Tricks for adjusting cam timing?

I fear I may run out of patience while adjusting cam timing on my '78 308.

Do any of you that have done a lot of cam timing changing have any tips you can share?
I can see now why we find reports now & then of people grinding pins down to make things line up. Is there math to predict what's the best move when I want to move the cam timing by 'x' degrees? Is there something better than developing a good feel for where the cams will get pulled retarded to when re-installing and tensioning the belt? Will my old belt I'm using to adjust timing with stretch and cause the new belt to give me incorrect timing!??! (egads, I hope not!)

Thanks for any "pro tips" that can be shared!

 

Are you trying to set the timing to factory specs or are you trying to change the factory cam timing for some reason?

I assume you are changing the timing from stock since setting the timing to factory specs is just a matter of lining up the marks (or verifying them first with a degree wheel if you feel the need).

But a degree wheel is what you need to change the timing to a particular spec. If you are not familiar with using them, there is plenty of info on the web about that. There are also pulley kits - like Forza's that will allow you to dial in some cam adjustment. This would be a good thing if you were changing timing on a regular basis as opposed to just setting it once.

But a degree wheel is the first thing you need to verify/set precise valve timing.

 

Best tip. Let a pro do it. Other instruments are needed such as a good TDC gauge. If you are stuck then the safe thing to do is put it on that old flatbed today.

 

The "trick" is, that to get 1 deg resolution, you must use the pin holes AND move the timing belt relative to the cam sprocket. The pin holes only give 3 deg resolution. The attached excel chart shows how to achieve any 1 deg position between -6, -5, -4 ... +5, +6 (a 12 degree range as each belt tooth corresponds to a 12 deg step). Unfortunately, this chart does not convey exact polarity/direction for advance vs retard -- it was generated only to show that you can not just put on the belt, and leave it on, and only use the holes (unless you get lucky ).
View attachment 308 Cam Adjust Calcs 3 hole -on- 5 hole pattern.xls

 

Thanks for your concern, guys. Mike, you're right, I'm going off the reservation here! I'm pretty secure in what I'm doing, and I think Steve's spreadsheet provides a good bit of what I was hoping to avoid science-ing out.

Funny, Steve, I was just trying to get my head around your statement about not needing to pull the belt off (and rectify it against your statement about moving the belt relative to the sprocket), when I realized most people would only be concerned with +/- 6 deg...

Thanks, more later!

 

Since it's come up in another post, I'm going to add some references to Steve's handy spreadsheet. It saved me much blood from bashing my head against my car, great tool!
Thank you very much for creating & sharing!

Here are some directions for using this fantastic tool:

If you view the entries in the first 2 columns as moving from left to right top to bottom (negative degrees are left, positive degrees are right) then the degrees of cam advance/retard you read from the last column are in CAM degrees (so multiply by 2 for crank degrees which is what you're measuring in and targeting) and positive numbers in that column mean retard.

Determine which holes you're in now and read how many degrees offset you have relative to zero. Then take your idea of how far you want to move and use the last column to see where you need to go, then make the necessary adjustments to your pulley orientation & cam hole used per the first two columns.

IOW, if you're in the second from right hole on the pulley (+25) and the center cam hole (0) that cam is offset +1 degree (that means it's retarded) relative to zero. If you're measurement from the crank is that you need to retard the cam 3 degrees, that's going from +1 to +4 on the right hand column. In this case you find +4 on the right column and then check the first two columns to see that you need to use the center hole on the pulley and the leftmost hole on the cam. Sometimes you have more than one option where an offset number appears more than once in the last column.

 

OK. I'm dense as a post.

How do you move the belt as the teeth will keep the cam gears in the same place.

I am Lost.

 

By physical disengaging the belt teeth from the sprocket teeth (i.e., removing the belt off the sprocket and then reinstalling the belt in a different position relative to the sprocket -- it helps to make temporary marks on both the belt and the sprocket to keep things straight).

Even though this scheme exploits a clever mathematical "trick", that minimizes the number of dowel holes needed in the cam flange and the cam sprocket, I think even F figured out that it just caused too much hassle/confusion downstream, as when they went back to two belts on the 355, they just added a bunch more dowel holes in both parts, so that regardless of the belt-to-sprocket relationship, there was always a pair of holes that would be nearly lined up (i.e., once the belt was put on it never had to be removed to get the cam timing right).

308/328 Cam Timing hole pattern
3 holes on cam flange
5 holes on cam sprocket
belt-to-cam sprocket relationship important to get a pair of holes to line up
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355 Cam Timing hole pattern
13~14 holes on cam flange
15 holes on cam sprocket
belt-to-cam sprocket relationship not important to get a pair of holes to line up
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I cringe whenever someone posts that the end of the dowel pin has been ground down on a 308/328 -- which just shows that the assembler didn't really know how this "hole + belt-to-sprocket" system worked on 308/328.

 

The timing of this thread could not be better. I'm struggling with achieving 104 on my intake (w/Webcam 1002 Grind) and 106 on my exhaust. I have a '75 and there are only three holes in my cam pulleys. Does anyone know if the same 25 degree spread occurs in the three-hole cam sprockets? If so, I'm assuming that only lines 12-22 of Steve's Spread Sheet would apply?
......Chris
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Can you take and post a photo of one of your 3-hole cam sprockets (viewed down the axis of the camshaft) similar to what's shown in that Fig 30 drawing? Might be possible to just measure the angle between the holes on the photo.

