[tamathumper]

And it's cheap.

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[ordy999]

Ok guys, message taken, I will check how much porsche do one for, I know sealey does one as well.



Thanks



Ordy

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[tamathumper]

Confusingly, the long ones (for manual transmission) are going for over $100 on eBay, when they're $65 on Pelican Parts.

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[flash]

i mentioned it because you are supposed to ALWAYS time the cams when doing the belts. it's a part of the procedure. check the workshop manual. all belts are not exactly the same length. any difference means the cam timing is off. that is why you have to reset it each and every belt change, assuming you want all of the performance available.

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[Cloud9...68]

[quote name='flash' timestamp='1365364262' post='141081']

i mentioned it because you are supposed to ALWAYS time the cams when doing the belts. it's a part of the procedure. check the workshop manual. all belts are not exactly the same length. any difference means the cam timing is off. that is why you have to reset it each and every belt change, assuming you want all of the performance available.

[/quote]



<img src="/forum/images/smilies/968/ohmy.png" class="smilie" alt="" />



Does anybody actually DO that?

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[flash]

lol - many don't. but, that's what separates the men form the boys, so to speak. it's right there in the workshop manual, but because it's a time consuming process, which also requires special tools, many people skip it. they figure "if nothing moved, the timing should be the same". they would be wrong. that's why porsche put the process in there, and specified the tools needed.



will the engine run without it? sure. you might even get lucky. you might not. will it hurt anything to be a little bit off? probably not.

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[Cloud9...68]

I see your point, although I didn't find anything in the manual that says that the cam timing needs to be set following replacement of the timing belt. The cam timing procedure immediately follows the cam belt replacement procedure in the manual, but I didn't see any statements linking the two, although I may have missed it, and things tend to be scattered in sometimes illogical places in the manual. Also, maybe my particular version doesn't mention it.



My concern would be that with all the pitfalls associated with the cam timing procedure, it seems that there's more risk of screwing it up than of leaving it alone. In addition to your discovery that you really need to pressurize the variocam with oil, how do you deal with the fact that this engine uses hydraulic lifters? It seems that to get it perfect, you'd have to fully warm up the car, then attack the procedure with a Formula 1 pit crew to finish the job before the lifters de-pressurized. I'm the farthest thing from an expert on the subject, but isn't the only true way to get the timing "perfect" to do it iteratively on a dyno, incrementally turning the camshaft along its adjustment grooves until you achieve your desired hp and torque response to rpm. But that would be a very expensive and time-consuming way to do it. I really need to read up on this stuff, as there is obviously a lot to it.

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[flash]

all true. you have to know what you are doing to get it truly right. the "safe" thing is not to screw with anything you don't have to. it just means you might leave power on the table. cam overlap is everything on these engines. degreeing that in is the key to power.



the issue with pressurizing with oil versus air is really only if you are using a new or dry part, as in the case of a rebuild. in a normal belt job, the oil is still in there, and air is fine.

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[Cloud9...68]

One of these days, when I get my head above water catching up on all the projects I've neglected these past two years as I was up to my neck in the 968 track car build (which still isn't done), I'm going to study up on the theory behind cam timing, its impact on overlap and the optimization of gas scavenging, and start a thread. I timed my cams following Sparky (Chris Jenning's) procedure as part of my rebuild before you did, so I wasn't aware of the need to use oil, which in my case would ideally have been the way to go, since my engine was bone dry. So, I'm sure my timing isn't perfect. But the engine revs smoothly, and feels strong, from the little I've driven it. But now that it's pressurized with oil, I need to go back one of these days and re-check it, using air. It would be nice if I could get a few hp back.

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[flash]

the best way to do it would be to use a degree wheel. hard to get one in there though if the engine is in place, hence the procedure they set up.

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[Cloud9...68]

Makes sense. I used a simple 360 degree protractor I picked up at Lowes that I attached to the crank, along with a marker I attached to one of the belt guide studs, to more accurately locate <acronym title='top dead center'>TDC</acronym> (I didn't like the idea of using a dial gauge touching the top of a piston to locate <acronym title='top dead center'>TDC</acronym>), which meant I had to turn the engine from the back using a handle I fabricated that I attached to the flywheel. But of course, I could only use this method with the engine out of the car, and I still used air instead of oil. Like I said, one of these days I'll start a new thread on this subject.



By the way, did your shop do anything to take into consideration the impact of the hydraulic lifters? Seems like this could be a fairly major factor, especially on a freshly-rebuilt engine whose lifters haven't been pressurized. Did they pressurize them in some way, or is this really not that big of a deal?

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[flash]

shouldn't matter. they don't change anything in the way of cam location. they only change how much the valves are opening.

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[Cloud9...68]

I see how the lifters woudn't impact anything if you're using a degree wheel, but if the engine is in the car, and you're consequently forced to use the deflection gauge method, wouldn't the degree to which the lifters are pressurized impact the reading on the deflection gauge, and thus potentially throw everything off?

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[flash]

why would it? the lifters are only pushing on the valves. they act in response to cam lobe, not the other way around. they don't change the cam positions. in fact, it might be easier to time the cams with the lifters deflated. there would be less resistance and would therefore be easier to move the cams around to set them.

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[Joes]

I agree, the lifters have bearing on cam timing. That is one job that I have not tackled, set it in the middle and let it go. I think that the Dyno method would be what I would try especially if there are any mods.

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[tamathumper]

Not sure how the lifters could have any bearing on cam timing. They are spring-loaded and aren't "connected" to anything, they are just pushed around by the cams, and assuming they are fully "pumped up" they don't change in dimension.

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[Cloud9...68]

As I think about it, I agree with you guys on the lifters not having any bearing on the cam timing. I was simplistically thinking that since the deflection gauge is placed on the lifter, its state of pressurization could impact the reading on the gauge. But since ithe degree of deflection of the part of the lifter that the deflection gauge's arm rests against is only impacted by the cam lobe acting on it, the degree to which it's pressurized shouldn't matter.



But to Joes' point, I have the same concern that my mods, particuarly the ceramic coated engine internals and the aftermarket cat back, could impact the flow dynamics. In particular, the fact that the exhaust gases should be hotter due to the ceramic coating (less of the heat transferred to the base metals, therefore more of it retained in the exhaust gases) will increase the gas velocity, and therefore impact (hopefully improve) the scavenging effect during the overlap. So I'm not convinced that the stock cam timing setting would even be optimum in my case. So, to get every last possible horsepower, I think I'd have to go the dyno route.

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[flash]

this is why there is variance. basically it adjusts the overlap. more overlap means more torque but less horsepower. less overlap is the reverse. all within limits of course

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[Lear35A]

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[Joes]

I'm sorry I don't know how that ended up like that. The lifters have NO bearing on cam timing. The procedure uses the lifter as a reference for where the cam lobe is positioned. Flash is right adjusting the cams moves the torque band (within reason). Adjusting the on the dyno doesn't involve removing the valve cover, it could be done relative quickly.

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