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Old 12-17-2004, 02:49 PM   #1
grw800
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Plastic Timing Gears?

I know from experience with my '78 K25 and '79 G15 that the plastic timing gears can be counted on to fail at right around 130K miles. If I knew then what I know now, the bent valves and bent pushrods could have been avoided by replacing the timing gears sooner. My neighbor has a '94 C10 that is nearing the magic number. Does the' 94 350 engine also have the plastic gears?
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Old 12-17-2004, 03:21 PM   #2
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While I can not say with 100% assurance...I am pretty sure the answer is no.
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Old 12-17-2004, 06:08 PM   #3
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does the 250 6cyl have plastic gears?
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Old 12-17-2004, 06:26 PM   #4
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How about a 92 350 in a truck?
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Old 12-17-2004, 08:41 PM   #5
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They went to metal gears in the V8's in the later engines as far as I've ever seen. The latest I've seen with the phenolic gear was an 85 if I remember correctly.

Beard, yes, the 250 should have 1 aluminum gear according to Santucci's 6 cylinder manual, but no plastic gears.

Last edited by Tx Firefighter; 12-17-2004 at 08:44 PM.
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Old 12-17-2004, 08:50 PM   #6
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Quote:
Originally Posted by Tx Firefighter
They went to metal gears in the V8's in the later engines as far as I've ever seen. The latest I've seen with the phenolic gear was an 85 if I remember correctly.

Beard, yes, the 250 should have 1 aluminum gear according to Santucci's 6 cylinder manual, but no plastic gears.
Sorry to say, I've not heard of that manual.

Thought maybe I was having problems with mine. Seems to be a good 6 buy no power range.

Thanks
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Old 12-17-2004, 08:52 PM   #7
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Chevrolet Inline Six-Cylinder power manual by Leo Santucci.

Buy one.

No joke.

Every 6 cylinder guy simply must have this book. It's under 20 bucks new. Has factory engineering drawings showing sizes of bolt holes, casting numbers, build up guidelines, everything.
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Old 12-17-2004, 09:16 PM   #8
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Quote:
Originally Posted by Blue Beard
does the 250 6cyl have plastic gears?
Correct me if I'm wrong, but the inline 6's have plastic counter rotating gears. No chain.
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Old 12-17-2004, 09:53 PM   #9
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The reason they have palstic or resin gears is to keep the noise down. I've had many late 60's early 70's engines have chains jump, or worse, plastic pieces come off the gears, and jam up the oil pump. fun!. you can really hear those metal gears whirring. Dunno 'bout later vehicles. kinda stopped caring about '82-up.
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Old 12-17-2004, 10:08 PM   #10
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Quote:
Originally Posted by Tx Firefighter
Chevrolet Inline Six-Cylinder power manual by Leo Santucci.

Buy one.

No joke.

Every 6 cylinder guy simply must have this book. It's under 20 bucks new. Has factory engineering drawings showing sizes of bolt holes, casting numbers, build up guidelines, everything.

Sounds like I need one of those to go with the 250ci I6 in our 18' tri-hull!
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Old 12-18-2004, 07:24 AM   #11
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Quote:
Originally Posted by grayw0lf
Correct me if I'm wrong, but the inline 6's have plastic counter rotating gears. No chain.
Negative

They have a steel crank gear that meshes directly with an aluminum cam gear. No chain, just gear to gear.
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Old 12-19-2004, 01:38 AM   #12
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I just disassembled my K10's 350. Looks to be never rebuilt. The plastic teeth on the cam sprocket were all there, just not altogether.

One could see about 30 stress fractures; half open cracks, half cracks that hadn't opened yet. The timing chain had mucho slop. At least an inch movement installed. I'm surprised the plastic held out as long as it did. I'd guess that the loose chain rode easy on the teeth so it didn't break. Just conjecture, really.
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Old 12-20-2004, 08:56 AM   #13
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My son's IL-6 had plastic gears. It was in a '74 Chevy. The gear went out on his and had to replace both of them.
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Old 12-20-2004, 09:43 AM   #14
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Just did a 91 suburban rebuild . It was a plastic gear unit. definatly stock. 2 missing teeth from the can sprocket so I had to pull the oil pan Hmm ... well I found 1 of them anyway. guess the other came out in an oil change or something alson the way.
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Old 12-23-2004, 08:49 PM   #15
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6-cyl. engines destined for car use were made with plastic timing gears, but not the same type of plastic used in V8's. Truck 6's had metal gears.
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