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Author Topic: Starter motor pinion clearance question  (Read 491 times)
bevans6
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« on: June 01, 2017, 07:46:00 AM »

So I am finessing the clearances with my MT647 install.  As you might recall, I couldn't find the correct ring gear and flex plate so I am using a ring gear that is a Cummins part.  It's now on the flex plate and on the engine and all clearances to the block are good.  It is 1 tooth larger in diameter than the 102 tooth MCI ring gear on the original flywheel (about .050" on the radius).  I took the solenoid off my old starter motor so that I could easily pull on the lever and put the pinion out into engagement.  It engages the ring gear fine, but only (I suspect) because the bushes inside the pinion are worn.  In other words it engages but with zero clearance between the teeth.  So I will now do the same trick with my new starter motor without worn bushes and see what I see.  I plan to machine the register on the starter motor to move it out some small distance, to create clearance.  My question is:  What is the minimal acceptable clearance between the teeth on the starter motor and the ring gear?

Thanks, brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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luvrbus
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« Reply #1 on: June 01, 2017, 08:29:35 AM »

With the Bendix chamfer drive there was never a specified clearance they are designed to catch 2 teeth on the flywheel when engaged as long as it engages you are good lol now the old Dyer non chamfer drive was a different story using shims   
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bevans6
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« Reply #2 on: June 02, 2017, 08:18:55 AM »

Well, success I guess.  I chucked the nose of the starter in my rotary table after I first determined which part faced the center of the crankshaft.  That is the radius I need to move the starter motor out on.  I chucked it up, found the radius of the register, then offset the nose with a .100" shim and cut the new radius.  Then I welded a 1" long bead on the opposite side ( which was hard as heck, a file would not touch that bead.  Flux core wire) and ground it so it matched the new radius.  This way I know the starter motor is fully offset when installed.  I popped it back in, for about the 10th time as I fussed with this, and let me say at this point that there is no "popping in" of a 42-MT starter, pulled on the lever and the pinion popped fully out and back as easy as you please.  Calling that OK for bush league...

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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daddysgirl
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« Reply #3 on: June 03, 2017, 08:58:15 AM »

and let me say at this point that there is no "popping in" of a 42-MT starter

Brian

Well Brian, from my perspective...there's NEVER "popping in" a starter. My 40MT weighs nearly as much as I do. Angry
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Andrea   Richmond, VA
1974 MC8 8V71/HT740 new in 2000 and again in 2017-
bevans6
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« Reply #4 on: June 03, 2017, 09:44:14 AM »

It appears that mine is also a 40MT.  My friend who deals in diesel powered stuff (generators, pumps, air compressors) says he thinks he has some new solenoids and some 24 volt motors in good nick.  So he will see what he has and I will have a spare starter.  That is the main drawback of doing this particular conversion.  Everything is either a stock "something" or a part that won't fail (like the flex plate) except for the starter motor nose, now that it's modified to move the starter out a tenth of an inch.  Not replaceable on the road without a sympathetic machine shop, so I am building a spare.  Although I suspect the starter noses are all interchangeable, the two I happen to actually have are different castings.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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Geoff
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« Reply #5 on: June 03, 2017, 03:04:55 PM »

Well Brian, from my perspective...there's NEVER "popping in" a starter. My 40MT weighs nearly as much as I do. Angry

Ha!  I have lifted my fair share of heavy starters since 1975.  If you are lucky, you can put the starter on your stomach before you roll under the bus/truck, take a deep breath, and hope it doesn't catch on anything on the way home.  If you are unlucky, you use a piece of cardboard to slide under, drag the starter towards you, and muscle it in.  Sometimes it takes a few tries.  That's when the cussing starts.

--Geoff
« Last Edit: June 03, 2017, 07:04:48 PM by Geoff » Logged

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kyle4501
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« Reply #6 on: June 03, 2017, 06:49:22 PM »

Glad to hear of your progress.
Could you have used a 39MT ?

A 42MT weighs 58 # & 19.58" long.
A 39MT (gear reduction) weighs 30.8 # & 16.25" long.

I really like the 39MT, was so much easier to install and it spins faster for easier starts.

I got mine off ebay for lots less than I ever thought I would. . . .


http://www.dieselusa.com/productinfo/Delco%20Electrical%20Specs%20and%20Seletion%20Guide.pdf
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« Reply #7 on: June 03, 2017, 07:04:51 PM »

LOL 58 lbs for a 42mt delco grab a 50MT some 8v92 used 79 lbs it is one heavy sucker overhead
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Dave5Cs
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« Reply #8 on: June 03, 2017, 07:05:07 PM »

on the 39MT how do you know what orientation to get or does it matter. I have the 6V71 N ,with 644 auto and is it 11 or 12 teeth?
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kyle4501
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« Reply #9 on: June 03, 2017, 09:16:06 PM »

on the 39MT how do you know what orientation to get or does it matter. I have the 6V71 N ,with 644 auto and is it 11 or 12 teeth?
I counted teeth on the one I removed. The nose on the one I got can be clocked differently as needed.
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kyle4501
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« Reply #10 on: June 03, 2017, 09:21:26 PM »

LOL 58 lbs for a 42mt delco grab a 50MT some 8v92 used 79 lbs it is one heavy sucker overhead
I was just going by the book - I know it was the heaviest 58 pounds I have ever messed with !


Now that you mention it, maybe I did have the 50MT . . . . . I had to use a floor jack to position it.  Shocked
(maybe I'm just getting old  Cry  )
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Life is all about finding people who are your kind of crazy

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« Reply #11 on: June 03, 2017, 11:46:00 PM »

When installing the big starters from the bottom and the configuration allows, I use one of the motorcycle straps that you pull to tighten as a safety net and aid. I hook one end of the strap to something on the block or run a bolt with large washer on it into an unused tapped hole and hook the strap to it. The other end I take over the top of the frame rail or similar or sometimes go back to itself. I configure the strap with a cradle loop hanging down positioned to catch the starter about mid ship. In the course of the lift I get the motor end of the starter into the loop first and then go on up into the mounting hole with the starter. Once in place I hold it with one hand and pull the tail of the strap with the other hand to snug it against the starter. Now you can relax and tweak the clocking (or catch your breath if your older like me) to put bolts in without having to worry. I have also used it in the course of removing some starters.
I keep two straps in the bottom of my box at work. Seems like I am always finding something they help hold out of the way, up in place, or aid in lifting.
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bevans6
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« Reply #12 on: June 04, 2017, 04:02:43 AM »

I might have been able to use a 39MT, but since I had the 40MT's they were effectively free, so hard to beat on cost.  We'll see what my friend has to offer, another free one beats an Ebay anything...  Smiley   If the engine was in the bus I could have used the jack trick, I've used the strap trick too (in fact did use it to pull the starter off the first time on this project) but since the engine is out and on a dolly I could just sit right beside it an curl it up under the cradle, and once it was stuck in the hole it would just hang there on it's own.  Then wiggle a bit to get a bolt started, and that's the hard part done.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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Geoff
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« Reply #13 on: June 04, 2017, 06:45:45 AM »

I counted teeth on the one I removed. The nose on the one I got can be clocked differently as needed.

I believe a Detroit starter is 11 teeth, the common number for truck diesels.  But when you want to buy a 24v it gets hard, and when you want a 24v left hand you better be at a starter rebuild shop in a big city.

--Geoff
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Geoff
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