GregBBRD

If you are suggesting that we should discuss this over on that forum, instead of here....not hardly. This would confuse those poor guys even more than they already are...

Even the "professional" that build these engines on a regular basis are clueless about this issue. Most all of these engines have the cam timing set wrong, if they follow the procedure in the WSM.

docmirror

We(968-ers) are in the process of having some of the cam timing metal blanks made for the correct profile to set the timing. The method in the WSM is torturously complex, in some ways vague, and counter-intuitive. However, I disagree that most people who use the procedure on that forum have their cam timing set wrong. It's a well known and discussed bugaboo, hence the current interest in making up the alum cam lobe profile blanks to take the guesswork out of the job.

I realize that the cam profile tool will only get the cams close, and not to within a few thousands of an inch as it were using the plunge method, but the variability won't be noticed by anyone except a racer, and they should know what they're doing inside.

GregBBRD

"Cam" reference tools are a complete waste of time, effort, and money.....because the intake cam can move! And I've yet to see a 968 in which someone has worked in the "cam area" that has the cam timing correct. 100% of the ones that I've checked are incorrect! 100%!

The problem is because the WSM has everyone setting the cam timing off of the intake lobe which has the "potential" to move around 16 degrees, because of the variable cam timing. They tension the chain with air pressure, which might work great when the tensioner is new, but simply doesn't work, once the tensioner has a bit of wear. If the tensioner "dips' when tuning the engine over, the cam timing will be off 6-8 degrees....every single time.

In the past, when I had to do these engines, I set-up a pressure pot and fed the tensioner a supply of oil at the proper pressure, to keep the tensioner "solid" and no allow it to "dip". This requires the attachment of a degree wheel and locating TDC, then the attachment of a couple of dial indicators. Chris Cervelli (genius) and I discussed this problem, at length, before he was about to work on his first 968 engine. I pointed out that the "procedure" in the WSM simply didn't work and told him what I had been doing.

Chris (again, being a genius) studied the problem and came up with the "ultimate" solution.

The "clue" is in post #13. No degree wheel, nothing special required. Install the cams with the proper number of links between the intake cam and the exhaust cam. Then proceed to set the cam timing off of the exhaust cam (which doesn't vary) and conveniently closes 1 degree away from TDC (at 1mm of lift.)

If the exhaust cam is set correctly, the intake cam must also be correct, as long as the chain is installed correctly. Completely eliminates "messing" around with the variable intake cam.

Stupid easy. Nothing required but a dial indicator on the exhaust cam that can measure 1mm of lift.

Done.

docmirror

Since the "cam" reference tool has a profile for the exhaust cam, and there is only one tooth that will correspond to the correct intake profile, my take is that if I put the exhaust cam in the profile of the tool, and set the crank to TDC - as long as the intake is in the profile of the gauge, and the exhaust is lined up snug, that should be just about that. I already said it won't be as tight as the plunge method, it'll be fine for everyone but the fastest.

I'm guessing the ones you get in your shop come from some of those mouth-breathing "those guys" over on the 968 board. Bunch a looooooooosers.

Done.

GregBBRD

Didn't say they were losers....or imply that.

I did say (or tried to say) that there is a lot of confusion about the 968 engine and I didn't want to add to that confusion.

You know that I'm trying to help people, here, right?

When I first started playing around with the cam timing and saw the tensioner "dip", I figured that shouldn't happen...or if it did, Porsche certainly had taken into account that movement. Called the two "leading" 968 mechanics/builders in the country and asked them about this. They said that the tensioner always "dips" when setting the cam timing and to just ignore it. "Set it like the WSM tells you to do and forget it."

Again, if the tensioner "dips" while trying to rotate the engine, while setting the cam timing, the cam timing is going to be off 6-8 degrees.

My conclusion was that if the two "leading" 968 mechanics/builders don't recognize the problem, not many of the "home guys" are going to get it, either....

Herman K

I started this thread to be informative about other possible uses for the Porken 32V tool and to get reactions related to past experiences by others and hear about any knew development.

I think it's un-called for to label others or call them losers on this thread.

docmirror

Since I'm one of those other guys, I'm referring to myself. I think Greg is spreading some incorrect information and his reference to the guys on the other board didn't sit well with me, as if we 968 owners can't figure out cam timing.

Have mistakes ever been made when setting the cam timing? Sure, the factory plunge method almost assures it. I gave a simple, quick, easy and moderately reliable method to get it right and was pooh-poohed.

Now, I'll follow up one more time. If everyone would turn to page 15-9 of the 968 WSM printing IV, 1992 edition. Cut out the shop-made profile tool(1:1). Use as template to make a wood, or aluminum profile. Install cams and tensioner. Set profile tool on the top of the head, with the "A" over the exhaust cam lobe, and snug it to the shape of the profile. Install the belt, rollers, gear and tighten the cam bolt while maintaining the lobe against the profile tool. Release the tensioner, and rotate the engine two times by hand. Recheck using the profile tool. Adjust exhaust cam to gear as needed to maintain the lobe in the profile tool. Recheck as needed.

