F54/P79 Swap Project

[Captain Obvious]

1 minute ago, 240260280 said:

There is less chain under tension on the tight side and more on the slack when you take up the slack (as mentioned above).

The only thing that changes the length of chain on the tight side is moving the cam closer to the crank. Moving the guide, not anything with the tensioner shoe will have any effect on that.

Part of the tensioners job is to keep the length of chain on the tight side constant. Even when the chain stretches.

When the chain stretches, each link will get a tiny bit longer. So with the same number of links on the tight side will result in the cam timing being slightly retarded.

[Captain Obvious]

We're probably saying the same thing...    

[Captain Obvious]

23 hours ago, madkaw said:

Don’t worry about chain slack, go for the CR you want . Move the guide to take up slack. Advance cam timing a bunch and roll with it!

Plug in 39cc chamber numbers for the MN47! I got my fingers crossed for my engine .

Thanks. I'm growing more confident the more I analyze it.

So what block are you putting the MN47 on? I'll punch 39cc into my calculations and see what I get.

[240260280]

7 hours ago, Captain Obvious said:

Thanks. I'm growing more confident the more I analyze it.

So what block are you putting the MN47 on? I'll punch 39cc into my calculations and see what I get.

FYI I did the same thing years ago when everyone said you needed Head Saver Shims.  It seemed to me they were not needed from the geometry.

I found one person on zcar.com who did what I thought and that was enough to try it. No problems after I did it.

If you have a hot cam, the shaving will bring the valves closer to to piston top so that is the only case where the shims may be helpful.

[Av8ferg]

So back to my experience moving the the cam sprocket. I remember when my buddy and I did this we had to release the chain from the sprocket because otherwise we couldn’t get the sprocket back on. CO back to your sprocket drawing (impressive BTW). You’ve labeled the teeth as 1-3. The angular distance from the center of the sprocket in 1 vs 3 to the center of the crankshaft (lower gear that sits over the crank) would be different...no? 1 is farther away than three. This results in more tension on the right of the chain as you move it. The chain tensioner can only take up slack on the left side. So when the chain stretches over time, the engine timing slowly retards. When you move the sprocket to the next position you transfer that slack to the side that has the ability to take up that slack (left side)...The tensioner can only do so much which is why shaving the head exceeds the capability of the sprocket position and tensioner to account for.
This is why I think my engine has chain slap. When I moved the sprocket this problem started. My chain is obviously overstretched.
Let me end this with the disclaimer....I’m no engine expert and borderline dangerous with my knowledge. I’m looking at this purely on observation. I’m not offended if you tell me I’m totally wrong and to sit back down and listen to the professor. I’m learning!


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[grannyknot]

While there are so many good minds talking about this subject I would like to ask a question about a timing fact/myth I've heard many times. 

Starting with a new chain, by deliberately advancing the cam gear to #2 or #3 you can gain more low down torque. True or false?

10 hours ago, Captain Obvious said:

Actually I am completely confident that I am 100% right and 0% wrong.

Bruce, this is one of those great lines that should be permanently fixed to bottom of each post regardless of whether you are right or wrong

[Captain Obvious]

1 hour ago, Av8ferg said:

The angular distance from the center of the sprocket in 1 vs 3 to the center of the crankshaft would be different...no?

No, the centerlines between the cam and the crank never change. That's why the holes have no effect on chain tension. Another example to help everyone think about it......

Pull your cam gear off.
Pry the locating pin out of the end of the camshaft.
Put the cam gear back without the pin and leave the center bolt just a little bit loose.

Now put a wrench on the flats of the camshaft and rotate the cam*. The cam will turn, but the cam gear will not. It will slip because the pin has been removed.

This will effectively change the valve TIMING, but does nothing to the chain tension. In fact, you can check the chain tension as the locating hole in the cam passes behind any of the three timing holes in the cam gear. No change in tension.

You can go a full turn on the cam like this and simulate ever possible valve timing, including the three fixed positions achieved by the locating pin. The valve timing will be changing wildly, but the tension never will. Does that make sense?

*This is an illustrative example only. While it's possible to perform this academic exercise, you must make sure you have the pistons in a position such that there cannot be any valve to piston collisions.

[Captain Obvious]

54 minutes ago, grannyknot said:

Bruce, this is one of those great lines that should be permanently fixed to bottom of each post regardless of whether you are right or wrong

Haha!! Love it!

I screw up way to often to do that!      Would be funny though!

[Captain Obvious]

1 hour ago, Av8ferg said:

So back to my experience moving the the cam sprocket. I remember when my buddy and I did this we had to release the chain from the sprocket because otherwise we couldn’t get the sprocket back on.

I think the only reason you guys are having trouble getting the cam gear back on using a different hole is because the holes aren't lined up with the pin. When you move to a different hole, you have to rotate the cam a tiny bit to get the new hole position to line up or the gear won't slip on.

That's the point.

You can rotate the cam a tiny bit, or you can rotate the crank tiny bit to get things to line up. But in either event, the overall tension has not chainged. Pun intended.

[Captain Obvious]

On ‎9‎/‎13‎/‎2019 at 10:13 PM, madkaw said:

Advance cam timing a bunch and roll with it!

@madkaw, another question... What is "a bunch"?

Did you advance it to bring it back to stock timing, or did you go beyond that and advance the timing past the original stock settings?

[Av8ferg]

So Grannyknot I should put “60% of the time I’m right every time”. Kind of like the cologne Sex Panther.

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[siteunseen]

I can say this from personal experience, can't explain it just say it.  True!

When I built my '77 I started on #3 with all new stuff.  It ran great and had plenty of lowend.  Two or 3 years later I did the '72 the same.  It hits the redline so fast I can't stand to drive it hard, like beating a cat it just just gets louder.  In the summer of 2018 I put the 280 back to #1 after I bought a wedge tool.  Ran a good bit worse than I was used to so within one measly day of driving I went back to #3.  Now the 240 is going back to at least #2, probably #1, but that chain is so damn tight I'm not sure I'll get the sprocket off and back on in the car. 

I read that Racer Brown write up on Datsun's 510, L20 I suppose. I came to the understanding, right or wrong's on me, advancing all three things the cam does actually improves performance and efficiency although you lose some top end power.  The 280 has an R200 so the redline came slower.  The 240 with the r180 goes up too fast and I don't like it. 

http://www.datsport.com/racer-brown.html  

  

Edited September 15, 2019 by siteunseen