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Starter Pinion/Ring Gear Mesh

cooler

Plastic
Joined
Feb 21, 2024
Location
British Columbia
hello and thanks to all that read my quire and respond,

I am developing an engine adapter and wish for advice regarding starter pinion/ring gear mesh tolerances. The engine, LS the transmission, Porsche/Audi. There are adapter kits commercially available however all are very thick requiring extensive chassis modification. I believe an adapter kit can be developed reducing thickness significantly mitigating chassis modifications.

All commercially available adapter kits use the large diameter LS ring gear and original starter location. The LS ring gear is too large for the Porsche/Audi bellhousing, so the adapters plate must house the flywheel between the engine and bellhousing mounting flanges adding significantly to its thickness. The adapter kit I propose uses an Audi ring gear that fits inside the Porsche/Audi bellhousing bringing the engine and bellhousing mounting flanges closer together and minimizing the thickness of the adapter plate.

The down side to the above is the starter must now be relocated closer to the engine block to engage the smaller diameter Audi ring gear but the LS starter will contact the block before the pinion engages the ring gear. A possible solution is to use a high torque gear reduction mini starter available for the small block, they are very compact and with some clearenceing should engage the Audi ring gear. Another solution is notch the oil pan and mount the starter down under.

Now for my quire. Is it possible to use the Audi ring gear with the small block starter/pinion gear given the following information. The small block and Audi pinion gears are both 9 tooth and to the best of my measuring skills, very similar diameter and tooth profile. The proposed Audi ring gear is 136 tooth/ 287mm in diameter. All LS ring gears are 168 tooth/358mm diameter with exception the LS4 is 142 tooth/303mm diameter but still too large to fit inside the Porsche/Audi bellhousing.

Audi ring gear pitch = 903mm circumference/136 teeth = 6.64mm
LSX ring gear pitch = 1125mm circumference/168 teeth = 6.70mm
LS4 ring gear pitch = 951mm circumference/142 teeth = 6.70mm

Note, Chevrolet ring gears regardless if they are 168, 153, 148 or 142 all have the 6.70mm pitch. Audi pitch is very similar at 6.64mm.
Picture below shows Audi ring gear on left, LS4 ring gear on right, high torque reduction gear starter pinion center.

ls starter.jpg
 
hello and thanks to all that read my quire and respond,

I am developing an engine adapter and wish for advice regarding starter pinion/ring gear mesh tolerances. The engine, LS the transmission, Porsche/Audi. There are adapter kits commercially available however all are very thick requiring extensive chassis modification. I believe an adapter kit can be developed reducing thickness significantly mitigating chassis modifications.

All commercially available adapter kits use the large diameter LS ring gear and original starter location. The LS ring gear is too large for the Porsche/Audi bellhousing, so the adapters plate must house the flywheel between the engine and bellhousing mounting flanges adding significantly to its thickness. The adapter kit I propose uses an Audi ring gear that fits inside the Porsche/Audi bellhousing bringing the engine and bellhousing mounting flanges closer together and minimizing the thickness of the adapter plate.

The down side to the above is the starter must now be relocated closer to the engine block to engage the smaller diameter Audi ring gear but the LS starter will contact the block before the pinion engages the ring gear. A possible solution is to use a high torque gear reduction mini starter available for the small block, they are very compact and with some clearenceing should engage the Audi ring gear. Another solution is notch the oil pan and mount the starter down under.

Now for my quire. Is it possible to use the Audi ring gear with the small block starter/pinion gear given the following information. The small block and Audi pinion gears are both 9 tooth and to the best of my measuring skills, very similar diameter and tooth profile. The proposed Audi ring gear is 136 tooth/ 287mm in diameter. All LS ring gears are 168 tooth/358mm diameter with exception the LS4 is 142 tooth/303mm diameter but still too large to fit inside the Porsche/Audi bellhousing.

Audi ring gear pitch = 903mm circumference/136 teeth = 6.64mm
LSX ring gear pitch = 1125mm circumference/168 teeth = 6.70mm
LS4 ring gear pitch = 951mm circumference/142 teeth = 6.70mm

Note, Chevrolet ring gears regardless if they are 168, 153, 148 or 142 all have the 6.70mm pitch. Audi pitch is very similar at 6.64mm.
Picture below shows Audi ring gear on left, LS4 ring gear on right, high torque reduction gear starter pinion center.

View attachment 439103
What does "LS" mean? When you use an abreviation you need to let folks know what it means for those not in on the secret. I can't tell what you are trying to do.
 
LS is a common Chevy V8 engine used in just about everything for the past 20 years.

