All,
Those who have been following my second season of trying my hand at "amateur" racing with the SCCA know that I had a timing chain failure at Mid-America in Omaha during my second race of the year.
I finally have my pictures back from the resulting engine rebuild.
Here are my lessons learned which may help prevent this from happening to some of you in the future.
Probable Cause: Failure of a timing chain link due to high RPM use:
- I had my PCM modified prior to last year's Runoffs to save two 3-4, 4-3 shifts at Mid-Ohio. This was probably worth a couple of tenths which was worth a few spots on the grid.
- While I won't say exactly where I had my PCM set, I will say it was north of 7000.
- During the race I was making a 3-4, 4-3 on the pit straight vice holding 3rd as some were doing in qualifying.
- The motor was a new 03 crate motor installed last July. It had 10 hours of break-in and was on it's sixth SCCA race weekend when it failed.
- I did not use RPMs over 7000 at the three races before the runoffs, or at Memphis, the first race of this year.
- I was using 7000+ at Mid-America in what I think is turn 4, a high speed left where the 3-4 shift point is at the apex.
- I believe that at high RPMs the timing chain either oscillates back and forth, or doesn't release as it comes off the sprocket and has to curl back to make it to the other sprocket, resulting in higher than normal stress on the links.
Result:
- Timing chain breaks, valves stop, pistons don't, pistons hit valves, valves bend or break, pistons weren't damaged (somehow)
Suggested Corrections:
- I've read that the 04 LS6 comes with a heavy duty timing chain from the LS2. Part number is 88958608. The dealer's computer doesn't yet show this as an LS6 part. I can't confirm this is the LS2 timing chain. Several different sources told me this chain is on the 04 LS6 motors which makes it legal for SCCA T1, so I bought one. It fits on the motor.
- On visual inspection, this chain doesn't appear to be any stronger than the old one, but the links are thicker (not much though).
- If you are running your PCM at over 7000, beware. The chain apparently can't sustain these kinds of RPMs indefinitely.
- GM Performance Parts sells a damper that bolts to the block in the area between the timing chain and the sprockets that limits the chains ability to whip or curl. I bought one to look at it. It is a little piece of plastic shaped sort of like a W that prevents the chain from curling inward. It bolts straight to two pre-existing holes on the block. I am not sure when GM started putting these holes in the block. A fellow forum member (who told me about this damper - thanks!) informed me the holes are not on his 99 FRC, but they are on an 02. I can confirm they are on my 02 and 03 motors.
- It appears GM is aware of the timing chain issue and has put a stronger chain in the LS2 and made a damper for high performance applications.
- If you take off your front cover for any reason, cam work, etc, there is no reason not to put this damper and a new LS2 chain on.
Cost of engine rebuild:
$400 - Two trips to Norfolk and back
$ 75 - Timing chain
$400 - gaskets and stretch bolts
$314 - six new valves
All in all not bad. But the DNF and the two missed races likely cost me the SCCA Mid-West Division T1 title to Mike McGinley, an SCCA veteran and 2003 SCCA Mid-Am champion in CSR and ITE classes who joined the T1 ranks in my division this year.
GM PART # 88958608
CATEGORY: Belt or Chain, Engine Timing
PACK QTY: 1 CORE CHARGE: $0.00
GM LIST: $107.10
OUR PRICE: $74.97
DESCRIPTION: CHAIN
From the 2004 GM Performance Parts Catalog: page 106:
88958607 Timing Chain Damper, LS1, LS6
“This timing chain damper is intended for high engine speed applications and is used to improve timing chain life. Some blocks require drilling and tapping- an instruction sheet is included. “
From GM Parts Direct:
GM PART # 88958607
CATEGORY: Belt or Chain, Engine Timing
DESCRIPTION: DAMPENER
GM LIST: $117.30
OUR PRICE: $82.11
Timing chain showing failed link and tooth missing from sprocket:
Result of piston/valve interaction: six dead titanium valves:
Rebuilt motor with new valves, timing chain & sprockets, gaskets, stretch bolts:
Motor lowered into place:
Connecting all the lines, fittings, etc around the motor before raising it into final position and bolting the lower suspension cradle to the frame:
The Garagemahal where rebuild was done:
A happier but still dirty racecar:
Those who have been following my second season of trying my hand at "amateur" racing with the SCCA know that I had a timing chain failure at Mid-America in Omaha during my second race of the year.
