Upper Cam chain

[Tonymig]

Hi everyone , I have a 68 2000 with original u20 motor. It starts and runs pretty well. I adjusted the valves while engine was hot and then check the cold and then hot again the next day. Minor adjustment. The reason why I checked them 3 times is that it sounds like they tap especially when cold. While I had the valve cover off I looked at the upper cam chain . It’s tight on the tensioner side and fairly slack on other side. Is thus normal? I can not find good info on what this chain suppose to be like or how to adjust the tensioner. I have 2 different manuals . I need your help. I hear a lot about the death rattle

[jrusso07]

Here's some info from a previous post....viewtopic.php?f=3&t=32846

[Gregs672000]

Most tensioners need to be shimmed to take up most but not all of the slack. Inspect the underside of the L part of the chain guide as it extends out and under the gear. If there are slots being cut into the L it is being hit by the chain. This eventually fatigues and snaps off, destroying the engine. The tensioner relies on oil pressure to tension the chain, which isn't present at start up, so it hits.

Some valve train noise is normal, with some louder than others. As you may have noted, the valve lash/adjustment actually loosen with heat. I set my lash 6in 8ex cold, and they'll be 8in 10ex hot. I run lash a bit tighter than spec, but not to risk burning a valve due to it not seating and transferring heat as it should.

[Tonymig]

Thanks for responding Greg. There is a little cover that allows excess (I think) to the tensioner area. Is this correct? If so Are you able to adjust tensioner from this location? I mis stated something in my opening question. The chain is tight on drivers side of car and loose on tensioner side. I am now afraid to drive the car for fear of ruining the engine. I went over my repair manual again and really nothing about adjusting the tensioner. Is there a better book then the one I got from sin city Datsun (hand book and service manual)? Thanks

[Gregs672000]

No FEAR, WE'RE HERE! Yes, you can access via the front plate, but you will need the valve cover off too. There is no adjustment to the tensioner... you remove it and add shims to the piston to take up most of the slack (but not all). This is not a complex project but you need to know a few things. One, the tensioner bolts are secured with locking plates that sometimes get a little more beat up than you like (I replaced mine with locking washers and some locktite but be careful as they can slide off the bolt and into the engine). Yours are likely fine to reuse. Stuff a rag down the front of the motor to stop anything that may fall in by accident. Two, the tensioner uses two gaskets. You may be able to reuse them if they're in really good shape, but otherwise you can purchase them from a vendor (probably as part of a tensioner shim kit) or make your own from thin gasket material from an auto parts store BUT you need to make sure you punch out for the oil hole that feeds the tensioner or you'll block it off (pretty obvious). You can relieve the tension some on the chain by rotating the engine back a bit (crank nut can be hard to reach depending on what's there) or try bumping the starter (coil wire or cap off so the engine cannot start) to see if you catch it at a slack spot. Some people use a zip tye to hold the tensioner compressed together with the shims, making it easier to manipulate and install. A very light dressing of gasket maker will probably keep the inspection plate from leaking if the gasket is still intact, otherwise it may need replacement and is not as easy to make. Finally what did the L look like? Did it have cuts in it? If so, consider cutting it off with a hack saw right next to the head, with lots of lightly oiled rags down the front of the engine to catch metal flakes, or just keep an eye on it if only lightly touched. With the shims on the tensioner, it won't be hit by the chain anymore. For shims you can use nylon washers that fit over the shaft, or buy a kit. Get a few shims and use enough to take up most of the chain slack but not all of it (leave say 1/8 -1/4"). The tensioner will make up the difference when oil pressure comes up... you're just taking up the slack before that happens.
Search the forum for pictures of shims installed etc, and see if any owners are nearby who could come over and advise/assist if you're unsure of things. Or post your questions and we'll help.

[Gregs672000]

To explain the chain and slack... if you were to rotate the engine around through its full range by hand you would watch the chain slacken, the tensioner extend and then slam back (without oil pressure, the internal spring is too weak). This ends up changing cam timing in relation to the bottom end (bad) and the slack in the chain on the drivers side (the slack goes from one side to the other as it rotates) can hit the L on the guide. I watched (in horror) this happen on the engine stand and could not believe how much the bottom end could move without the cam rotating. The shims will take care of all of that. All U20 upper tensioners should be shimmed regardless of the condition of the L.

[spl310]

I have seen modified L tensioners that have a bolt installed into the back of the tensioner. Has anyone done this with a U20 tensioner?