U20 Rebuild Upper Tensioner check

[sdb8100]

I'm getting towards the later stage of my U20 build. I just installed the cam gear onto the cam of a completely rebuilt head by Dave P. All timing components are NEW (Chains, sprockets, tensioners, gaskets, hardware, etc). When installing the new UPPER TENSIONER I found that with the foot compressed all the way it was still quite difficult to rotate into position and line up the upper bolt hole. I needed to press down hard on the far end of the tensioner back plate for leverage to rotate into position (bottom bolt was already installed and acting as pivot).

These are all new components so they should be TIGHT. The chain will eventually stretch. This is not my first rebuild, but it is my first Datsun rebuild so I just wanted a gut check from those more familiar with this u20 motor.

Once installed I can rotate the motor by the crank bolt with a breaker bar with relative ease.

Thx!

[jrusso07]

Sounds awful tight to me. I put new gears and chains on my U20 and had little to no resistance mounting the tensioner. So with the tensioner mounted is the foot fully compressed or can it move in and out a little? Can you post pick of tensioner foot against chain showing foot compression in tensioner body?

[JT68]

You need at least.030-.060" freeplay for the tensioner foot with ALL the chain slack on the tensioner side. With the chain and sprocket fully installed, have someone pull the cam CCW with the crank stationary to put full tension on the driven (non-tensioner) side. .060 is a good number, but the tensioner foot will probably survive with .030.

[sdb8100]

The tensioner looks to be just about bottomed out. I took off the tensioner and then reattached. The second time I didn't need a tool and was able to rotate by hand with medium force. See images and link to vid.

tensioner-2.jpg

tensioner-1.jpg

Link to video of chain slack prior to upper tensioner install:

Video of chain slack without upper tensioner

[JT68]

And if you put tension on the opposite side, there is no additional slack at the tensioner?

[JT68]

If you take a large flat screwdriver and pry the foot away from the tensioner, (like oil pressure will), how far out will it go wilth moderate effort? A photo would be good of this too.

[jrusso07]

I'm not sure what is wrong. Did you reduce tension on the chain as JT68 recommended?

In the video, the chain guide looks out of place. I am accustomed to having the hole in the evil L line up with the center of the cam gear. Yours look low and to the left - maybe just camera angle?

Here's a pic of what I mean

[sdb8100]

I think you pin pointed it. My Evil L does not match up with center of Cam at all. It looks like its bent to the left and down. When I disassembled the motor the PO had removed the L so I had no reference that it was supposed to be right on center. It must have be a damaged part. The rest looks alright, but it's probably torqued in some way if the L is that far bent. Well that sucks.

[JT68]

I'm not so sure. Yes, i would have cut that pos-L off, but I'd be surprised if the guide itself is damaged in any way due to the L being damaged-never seen that. (Hate for you to replace the guide only to find the same issue).

Can you realize any play at the tensioner foot with the big screw driver? If so, it probably won't matter since the tensioner is always under load once there is oil pressure.

Nissan head gasket?

[jrusso07]

Sorry man. Maybe you can straighten it in place? There is a dimensional drawing of he guide on Dean's website/store.

Here https://www.datsunparts.com/2615

Good Luck!

I just saw JT68s response. The evil L position may have nothing to do with the chain tightness. The frame of the chain guide is very rigid. I am not sure how it could be distorted. My input was on ly an observation of what didn't look as expected

[Gregs672000]

Have you rotated it (the engine) yet? It gets tight, then slackers, then tightens again...

[Gregs672000]

Impossible to install the chain guide wrong. It's just the lack of slack in the chain. Rotate the engine with the tensioner in and watch its action.

[sdb8100]

It rotates fine from the crank with a breaker bar. Yes I did notice it gets tight, then slack and so forth. Here is the picture of me pressing out the plunger with a tool. There is some minor play in the tensioner that exposes the plunger shaft when I press out with the tool.

I def did not install the guide wrong, but the L is jacked up as it does not line up at all with the center of the cam.

IMG_7872.JPG

[JT68]

That is about .060" play. You have to load it like that to get a realistic measurement because when the engine is at speed, there is zero slack on the driven side.

You could ask him, but my guess is Dave used the thickest camstand shims he could without messing up the cam geometry and that took up most of the slack. Should be fine I think.

Personally, I would cut away the L, it is quite unnecessary and can do some REAL damage, otherwise I think you are OK.

[sdb8100]

I think I’ll remove the L since it’s damaged already.

Thanks for all your help and input.