Will that mesh work? Yes. It might not last 150K miles...but it will work. It's a low RPM arrangement so if it's a little sloppy that's not gonna kill you.

It does look like you have the pinion gear closer to the LS flywheel than the Audi flywheel...I assume that's just the photo but in real life you should move the pinion as close as you can to the ring gear without binding. I'd try to achieve about .010" clearance.
 
Mount starter to engine with matching OE flywheel/ring gear installed. Measure backlash with bendix extended. (works good to disassemble starter and jamb stuff inside to hold bendix out)

Rig up new starter/flywheel/ring gear in an adjustable, but rigid fashion. Adjust center distance to achieve exact same backlash.

Now precisely measure new starter center distance WITH BENDIX RETRACTED.

Now model your dohickey.

Err on loose. DO NOT MAKE IT TOO TIGHT.

starter location position sweet spot is about 5 thou for 12 pitch. Don't fuck it up.
 
The LS engine has become the, well, small block Chevy of the modern era. Which means everyone is swapping it into everything. The first 5 times it was done, it was cool. The 43 million times it's been done after? Not so cool....it's become something people make fun of (sorry OP).

If it were a dance, it would be the macarena. Gnome Sane?
 
The LS engine has become the, well, small block Chevy of the modern era. Which means everyone is swapping it into everything. The first 5 times it was done, it was cool. The 43 million times it's been done after? Not so cool....it's become something people make fun of (sorry OP).

If it were a dance, it would be the macarena. Gnome Sane?

The first few I saw, I thought "Cool, LS swap!"
Now I just think, "Gee, another LS swap"
Can't deny the durability and low (salvage yard) cost of them though.
 
I can appreciate a really well done LS swap. Sadly 99% are unfinished hackjobs.

I'm trying to scare up a 401 for a rare AMC and it's absurd how often I'm told I just need to LS swap it. "Oh great idea! Why bother keeping any smidgen of interesting automotive history alive!"
 
The OPs ring gears are noticably different pitch ...............which will almost certainly mean a lot of noise cranking .....it may be possible to fit a correct pitch pinion .......however ,usually an extensive junkyard knowlege is needed to know where to find one.
 
The OPs ring gears are noticably different pitch ...............which will almost certainly mean a lot of noise cranking .....it may be possible to fit a correct pitch pinion .......however ,usually an extensive junkyard knowlege is needed to know where to find one.

Automotive ring gears and starters actually have basic worldwide standards. That looks to be a 12 pitch setup there. Next closest is 10 pitch. 10 pitch won't even remotely come close to meshing with 12.

It looks fine to me, just set too close for the picture is all.
 
Why not just take the starter pinion that matches flywheel of choice and mate it to the starter you intend to use.

I don't recall if the starter gear is made into the shaft or a press fit. But should be doable by a competent machinist.

Hodge
 
Why not just take the starter pinion that matches flywheel of choice and mate it to the starter you intend to use.

I don't recall if the starter gear is made into the shaft or a press fit. But should be doable by a competent machinist.

Hodge

Starters from different manufacturers are made different.

Denso starters are used as retrofit "mini starters" because you can swap pinions within their huge range of applications and the front housing unbolts.
 
Be like the CAV CA45 starter ...a wide range of metric,DP ,LH and RH pinions .......catch being they cost $500 each.......my favourite starter is the Bosch 6" axial ,marvellous starter.
 
Thanks for your responses, very helpful.

Question: How much clearance should the ring gear have to anything on the back of the engine?

The starter is likely to be position where there is no starter pocket on the bellhousing. If the ring gear is positioned as close as practicable to the engine, the pinion gear may not need to protrude beyond the adapter plate and into the bellhousing interface. I would like to avoid notching and weakening the bellhousing if possible.

thanks again for your insight.
 
Thanks for your responses, very helpful.

Question: How much clearance should the ring gear have to anything on the back of the engine?

The starter is likely to be position where there is no starter pocket on the bellhousing. If the ring gear is positioned as close as practicable to the engine, the pinion gear may not need to protrude beyond the adapter plate and into the bellhousing interface. I would like to avoid notching and weakening the bellhousing if possible.

thanks again for your insight.

Do you have room for a starter and ring gear at the front of the engine?
 
The OPs ring gears are noticably different pitch ...............which will almost certainly mean a lot of noise cranking .....it may be possible to fit a correct pitch pinion .......however ,usually an extensive junkyard knowlege is needed to know where to find one.
In that case, it will sound just like every other chevy that had the starter replaced by someone who didn't have a clue... 🤣
 








 
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