5.3 timing marks

[972sparky]

If you are only replacing the chain / sprockets, then it does not really matter what marks are where as long as you do not move the cam or crank in the process.

 

[MassHoe04]

If you are only replacing the chain / sprockets, then it does not really matter what marks are where as long as you do not move the cam or crank in the process.

I did timing gear and chain replacement on my 05 Jeep 4.0. It's and inline 6, but as @972sparky described it, the process for gears and chain replacement is basically the same.

It was a manual transmission, so I had to make sure it was in gear with the wheels chocked and the parking brake set. That was done to lock the entire drive train in place and make sure nothing could move the crank or the cam in the process of replacing the timing set.

Was super easy (once the radiator, fan, belts and covers were all out of the way)! As long as the cam and crank don't budge, you should be good.

 

[rockola1971]

If you are only replacing the chain / sprockets, then it does not really matter what marks are where as long as you do not move the cam or crank in the process.

While this is very much true and the most difficult because it is hard to know for sure that nothing has moved (and the cam will try to move on you depending on where it is at) and it only takes one tooth to be off to potentially cause a problem. Its just easier using #1 TDC since the marks align up and down from one another and very obvious if anything has moved during reassembly.

 

[Ken early]

LS block timing marks are just like Gen 1 and 2 SBC. They never changed the timing mark relationship on SBC v8's between generations. Just the firing order.
Cam gear mark should be at 6oclock and crank gear mark should be at 12oclock while #1 piston is at TDC.

You should feel compression while piston is on its way up to TDC because both exhaust and intake valves are closed. Depending on timing the spark would happen around 12 deg BEFORE TDC (BTDC).

Is OP sure he is actually physically checking the #1 and not #2? #1 is drivers side very front cylinder.

Yes, drivers side front cylinder. Stuck my finger in the hole and felt for pressure, then found TDC with a pencil. Dead on 12:00. Then ran it around 180° With my finger in again as it came up, no pressure. I found TDC, again dead on at 12:00, but left it in this position to mount the chain so the marks are pointed at each other. We’ll find out if I got it right soon…

 

[Rocket Man]

Yes, drivers side front cylinder. Stuck my finger in the hole and felt for pressure, then found TDC with a pencil. Dead on 12:00. Then ran it around 180° With my finger in again as it came up, no pressure. I found TDC, again dead on at 12:00, but left it in this position to mount the chain so the marks are pointed at each other. We’ll find out if I got it right soon…

Rotate the crank a few turns by hand to see it anything hits or binds before you hit that starter. I always do a few revolutions in order to make sure the dots line up, and to just double check.

 

[972sparky]

Yes, drivers side front cylinder. Stuck my finger in the hole and felt for pressure, then found TDC with a pencil. Dead on 12:00. Then ran it around 180° With my finger in again as it came up, no pressure. I found TDC, again dead on at 12:00, but left it in this position to mount the chain so the marks are pointed at each other. We’ll find out if I got it right soon…

You will be fine as long as you put them back as you took them apart.

 

[rockola1971]

Yes, drivers side front cylinder. Stuck my finger in the hole and felt for pressure, then found TDC with a pencil. Dead on 12:00. Then ran it around 180° With my finger in again as it came up, no pressure. I found TDC, again dead on at 12:00, but left it in this position to mount the chain so the marks are pointed at each other. We’ll find out if I got it right soon…

This does not sound right at all. You should have felt compression as #1 was going up to TDC.(You wouldnt feel compression if one of the valves was open) Then when #1 reached TDC your crank gear timing mark should be at 12 oclock and your cam gear timing mark should be at 6 oclock and both should be straight up and down from one another like in the following pic. If you are actually at TDC for #1 then both intake and exhaust valve rockers will be loose. If you are not at TDC for #1 with marks aligned correctly then you are 360 deg out. As far as the engine goes, it doesnt care which one of the 2 that you put the new gears on as long as they are aligned. The problem comes in when 360deg out the valves are under tension and this causes the cam to want to rotate advanced and it could be a fight getting it back into its proper spot while putting chain with cam sprocket on during assembly. Remember at that point you will be fighting valvespring tension that is wanting to cause the cam to advance (rotate) forward.

But it really doesnt matter at what position the cam and crank is as long as the new timing set is put on at the same exact position with chain on sprockets, its just much more difficult to do when you are fighting valvespring tension trying to rotate the cam on you. Its been the norm since 1955 with GM v8 engines using #1TDC, probably the same for all GM's prior engines too equipped with timing chain and gears.

 

[Ken early]

This does not sound right at all. You should have felt compression as #1 was going up to TDC.(You wouldnt feel compression if one of the valves was open) Then when #1 reached TDC your crank gear timing mark should be at 12 oclock and your cam gear timing mark should be at 6 oclock and both should be straight up and down from one another like in the following pic. If you are actually at TDC for #1 then both intake and exhaust valves will be loose. If you are not at TDC for #1 with marks aligned correctly then you are 180 deg out. As far as the engine goes, it doesnt care which one of the 2 that you put the new gears on as long as they are aligned. The problem comes in when 180deg out the valves are under tension and this causes the cam to want to rotate advanced and it could be a fight getting it back into its proper spot while putting chain with cam sprocket on during assembly. Remember at that point you will be fighting valvespring tension that is wanting to cause the cam to advance (rotate) forward.

But it really doesnt matter at what position the cam and crank is as long as the new timing set is put on at the same exact position with chain on sprockets, its just much more difficult to do when you are fighting valvespring tension trying to rotate the cam on you. Its been the norm since 1955 with GM v8 engines using #1TDC, probably the same for all GM's prior engines too equipped with timing chain and gears.

Sorry, I said 180° when I meant I rotated the crank 360°, a full rotation, so that the marks aligned as in the photo. The cam only rotated 180°.

 

[rockola1971]

Sorry, I said 180° when I meant I rotated the crank 360°, a full rotation, so that the marks aligned as in the photo. The cam only rotated 180°.

Me too...i meant 360deg. I corrected mine.

 

[Rocket Man]

If I rotate the crank 1 turn, the marks are then pointed at each other, but then the #1 piston is on the exhaust stroke. I understand the 2:1 ratio, and I rotated the crank all the way around, checking the piston to make sure I had it at TDC on compression, because that’s what the manual and pretty much every reference I’ve found say to do. Seeing my known good engine set up with the cam 180° off kind of blew my mind. I’ve seen some comments that it doesn’t matter if the cam is off 180° because the sensor controls spark and injection, but that just feels wrong.

I do not know where you read this is supposed to be done on the compression stroke. Alldatadiy.com which is the online version of the factory service manual, doesn’t mention anything about that. It just states to rotate the crank pulley until the mark is at 12:00 and then install the chain with the cam pulley at 6:00 and the dots lined up. Here’s a screenshot of that page.