I finally have my pictures back from the resulting engine rebuild.
Here are my lessons learned which may help prevent this from happening to some of you in the future.
Probable Cause: Failure of a timing chain link due to high RPM use:
- I had my PCM modified prior to last year's Runoffs to save two 3-4, 4-3 shifts at Mid-Ohio. This was probably worth a couple of tenths which was worth a few spots on the grid.
- While I won't say exactly where I had my PCM set, I will say it was north of 7000.
- During the race I was making a 3-4, 4-3 on the pit straight vice holding 3rd as some were doing in qualifying.
- The motor was a new 03 crate motor installed last July. It had 10 hours of break-in and was on it's sixth SCCA race weekend when it failed.
- I did not use RPMs over 7000 at the three races before the runoffs, or at Memphis, the first race of this year.
- I was using 7000+ at Mid-America in what I think is turn 4, a high speed left where the 3-4 shift point is at the apex.
- I believe that at high RPMs the timing chain either oscillates back and forth, or doesn't release as it comes off the sprocket and has to curl back to make it to the other sprocket, resulting in higher than normal stress on the links.
Result:
- Timing chain breaks, valves stop, pistons don't, pistons hit valves, valves bend or break, pistons weren't damaged (somehow)
Suggested Corrections:
- I've read that the 04 LS6 comes with a heavy duty timing chain from the LS2. Part number is 88958608. The dealer's computer doesn't yet show this as an LS6 part. I can't confirm this is the LS2 timing chain. Several different sources told me this chain is on the 04 LS6 motors which makes it legal for SCCA T1, so I bought one. It fits on the motor.
- On visual inspection, this chain doesn't appear to be any stronger than the old one, but the links are thicker (not much though).
- If you are running your PCM at over 7000, beware. The chain apparently can't sustain these kinds of RPMs indefinitely.
- GM Performance Parts sells a damper that bolts to the block in the area between the timing chain and the sprockets that limits the chains ability to whip or curl. I bought one to look at it. It is a little piece of plastic shaped sort of like a W that prevents the chain from curling inward. It bolts straight to two pre-existing holes on the block. I am not sure when GM started putting these holes in the block. A fellow forum member (who told me about this damper - thanks!) informed me the holes are not on his 99 FRC, but they are on an 02. I can confirm they are on my 02 and 03 motors.
- It appears GM is aware of the timing chain issue and has put a stronger chain in the LS2 and made a damper for high performance applications.
- If you take off your front cover for any reason, cam work, etc, there is no reason not to put this damper and a new LS2 chain on.
Cost of engine rebuild:
$400 - Two trips to Norfolk and back
$ 75 - Timing chain
$400 - gaskets and stretch bolts
$314 - six new valves
All in all not bad. But the DNF and the two missed races likely cost me the SCCA Mid-West Division T1 title to Mike McGinley, an SCCA veteran and 2003 SCCA Mid-Am champion in CSR and ITE classes who joined the T1 ranks in my division this year.
GM PART # 88958608
CATEGORY: Belt or Chain, Engine Timing
PACK QTY: 1 CORE CHARGE: $0.00
GM LIST: $107.10
OUR PRICE: $74.97
DESCRIPTION: CHAIN
From the 2004 GM Performance Parts Catalog: page 106:
88958607 Timing Chain Damper, LS1, LS6
“This timing chain damper is intended for high engine speed applications and is used to improve timing chain life. Some blocks require drilling and tapping- an instruction sheet is included. “
From GM Parts Direct:
GM PART # 88958607
CATEGORY: Belt or Chain, Engine Timing
DESCRIPTION: DAMPENER
GM LIST: $117.30
OUR PRICE: $82.11
Timing chain showing failed link and tooth missing from sprocket:
Result of piston/valve interaction: six dead titanium valves:
Rebuilt motor with new valves, timing chain & sprockets, gaskets, stretch bolts:
Motor lowered into place:
Connecting all the lines, fittings, etc around the motor before raising it into final position and bolting the lower suspension cradle to the frame:
The Garagemahal where rebuild was done:
A happier but still dirty racecar: