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Hello everyone,

It's been a while since I've been part of the ZCar community, but I'm back and I have a question. I've been doing a tune-up on a '76 280z, and noticed that the cam timing has retarded slightly due to timing chain growth. I'm considering an early advancement of the cam timing to the next dowel hole on the sprocket - advancing the cam beyond stock timing by maybe 3 degrees or so. Has anyone done a "preemptive" cam timing advancement? I understand how it changes the power band dynamics - I just wanted to get opinions before doing it. My only concern is piston-valve clearance, but with such a minor change, I'm assuming that won't be an issue. A member of another forum encouraged me to go ahead and advance it all the way to the 3rd spot on the sprocket, but I'm inclined to be cautious.

Thoughts?
 

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Hello everyone,

It's been a while since I've been part of the ZCar community, but I'm back and I have a question. I've been doing a tune-up on a '76 280z, and noticed that the cam timing has retarded slightly due to timing chain growth. I'm considering an early advancement of the cam timing to the next dowel hole on the sprocket - advancing the cam beyond stock timing by maybe 3 degrees or so. Has anyone done a "preemptive" cam timing advancement? I understand how it changes the power band dynamics - I just wanted to get opinions before doing it. My only concern is piston-valve clearance, but with such a minor change, I'm assuming that won't be an issue. A member of another forum encouraged me to go ahead and advance it all the way to the 3rd spot on the sprocket, but I'm inclined to be cautious.

Thoughts?
Three degrees with not cause valve to piston problems. If its only slightly retarded I would leave it alone.
 

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You can do that and it won't hurt anything but be sure to jam a piece of wood or a short piece of pipe down in between the chain sides so your tensioner stays in it's hole, otherwise you will have to pull the front cover off the motor to put it back in. Ask me how I know.
 

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1983 280ZX Turbo
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To follow up on that note, to hold the chain tensioner in place. If you just "jam a piece of wood" into the chain I guarantee you will have to take off the chain cover. It's a big pain in the butt. The chain tensioner is hear the bottom of the chain and the wedge has to block the chain from moving inwards or the tensioner will jump out of place. The bottom half of the wedge is long and skinny.

Research this, get a drawing of the exact shape of the wedge needed, and do not use anything else. It's called a wedge but it's really rather long and narrow at the bottom; it's not really a wedge with straight edges.

And yes, I learned this the hard way. It's helpful to find pictures of the chain so you can see where the tensioner actually is.

I found a picture. The tensioner is on the left side of the chain about four inches above the bottom gear. You can see the wedge needs to be skinny at that point to get between the tensioner side and the metal guide that's holding the other side of the chain. There are drawings that give you the right shape for the wedge. In this photo there is a nylon cable tie around the tensioner holding it in place. The wedge goes in from the top, where you see the gear on the cam, so it's long and skinny.

 

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Hello everyone,

It's been a while since I've been part of the ZCar community, but I'm back and I have a question. I've been doing a tune-up on a '76 280z, and noticed that the cam timing has retarded slightly due to timing chain growth. I'm considering an early advancement of the cam timing to the next dowel hole on the sprocket - advancing the cam beyond stock timing by maybe 3 degrees or so. Has anyone done a "preemptive" cam timing advancement? I understand how it changes the power band dynamics - I just wanted to get opinions before doing it. My only concern is piston-valve clearance, but with such a minor change, I'm assuming that won't be an issue. A member of another forum encouraged me to go ahead and advance it all the way to the 3rd spot on the sprocket, but I'm inclined to be cautious.

Thoughts?
I have done Many ! Slightly retarded cam timing will give you more power at higher RPM, Straight up is your best bet for all around. Don Ahrens Owner of Ahrens Z Car Specialist since 1982. We now Go by Ahrens Auto. I built Bill Coffeys fabulous 1970 240z that will be featured in Z Car Magazine.
 

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watch out for the timing chain guide, esp the bolts used on the thermostat. One of the bolts has a thru hole that if you use too long a bolt can push the guide into the chain.
You should also look at the tight side guide (same one that can be affected by the wrong bolt per above) and look for wear of the plastic. the chain will eventually wear the plastic and if it goes too far the chain can grab the guide and rip it off. This happened to me on a cross country trip, lucky me the guide fell down and lodged in a place where it did not harm (other than rubbing on the chain for a while). Could have been much worse if it had managed to fall between the chain and the lower sprocket. Anyway If you end up seeing wear I would HIGHLY recommend you bite the bullet, pull the cover and replace the sprockets/chain/guides/tensioner. Its not that hard to do, can do it with the engine installed. Just get the rad out of the way. The hardest part for me was getting the AC bracket out of the way (it was blocking ONE TC cover hole). Good time for a coolant and pump replacement while you are at it. This seems like a lot of work, and it is, but you don't want to ignore it IF the guide is worn....
 

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The timing chain wedge tool on amazon isn't that good when you consider all the angles. Back in my dealership days I use to use the one made by Kent Moore. It had a rope with a handle on it like one of them at amazon. Sounds pretty handle BUT, the rope and handle get in the way and can fall over when you're setting the head on the block. I sell one that I make out of oak for 6.95 and usually carry at least 10 of them in stock to sell. See enclosed pic. I bought a bunch of oak dunnage years ago so I have lots of it. It should last you forever if you don't lose it. I use to make them out of fir but had to replace them after 5 or so years of use because they would start to splinter. Keep in mind that I was doing a lot of heads at the time. I put a hole in my wedge so that I can reach in there with a windshield pic to retrieve it after I'm done with it. So far I've been using the same one for over 15 years and it hasn't started to deteriorate yet. When someone buys a chain wedge from me I also include my written instructions on how to setup your chain properly including how to install and remove the wedge. I agree with most of what the others before me said. To go a step further, if it's not broke don't fix it. Z man of Washington
 

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Discussion Starter #9
Thanks for the input, everybody. And yep - around 19 years ago, I spent my 21st birthday cursing in the snow as I realized my home-made tensioner retainer had failed to do its job. That made for a long and frustrating week!
 

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As I recall from 40 years ago, the service manual for my 1980 4x4 720 pickup showed a wooden block like the one pictured above but with a pull rope thru it. I made mine out of a piece of aluminum pipe with a pull wire thru holes I drilled in the side. I used it many times as I monkeyed around with the cam timing, but the first time, I did not read the manual and just pulled the cam gear off like I had done so many times when doing head gasket replacement on Chevy LUVs (I worked at a Chevy dealership in high school). Then I could not get the cam gear back on and I called a friend who worked at the Datsun dealer and he gave me the bad news.
 
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