help in calculating suitable centers for starter pinion vs. ring gear

[510rob]

I am converting a transverse engine to rear wheel drive.

I have made a flywheel that uses a 106 tooth 10 pitch ring gear with a o.d. of 10.681"

The starter motor I sourced uses a 9-tooth pinion gear, but the gear itself doesn't seem to have any "standard" gear dimensions that I can use for calculating it's, well, imaginary position in AutoCAD before I start cutting metal (or spend money to have an intermediate plate water-cut).

I have had trouble determining the correct position for the starter motor because of what seem to be screwball numbers used for starter pinions. My Bosch Automotive Handbook talks about radical addendum modifications (10/12) and stub tooth profile models (P8/10), but does not list any standard numbers for starter pinions that are agreed universal or internation standards. That book says, "...starter gear teeth require far more backlash than constant-mesh gears, due to the starter engagement process. Such backlash is best achieved by increasing the distance between centers."

Great stuff... but how much do I increase the mystery numbers by?!? (groan!)

I received a data sheet from a starter remaufacturer for the model of starter I will use, but it wasn't much help at all.

Does anyone have any tips, insights, experience, data related to my dilema?

 

[EngJW]

I have done this before and it is not easy. The teeth are usually dual pitch, meaning they have a stub tooth form, and sometimes the pinions are specified like 9 teeth on a 10 tooth blank. It takes some specialized gear knowledge to interpret all this. There is a section in the SAE handbook which describes some of the calculations.

One way or another you will have to find out the exact pitch number for both ring and pinion. If they are not the same they will never mesh. After that, you could check in at the gear forum here. Some of the guys have computer programs where they can plug in the numbers for you.

Sorry about all the mumbo-jumbo. It probably won't help much.

 

[510rob]

Thanks for the answer - Even if there is a bunch of special gear terminology, it does make sense and any info is helpful (if I don't understand it, I'll go and learn and read about it until I do understand it!). In my initial search for info, I did so much looking around for data that I started to educate myself about the whole specialization of gears, and then realized I was off on a search for one small non-standardized branch of gears. I'm an electronics guy, not a gear guy, but I'm still a gearhead!

As far as pitch for both gears, the 106 tooth ring gear I'm using is listed as 10 pitch, and came from a Toyota application. The starter I'm using came from a Toyota with a 115 tooth ring gear that is listed as being 10 pitch. I figured (hopefully this was a sound assumption) this should be a safe starting point. Does this imply the ring gears are both 10 pitch, or is there some more accurate information I need to obtain/measure related to the ring gear?

What would you suggest I could/should measure for furthering any assistance with respect to the pinion gear?

 

[tbuelna]

510rob,

If you are using a ring gear from Toyota, it is likely a metric module gear standard.

And engJW is correct- starter pinions and ring gears are usually manufactured to weird combinations of blank size, pitch diameter and addendum dimension.

Good luck.
Terry

 

[Metalguy]

Given the very short-time usage, just set the distance real tight-even a little interference. Then use thin shims to set it during starter install. When you buy a rebuilt Chevy starter it comes with 3 shims.

What did you make the flywheel from?

 

[510rob]

It's not an application that uses shims. The starter slides into a bore in the intermediate plate. The intermediate plate, block, and bellhousing are all located by a pair of dowels. The starter will physically bolt to the bellhousing using two long(ish) bolts, but the accurate (or somewhat accutare) location of the starter is determined by the position of the starter hole in the intermediate plate.

I bought a large piece of HTSR 4140, tried to turn it myself, but after what seemed like my polishing two carbide tools on the disk of Kryptonite (to my limited experience), I decided I had no business turning an 11" disk of heat treated chrome moly... ...so I took it to a friend's machine shop and had him turn it for me instead! Yahoo!

 

[Greenlight]

You can set it up with 0.030" clearance between the peak of the starter drive gear and the base of the flywheel teeth.

Some of the older automotive service manuals used 0.025" to 0.040" as the recommended clearance when the starter drive gear was engaged to the flywheel.

 

[510rob]

That's an interesting idea. Do you know what manuals/manufacturers published that info?

 

[patdaly]

Rob, just about all of the aftermarket MFGs use .025-.040 in their instructions. Seems like a bunch, but I set my last one at .025 on a 489 CI BBC and it has worked well for 8 years now.