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"May the Schwartz be with you"
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Discussion Starter · #1 ·
I was working on my Audi tonight and had a thought...

If I was to shave the heads a tad for added compression, would it throw of my cam timing due to shorter belt length?

I haven't looked into this yet but I am sort of curious about it...anyone with experience?
 

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Does your engine have a belt tensioner on it? I've always been under the impression that the tensioner would take up the extra slack. Kinda like when a timing belt stretches from age...
 

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"May the Schwartz be with you"
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Discussion Starter · #3 ·
Blazin72 said:
Does your engine have a belt tensioner on it? I've always been under the impression that the tensioner would take up the extra slack. Kinda like when a timing belt stretches from age...
My thought is that the cogs on the belt will not line up properly, therefore either advancing or retarding the cam...I really haven't looked into this at all yet. I don't see how the tensioner could compensate.
 

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any newer car engine has a specific specification on what thickness heads can be milled off. this is due to reasons just like this, and interference engines/ valve clearence ect... really milling the head enough to increase the compression any substancial amount will probably go over the spec, and will do somthing to the engine. call 1-800 VW parts and talk to Eric, he probably has the spec you need.
 

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As all Benzs are chain drive we use offset keys to set them up. Hell, when the first 380s came out in 81 we had to check cam timing on any with idle quality complaints as they were out from the factory.
Yes, your cam timing will either advance or retard - depending on the tensioner position. Adjustable sprockets are made for most rubber band engines so there should be one to suit yours.
 

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Discussion Starter · #6 ·
matt167 said:
any newer car engine has a specific specification on what thickness heads can be milled off. this is due to reasons just like this, and interference engines/ valve clearence ect... really milling the head enough to increase the compression any substancial amount will probably go over the spec, and will do somthing to the engine. call 1-800 VW parts and talk to Eric, he probably has the spec you need.
That is exatly what I was thinking. I suppose I shall have to take some measurements and angles so that I can calculate exactly how much off it would be. With that in mind, I can then grind a cam to fit the difference.
 

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Discussion Starter · #7 ·
IanRiordan said:
As all Benzs are chain drive we use offset keys to set them up. Hell, when the first 380s came out in 81 we had to check cam timing on any with idle quality complaints as they were out from the factory.
Yes, your cam timing will either advance or retard - depending on the tensioner position. Adjustable sprockets are made for most rubber band engines so there should be one to suit yours.
If you can locate available parts for a 1989 Audi 2.0 8v then let me know. As far as I can tell there is squat available for them.

Thank you for your input, but I truly feel that I will have to manufacture the needed parts myself. I was just curious if anyone else here has overcome this issue.

It definately would be great if I could order something... :)
 

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Whenever I'm up against something like this, I try to take it to extremes to figure it out. My thinking is that even if you could move the head down several inches, as long as the crank and the cam pulley were phased to each other in the correct way, you'd be golden. Think of it like this: If you could lock the cam sprocket and the crank sprocket in position and build an idler pulley off to the side and take up all the slack, the pulleys would maintain their relationship with each other. Makes sense to me.
 

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I should have mentioned that timing chain/belt tensioners are not on the tension side of the gear, but on the slack side. If they were on the tension side, the wear rate would be horrible.

So when you mill the head the cam centerline gets closer to the crank centerline, in effect the chain is getting longer, retarding the cam timing.

If you .030 off the head, you retard the cam about 5* roughly.
 

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www.autotech.com
Check it out, they list adjustable sprockets for a wide variety of dak daks (VWs) but as most early porsche 924/vw/audi engines are the same I reckon you're in luck. It took about 70 secs on google.

If not, ring George Jetson @ Hanna Barberra. He used to work for cogswell cogs and may now work for spacely sprockets - opps, that's only a cartoon.
 

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Discussion Starter · #13 ·
xntrik said:
So when you mill the head the cam centerline gets closer to the crank centerline, in effect the chain is getting longer, retarding the cam timing.
True, but the driving portion of the belt is not on the tensioner side, so in effect moving the cam gear closer to the crank will in effect shorten the belt, although more slack would be produced on the tensioner pulley side.
 

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Discussion Starter · #14 ·
IanRiordan said:
www.autotech.com
Check it out, they list adjustable sprockets for a wide variety of dak daks (VWs) but as most early porsche 924/vw/audi engines are the same I reckon you're in luck. It took about 70 secs on google.

