harmonic balancer slipped/timing chain jumped ???
Thread Starter
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
harmonic balancer slipped/timing chain jumped ???
my buddy brings his 79 l48 4spd over and its just not running as smooth as before....
So I take out my timing light and start to look at his timing and there is no timing mark visible....move it around to different plug wires and on two we can see a mark at about 33* ATDC thats it...
so here the questions
1. how much does a timing chain have to jump to make an index mark disappear from sight, and if it jumps that much will the car run?
2. if the harmonic balancer slips is the outer ring balanced differently around the perimiter so that it would create a vibration?
3. why is the outer ring mounted on a rubber ring?
So I take out my timing light and start to look at his timing and there is no timing mark visible....move it around to different plug wires and on two we can see a mark at about 33* ATDC thats it...
so here the questions
1. how much does a timing chain have to jump to make an index mark disappear from sight, and if it jumps that much will the car run?
2. if the harmonic balancer slips is the outer ring balanced differently around the perimiter so that it would create a vibration?
3. why is the outer ring mounted on a rubber ring?
Last edited by bobs77vet; May 4, 2005 at 10:02 AM.
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
you know me i can't explain thing's real well , i'd check the dampner first
yes it can feel different but doesn't have to
rubber is to absorb the shock of combustion ... iv'e seen 2 teeth jumped and still run BUT
it was really bad
yes it can feel different but doesn't have to
rubber is to absorb the shock of combustion ... iv'e seen 2 teeth jumped and still run BUTit was really bad
Thread Starter
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by comp
... iv'e seen 2 teeth jumped and still run BUT
it was really bad
it was really bad
i'm guessing the harmonic balancer slipped some how...
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
Bring the number one piston up to top dead center and see where the mark is on the harmonic damper. Since the timing mark is nowhere in sight, all you want to is to check if the balancer slipped and accuracy (a few degrees) of TDC is not important when checking this. You are not setting the balancer to TDC, you are checking to if it slipped a bunch.
I don't think you can use another plug wire (Except #6) because the hd is marked for #1.
I don't think you can use another plug wire (Except #6) because the hd is marked for #1.
Thread Starter
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by mandm1200
. Since the timing mark is nowhere in sight, all you want to is to check if the balancer slipped and accuracy (a few degrees) of TDC is not important when checking this. You are not setting the balancer to TDC, you are checking to if it slipped a bunch.
.
.
i have a 60* dial back timing light....it was not in sight any where in any position from the drivers side fender either ATDC or BTDC...at any "dialed back position", so thats looking at what... 1/3 of the Harmonic balancer?
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
If a chain jumped that much, the engine wouldn't run. Basic way to check the balancer: the timing mark is in line with the crankshaft keyway. I'd bet the outer balance ring spun on the inner hub. If you take the lower pulley off, you'll probably find it has also moved back on the hub, often to the point where it rubs the front cover (a bad thing).
Hans
Hans
Thread Starter
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Wrencher
.. I'd bet the outer balance ring spun on the inner hub. If you take the lower pulley off, you'll probably find it has also moved back on the hub, often to the point where it rubs the front cover (a bad thing).
Hans
Hans
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
The inner hub is un-balanced. The outer ring is installed with the rubber "band", then balanced (drilled) with the rotating assembly. When it slips, the balance goes away a bit, but it probably wouldn't be very noticeable unless it was perfect to begin with. The crank, flywheel, pistons, etc. would still be right.
Hans
Hans
Racer
Joined: Nov 2000
Posts: 290
Likes: 0
From: Omaha, NE
Try small adjustments of the distributor to see IF the motor ever smooths out. Then check the timing. I would think if the timing chain was that loose the mark would be jumping all over the place when using the timing light. He may just have a bad plug or plug wire. What work was done to the motor last? I would start there and look for the simplest things first. Good luck
Intermediate
Joined: Jun 2004
Posts: 40
Likes: 0
From: Edmonds WA
harmonic balancer
I recently experienced the same problem. It turned out to be the outer ring slipped on the hub of the harmonic balancer. If you determine the harmonic balancer slipped and you want to keep it stock for NCRS purposes I suggest you send yours to Damper Dudes for rebuilding.
They rebuilt mine in a one day turn around for about $60.00. I couldn't be more pleased. They are reputable and honest. Check them out at damperdudes.net.
They rebuilt mine in a one day turn around for about $60.00. I couldn't be more pleased. They are reputable and honest. Check them out at damperdudes.net.
