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Geometry and timing seems a little odd

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Calan

DSM Wiseman
7,251
362
Jan 16, 2007
OKC, Oklahoma
Brian (19Eclipse90) and I spent a while tinkering with my t-belt last night after replacing the head, and we noticed something a bit odd was happening.

Before dropping the head on, I was rotating the crank and checking things over, and noticed that when the pistons were at absolute top dead center, the notch on the crank plate was about 5* (1/2 tooth) past the pointer that is cast into the front case. I never noticed it when the motor was on the stand, but I never checked it that precisely either. With the pointer lined up exactly, the piston has just barely reached the top of the stroke, if that.

So anyway, I didn't think too much about it, and we installed and tensioned the belt. I used a straight edge to make sure the cams were dead on, and then locked them down with one of Jay White's cam gear locking tools. I worked from the cam gears going clockwise, and around the tensioner pulley last as usual. Once we FINALLY got the tensioner pulley in the right place (it was being a PITA for some reason), the tensioner is where it should be and passes all the usual tests (drill bit, grenade pin slips in and out,. etc).

Here's the kicker... no matter how many times we attempted to re-time it and play with belt tension, the crank sprocket always ends up at that 5* ATDC point when everything lines up and is "comfortable". Here is roughly what it looks like:

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When I try to go an extra tooth to correct for it, I end up with the crank BTDC, and the pointer looks like this:

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Trying to gain a tooth on the intake or exhaust cam gear just throws the cams out of time with each other, and doesn't help things at the crank.




So, I have two questions...

1. Considering only the short block, how come when the #1 piston is at true TDC (slightly after max travel but before any downward travel), the crank plate doesn't line up? Is it just a fact of life for the stroker geometry, and I've just never noticed it?

2. Once the motor is timed, which way will the crank sprocket try to rotate as you increase or decrease distance from the cam centerlines to the crank? At first my thought was that the crank was rotating slightly CW because I have decked the block and shaved the head, but... I am running a thicker HG now which should more than offset that; so I would think the crank would want to sit a little BTDC if anything.

Thoughts?
 
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Thinking outside the box here. Would it be possible to correct any differences with adjustable cam gears?

Aside from that I know different motors but when I did my t-belt I didn't match up exactly either. I would personnaly go with your first picture.

Since you machinead the head. If it does change the crank should sit a little ATDC to pick up the slack. How thick of a head gasket and how much did they shave off?
 
Thinking outside the box here. Would it be possible to correct any differences with adjustable cam gears?

Yeah. I have ACGs, and actually played with the exhaust cam a little to see what happened as far as the cam relaxing; but it shouldn't make any real difference until the motor is running. The outer ring of the gears with the alignment marks and the t-belt teeth will always be in the same place in relation to the crank, if you use the factory alignment procedure and have them locked in place. All your doing with the ACGs is changing the timing of the valve events internally in relation to the crank; not the positioning or tension of the t-belt. (You're also changing the ignition timing to some degree, if adjusting the intake gear). I know I can use the gears to make up for it in the end if necessary, but I'm really curious as to why the static t-belt alignment is like this in the first place.

When I put the motor together a couple of years ago, I degreed the cams to match the cam card specs. With the deck and head being slightly shaved (I forget how much, but it wasn't a lot) and a .051" MLS HG, I ended up with the intake at +3* and the exhaust -3* to get back to spec.

This time I'm using a .066" HG to lower the compression a tad and gain a bit of wiggle room on the valves. I had the head shaved .004", and lost maybe .001" by hand-lapping the block. So the net affect is that my cam CL to crank distance should have increased by .010" since the cams were first installed and degreed, if my math is correct.

All of this brings up another question... does anyone know which way I should go on the cam gears (and by how much) to compensate for the height that has been added (since they were last degreed)?
 
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I have the same problem on my 2.0l. It doesnt have the ability to line up right with the T. Mine is currently set like the 2md picture you posted. We thought mine was off due to the adjustable cam gears so we installed stock ones.
My car spools late and takes 1 1/2 sec to get boost back after shifting...could this be why?
 
How worn is the trigger plate? If the notch in it has excessive play it could also be inaccurate when the crank sprocket/bolt was put in.
 
