Captain Obvious

Yeah, I'm gonna try just one very last time and then give up....

And no zip ties were harmed during this procedure.

I'm not confused at all, and the proof is in the pics. System with cam gear in position 1: I rigged up a little wire pointer to indicate TDC. Doesn't have to be exactly dead nuts on TDC as long as it's the same spot each time: Here's the timing marks in position 1: Then I used my chain wedge tool (just like if I were doing this in the car). Tool wedged down into place: Take the cam gear off: Move the gear to position 3 and take out the wedge tool: Here's the system in position 3: Here's the timing marks in position 3. The valve timing has become advanced compared to position 1. Exactly as one would expect: Now... For the chain tension. I used a feeler gauge to measure how far out the adjuster is. This is position 1: Measuring the feeler gauge, the tensioner is out about .115 with cam gear in position 1: Repeating the measurements for position 3: End result? The adjuster protrudes the same amount regardless of the cam gear position:

Rut roh! Well as I said, I've not proven my calculations to be correct, but with a .049 (1.244mm) thick head gasket and .005 off the block I get 11.54:1 I get 502.45 cc uncompressed volume and 43,55 cc compressed for a result of 11.54. Remember, I'm just a guy with a spreadsheet. You got any airports near you? LOL!!

Nope. What he said. It's four (crank) degrees per position change:

I disagree completely. I do not believe it depends on the perspective of the viewer. I say that the tension on the chain is independent on which cam index hole 1-3 is used. Would you believe me if I took some pics? I'll put the gear in position 1 and take a pic of the tensioner. Then I'll move the gear to position 3 and take another pic of the tensioner. My belief is that the tensioner will look identical in both those pics. I say the plunger will be the same distance out regardless of what hole the cam gear is in.. If I show you, would you believe it then? What say ye? Haha!! @240260280 I challenge thee to a geek-off.

Awesome! What kind of gas are you going to use with that CR? And BTW, when I run the CR on your combo, I get a slightly higher number than you do. I get 11.42:1, but I've not reached the point where I'm completely confident in my numbers, What number are you using for head gasket thickness after it's been crushed into place? I get 11.42:1 with a .120 thick head gasket on an F54 and a 39cc chamber.

@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?

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.

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

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.

Anyone notice the floormats?

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.

We're probably saying the same thing...

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.

Here's another way to think about it... Within a small amount of manufacturing tolerance, the centerline axis of the cam gear must always be on the same axis as the camshaft. It if weren't, the gear would wobble eccentric and make the chain tighter in one spot and looser in another. If changing to a different indexing hole is expected to have an effect on the chain tension, then what happens when you rotate the cam 180 degrees? Does it get extra loose?

Actually I am completely confident that I am 100% right and 0% wrong. Changing the cam gear to a different index hole has absolutely nothing to do with chain tension. It changes relative teeth position, but not chain tension. This is what the different index holes do... They change the relative position of the gear teeth to the hole. (Which changes the relative position of the teeth to the cam lobes.) But it does nothing to the overall tension on the chain. Remember this pic? : The reason they say you can use a different hole to account for chain stretch is ONLY to bring the valve timing back into spec. It won't tighten up the chain any... That's the tensioner's job.

Oh, and I'm not worried about the valve timing. I've got a lathe and I've already verified that I can set-up to bore the locating pin hole: I didn't cut any metal yet, but if I need to, I can adapt to the offset bushings.

So now I'm not sure if your kidding or not... You do know that the timing hole you use has absolutely no effect on how tight the chain is, right? Haha!!

I completely forgot about that. I had talked about it before, but by this time, my brain was full. So I slotted mine some and it's almost back to where it should be. I'm confident with a new set of non-worn guides, I'll be able to make that work fine. Thanks for the reminder!!

I do it all at room temp with the hydraulic press. No muss, no fuss. Just money.

Haha! They're talking about that car on the Fiero forum right now. Could be mine under all that custom stuff. Doubt it, but could be!

You were right.... It was still early. This ones better. .

Yeah, that .047 difference really changed the position of the tensioner. However, forgot to mention... The chain guides and tensioner shoe are worn in that pic. If they were new unworn, it wouldn't be quite so bad. I can also slot the slack side guide holes a little to bring it in closer to the chain. I'm thinking that my sweet spot of "low hanging fruit" could be about .040 off the head, get new chain guides and tensioner shoe and slot the bottom hole of the slack side guide a little bit.

I've run the compression ratio numbers through my spreadsheet and came up with the following... F54/P79 stock - 8.83:1 F54/P79 with .040 shave - 9.37:1 F54/P79 with .080 shave - 10.0:1 Is 9.37:1 still in the realm of regular grade gas?