U20 Rebuild Upper Tensioner check

Tech tips and how to's

Moderators: notoptoy, garth, S Allen

User avatar
sdb8100
Roadster Nut
Posts: 68
Joined: Mon Aug 15, 2016 3:39 pm
Location: Pittsburgh, PA
Model: 2000
Year: High Windshield-68-70

U20 Rebuild Upper Tensioner check

Post by 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!
'69 Datsun 2000 Roadster l Pittsburgh, PA

User avatar
jrusso07
Roadsteraholic
Posts: 1373
Joined: Sat Aug 02, 2008 9:02 am
Location: Penn Yan, NY
Model: 2000
Year: High Windshield-68-70

Re: U20 Rebuild Upper Tensioner check

Post by 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?
Joe

1969 SRL311 - Solex
1970 SPL311 - U20 mod
1970 SRL311

JT68
Talented Enthusiast
Posts: 2028
Joined: Sun Jan 27, 2013 9:43 am
Location: Cumming, GA

Re: U20 Rebuild Upper Tensioner check

Post by 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.
JT/LT
Datsunrestorationproducts.com
The very finest parts for your 311!

User avatar
sdb8100
Roadster Nut
Posts: 68
Joined: Mon Aug 15, 2016 3:39 pm
Location: Pittsburgh, PA
Model: 2000
Year: High Windshield-68-70

Re: U20 Rebuild Upper Tensioner check

Post by 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
You do not have the required permissions to view the files attached to this post.
'69 Datsun 2000 Roadster l Pittsburgh, PA

JT68
Talented Enthusiast
Posts: 2028
Joined: Sun Jan 27, 2013 9:43 am
Location: Cumming, GA

Re: U20 Rebuild Upper Tensioner check

Post by JT68 »

And if you put tension on the opposite side, there is no additional slack at the tensioner?
JT/LT
Datsunrestorationproducts.com
The very finest parts for your 311!

JT68
Talented Enthusiast
Posts: 2028
Joined: Sun Jan 27, 2013 9:43 am
Location: Cumming, GA

Re: U20 Rebuild Upper Tensioner check

Post by 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.
JT/LT
Datsunrestorationproducts.com
The very finest parts for your 311!

User avatar
jrusso07
Roadsteraholic
Posts: 1373
Joined: Sat Aug 02, 2008 9:02 am
Location: Penn Yan, NY
Model: 2000
Year: High Windshield-68-70

Re: U20 Rebuild Upper Tensioner check

Post by 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
You do not have the required permissions to view the files attached to this post.
Joe

1969 SRL311 - Solex
1970 SPL311 - U20 mod
1970 SRL311

User avatar
sdb8100
Roadster Nut
Posts: 68
Joined: Mon Aug 15, 2016 3:39 pm
Location: Pittsburgh, PA
Model: 2000
Year: High Windshield-68-70

Re: U20 Rebuild Upper Tensioner check

Post by 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.
'69 Datsun 2000 Roadster l Pittsburgh, PA

JT68
Talented Enthusiast
Posts: 2028
Joined: Sun Jan 27, 2013 9:43 am
Location: Cumming, GA

Re: U20 Rebuild Upper Tensioner check

Post by 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?
JT/LT
Datsunrestorationproducts.com
The very finest parts for your 311!

User avatar
jrusso07
Roadsteraholic
Posts: 1373
Joined: Sat Aug 02, 2008 9:02 am
Location: Penn Yan, NY
Model: 2000
Year: High Windshield-68-70

Re: U20 Rebuild Upper Tensioner check

Post by 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
Joe

1969 SRL311 - Solex
1970 SPL311 - U20 mod
1970 SRL311

User avatar
Gregs672000
Roadster Fanatic-Site Supporter
Posts: 6901
Joined: Fri Aug 07, 2009 11:47 pm
Location: Tacoma, WA

Re: U20 Rebuild Upper Tensioner check

Post by Gregs672000 »

Have you rotated it (the engine) yet? It gets tight, then slackers, then tightens again...
Greg Burrows
'67 2000 #588
Tacoma, WA

User avatar
Gregs672000
Roadster Fanatic-Site Supporter
Posts: 6901
Joined: Fri Aug 07, 2009 11:47 pm
Location: Tacoma, WA

Re: U20 Rebuild Upper Tensioner check

Post by 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.
Greg Burrows
'67 2000 #588
Tacoma, WA

User avatar
sdb8100
Roadster Nut
Posts: 68
Joined: Mon Aug 15, 2016 3:39 pm
Location: Pittsburgh, PA
Model: 2000
Year: High Windshield-68-70

Re: U20 Rebuild Upper Tensioner check

Post by 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
You do not have the required permissions to view the files attached to this post.
'69 Datsun 2000 Roadster l Pittsburgh, PA

JT68
Talented Enthusiast
Posts: 2028
Joined: Sun Jan 27, 2013 9:43 am
Location: Cumming, GA

Re: U20 Rebuild Upper Tensioner check

Post by 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.
JT/LT
Datsunrestorationproducts.com
The very finest parts for your 311!

User avatar
sdb8100
Roadster Nut
Posts: 68
Joined: Mon Aug 15, 2016 3:39 pm
Location: Pittsburgh, PA
Model: 2000
Year: High Windshield-68-70

Re: U20 Rebuild Upper Tensioner check

Post by sdb8100 »

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

Thanks for all your help and input.
'69 Datsun 2000 Roadster l Pittsburgh, PA