I have the same problem on my 2.0l. It doesnt have the ability to line up right with the T. Mine is currently set like the 2md picture you posted. We thought mine was off due to the adjustable cam gears so we installed stock ones.
My car spools late and takes 1 1/2 sec to get boost back after shifting...could this be why?

Definitely could be. If you have it set like the second pic and it's anything like mine, then you are probably a tooth off. The valves are expecting TDC, but the piston isn't quite there yet.

How worn is the trigger plate? If the notch in it has excessive play it could also be inaccurate when the crank sprocket/bolt was put in.

Like new. Everything was checked and/or replaced 10k miles ago when I built the motor.
 
We did like you and tried to correct it bit it would allways be a little in front or behind....would it be better if I changed it back to look like the first pic?
 
We did like you and tried to correct it bit it would allways be a little in front or behind....would it be better if I changed it back to look like the first pic?

Hard to tell without seeing your setup in person. I know for a fact that when my crank plate is positioned like the first pic, I'm at true TDC. With the crank positioned like the second pic, I'm definitely a little before TDC.

I'm just not sure why the crank plate is off a little, as that has nothing to do with timing or the head. I think it has to be because of the stroker geometry, but I figured I would have noticed it before now.
 
Just as the cam shaft will move slightly, the crank will also wants to move too and here might be a reason why. As you turn the crank sprocket to line up with the timing mark, the crank will go into the compression mode. with the spark plugs in the motor, that compression in the cylinder wants to push back that pressure. That is what i think its happening now. As you turn the crank and once that crank sprocket is line up, the compression wants to drive that sprocket backwards. Just like the cam gears, you need to keep the crank sprocket still.

Pull all the spark plugs so the pistons don't have to fight that compression. If everything is in spec in accordance to the head and block being milled, the problem should not be in that aspect. of course, unless its milled too much and you don't know it(but you do). Try removing all four spark plugs and do the timing again. Hope this helps...
 
Just as the cam shaft will move slightly, the crank will also wants to move too and here might be a reason why. As you turn the crank sprocket to line up with the timing mark, the crank will go into the compression mode. with the spark plugs in the motor, that compression in the cylinder wants to push back that pressure. That is what i think its happening now. As you turn the crank and once that crank sprocket is line up, the compression wants to drive that sprocket backwards. Just like the cam gears, you need to keep the crank sprocket still.

Pull all the spark plugs so the pistons don't have to fight that compression. If everything is in spec in accordance to the head and block being milled, the problem should not be in that aspect. of course, unless its milled too much and you don't know it(but you do). Try removing all four spark plugs and do the timing again. Hope this helps...

I don't have plugs installed and I'm not fighting any cylinder pressure. The location of the crank shown in those pictures is with the crank turned CW to the point of all slack on the back side of the t-belt being taken out, and then setting the tension properly.

In neither case shown above does the crank want to move on it's own, since the cam gears are locked in place. If they weren't, then the cams would let the crank turn a little as the lobes relax against the valve spring pressure, but that is not the case here. (Yet another reason that Jay's timing tools are so useful! ;)).
 
"CW" are you referring to turning the crank counter clockwise after the timing is set?

Yeah, i am familiar with jay's timing accessories. That keep the cam gears stationary. with that in mind, sometimes the crank needs to be like the picture on the bottom before the timing belts goes on. once the timing is put on the cam sprocket, get a half inch and turn the sprocket clockwise to set the tension to line the sprocket back up. once that line up, then you can continue putting the belt on the last exhaust cam gear. you are initially letting the crank sprocket ride the timing belt to the point where it line up the mark.

i also heard that if you are using 2.4L block sometimes the timing is the issue(not lining up). But, i don't have the facts to back that up.
 
"CW" are you referring to turning the crank counter clockwise after the timing is set?

CW = clockwise
CCW = counter-clockwise

sometimes the crank needs to be like the picture on the bottom before the timing belts goes on. once the timing is put on the cam sprocket, get a half inch and turn the sprocket clockwise to set the tension to line the sprocket back up. once that line up, then you can continue putting the belt on the last exhaust cam gear. you are initially letting the crank sprocket ride the timing belt to the point where it line up the mark.

