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Hummer H3For the Hummer driver who wants the rugged look and off road capabilities of the Hummer, but in a smaller size and with a more fuel economy friendly engine.
Have you rotated and aligned the cam sprocket marks to the chain? Can't see the crank, but you could pull #1 spark plug to measure for TDC.
I have not, but I should do that. Then I'll know if it jumped. I have noticed that while the chain is fairly taut up top between the sprockets, I can see where it's dropping down towards the crank sprocket the chain seems loose. I'm not sure if that's normal. I also took some video of the chain while I rotate the crank. The chain moves, but every so often it jumps forward and makes a clank. The jumping forward part makes sense (valve spring pressure) but that clank unnerves me a bit. I need to take a look at the video once it's off my phone and onto a bigger screen, then I will post it here. I want to see if it's jumping teeth.
OK, ugh...bigger screen, it's definitely jumping teeth (10 second mark or so): Timing chain movement
Based on that, I'm betting I have a failed tensioner. What are the chances I have at least one bent valve? It ran (REALLY poorly) so I shut it down, then tried to start it and it felt like the starter was just spinning freely (it wasn't, the accessory belt was turning, but it seemed to spin faster and of course didn't start the truck). I'm not really even sure how to tell.
I have yet to find a definitive source, but I have come across a few articles that describe this engine as an interference engine. Maybe someone here can confirm. If so, I believe you will have bent valves at best.
Couple things. Chain tension will be loose now as the chain tensioner use oil pressure to exert pressure against the chain. The Atlas Series engine has hydraulically actuated timing chain tensioner that requires the oil pressure to first come up to add the required tension to the timing chain. Over time the chain will stretch, but the tensioner has ratches that will eventually allow it to click over to the next position to correct for the slack in the chain. Sort of like self adjusting brakes worked.
As I said way back when, your chain jumped and timing is out of whack. You need to replace the tensioner and guide, #s 13 and 11 respectively. I would replace the stretched chain as well while you are in there.
GM TSB 06-06-01-017G covers the revised cylinder head and timing chain service procedures for these engines. Simplistically, remove the chain tensioner and guide, line up the timing marks, install new tensioner and guide.
That sounds reasonable, I just wish I could know ahead of time if I had bent valves. I wouldn't bother doing this work if I did. Oh well, fingers crossed!
Brothapig, I've heard its an interference engine as well, although that doesn't necessarily mean bent valves are a sure thing. It was running, and I shut it off. I'm sure it had already skipped by then, but maybe when the starter was spinning it, it didn't jump that much again. I don't know. Glass half full I guess!
One thing I don't know...is there a position of the crank such that you can rotate cams around without hitting anything? I can't just put it at #1 TDC and lock everything in place here, because I've already skipped. On my 928 if I put it at 45 BTDC and lock the flywheel there, I can spin the cams all day to get them set up right and not hurt anything. Just not sure about this motor. Maybe it's included in the service manual, I haven't got that far.
Last edited by bureau13; Aug 12, 2020 at 10:50 AM.
to know if the valves are bent you have to make sure the timing is correct then you need to run a compression check. you can also pull the plugs and get a borescope inside the chamber to see if the tops of the piston got hit.
That sounds like a good idea, at least rule out something obviously catastrophic. Doing the compression test pretty much means fixing it first, so I think that's what I will go ahead and do.
Originally Posted by bronxteck
to know if the valves are bent you have to make sure the timing is correct then you need to run a compression check. you can also pull the plugs and get a borescope inside the chamber to see if the tops of the piston got hit.
Maybe I should retitle this thread "Very Slow Timing Chain Procedure" or something.
I have only had a small amount of time to work on this thing as there were other priorities. Anyway, so far I have removed the valve cover (obvious from above) removed the fan clutch (this was way easier than expected, the clutch was not on very tight at all, really) and the water pump. Walking my way through the service manual procedures, and I am at the "remove harmonic balancer" stage. Do I REALLY have to remove the radiator? I know it's not THAT hard, but it's one more thing to take off that I'd just rather avoid. Maybe I can't. I don't remember that step in the procedures when I was going through it at the beginning though.
Minor rant: I'm spoiled from all the user-generated tutorials for my other car. As a DIY-er I really do not like factory manuals. They seem to have a special tool for every damn thing, whether its needed or not. "Use the Special Tool For Fan Clutch Removal," for instance. Completely unnecessary, at least for my truck. I know, however, that SOME of these specialty tools will need to be purchased or rented. Anyone know which ones I for sure need? At a glance, I'm pretty sure I need the flywheel lock and the thing that keeps the camshafts locked in position. Also, some kind of gear puller for the balancer, but I suspect a generic one will do just fine.
OK, I found a puller that claims to not require the radiator to be removed. We'll see.
I'm also going to need a flywheel lock. GM wants a kidney for the official part, which is infuriating, it's just a chunk of metal with teeth. Surely there is an aftermarket tool that fits? There's a Lyle tool on Amazon that showed up in a search but I can't actually find anyone confirming that it fits. Has anyone here found a solution that isn't the official GM part?
