How much timing chain slack is O.K.?
11-04-2009, 07:30 PM
#1
How much timing chain slack is O.K.? My car has been backfiring and I have been trying to figure it out. We pulled the timing cover today and verified that the cam is still in time. However, we noticed a bit of slack in the chain. How much is acceptable? On my bike, I can pull on the chain in between the sprockets and measure the play. Is there a spec for this on an LT1?
Thanks in advance.
Thanks in advance.
11-05-2009, 11:34 AM
#3
Results and more questions O.K., I just measured it. It's about 1/2" or more. Time to replace?
Could it be b/c the block was align bored? It was really tight when I installed it, but it started backfiring after a 6500 run and is now dead in the driveway.
If so, which timing chain to use? I have read about the Cloyes 3145, but Summit has several versions, all with the disclaimer "not for LT1".
I have EWP, vented Opti, Precision Industries dampener and hub, dremel tool.
Thinking double roller for a 7000 rpm engine. Keyed for degreeing the cam? Can that be done with the engine in the car? Heads are studded.
Could it be b/c the block was align bored? It was really tight when I installed it, but it started backfiring after a 6500 run and is now dead in the driveway.
If so, which timing chain to use? I have read about the Cloyes 3145, but Summit has several versions, all with the disclaimer "not for LT1".
I have EWP, vented Opti, Precision Industries dampener and hub, dremel tool.
Thinking double roller for a 7000 rpm engine. Keyed for degreeing the cam? Can that be done with the engine in the car? Heads are studded.
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11-05-2009, 12:49 PM
#11
6500 then backfires followed by dead car indicates a bad rotor in the opti. Plastic rivits prob sheered off.
I didnt measure mine, but my new GM timing set had a decent amount of play in the chain. If I had to guess Id say 1/4-1/2" play. Seemed rather loose to me but every LT1 I took apart was the same regaurdless of miles on the engine.
I didnt measure mine, but my new GM timing set had a decent amount of play in the chain. If I had to guess Id say 1/4-1/2" play. Seemed rather loose to me but every LT1 I took apart was the same regaurdless of miles on the engine.
11-05-2009, 01:09 PM
#12
I've gone thru the Opti, all is fine. I also put another factory unit on there, just for grins. I also checked the wires with an inductive timing light, replaced the plugs, tried a different ICM and coil. No change.
The timing set a is new stock unit, I was just surprised to see so much slack in it.
Going to try another set of plugs (I run NGK TR-6's b/c I am F/I) and gap them tighter. Been running .035, going to try .030.
The timing set a is new stock unit, I was just surprised to see so much slack in it.
Going to try another set of plugs (I run NGK TR-6's b/c I am F/I) and gap them tighter. Been running .035, going to try .030.
11-05-2009, 03:00 PM
#15
It is virtually impossible to start. I can get it to start if I floor the accelerator pedal, but it has a steady backfire and sounds like crud. It won't idle.
It cranks fine, is getting fire, checked each plug wire with an inductive timing light. All fuses are fine. Even when attempting to start, it backfires like mad, even through the intake (seen fire, even).
It cranks fine, is getting fire, checked each plug wire with an inductive timing light. All fuses are fine. Even when attempting to start, it backfires like mad, even through the intake (seen fire, even).
11-05-2009, 03:22 PM
#16
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Dunno if you've done plug wires recently or when this started happening, but from what you are describing could also be from plug wires being routed incorrectly. Other than that it does sound like a timing problem of some sort.
I would also start to point a finger at the rotor on the opti. They have been notorious for the rotor screws coming loose, causing the rotor to spin freely firing any cylinder at will.
I would also start to point a finger at the rotor on the opti. They have been notorious for the rotor screws coming loose, causing the rotor to spin freely firing any cylinder at will.
11-05-2009, 03:23 PM
#17
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If you checked ignition and you are getting spark double check your wires aren't crossed and then move on to fuel. Since you have to floor it goes into flood mode, ie no fuel being delivered anymore, maybe there is a regulator or pressure issue?
11-05-2009, 03:37 PM
#18
Regulator is new, as are the injectors. Fuel pressure is right at 45 psi. Plug wires are new, and I triple checked that they are going to the correct plugs. Rotors on both Optis were Loctited, and I verified that they were not loose. Plugs are wet when removed, indicating lots of fuel supplied. Also removed fuel rails and verified that the injectors were not leaking. Fuel pump is a Racetronix Walbro with the Racetronix hotwire kit.
11-05-2009, 04:58 PM
#20
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You're running MSD 8.5 wires still, correct? Burnt, arcing? I thought I remember reading somewhere that the opti has to go back together a certain way or else it won't work. Had to do with an alignment issue of some of the internal parts? Just thought I would toss that out there since you mentioned both units you tested on the car were torn apart and put back together.