Starter motor engages then slips out

[ElMariachi]

I just replaced the starter motor in my '76 280z.  The original symptom was that the starter would spin fast but not engage the flywheel.  The ring gear has some wear on the teeth edges but no broken teeth.  The new starter does the same. 

I pulled the plugs and put a hand switch on the solenoid.  When I trigger the solenoid the motor will turn the engine a little bit and then the starter motor will spin but not rotate the crankshaft.  Any help would be greatly appreciated.  Thanks.

[Zed Head]

Has it ever worked for you or did you just buy someone else's problem?

[ElMariachi]

It's worked great for the last year since I bought it.  I've been doing a lot of work on it and have been using it a lot more now that it's running well.  

[Zed Head]

Is it an automatic or manual?  Might not matter but good to know.

If I had your problem I'd probably try to lever the starter away from the ring gear while I tightened the starter bolts.  Crude, but it seems like the starter gear teeth aren't fully engaging with the ring gear.  Maybe the wear on the ring gear teeth is enough to finally cause binding, from what was a tight tolerance.

Actually, an even simpler quicker test is to loosen the starter bolts slightly so that the starter can move away when actuated and let the teeth mesh.  It should be fine for a few starts as a test.  If it works you'll know that you have gear meshing problem.

Edit - do you still have the old starter?  Take a close look at the teeth on the drive gear.  You might find that they've not been fully engaging in the past.  Might be a clue.

Edited August 31, 2021 by Zed Head

[dutchzcarguy]

7 hours ago, ElMariachi said:

replaced the starter motor in my '76 280z. 

Could be with a faulty starter, you used a original or a (one on the many bad) copy('s)? 

2 hours ago, Zed Head said:

Take a close look at the teeth on the drive gear.

Yep and on both starters.. and... a picture tells us a thausand things more than words haha...  (I never heard of this problem but i thought a weak spring in your starter/startrelay is the culprit.. they can have that problem both..)

[ElMariachi]

Pictures of the ring gear and old starter motor pinion attached.  There is some wear on the ring gear but just on the tooth tips.  The starter had hardly and wear.

I did some measurements. From the outside of the bell housing cover plate to the nearest edge of the ring gear is about 18mm. On the starter motor the pinion gear starts at about 8mm from the cover plate interface so the gear has about 10mm travel before it could begin to interface with the ring gear. The pinion gear appears to have 13 mm travel leaving only 3mm to of gear teeth mesh. Since the pinion gear is rounded and the ring gear front tooth edge is worn there is probably little to no contact between the gear tooth faces.

Can anyone recommend a starter motor that is ~8mm longer or a source for drawings of motors that I could search through?

[Yarb]

The gear reduction starters don’t specify automatic or manual transmission. Up to 1978 they specified trans type. I’m wondering if the automatic starter might have a shorter bendix throw to the flex plate which might explain it barely reaching the flywheel. Unlikely since you said it was working previously but Just a thought. Recently did the a/t to manual conversion and the difference is a spacer on the crankshaft to the flex plate. Hopefully others will chime in. I’m sure you’ve bench tested the starter under power correct?

[Zed Head]

I think that your ring gear might be shot.  The starter gear gets driven in to the ring gear only by the strength of the starter solenoid magnetic field.  It's designed to slide smooth teeth in to smooth teeth, not crunched teeth in to mangled teeth.

You can get new ones, but a new flywheel is almost the same cost.

Hard to find a good picture in a product listing but I did find a Google remnant, below.  

https://zcardepot.com/products/ring-gear-for-starter-flywheel-240z-260z-280z

[Zed Head]

31 minutes ago, Yarb said:

Recently did the a/t to manual conversion and the difference is a spacer on the crankshaft to the flex plate.

Might be that the flywheel is sitting too far from the block.  A measurement from the back of the flywheel to the dust cover (the thin metal plate) would be good.  Somebody could compare to theirs if they have an engine handy.

p.s. the ring gears are press fit on to the flywheels.  Yours might have moved.  Hard to tell, that's why a measurement to the flywheel will be best to compare to others.  If that shiny flywheel surface is flat, that's a lot of space that might have been covered (Edit - added red lines for emphasis).  I'll see if I can find an image of the back of a flywheel.

 

Edited September 1, 2021 by Zed Head

[Zed Head]

Found an image of a Sachs.  Quite a few mm difference by eyeball.

https://www.ebay.com/itm/293381977250?fits=Model%3A280Z&hash=item444eedb4a2:g:Yb0AAOSwkwxd-Umn

[Zed Head]

57 minutes ago, Yarb said:

Up to 1978 they specified trans type. I’m wondering if the automatic starter might have a shorter bendix throw to the flex plate which might explain it barely reaching the flywheel.

Wonder what the difference is?

https://www.rockauto.com/en/catalog/nissan,1976,280z,2.8l+l6,1209226,electrical,starter+motor,4152

p.s. if I had a spare engine a bunch of flywheels like I used to I'd go take some measurements.  Yarb might have hit on a solution.  Trade your starter in for a 1978 or ZX gear reduction starter.  Maybe it has more throw for the gear.

https://www.rockauto.com/en/catalog/nissan,1978,280z,2.8l+l6,1209260,electrical,starter+motor,4152

Edited September 1, 2021 by Zed Head

[Yarb]

I actually just purchased a rebuilt Hitachi starter off of amazon. Was a little skeptical whether it was truly a genuine rebuild or a Chinese knock off. It had the proper stamping on the casing. Looks like they just reduced the price by 20 percent as well

https://smile.amazon.com/dp/B000CAV0X4?psc=1&ref=ppx_yo2_dt_b_product_details