Another timing belt question (I searched)

[doublestuff]

Hey folks,

Yesterday I was finally at the "tensioning" phase of my timing belt/WP/FOES job on my early '85 944. Following Clark's procedure, it says to turn the engine through two full rotations, then turn it COUNTERCLOCKWISE 10 degrees, then to tension the belt. The problem I am having is that the counterclockwise rotation puts slack into the upper section of belt where the tension reading is supposed to be taken. Using Porsche Special Tool 9201, I couldn't get it to read even 1 (supposed to get it to 4), no matter how much I turned the eccentric. By turning the engine back clockwise enough to take out the slack, I was able to get the tension spot on.

I've emailed Clark, but does anyone know, is taking out the slack part of the procedure, or am I missing something else? I'm a weekend or two away from driving this thing again, and I don't want to find out I screwed up when I turn the key....

Thanks!

[Bradical]

A lot of people report issues with the cam timing mark slipping back a tooth or two and it's because you have to make an effort to remove as much slack from that point before tensioning as you can. It sounds like you need to re lock at TDC and try to push the cam belt a few teeth back on the cam pulley before you start tensioning.

[v2rocket_aka944]

I've never rotated backwards to get the belt right, but I don't use that belt tool either.

[thomasryan]

The balance tensioner can swing down or up to set the tension and the idler (non cogged pulley between the lower balance shaft cog and the water pump) should have clearance on both sides....it does not touch the balance belt.

I would have to look but the lower balance adjuster needs to swing up.

Edit...did you replace the other rollers or the seal drag is holding the balance cogs tight?

[Jim Chambers]

I saw a post contained within a thread in the last month or so which was a very clear diagram and procedure for belt install. The poster recommended a method which removed slack one section at a time. I thought I book marked it but did not. I have searched and cannot find it.
Can anyone here find it? I guess it could have been on Rennlist board if not here.

[thomasryan]

The 924.org picture gram?

[Jim Chambers]

That's it. Thanks Thomas. This might help doublestuff.

924Board.org :: View topic - How to set the timing and balance shaft belts on a 924S/944

[alfadoc]

Originally Posted by v2rocket_aka944

I've never rotated backwards to get the belt right, but I don't use that belt tool either.

+1
90 degree twist method here. That Krickit tool as an absurd waste of time.

[Jim Chambers]

alfadoc, more detail on 90 degree method please. I have the later spring tensioner. I was planning to purchase the arnnworx gauge.

[Bradical]

Originally Posted by alfadoc

+1
90 degree twist method here. That Krickit tool as an absurd waste of time.

I agree, but

[Bradical]

Originally Posted by Jim Chambers

alfadoc, more detail on 90 degree method please. I have the later spring tensioner. I was planning to purchase the arnnworx gauge.

He is referring to the calibrated thumb method, wherein you tension the cam belt to where it can only be twisted 90deg, and the balance belt to were it can only be twisted 180deg. If you are planning on using calibrated thumb, I would watch Van's belt video on YouTube, he gives a pretty detailed explaination on what a properly tensioned cam belt should feel like.

The arguement here is that belt tensioners were rolled out by the factory to make sure all of their technicians were properly calibrated more so than their belts if you know what I mean. In my opinion the belt tensioning gauge is one way of taking the responsibility of a broken timing belt off of the person who tensioned it.

[alfadoc]

Early cars I do the twist method. Spring loaded? Piece of cake. I do those the way we did the gazillion Fiats, Alfa V6s and Ferraris that passed through my shop. Loosen the tensioner so it comes to bear against the belt. Rotate engine two full revolutions (four times around for the crank). While the engine is at a point just past TDC, where the slack of the belt is fully eliminated by the tensionser, tighten everything up.

That's how I do it. You use the technique that feels safe for you. When I first got into 944 ownership, I decided I wasn't buying in to all the black magic of timing belt installation. That being said, I suffered a broken belt on my first 944. The previous owner had paid a Porsche shop to do it. 5 years and only 22K miles in, it stripped on startup one very cold Colorado winter morning.

[kevingross]

Double, if there is no tension possible in your belt after turning the crank back a bit and with the eccentric max'ed, I think there's something basic and wrong in how the belt or idlers / rollers / etc. are installed.

Are you sure you have the right cam belt for a 944? Is it routed properly, and are the idlers / pulleys, etc. all installed in the right place?

I've used the factory procedure and tool for many years, including turning the crank back, never seen quite this problem.

[doublestuff]

First, thanks everyone for all the info, especially those of you who actually seemed to read what I was asking....

I guess the question I'm trying to answer is - am I supposed to turn the engine counter-clockwise 10 degrees, do nothing else, and check the tension? Or am I supposed to turn the engine counter clockwise, then clockwise enough to take out the slack, then check the tension?

Kevingross, I checked the belts, rollers etc against the parts I removed, and I'm pretty confident that everything is right and routed correctly. Now that I have taken the slack out I have the correct tension, it's just the taking-the-slack-out part I'm unsure of.

Regarding the twist method, I can barely get enough fingers in the space allowed to twist more than 90 degrees, no matter how slack the belt is. If I didn't have the Porsche tool, I might go for it, but I'd really like to have numbers to work with rather than guessing.

Clark's site is highly recommended by users on this forum, and other procedures I've used have been great. I'm just trying to figure out if there is a bit of info missing from this one, or if I've made a mistake somewhere and need to start over. I'd LOVE to hear from someone who has followed the Clark's procedure and knows whether I should be taking the slack out of the belt after the 10 degree counter-clockwise rotation.

[Bradical]

The 90deg twist on the cam belt is done with the water pump guide plate removed, i dont know if maybe thats why its a tight fit for your fingers. That point is probably moot now

[doublestuff]

That makes sense, Bradical.

[Bradical]

Doublestuff... Watch Van's videos. He has a 3-parter and i garuntee that after seeing him explain everything you will feel alot more at ease...

http://youtu.be/nqc0mm-7ukY

Part 2 and 3 should pop up easily

[thomasryan]

Double....let's talk timing belt.

From what I have read,

You have everything installed and your tension is pretty close.

Turning the motor over by the crank pulley, you actually pull all the slack out of the longest run where you gauge tension by whatever method. When you turn the motor by hand, the valve train creates the resistance, so by turning the crank backwards 10*, you are moving the slack to where you are measuring. (Assuming the cam stays from the spring pressure.



Now the balance belt....

It can kinda free wheel on all the pulleys and cogs except for the crank cog.....which is a different dynamic than the timing belt. The slop or slack will actually end up on the outlet side (passenger) of the crank cog. Since everything is free to rotate, whatever tensioning measuring method you use will pull the slack to the longest run between the balance shaft cogs.

The idler that is in the triangle of the water pump pulley, crank and lower balance cog needs to be out of the way to take the measurement.
It serves a dual purpose;
1) to keep the slack in the belt coming off the crank from hopping a tooth on the lower
balance cog. (Van sets this gap with a credit card)
2) to dampen the vibration of the belt on the longest run between the two balance
cogs. (The belt should be a molecule away from this pulley/roller on the longest run)

If you have difficulties here, the balance tensioner needs to be rotated up AND keeping the same tension.

I had difficulty and realized this is where I made this mistake.

[thomasryan]

Its magic when it whines))lol

[doublestuff]

Originally Posted by thomasryan

so by turning the crank backwards 10*, you are moving the slack to where you are measuring.

So, again, the question I am (still) trying to get answered here is - am I SUPPOSED to induce this slack by turning the engine back 10 degrees, or am I supposed to take that slack out?!?!?!?