If not, ring George Jetson @ Hanna Barberra. He used to work for cogswell cogs and may now work for spacely sprockets - opps, that's only a cartoon.
Thanks for the link, like I said I was just thinking out loud last night and hadn't actually searched for anything.

According to the website, this is the correct part...it doesn't state thatit's for an 8v though...

Vernier Adjustable Alloy Cam Gear, Mk4 2.0L
p/n 10.109.405K
 

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Discussion Starter · #15 ·
IanRiordan said:
An 89 2l? thats only a passat engine, check vw and porsche a/market as well as jap stuff for something that fits.
I know that it's VW material, but the 8v engines are very limited when it comes to aftermarket products. Add in that it runs Bosch CIS-E fuel injection and it just doesn't seem like it was a very popular engine.
 

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techinspector1 said:
Whenever I'm up against something like this, I try to take it to extremes to figure it out. My thinking is that even if you could move the head down several inches, as long as the crank and the cam pulley were phased to each other in the correct way, you'd be golden. Think of it like this: If you could lock the cam sprocket and the crank sprocket in position and build an idler pulley off to the side and take up all the slack, the pulleys would maintain their relationship with each other. Makes sense to me.
I was thinkin' about this and now realize that in order to maintain the relationship of the sprockets, you would have to use idlers on both sides to bow the chain into a diamond pattern, not that it makes any difference in the context of this thread.
 

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Lonestar said:
True, but the driving portion of the belt is not on the tensioner side, so in effect moving the cam gear closer to the crank will in effect shorten the belt, although more slack would be produced on the tensioner pulley side.
Excuse me. I don't want to turn this into some debate...

but when the head/cam gets closer to the crankshaft, (the belt is still the same length) the belt seems longer....so the cam gear rotation is behind, that is counter-clockwise from where it should be..... thus retarded.

The tensioner only takes up slack and maintains proper tension on the belt to keep it from jumping teeth.
 

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Discussion Starter · #18 ·
xntrik said:
Excuse me. I don't want to turn this into some debate...

but when the head/cam gets closer to the crankshaft, (the belt is still the same length) the belt seems longer....so the cam gear rotation is behind, that is counter-clockwise from where it should be..... thus retarded.

The tensioner only takes up slack and maintains proper tension on the belt to keep it from jumping teeth.
No debate, we're saying the same thing only in different ways.

When standing in front of the car looking at the engine, it rotates counter clockwise. The tensioner is on the left side, so if the head were to drop down, the drive side of the belt (right) would essentially get shorter and the cam sprocket would rotate clockwise to compensate therefore retarding the cam.

If, instead of a belt and tensioner, you used a normal timing chain configuration, you would need a shorter chain...that is what I was trying to say. By moving everything closer together, a shorter distance is created arround the pullies requiring the tensioner to have more slack to take up. Obviously, the belt is not going to get any shorter, but if enough slack was created that the tensioner could not compensate for then a shorter belt would be required.
 

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Discussion Starter · #19 ·
techinspector1 said:
Whenever I'm up against something like this, I try to take it to extremes to figure it out. My thinking is that even if you could move the head down several inches, as long as the crank and the cam pulley were phased to each other in the correct way, you'd be golden. Think of it like this: If you could lock the cam sprocket and the crank sprocket in position and build an idler pulley off to the side and take up all the slack, the pulleys would maintain their relationship with each other. Makes sense to me.
To keep the proper phasing I would have to remove enough material from the head/block to equal the spacing of the teeth on the belt...anything in between would not work.

Considering there is like 1/2" - 3/4" or so between the teeth, I don't think it would work...even taking into account that a little trig would be required to ascertain the correct amount to remove as the belt is on an angle to the line between the center of the crank and cam.
 

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Discussion Starter · #20 ·
techinspector1 said:
I was thinkin' about this and now realize that in order to maintain the relationship of the sprockets, you would have to use idlers on both sides to bow the chain into a diamond pattern, not that it makes any difference in the context of this thread.
Yes, that would work, although I am not about to go that far in depth on this car. The adjustable cam sprocket that was mentioned previously would be the way to go in this case.

The deal here is that I am kind of stuck with the car as I have way more into it then it will ever be worth (new engine, trans, etc...)

However, I do have the old engine on a stand and was just thinking about rebuilding it. I figure some head work would be a good place to start. I don't want to go crazy on it or anything, just give it a little more guts. The car drives fine with a top spedd of about 120 which is more than sufficient...it's just kind of a dog on acceleration.
 
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