1970 C3 LS5 (Timing chain question)
Le Mans Master
Joined: Jun 2006
Posts: 6,400
Likes: 1,226
From: Tampa Florida
If you think your '70 has the original timing gear set, replace it ASAP!
Original GM crappy timing gear
New Cloyes double roller timing gear set
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,335
From: North of Toronto - Ontario
The BBC (and SBC IIRC) is an interference engine so if it doesn't quit right away there's a good chance the pistons and valve are going to try to be in the same place at the same time....
M
M
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Thread Starter
Instructor
Joined: Oct 2020
Posts: 245
Likes: 120
From: Montreal, Canada
No issues, just curious. I know timing chains (in general) have a shelf life.
My car has 96,000 miles showing on the odometer so I think it's time to look into this.
Are there any tell-tale signs before a chain goes? Like a clickety-clack sound maybe?
My car has 96,000 miles showing on the odometer so I think it's time to look into this.
Are there any tell-tale signs before a chain goes? Like a clickety-clack sound maybe?
Racer
Joined: Jul 2018
Posts: 331
Likes: 123
From: Sandusky, OH
Chevy used to have a truck version that was wider gears and chain. Jenkins prefer nylon teeth to steel teeth to not transfer crank harmonics to the cam and timing. I used it for my 396 D/SA Camaro back in the day with no issues for a few seasons. If that stock chain set lasted 50+ years and 96k miles, then a truck replacement ought to be good to go......
Steve O.
Steve O.
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I don't know, I've seen em pretty bad and still idling O.K.
I would be pulling that balancer, waterpump and cover.
I would be pulling that balancer, waterpump and cover.
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
I have never seen a timing chain break.. they wear out and stretch, the gears may wear down and the chain jumps a tooth or 2, your engine may run but will run very crappy.
depends on your cam lift whether your piston may kiss a valve or not. every 45 degrees of crank rotation you have a valve that is totally open.
depends on your cam lift whether your piston may kiss a valve or not. every 45 degrees of crank rotation you have a valve that is totally open.
Last edited by joewill; Dec 29, 2020 at 09:10 AM.
Thread Starter
Instructor
Joined: Oct 2020
Posts: 245
Likes: 120
From: Montreal, Canada
The cam is stock, if that helps any.
Specs per the 1970 Chassis Service Manual:
Intake: 0.2714"
Exhaust: 0.2824
Lobe lift: +/- 0.002"
Anyway, worth checking out I guess. Can't hurt.
Thanks.
Specs per the 1970 Chassis Service Manual:
Intake: 0.2714"
Exhaust: 0.2824
Lobe lift: +/- 0.002"
Anyway, worth checking out I guess. Can't hurt.
Thanks.
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
multiply that with your rocker arm ratio of 1.7 gets you .4614 and .4801 total lift.
now calculate how deeply recessed your valves are in your head, taking into account any past milling and past valve jobs and your piston dome valve reliefs cut into the top, and your head gasket compressed thickness,
then add a valve float factor for hydraulic lifters in case the chain fails at high rpm.
the exact answer is hard to get to.
now calculate how deeply recessed your valves are in your head, taking into account any past milling and past valve jobs and your piston dome valve reliefs cut into the top, and your head gasket compressed thickness,
then add a valve float factor for hydraulic lifters in case the chain fails at high rpm.
the exact answer is hard to get to.
Burning Brakes
Joined: Apr 2020
Posts: 790
Likes: 419
From: Western NY
Back in the early 80's i had the nylon teeth on the cam gear fail. was pulling in the driveway and the engine just quit. the mistake was trying to start it not knowing what happened. bent a bunch of valves. with 96k miles probably not a bad idea to replace the chain and gears. mine gave no sign of going. it was running perfect until it wasn't.