Does each cam sprocket just have 3 holes, or 2 sets of 3 holes?

If it only has 3 holes, my guess would be that the angle is 26 deg (or 22 deg) because this would give a total range from -6 deg to +6 deg (12 deg total -- which it needed because that corresponds to the distance of one belt tooth pitch) but in equal 2 deg steps. I've attached the excel file expanded to cover this case (using 26 deg, but 22 deg gives the same result).
View attachment 308 Cam Adjust Calcs 3 hole -on- 5 hole pattern and 3 hole -on- 3 hole pattern.xls

 

I am still not catching how revolving the rind around the orange gets you anything.

Can someone give a center starting point and then play by play to achieve each degree.

For the crainally challenged?

Bitte?

 

Maybe you should buy a 355 The rind (belt) is fixed to the crankshaft. It's the orange (sprocket) that rotates one way (say +24 deg = 2 belt pitches), and then the orange pits (cam) rotates back the other way (say -25 deg) -- so the net change between the rind and the pits is small (-1 deg). I'll try to make up a figure to better explain/illustrate, but you aren't exactly paying me a reasonable hourly rate...

 

Steve, I've taken a couple of shots of the 1-4 cam sprockets. I've removed the retaining nut because they partially obscure the view of the three holes on the cam sprockets. However, I left the retaining pins in on both cam sprockets. It is clear that the three holes on the camshaft do not line up with the three holes in the cam sprocket, but I will have to work with my degree wheel a bit more to get an estimation of how far the timing moves with each pin/hole configuration.
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My thought exactly.

 

No issue. I got it now.

The way I read your original post it implied that moving the belt actually changed something.




PM me a PayPal address and Rate Sheet. I have paid others.

 

No Guys. This is why I decided to buy the freaking car.


DIY WHEN EVER possible.

 

That is the key line here. I get the mechanics behind this but there is a lot of careful planning involved, not for the faint of heart. This guy knows what he is doing and will get through this eventually. I don't have the time or experience to attempt it. Hats off to him and Steve for the efforts. The excel chart is amazing, to 1 degree yet! Sort of reminds me of juggling three balls then someone throwing in a forth. (Three sprockets + belt)

 

Robert,

This is the first car I ever did more than change the oil on. I cannot tell you all the things I have dove into so far and found little so far "above my pay grade," once I understand the "ins and outs." Right now cams, sprockets, shims and belts are scattered all over my garage floor. My car was seriously messed up and by an appearantly certified mechanic no less. (NO !!! that is not an inditment of all mechanics. Not by a long shot so let's not anyone go there.)


I always ask first as seemingly "stupid easy sh_t" may just not be so. I have been stopped by my "gurus" from making a couple of serious mistakes cause I am very truthful about my experience level and am NEVER afraid to ask the "Stupid Question."


I am having one hell of a great time.

By Christmas I will either have blow it up or have it running like a torpedo on Angel Dust.


I do have a preference of the two possible outcomes, natually.

 

Mark,
At the risk of hijacking the thread, I too have found some interesting limits on my real abilities while working on the car. My truth moment came while trying to figure out fuel pressure levels cold vs hot etc. I would take multi-carb setups like my old jag any day over this. But once I do it with a "guru" I own it. Guess I am just a visual learner. Most other tasks I have attempted and completed I feel pretty good about considering I am an old dog and..........

 

Yes, moving the belt (relative to the driving sprocket/crankshaft) would have no effect. I didn't know that the early 308 had fewer holes on the cam sprocket, but I'd say that this important, and more-difficult procedure has almost been ignored in the F technical documents -- maybe because it was/is just too complicated to explain well and then translate clearly . I love the utterly vague description that they give in the 308GT4 WSM where it just says "research the correct pulleys orientation, then lock them with the dowels".

I can't find anywhere in the early stuff any mention of the tolerance (was curious to see if they went from a +/- 2 deg tolerance on the early 308 and then added more holes to give a possiblity to hold +/- 1 deg when the emission stuff came along). If anyone knows where F put a tolerance down for these angles on a 308, please post where.

 

Considering you are going this far and I would assume you will be doing other tweaks pending these results I would think it would be better to buy a set of adjustable timing sprockets.

 

my 78 euro 308 had the original plastic cam sprockets that were quite worn down at the teeth (check yours). now replaced with the fully adjustable aluminum versions and the timing was dialed in nicely. FYI

 

Ran across this thread and was wondering if the mathematics behind the "three pulley holes and three camshaft holes" was ever determined exactly.

I went back and looked at some notes I had taken but couldn`t tell exactly what I`d been able to determine; I remember concluding at the time, perhaps in error, that some of the nine possible combinations were "repeats" that didn't change the timing.

Thanks,

GF

 

Thought this was a legitimate question ... I`m not in a position to take the engine apart again just to study this. If no one has the parts separated from the heads and can ascertain the relationship between the three pulley holes and the three camshaft holes, guess I can burn that bridge if I come to it again.

GF

 

There is a diagram in the WSM. The 3 holes in the camshaft bosses are 28 degrees apart, the 5 holes in the pulley are 25 degrees apart and the belt teeth are 12 degrees apart. There should not be any duplicates.