Crankshaft Removal Interruptance
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Joined: Oct 2019
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Crankshaft Removal Interruptance
I was just about to remove the crank from my '08 H3 3.7L when I removed the rear plate from the block and discovered the mini timing chain driving two small sprockets from one on the crank. All three have alignment marks, so I spun the crank to TDC on piston #1, but the marks are all over the place.
Since the cams are driven and timed by the front timing chain, is it a case of these sprockets merely having the marks from the manufacturer, but there is no timing alignment involved ? I'm not sure what both sprockets are even driving.
Since the cams are driven and timed by the front timing chain, is it a case of these sprockets merely having the marks from the manufacturer, but there is no timing alignment involved ? I'm not sure what both sprockets are even driving.
Junior Member
Joined: Aug 2019
Posts: 10
I do not have any specific experience with our motor but generally what you have there is 2 balance shafts.
The timing marks will only realign every 130 something rotations.
Typically you just set all the marks correctly to their mating marks during reassembly and you will be fine.
However, I have seen motors where that will allow the balance to be 180 degrees out for some reason.
You are going to need to get a hold of a service manual if you want to be 100% certain on the procedure
The timing marks will only realign every 130 something rotations.
Typically you just set all the marks correctly to their mating marks during reassembly and you will be fine.
However, I have seen motors where that will allow the balance to be 180 degrees out for some reason.
You are going to need to get a hold of a service manual if you want to be 100% certain on the procedure
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The two driven sprockets are not symmetrical. One drives a shaft down the side, which could then drive the balance shafts (completely forgot about those). The other is at the bottom and drives a set of worm gears. The balance shafts would definitely need to be timed.
Junior Member
Joined: Sep 2018
Posts: 23
From: Traverse City MI
Replaced mine last year. Definitely timed. The wear was so bad that you could hear the chain links rubbing on the tensioner mounting plate. I belive that the marks are aligned only on every seventh rotation. Get the timing wrong and you'll have a 4900 pound vibrator.
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Update:
First, Crispins you were correct sir ! The two sprockets are driving the two balance shafts, with one also driving a set of worm gears, which I suspect is the oil pump.
Second, the timing marks on the three sprockets need to be at noon, 2:30, and 4:30. Yikes. Also, the three black links in the chain have to match those same marks, and that only occurs every eleven rotations.
Hands down the wackiest engine I've ever rebuilt. Well, the crank is at the machine shop.
First, Crispins you were correct sir ! The two sprockets are driving the two balance shafts, with one also driving a set of worm gears, which I suspect is the oil pump.
Second, the timing marks on the three sprockets need to be at noon, 2:30, and 4:30. Yikes. Also, the three black links in the chain have to match those same marks, and that only occurs every eleven rotations.
Hands down the wackiest engine I've ever rebuilt. Well, the crank is at the machine shop.
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Donald Austin
Hummer H3
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Aug 29, 2018 12:39 PM
