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issues with tdc 4.0 re-indexing a distibutor.

B

barneycj-8

NAXJA Forum User
Location
Orem, UT
:gee:Ok I have searched and looked up finding tdc on 4.0 and re-indexing a 4.0 distributer. ok here is the issue have 96 I wheeled to death one day going to work lost all power wouldn't run check compression cyl 1 0 psi took off head 1 inch hole in piston. so bought a used older motor put all 96 sensors fuel injection new crank position new disributor. issue is with tdc no matter what I do when I put mark on dampner at "0" 1 piston isn't up at top of cylinder. I was wondering if there a difference between older dampner and 96 engine used orig dampner but all of front end of engine brackets and accesories are all off 96 this is giving me fits which is new to me any help would be appreciated and if I am being an idiot set me straight light me up. Oh yea I have sey mark though not seeming to be tdc put in dist point to 1" on cap kind of back fires but still no run. thanks in advance:gee:
 
balancer was the same from at least '87-'96, so that shouldn't be a problem. Is it possible that your balancer has begun to separate and allowed the outter ring to "spin" on the center hub? It would tell you that you were at TDC when the engine wasn't really there.

Pull the #1 plug and turn the engine 'til you get a strong puff of air exiting the hole. At this point, I've used a wooden dowel stuck in the hole to determine when the piston stops moving up and begins to reverse direction. This is true TDC and you can verify if the balancer is also showing TDC or if it's spun.
 
Shorty said:
balancer was the same from at least '87-'96, so that shouldn't be a problem. Is it possible that your balancer has begun to separate and allowed the outter ring to "spin" on the center hub? It would tell you that you were at TDC when the engine wasn't really there.

Pull the #1 plug and turn the engine 'til you get a strong puff of air exiting the hole. At this point, I've used a wooden dowel stuck in the hole to determine when the piston stops moving up and begins to reverse direction. This is true TDC and you can verify if the balancer is also showing TDC or if it's spun.
Click to expand...
x 2 - Also, If you miss TDC NEVER CRANK BACKWARDS. Start a new rotation.
 
Going back 20*, then forward, is easier than going forward another 720*. You just want to avoid opposite slack, which is why you don't go backwards exactly to 0*.
 
still cant find tdc have valve cover off to watch valves go up and down was told should be at: "4) Rotate the crankshaft using a socket wrench with a 19mm socket until the notch on the crankshaft pulley lines up with the "0" mark on the timing cover (below). The valve springs on the no.1 cylinder should be relaxed and the valves closed. This will indicate that the no.1 piston is at TDC at the end of the compression stroke. If the springs are compressed, the valves are open (end of exhaust stroke) so you'll need to rotate the crank pulley another 360*.

5) Once you've verified that the no.1 piston is at TDC on the compression stroke (both valves closed), the rotor on the distributor should be pointing near (but not at) the mark for the no.1 plug wire terminal."
but when I did this the piston was not all the way up was I out 360 and it says pointing towards but not at should it be a little counter clock wise of it or clock wise of it this is giving me fits. can someone please explain again thanks.
 
barneycj-8 said:
The valve springs on the no.1 cylinder should be relaxed and the valves closed. This will indicate that the no.1 piston is at TDC at the end of the compression stroke.
Click to expand...

That is incorrect. When both springs finish closing that only indicates the BEGINNING of the compression stroke, when the piston is near BDC. You can not use the valves as an indicator of TDC, only to see where the compression stroke begins. You then need to check where the piston is in the bore and find when it comes up to TDC while rotating the crank CW.
 
Yeah, you have to watch to see the intake valve finish closing, then you know you are on the compression stroke, but not yet at TDC. Keep rotating until the dowel stops moving at the top of the stroke. That is TDC. In this case ignore the mark on the harmonic balancer as we don't know if it is accurate. You can check it, however, if it lines up at TDC.

Technically, it isn't 100% TDC. Its just at the dwell around TDC. However the only way to find 100% TDC is to either use a piston stop and a degree wheel or pull the head and use a dial indicator and a degree wheel. Which is the first step to degreeing a cam in. However, in this case you don't need such accuracy. TDC via the piston is good enough for dropping a distributor in.
 
jeepman121 said:
:huh: Must be a straight 6 thing....Instructions for a 350 say it's a no no.
Click to expand...
It's a no-no on some engines that use tensioning rails and the like, because it can slacken the chain so much that it either skips teeth or breaks the chain when it restarts. Don't ever do it on a Mercedes diesel, for example. The XJ chain has no tensioner, so it's safe to do.
 
Does that go for engines with hydraulic or spring tensioners? I can see how it would effect a hydraulic tensioning device. You reverse engine direction, tensions normally slack side, pushes in hydraulic tensioner and on the first start you have a slack chain.

Off topic I really don't understand the tensioner in the 4.0L considering it is on the tension side to begin with.
 
Talyn said:
Does that go for engines with hydraulic or spring tensioners? I can see how it would effect a hydraulic tensioning device. You reverse engine direction, tensions normally slack side, pushes in hydraulic tensioner and on the first start you have a slack chain.

Off topic I really don't understand the tensioner in the 4.0L considering it is on the tension side to begin with.
Click to expand...
I would guess hydraulic as the obvious case, and the one in which I've actually seen it happen (Merc. diesel), but even with a spring tensioner it might depend on how stiff it is and how everything is routed, enough to make me cautious. I'd at least make very sure to manually turn the engine over before starting it.
 
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