[Cloud9...68]

Same with mine - the balance shafts should definitely rotate very freely in their bearings. Somehow I suspect I'm not understanding what you're describing, though. Would you mind posting a picture of what is tight?

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[speedysprocket]

The one piece bearing is pressed into the balance shaft end housing. Try to insert the balance shaft into that bearing, and it goes it fine till the last 1/8", then is very tight. I can still turn it by hand, but just doesn't seem right.

On a lighter note, got the crank and scraper all bolted in…!

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[MB968]

Edit: Wrote the post below before your post above was up. Rather than rewrite, here are a few added comments. If it is only the last 1/8 inch, and as you describe, my guess is that you mushroomed the end pressing it in. I would use a metal scraper (assuming the bearing mat'l is soft) to remove some mat'l from that last 1/8". I don't like using sand paper, as the grit is quite abrasive and could get into small crevies and may be difficult to clean completely. Just remove it very slowly until you get the required fit. Loosing that small amount of bearing shouldn't be an issue. I don't recall any history of these bearings wearing out quickly.



Edit #2: Don't be too concerned if the finish of the scraped bearing isn't as good as you'd like it to be. Decades ago, when we used to hand scrape Babbitt bearings we didn't want too smooth of a finish (for other reasons). The divits can actually serve as small hydrodynamic bearings which can add to the "lift" of the bearing.



Also, could you post a picture of the inside of the sleeve. I'd like to see how the oil gets in and out of the bearing. Want to make sure my suggested fix won't compromise the oil pressure in the bearing.

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As I recall, the bearing is just a sleeve bearing that gets oil pressure to act as a hydrostatic fluid bearing for the bal. shaft. I'm fairly familiar with sleeve/fluid bearings as they weren't uncommon on our machinery. When you pressed the bearing into the housing, is it possible that you deformed one end of it. If this is the case, and if it goes in one end with no issues, and it is just the opposite end where it is tight, you may be able to save the sleeve.



Can you tell what type of material the sleeve bearing surface is made from. If it is a soft mat'l like main or rod bearings it should be easy to remove the excess mat'l/lip at the one end and you should be OK. But, this is only if you can clean up the lip that was caused by the install process without messing up the rest of the sleeve. If it is much more than this small amount of area that needs to be cleaned up for a sliding fit, I would press out that sleeve and put in a new one.



As others have said, the housing should definitely be a loose fit on the bal. shaft. Don't use it if it won't slide in/spin freely, as it could lead to a much bigger disaster.

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[speedysprocket]

I did use a red scotch pad a little on it and I was putting polish on that part of the bearing, and using the balance shaft to work it in. I may try more of that, or just another new bearing.

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[speedysprocket]

Well that was a bad balance shaft bearing. Finally got it almost all together! Timed the cams last night. Had to read the manual a couple times and have the engine in front of me to finally understand it but I think it came out right on! Learned a lot putting this together; if I ever have to do it again, it should be a lot quicker...

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[flash]

one of the hardest parts is pressurizing the variocam (which must be done to set the cam timing) and having it be right. a dry or worn variocam valve leaks and throws the cam timing off. the other issue is getting bot dial indicators to stay put during full rotations. they love to dance around, and then you have to start all over.

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[speedysprocket]

I made an adapter to pressurize the adjuster. The adjuster needed a little help getting pulled up while pressurized, but I'm guessing the oil will act better on it that air, and with the way the cams rotate, the exhaust cam should want to pull the intake cam on the bottom, allowing the top pad to move up more easily. Once it was extended, it stayed there, then returned when the air was shut off.

And I didn't use a dial indicator for number 4 <acronym title='top dead center'>TDC</acronym> in addition to the lifter gage. I found <acronym title='top dead center'>TDC</acronym> prior to putting the head on and marked the crank.

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[flash]

yeah - the key is to be able to read both gauges at the same time, and set the cams as they ramp. they are very touchy, and it's amazing to see how very little movement changes the readings a lot. also, you have to roll the engine around a couple of times, and watch the gauge each rotation. you can't do that without a second gauge.



i would go back and do it again.



heck, with the engine out, i would use a degree wheel. they couldn't figure out how to do that with the engine in the car, hence the dual gauges.

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[speedysprocket]

So what's the point of the second gauge if I found and marked <acronym title='top dead center'>TDC</acronym> prior? Rotate the engine until intake valve one has .38mm or .015" or lift, loosen the cam gear, continue to rotate engine until piston four is at firing <acronym title='top dead center'>TDC</acronym>, then lock cam gear. That's it in a nutshell, right? <acronym title='top dead center'>TDC</acronym> range on the gauge is like 7-10 degrees of crank rotation anyways, that why I found where it starts and ends, then placed my reference mark between the two for <acronym title='top dead center'>TDC</acronym>.

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[flash]

the TDC mark is not true TDC. it's a reference point, but the gauge is how you tell what TDC really is. common mistake. again, you have to rotate the engine at least a couple of times to check your setting too.



as an example of how off the marks are, you will never get all of the gear and pulley marks to line up when you do the belts. i have yet to see one close. there is always one that is about a half tooth off.



getting this wrong can easily mean a 10hp difference. cam timing is everything on this car. it's not like the 944. the engine will run, but won't necessarily put out everything it has to offer. the upside is that depending on which way you swing the cam overlap, you can play with where torque and horsepower peaks are.



even the variocam can be a problem. when i rebuilt mine, the dry valve resulted in a 13 degree change at the exhaust cam. we had to pressurize it with oil to get it right

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[speedysprocket]

So the tensioner is rebuildable?

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[flash]

no idea. i am talking about the variocam valve, not the timing belt tensioner. we were able to seal things up with oil and pressurize the valve fully. with air only it leaked and would not fully activate. basically it's like an automatic transmission valve in how it operates.

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[speedysprocket]

Yes, I meant the chain tensioner, or vario cam valve. I put a brand new belt tensioner on the engine.

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[flash]

cool - yeah - it really shone a light on the failings of the procedure. it presumes that you either have a valve with oil in it, or a brand new one, and are not putting a freshly cleaned used valve in there. it needs extremely tight clearances internally in order to seal up and hold full pressure. like i said, the difference was about 13 degrees. that's huge.



the other reason you need the dial indicator is that the needle "floats" as you ramp up and over TDC (which you noticed). for that reason alone, the timing marks are essentially useless. if you have a degree wheel, that's one thing, but the marks are not dead on, regardless of the term TDC. since you have to rotate the engine around, you lose TDC without a dial indicator or degree wheel to tell you that you are back there again.



pain in the butt, and a lot of shops skip the cam timing. like i said though, it will run, but if you want everything out of the engine, you have to do it right.

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[speedysprocket]

Not sure if it was clear how I did <acronym title='top dead center'>TDC</acronym>. I made my own marks. I used the balance belt gear on the crank and the metal guard rail to make true <acronym title='top dead center'>TDC</acronym> marks. Those are what I lined up for the .39mm lift. The cam gear was also very close to what looks like marks from the original factory setting. And as far as the varior cam actuation, I applied pressure and the bottom immediately pulled up. I helped the top move up to what felt like fully extended and watched the intake cam advance. According to what I read in the manual and actually doing it, I am confident in what I did. Not trying to say you're wrong, for lack of better words, but I think we're just not fully understanding what we're each saying.

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[flash]

quite possible there is a communication issue. it happens.



what i do know is that my builder, who is arguably one of the best in the country, discovered the issue, discussed it with the 2 leading 968 engine "experts", and they both had no idea this issue existed. when it was pointed out to them, they agreed that it was a problem, and that the book method is not perfect. they also agreed that there was no way to nail it without at least 2 indicators.



i suppose if you used an indicator to first determine TDC on the exhaust cam, mark it, and then went in and set .039 on the intake cam, you might get it once. the problem would then be verifying it after rotating the engine 720 degrees, which must be done. since you can't move the indicator off the lifter, you still don't have a real reading on the other side, so you still aren't sure.



again, had we not have put a degree wheel on the cam, we never would have found the problem. but, since all uber high end builders use a degree wheel, so as to exactly place the intake cam relative to the exhaust cam, it popped up right away. we had to use the indicators though to make sure that we had TDC for the degree wheel, and then again to verify cam overlap.



the problem is that there is no room for a degree wheel with the engine in the car, which is why porsche specced the 2 indicator method. what they failed to do was give instructions about the variocam valve.



the other issue is with the variocam valve. i think your method is suspect. there is a very specific amount of excursion of the valve for proper operation. it is not fully extended. that's why the pressure method is used, and exactly why a used dry valve doesn't work. the system waits until a certain amount of oil pressure is there, which then allows activation of the valve, dependent on rpm point, which then rotates the cam. it doesn't move a little with less pressure. it's all or nothing. pulling it up manually could easily move the cam more than it is supposed to.



there is a thread here with diagrams on how the variocam works

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[KRAG50]

One way or the other the cam sprocket is tied to the crank with a belt, I guarantee a bit of slop, maybe only a few thousands as the teeth compress into the steel pockets, as you rotate the crank through to the beginning of the intake stoke the rotation minimizes any potential take up. Also if you set <acronym title='top dead center'>TDC</acronym> marks from the number four position, relaxed, with the head off, there could be a little variation between number four wrist pin etc, etc, and number one where you are actually going to take the measurement.

Last the rotation of the cam vario chain wants to cause the pistons of the vario mechanism to collapse, pressurized oil resists this much better than air, even without air leakage.

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[flash]

given how old the car is, the design was way ahead of its time. it's touchy and a bit clumsy to set, but it works great when done right.

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[mbardeen]

I'll be retiming my cams soon-ish (February time frame), so I'm interested in how you made your adaptor, Speedy. I also wonder if I'll need to worry about the oil method. My variocam valve will not be rebuilt, nor be out of the car for a long time.



My understanding is that using air should work well enough, correct?

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[flash]

that seems to be the case. the idea is to form a hydraulic seal. once that happens, then it moves like it should, and settings can be made.

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