are called coals in Finland. Same thing in Sweden (in Swedish). So, just for the confusion of it all :slight_smile:

The broken magnet is what makes the deal for me, no point putting this thing together again other than to be able to send it off in one piece when I buy a re-manufactured one.

#16

The internal damage is more obvious on the other side. Time for a new/rebuild unit.

#17

You could, if you so choose, epoxy that magnet back together with JB Weld. It’d work fine. But I cannot disagree with the decision to just trade up to a rebuilt.

#18

Went ahead and bought a new starter motor on amazon.com

Bosch Reman SR9492X Starter Motor

Tax return money well spent :slight_smile:

Will replace the O2 sensors as well, since the exhaust is off, but that’s another thread.

#19

same in French : brushes are called “charbons” (exactly translating as “coals”)

#20

Agreed. Two translations into English - 1) Coal or 2) Carbon. More specifically, graphite (which happens to be the conductive form). The latter word would be agreeable to all, I suppose