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macBdog

hi gang.

I just changed my fuel filter, air filter, alternator belt and timing belt. I started the car back up and it took a while to crank which I figured was the fuel filter filling up. Started fine but I noticed a new high pitched noise to the engine sound. it also idled quite a bit slower than usual and as I listened, the idle speed was getting slower. The high pitched noise was also more prominent.

I only had it running for a few mins and was a little scared since I am a newbie to this kind of stuff. Could I have put too much tension on the timing belt? I read the "only just turn the belt 90 degrees on the long side" from the manual but I couldnt really decide where to leave it so I left it tighter than before....

thoughts? im a little freaked out...

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1979 931 with a 350 chev
1973 911E with EFI

Smoothie · Posted: Sun Sep 19, 2004 2:36 pm Post subject:

Yeah that instruction to turn the belt 90* isn't very accurate since not everyone has the same strength in their fingers. The belt will whine up a storm if it's too tight. You just need to loosen the belt, but loosen just enough to eliminate the whine.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

macBdog · Posted: Sun Sep 19, 2004 3:05 pm Post subject:

Thanks heaps for that, I have loosened it off quite a bit and the whine has gone. I still notice a high pitched noise so I think ill back it off just a bit more.

The idle speed problem tho seems to be persistant. Idles around 850 at startup and then the idle gets lower and lower till its sub 500 and about to stop the engine after a few minutes. What could I have bumped/knocked/buggered up?

Also since the timing belt cover is off, I noticed the timing belt is only 90% on the cam sprocket, it doesnt line up properly.... Is this normal?
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1979 931 with a 350 chev
1973 911E with EFI

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Did you check the tensioner pulley bearings, or replace the tensioner pulley when you replaced the timing belt?

Many people are under the mistaken idea that if the pulley spins super free, then it is still okay. In fact, when the pulley spins super free, then it will probably die soon, and should be replaced ASAP. The reason why is because the grease that used to lubricate the bearing is all gone. When this happens, the bearing will usually start to whine, before it fails completely.

A good tensioner pulley should feel like a new pulley. Rotated by hand, it will turn smoothly, but you can feel the friction from the grease inside.

While you were replacing the timing belt, did you take the time to check/set the valve clearances, and replace the plastic camshaft oil supply elbow?

I suspect that you idle problem is probably due to leaking vacuum lines, with the mixture and idle speed adjustments incorrectly set when the engine was cold, instead of when it was warmed up.

macBdog · Posted: Sun Sep 19, 2004 6:07 pm Post subject:

Thanks for the tips gohim, im a newbie jumping in the deep end so any advice is appreciated.

I did not replace the tensioner pully bearings... is it a hard job? is it possible to do with the engine in the car?

I didnt set the valve clearances either but im not sure this affects the idle speed.

I DID replace the air filter which means I pulled some vacuum lines which may be leaking, ive double checked that they are where they should be, anything after that im not sure.

Should I have re-set the mixture and idle speed adjustments post timing belt change? They were set fine before (ie the car idled fine) and I didnt know I had to change them.

I also mucked around a bit more with the timing belt tension setting.. backed it off heaps and found that the timing belt sat dead centre of the cam pulley which I was happy with... but it also made a birdlike squeeking sound and some of the writing got rubbed off the belt and there was a burnt rubber smell.. so that looking like too slack.

Now ive given it a smidgen of a tighten and there are no weird sounds and the belt has returned to its 90% on cam pulley position and the idle speed problem is still there.

GAH!
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1979 931 with a 350 chev
1973 911E with EFI

D Hook · Joined: 02 Nov 2002 Posts: 3158 Location: Omaha, NE

If you happened to jump one tooth on the belt, wouldn't that be enough to affect the idle speed, either speed it up or slow it down since the timing would be changed? I just finished installing a new idler pulley and I zip tied my belt to the cam sprocket in two places so it couldn't slip while it was so loose. BTW, the bearing Gohim speaks of are inside the idler pulley and the whole assembly gets replaced at once. It was cheap here in the states but the one I got as a replacement needs a special wrench for tightening the pulley, instead of just a spanner. Also, the original bolt was too long so had to get a shorter one. No big deal, just FYI.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

The tensioner pulley is a standard four cylinder watercooled VW engine part used on the 1.6L to 1.9L engines. You can get one from most anyplace that sells VW parts.

The tensioner that uses the pin spanner instead of a conventional wrench superceeded the orignal part close to fifteen years ago. Again, the pin spanner wrench needed to hold the newer type tenioner pulley is a standard VW tool used on the watercooled engines.

If the backside (smooth side) of the timing belt shows "burn" marks, it is too loose, and is beating itself to deth against something. The belt should be tightened immediately.

Replacing the tensioner may cure the problem with the timing belt not "tracking" true on the camshaft gear.

Lizard · Posted: Mon Sep 20, 2004 3:37 am Post subject:

I have seen tensioners of the wrench style, but with the grove in the center of it like the pin style tensioners.
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3 928s,

Kenodog · Joined: 25 Jun 2003 Posts: 2669 Location: Vancouver,B.C.

