305 timing chain

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305 timing chain

Postby mirage_brat » Wed Aug 17, 2016 1:30 am

Hi i had a 305 that was rebuilt in 2012 and to this day it only has 6000-7000 miles on it... long story short i was at the our local car show this weekend and we getting ready to go on the dam cruise to show all the cars off to all the campers... well halfway through it my timing chain snapped and i sm clueless on what could have caused it to break any ideas??? :?: :censored: :bang:
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Re: 305 timing chain

Postby CaptainPainn » Wed Aug 17, 2016 9:21 am

What kind of timing chain was it? Was it a cheap $30 one?
1976 GMC Sprint (Daily Driver)
1976 Vega hatchback
1977 Vega Kammback (Main Project)
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1985 K10 long bed (Daily Driver)
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Re: 305 timing chain

Postby cjbiagi » Wed Aug 17, 2016 2:01 pm

May have just been a chain failure, I have a double roller chain in mine, been in there since 1984.......Did the chain actually break or was it a sprocket failure? I have heard of some problem with lower quality sprockets.
Clyde.........75 Monza 2+2
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Re: 305 timing chain

Postby cammerjeff » Wed Aug 17, 2016 3:26 pm

I have also had a Crank Keyway snap on a car that I bought that the previous owner had changed the cam and chain, he installed a 4 degree advanced crank keyway and it snapped. If it was an OEM replacement "silent" chain, they can stretch and snap. But sometimes things just break.
Jeff R

78 Sunbird Safari Wagon, 3.8 N/A, 1971 Catalina Freeway Enforcer
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Re: 305 timing chain

Postby spencerforhire » Wed Aug 17, 2016 9:38 pm

If a timing chain breaks after only 6000 or 7000 miles, there's really only two possibilities-
1- It was a defective(and most likely cheap) chain.
2- It was installed improperly.

I once had a chain fail in a race engine; a double roller, I had visually checked it when I bought the engine used; everything was tight and appeared to be fine. But 30 or 40 passes later, the chain in a dozen pieces along with a pile of shrapnel had liberated itself out of the hole it tore in the front cover. A spectacular failure at 6000+RPM that also bent 11 valves and 5 pushrods.
Post mortem revealed the most probable cause- a 3-keyway aftermarket bottom gear, mated to an OEM chain and top gear. Obviously not compatible in some way(pitch, or possibly roller size) the chain had sheared ALL THE TEETH from the top gear before it failed. Somebody cheaped out, or possibly just didn't know any better and put some mis-matched parts together, with disastrous consequences.
The "fleet"-
77 Vega Estate wagon- project(someday)will have TPI305/T-5, S-10 spindles/axles
72 Vega HB Drag Car -383/'Glide/9"(9.35@146.19)(5.94@117.28 1/8th)
76 Vega GT- 400/4spd/9" retired from active duty(rusty)
03 Silverado 2WD ex.cab (work truck/parts hauler)
04 Silverado 2WD ex.cab (retired)
06 Haulin' 20ft enclosed car transporter
93 Suburban- 350/4L60(retired)
00 Saturn SW2- wife's car
01 Saturn SC2- younger son's project
00 Saturn SL2- daughter's car
98 Saturn SW2- spare
and 3 more Saturn "parts cars"
Note- the very act of listing all of these has made me realize I have some kind of problem.....

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Re: 305 timing chain

Postby mirage_brat » Wed Aug 17, 2016 10:44 pm

Im thinking a tooth snapped off the gear and got caught in the chain which snapped it and sheared all the teeth off the crank gear... it was only a single roller chain...
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