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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old September 26th, 2015, 05:57 PM
Texas63GMC Texas63GMC is offline
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Default starter shims

what is the correct way to shim a starter in the V6? my starter engages the flywheel, but wont retract enough to clear the flywheel when the motor starts.... are the shims the same for a small block chevy? if not, are they available?
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Old September 26th, 2015, 06:18 PM
bigblockv6 bigblockv6 is offline
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Default Re: starter shims

Small block Chevy shims will not work and it all has to do with the way the V6 starter mounts straight into the bellhousing while other GM engines starters mount underneath the engine block. There are no shims.
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Old September 26th, 2015, 07:39 PM
Texas63GMC Texas63GMC is offline
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Default Re: starter shims

Ok. then what would you do to trouble shoot it?. The engine is a 351C (i think) and was rebuilt as was the starter. The starter came on the engine, so I assume it is the correct one. I never heard it start or run before the rebuild.
when the key is turned on, the starter engages the flywheel and everything sounds normal. After the key is released, the starter keeps spinning if the engine doesn't start. If it does start, you can hear the starter still engaged
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Old September 26th, 2015, 07:51 PM
bigblockv6 bigblockv6 is offline
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Default Re: starter shims

If the starter drive gear stays engaged to the flywheel ring gear that is an alignment issue and the only way I can see the need to move the starter gear away from the ring gear would be to slightly oblong the mounting holes in the starter to move it away from the ring gear. Ran into a problem like this on a Jeep with an Advanced Adapters automatic trans adapter from GM to Jeep. It was obvious that advanced adapters didn't get the spacing right and it ate up the ring gear on the flexplate.
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Old September 26th, 2015, 09:16 PM
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AZKen AZKen is offline
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Default Re: starter shims

It's probably that the starter was not properly rebuilt and/or has a malfunctioning solenoid or key switch or wiring.....not shims. If you did not rebuild it yourself, ask what was done and what was replaced. Many mechanics know nothing about GMC V6's and treat them like Chevys....with Chevy parts. As pointed out by BBV6, there is much more possible tolerance buildup in the Chevy type mount than GMC. Chevy has up/down and in/out tolerance. GMC has only in/out. (regarding this era)
Starters have an "overrunning clutch" design, they have specific procedures and specs for rebuilding, especially location of the pinion gear. They do not have shims between mounting flange and bell housing, according to my 1960 manual. As stated, no shims, don't use any. Fix what is wrong.
The symptoms you describe point to the Solenoid: Weak return spring, weak electromagnet, binding shift lever, wrong parts, loose wire connection, pinion gear location not calibrated.
Second possible is momentary portion of key switch.

Last edited by AZKen; September 26th, 2015 at 10:11 PM.
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Old September 27th, 2015, 08:20 AM
George Bongert George Bongert is offline
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Default Re: starter shims

Greetings Texas63GMC!

I agree with AZKen. The fact that the starter does not disengage and keeps running indicates a problem with the ignition switch, weak (or missing) return spring in the solenoid, or binding solenoid plunger. I have never seen a shift fork bind up in a GM starter of any kind. The first thing I would check is the circuit between the ignition switch and the solenoid to make sure that when the switch is released from the start position that there is no voltage going to the starter solenoid terminal. You can do this by disconnecting that lead from the solenoid and connecting it to a test light. Because of the location of the starter, this will probably require a second person to observe the test light while you operate the ignition switch. If the ignition switch passes this test, then you will have a problem with the starter itself. I know that this will sound far fetched, but there is always the possibility that the re-builder failed to install a return spring in the solenoid. I've seen stranger things happen. I hope this helps!
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