I got a new pulley,cost $20 or so,and found that a tool I have for working on my bicycle fits into the pin holes perfectly.It's made by a company called Park Tools and should be available at just about any bike store.And the best part is it only cost around $6 bucks.
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1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

macBdog · Posted: Mon Sep 20, 2004 7:29 am Post subject:

Ok I reckon ive got a good idea of what has gone wrong.

* When i changed the timing belt I couldnt understand the first step about rotating the large bolt on the idler pulley so the indicator mark on the cam cover was pointing at some mark on the cam pulley. So I changed the belt anyway.

* The new belt is not sitting in the same spot as the old - either a tooth advanced or retarded. So after the engine is warmed up the timing is out and thus the idle speed is waay too low and the engine doesnt stay running.

* My idler pulley needs replacing which is why the belt is not tracking centre on the cam pulley. Not a cause of the idle problem but needs doing anyway.

Would this scenario yield the results ive got? And if so..

* How do I make sure the timing belt is in the right spot? Should I have rotated the engine to TDC before doing it? What does that first step do/mean? How do I adjust my timing belt/and or timing to make it "right"?
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1979 931 with a 350 chev
1973 911E with EFI

macBdog · Posted: Mon Sep 20, 2004 1:37 pm Post subject:

After a chat with the local mech I now have an even better idea of what ive done wrong:

I didnt rotate the cam and engine to TDC before putting the new belt on. Thus I have stuffed up my timing nicely. So to rectify the situation Im gonna:

1. Take the alternator belt off for easy access. Take off the timing belt again and pretend I didnt bugger it up in the first place.

2. Rotate the engine using the large bolt on the oil pump so the engine is at TDC.

3. Replace the tensioner roller/idler pulley.

4. Replace the timing belt and put the alternator belt back on.

Sound good? Should I rotate the engine AFTER I take the timing belt off or before? Does it matter? What bolt do you use to turn the engine over? Any feedback would be great.. you guys have been legends so far.
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1979 931 with a 350 chev
1973 911E with EFI

Smoothie · Posted: Mon Sep 20, 2004 3:31 pm Post subject:

It's an interferance engine meaning the valves and pistons will collide if it's far enough out of time. You're apparently not that far off, so leave the belt on while you're setting it to tdc. There are 2 ways to do it - one is to have the car on a level surface, put it into a high gear and push the car forward or back while looking at the timing mark on the crank pulley to get you close to tdc, then refer to the mark on the flywheel to get it exact. The other way is to use a socket wrench on the crank pulley bolt and turn clockwise*. I prefer and always use the car-push technique.
Removing the spark plugs will allow easier-smoother turning of the engine, but it's not necessary.
Once it's at tdc, leave the transmission in gear and engage the parking brake to keep it there, then remove the belt (just from the cam sprocket), turn the camshaft sprocket to tdc** using the pointer on the valve cover and the correct mark on the back of the cam sprocket***.
Replace the tensioner roller, feed the belt around from the crankshaft sprocket, counterclockwise around the cam sprocket****, then to the right of the tensioner wheel, rotate the tensioner counter(anti)-clockwise***** to tension the belt, then tighten the tensioner nut (or bolt).

* - there's a relatively fragile locating pin between the crank pulley and crankshaft that's not completely impossible to break while turning the engine by the crank pulley bolt, so I avoid using it.

** - turn it in the direction that'll get it lined up in the shortest distance. It should only be off slightly. If you take the long way-'round, you'll collide valves with #1 and #4 pistons which are at tdc.

*** - the correct mark is on the back of the cam sprocket and located at a valley between two teeth. Some cam sprockets have another mark located right at one of the teeth - that would be the wrong one.

**** - you might find the marks don't line-up exactly at this point. I always rotate the cam 1/2 tooth clockwise (as viewed from the front) - then the marks come into closer alignment with the marks as the belt is tensioned.

***** - by rotating the tensioner counter-clockwise during tensioning, belt tension will be pushing on the tensioner clockwise - that'll tend to keep the nut/bolt tight rather than loosening it.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

macBdog · Posted: Mon Sep 20, 2004 9:15 pm Post subject:

Smoothie, you rule

And so does everyone else who helped me. Ill let yall know how it goes.
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1979 931 with a 350 chev
1973 911E with EFI

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

This thread <click> should give you what you need.
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'79 Eurospec 931

macBdog · Posted: Tue Sep 28, 2004 10:14 am Post subject:

Update: All fixed and running like a dream!!

The things that I did wrong were:

*Not having the cam and crank in unison when replacing the belt
*Not feeding the belt on CCW from the crank to the cam pulley
*Not finding the "sweet spot" in the tensioner roller tension where there was no whine and the belt was tracking centre of the cam pulley.

So thanks again to everyone. I get the car on the road this week!

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1979 931 with a 350 chev
1973 911E with EFI