Checking timing chain for slack
Thread Starter
Burning Brakes
Joined: Jan 2015
Posts: 875
Likes: 76
Checking timing chain for slack
On an 89. Was going to be changing a leaking water pump. But thought of checking the timing chain for how much slack it has first.
I've read you take the Distributor cap off. Then rotate the crank balancer clock-wise so the timing mark lines up with 0*. Then you stop. Then you slowly rotate the crank counter-clock wise and stop right when you notice the distributor rotor start to move. Then you look at what degree mark you are on to tell you how many degrees of slop there is.
Has anyone done this? And what amount of degrees of slack is acceptable?
I thought about taping down a long thin wooden dowel on top of the center of the rotor to better help see when the rotor starts to move.
I'm replacing the water pump, but don't really want to do a timing chain if it's in spec. I think the sprockets are all metal on the 89 year I believe. But I may be wrong. I know earlier ones were plastic.
I've read you take the Distributor cap off. Then rotate the crank balancer clock-wise so the timing mark lines up with 0*. Then you stop. Then you slowly rotate the crank counter-clock wise and stop right when you notice the distributor rotor start to move. Then you look at what degree mark you are on to tell you how many degrees of slop there is.
Has anyone done this? And what amount of degrees of slack is acceptable?
I thought about taping down a long thin wooden dowel on top of the center of the rotor to better help see when the rotor starts to move.
I'm replacing the water pump, but don't really want to do a timing chain if it's in spec. I think the sprockets are all metal on the 89 year I believe. But I may be wrong. I know earlier ones were plastic.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
This is the slack my timing chain had in it after roughly 100K miles. The new chain had almost exactly the same amount of slack. I have heard that timing chains will last 200K miles.
Note that the crank is turning the cam by pulling on the driver's side of the cam gear. The slack on the passenger side is not important.
Note that the crank is turning the cam by pulling on the driver's side of the cam gear. The slack on the passenger side is not important.
Burning Brakes
Joined: Apr 2016
Posts: 781
Likes: 73
How many miles? SBC timing chains are pretty robust. 200k miles plus is pretty normal.
GM learned many, many years ago that the nylon cam gear did not hold up. Back in the days when I worked on other folks cars I replaced quite a few of those. Those were only good for 100k miles or so.
Depending on your mileage, I would replace the water pump and not worry about the timing chain.
GM learned many, many years ago that the nylon cam gear did not hold up. Back in the days when I worked on other folks cars I replaced quite a few of those. Those were only good for 100k miles or so.
Depending on your mileage, I would replace the water pump and not worry about the timing chain.
Thread Starter
Burning Brakes
Joined: Jan 2015
Posts: 875
Likes: 76
This is the video I watched:
It's a different engine. But the important part is about halfway in. But he took the distributor cap off, and rotated the crank clock-wise stopping with the hub mark at the 0* timing mark with rotor pointing at #1. Then he started to rotate the crank hub counter-clockwise and stopped as soon as he saw movement in the rotor. Then he looked at the timing to see the degrees to see what degree the timing mark was now sitting out.
If I recall correctly, he said less than 7 degrees you are good. But if it's close to 7, then it's getting loose. And if it's over 7 degrees the chain is too loose.
Don't know how this applies to the L98 or at all.
It's a different engine. But the important part is about halfway in. But he took the distributor cap off, and rotated the crank clock-wise stopping with the hub mark at the 0* timing mark with rotor pointing at #1. Then he started to rotate the crank hub counter-clockwise and stopped as soon as he saw movement in the rotor. Then he looked at the timing to see the degrees to see what degree the timing mark was now sitting out.
If I recall correctly, he said less than 7 degrees you are good. But if it's close to 7, then it's getting loose. And if it's over 7 degrees the chain is too loose.
Don't know how this applies to the L98 or at all.
Thread Starter
Burning Brakes
Joined: Jan 2015
Posts: 875
Likes: 76
How many miles? SBC timing chains are pretty robust. 200k miles plus is pretty normal.
GM learned many, many years ago that the nylon cam gear did not hold up. Back in the days when I worked on other folks cars I replaced quite a few of those. Those were only good for 100k miles or so.
Depending on your mileage, I would replace the water pump and not worry about the timing chain.
GM learned many, many years ago that the nylon cam gear did not hold up. Back in the days when I worked on other folks cars I replaced quite a few of those. Those were only good for 100k miles or so.
Depending on your mileage, I would replace the water pump and not worry about the timing chain.
Looks like the most problems I see with timing chains on these cars are the nylon gears breaking or teeth chipping off.
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
A failure from a loose chain/worn cam gear always occurs at idle speed.
Check the balancer where the timing cover seal rides if it has a groove worn into it from the seal Felpro makes a sleeve that will fit the balancer & restore the seal area.
Check the balancer where the timing cover seal rides if it has a groove worn into it from the seal Felpro makes a sleeve that will fit the balancer & restore the seal area.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Gm started to move away from the "silent mesh" or nylon timing gears in all engines as the went to roller cams. The snapping action caused by the rollers as they crested peak lift tended to cause cam gears to fail prematurely. In the case of L89 1987-88.
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Burning Brakes
Joined: Apr 2016
Posts: 781
Likes: 73
A actual chain failure on these engines is pretty rare. The cam gear usually fails first.