You may have misunderstood, or I might not have been as clear as I should have. :)

When both cam gears are perfectly aligned and locked in place so they can't move, and the t-belt is then installed...the crank can only be in one of the two places shown; not in between. This is irrelevant of the tensioner, exhaust cam relaxation, etc. It's simply a matter of where the teeth fall between the intake gear and the crank gear (the oil pump is also irrelevant since I don't have balance shafts).
 
I think this thread would have saved me a lot of headach and thousands of dollars if it was started 2 years ago...thats how long ive been having this issue. Thank you.
I will be sticking somthing in cylinder one to measure TDC when I get home.
 
Don't know how old you guys are, but when I was building the small block chevy"s, we had to use a degree wheel to find TDC. A lot of the crank keyways were cut slightly off. Wonder if that could be the problem here.
 
It's definitely got to be a geometry issue between the camshaft centerline and the crankshaft centerline.

I wonder if this ould work:

Match the cams straight up, and slide in the Jay Racing fixture. then loosen all of the adjusting nut on the gears. Then, rotate the crankshaft to line up to the timing mark, while allowing the cam sprocket to move independently of the cams. That should put everything at zero, even though the adjustment points on the cams gears won;t be at zero. Then, you can redegree from there.

I've never done thins, so someone correct me if I'm way off base.
 
Don't know how old you guys are, but when I was building the small block chevy"s, we had to use a degree wheel to find TDC. A lot of the crank keyways were cut slightly off. Wonder if that could be the problem here.

<<< Old enough to know about SB Chevys and the crappy nylon-coated timing gears that came out when GM first decided they would be a good idea for quieting the valve train noise. LOL

I don't think the crank keying or backing plate is an issue; I've never seen this on anything other than this 2.3l, and I think it's just a matter of inaccuracy at TDC due to the dwell time at the top of the stroke. I think the only reason it's an issue now is that I've changed my deck height enough that it's more obvious than it was before.

Match the cams straight up, and slide in the Jay Racing fixture. then loosen all of the adjusting nut on the gears. Then, rotate the crankshaft to line up to the timing mark, while allowing the cam sprocket to move independently of the cams.

Paul,

Are you saying to purposely misalign the cam gears, and then use the ACGs to try to get valve timing back in line once you remove the lock?

If you align the marks on the gears and lock them in place....rotating the inner gear inserts (cams) won't do anything as far as the t-belt alignment is concerned; you'll just be changing the valve timing internally. The outer rings with the marks and t-belt won't move once locked, and are still related to the crank sprocket in the same way.
 
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I had this same issue on my 2.3, mine wasn't nearly as much CW as your first picture but I would assume that to be due to the decking and change of geometry that was created by doing this. In my opinion, I would defiantly go with what you KNOW is TDC rather than what the timing marks are trying to tell you
 
I have done lots of heads on various vehicles. After getting them resurfaced usually I try and get a new thicker HG to make up for the material that was taken off. If i cant get the proper gasket and not to much material has been taken off ive just put them back together and that 5* or half a tooth wont affect performance, on a stock car anyways, if your sqeezing everything out then yes i can see it. Also make sure your belt tension is correct, if your over or under you can have the results your having.
 
I have done lots of heads on various vehicles. After getting them resurfaced usually I try and get a new thicker HG to make up for the material that was taken off. If i cant get the proper gasket and not to much material has been taken off ive just put them back together and that 5* or half a tooth wont affect performance, on a stock car anyways, if your sqeezing everything out then yes i can see it. Also make sure your belt tension is correct, if your over or under you can have the results your having.

Well my car made 450 whp on the dyno with a fp3052...then on the same dyno I made 450 with a 3082hta with bigger injectors... Thats a 52lb/min turbo and a 70lb/min turbo. It wass 450 at 5500 rpms then just syarts falling off...then the more boost we ran the less hp it made.

Edit: actually im on the right side of the timing mark so that should make me a full tooth (10 degrees) off correct?

Sorry for thread jacking.
 
Paul,

Are you saying to purposely misalign the cam gears, and then use the ACGs to try to get valve timing back in line once you remove the lock?