Have a nice day. Do not worry about the intake cam, it will adjust when oil pressure and the variocam operate. All you need to do with the intake cam is have it on the right tooth of the cam chain sprocket to fit in the profile tool.

Cloud9...68

Greg,

Another 968 owner here who set his cam timing using the WSM method, so I find your insights and experience very interesting, to say the least. Could you please fill in the details about exactly how you recommend setting the cam timing off the exhaust cam, step by step? I'm very interested to hear how your recommended method compares to the one in the WSM. Thanks very much.

Herman K

Without the name calling your continued comments are appreciated and respected.

Thanks

MB968

Well, you can probably guess from my sig that I'm a 968er. So, as someone who worked professionally in a high precision world (our tightest tolerance were 1/2 a micron, yeah very difficult to measure, but it can be done) I appreciate Greg's comments for the inaccuracy issues that stem from using the intake cam albeit via the chain and tensioner. And yet since I'm not trying to win races, I appreciate the easy of using a profile template as mentioned by doc.

But, here is my twist on the thought process going on here. Is is possible that Porsche wanted us to use the intake cam/valve because the power of the engine is a lot more sensitive to the proper setting of the intake, and let the exhaust fall where it may??

GregBBRD

Are you serious? You need to get a little better grip. Really, you do.

I'm just trying to help Herman, here, not trying to "spread incorrect information".....[COLOR="Blue"]I'm actually trying to do just the opposite.[/COLOR]

It's a free world with lots of people doing different things. You can set your own cam timing with a yardstick and an axe....I could care less.

To review:

1. Herman is working on Joe's new 968. He's never messed with cam timing on a 968 and only has the WSM to go by.

2. I found that the method for setting cam timing, in the WSM, doesn't work, once the tensioner has wear on it. The "air method" doesn't hold the tensioner solid, once there is wear in the tensioner. The tensioner will "dip" when the engine is rotated. The cam timing will be off 6-8 degrees.

3. I found that every engine that I've touched that has had the cams "removed or played with" have them incorrectly set.....because people use the method in the WSM. 100% of them!

4. I called the "leading" 968 engine builders and found out that they, too are setting the cam timing according to the book and ignoring what happens when the tensioner dips.

5. I found two entirely different methods of setting the cam timing accurately and easily. I'm simply offering these methods as an alternative method.

6. I see very little reason to argue or call people names about his subject. I'm HARDLY trying to spread incorrect information....I'm trying to show that people might be using incorrect information. I'm just trying to help.

gb

GregBBRD

Are you serious? You need to get a little better grip. Really, you do.

I'm just trying to help Herman, here, not trying to "spread incorrect information".....I'm actually trying to do just the opposite!

It's a free world with lots of people doing different things. You can set your own cam timing with a yardstick and an axe....I could care less.

To review:

1. Herman is working on Joe's new 968. He's never messed with cam timing on a 968 and only has the WSM to go by.

2. I found that the method for setting cam timing, in the WSM, doesn't work, once the tensioner has wear on it. The "air method" doesn't hold the tensioner solid, once there is wear in the tensioner. The tensioner will "dip" when the engine is rotated. The cam timing will be off 6-8 degrees.

3. I found that every engine that I've touched that has had the cams "removed or played with" have them incorrectly set.....because people use the method in the WSM. 100% of them!

4. I called the "leading" 968 engine builders and found out that they, too are setting the cam timing according to the book and ignoring what happens when the tensioner dips.

5. I found two entirely different methods of setting the cam timing accurately and easily. I'm simply offering these methods as an alternative method.

6. I see very little reason to argue or call people names about his subject. I'm certainly not trying to spread incorrect information....I'm trying to show that people might be using incorrect information.

I'm just trying to help people with my own experience. Try to keep in mind that all I do is work on older Porsches....and might see a little bit more of them with problems than you do....

gb

FRporscheman

That is exactly how I've done my 968s (always after putting in a new chain to eliminate error from stretch). I recently was loaned the factory tool so I want to try resetting one of my engines, with a before/after comparison to see the difference in methods.

BTW, that cam "reference tool" is not for fine tuning of timing. It's just to make sure your cams aren't installed wrong (off by 1 or more teeth).

I'm a 968 guy all the way, but I've been compelled to stay out of that forum for a while now.

Cloud9...68

Could you please clarify exactly how you timed your cams? And what do you mean by the "factory tool"? Thanks.

FRporscheman

Search the archives
https://rennlist.com/forums/5314215-post4.html
After 5 years, the only thing I've changed is to use dial indicators instead of eyeballing it. If you're happy being within 1 degree, you can eyeball it. Pro tip: get the exhaust valves to JUST have closed, and put the crank at 1 degree BTDC by putting it 0.0067mm (0.2638 thousandths inch) lower than TDC (before, not after). My formula for finding that:
0.5*stroke*(cos(angle)-1)

I was loaned the factory tool for pressurizing the variocam unit and using 2 dial indicators to set the intake cam timing, as per the Factory Workshop Manual. I have very little faith in it, but I've never tried it, and I won't knock it 'till I try it. But I'm already sure that the method of setting the timing via the exhaust cam works better.