If you align the marks on the gears and lock them in place....rotating the inner gear inserts (cams) won't do anything as far as the t-belt alignment is concerned; you'll just be changing the valve timing internally. The outer rings with the marks and t-belt won't move once locked, and are still related to the crank sprocket in the same way.
Excuse my brain fart. For what I said to work, you've have to hold the cams up and together (somehow) while allowing the cam gear teeth to turn independently.

But yeah, your timing marks are pretty much null and void with the slightly modified geometry. As mentioned, you just got to go with what you know is TDC and adjust it out in the gears.

Edit: actually im on the right side of the timing mark so that should make me a full tooth (10 degrees) off correct?
1 tooth = 7.5 degrees
 
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Excuse my brain fart.

Well you've been away a while and are out of practice...so I think we can let it slide just this once. LOL


*******


Lets look at this from a simpler perspective. Maybe it will help some of the newer people understand a little better what I'm getting at. Hell, maybe it will help ME understand what I'm getting at, or someone can tell me I'm seriously confused. :D

Being the engineering type, I like to think of things in terms of degrees of freedom and constraints...so lets do that with the timing belt. Forget about ACG's and what's going on internally with the valves; lets assume stock gears and work on simply aligning the t-belt.

I like to think of the back half of the t-belt (intake gear, idler pulley, and oil pump) as being constrained. If the intake and exhaust gears are perfectly aligned and the intake gear is locked in place, nothing can move until you get past the crank sprocket; everything is determined by where the belt falls on the gears' teeth. Once you get past the crank, then you have the tensioner and exhaust gear which can move, allowing the belt tension to change between the crank and intake gear. (But, that is irrelevant to this discussion, as you'll see in a minute).

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In the pic above, the red shows what has been locked down, once the gears are aligned (purple line). Because of this, the green part of the belt is also locked down and shouldn't have any slack until you get past the crank, at which point the tensioner goes to work. Given that, the mark on the crank plate will end up where it will, based on how close the gear teeth are to being truly aligned with TDC. The tensioner and exhaust cam/gear have no effect on it and are out of the picture at this point.

In my case, rotating the crank one way or the other when it's closest to TDC and then slipping the constrained belt over it puts it in one of the two positions shown in my first post. The only possible thing that can change that is how high the head sits off the block. If the head goes higher, the crank will rotate CCW as the belt pulls upwards; if the head goes lower, the crank will rotate CW.

That is what bothers me. Even assuming this block and head were machined more than I know about, I don't know how I could possibly be lower than stock since I'm using a .066" thick HG. Assuming the stock gasket was .043" (and correct me if I'm wrong on that), I've gained .023" in deck height with the current gasket. Now if we subtract some machining over the years (the .005 I just did plus another .015" for good measure), I'm still at a higher deck height than stock...and .020" of machining would be quite a bit I think. :).

Still with me?

So if I'm higher than factory deck height, my crank mark at TDC should fall on the CCW side of the pointer, given what I said above about the way it should rotate. Even if I really am lower than factory deck height, I don't think it would be nearly as much as I'm seeing based on the CW crank rotation.

So when you add together the fact that my crank is already CW of where it should be at TDC for some reason (short block; no timing involved), plus what I explained above about the timing...I can't put together why my crank mark falls where it does. I'm almost exactly 1/2 tooth in between as far as the timing goes.

Clear as mud now? Am I totally losing my mind? LOL
 
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I have ran into this many times with the 4G63 engines I have put together over the years. The crank mark hardly ever lines up perfect, and it is always worse when the head and/or deck have been shaved. I have seen it on all the variations 2.0, 2.3, 2.1 and 2.4, both 6 and 7 bolt.

This is simply why it is best to degree your cams (if possible) after the head or deck has been surfaced. As stated above, on a stock car you usually don't notice it at all. If you are fully building your engine and going for high HP, then you should degree your cams and check for valve to piston clearance.

If you can't degree, and your not worried about valve clearance, then you could dyno tune it and adjust the cam gears for max power in the range you want.
 
Dave! (I knew he'd show up eventually. :p)

So which side of the crank mark do you usually end up on? CW or CCW of it? Also, any idea why I'm seeing true TDC when the crank mark is a bit CW of where it should be? (with the head off BTW).

Are you factoring in the block being decked? My block and head were both done.

Yes. Please see post #22, third paragraph under the pic.
 
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