924Board.org

[Eliza]

Hello all,

I need your collective wisdom.

My 1985 RoW 924 N/A was at my longstanding workshop last Friday for an oil change.

When I parked the car she was running spot-on. When I left late that evening after having a long chat with the shop owner ( well after closing ) I noticed my baby was running like crap. Idle speed was around 700 all of a sudden, no power at all, sluggish to accelerate. I carefully nursed her home, thinking maybe massive vac leak, but all was fine.

Luckily, I could take the car back to the workshop Saturday. Still running crappy, as confirmed by the workshop owner - I'm always VERY skittish about my baby, so I was glad he confirmed. We checked CO, all fine. Next thing he ckecked was valve timing, and found the flywheel one tooth off. Belt was tensioned properly, it's 10k km old, and looked good - no fraying, no missing teeth, no nothing. He reinstalled it, tensioned it, car running well as it did before the oil change.

I am not sure what to make of the belt being spot-on when I arrive and one tooth off when I leave that same day, without it needing touching. I am now wondering, is there any "natural" way this could have happened with a properly tensioned belt? If it HADN'T been properly tensioned, would skipping wait for 10k km to occur?

I think what I'm really asking is, is there a reason to suspect the mechanic who did the oil change did something else as well, or could this really just have happened?

I voiced my concern to the shop owner - and although I appreciate he won't lay blame at the mechanic without proof, I felt he tried to talk his way out of the responsibility I think he has as shop owner.

I'm a bit shaken up because I'd hate to have to find somewhere else to take my cars - which I still would if I were certain something got messed up without the mechanic being above board about it.

Sorry for the long rant - what would you do? I am lacking the technical knowledge needed to sanity-check my suspicion, but it is very much there.

Thanks in advance for any input you may want to share!

Take care,

Eliza
_________________
1985 924 NA RoW
1981 931 S2 RoW

[morghen]

What do you mean the flywheel one tooth off?
The flywheel is bolted to the crankshaft and cant be one tooth off.

Maybe you mean there is a one tooth difference between the crank pulley being at the mark and the cam pulley being at the mark?
This can happen naturally if you change from 4th to 2nd while at +5000RPM...the belt could jump a tooth if not tight and some scenario like above.
Also...the mark on the crank pulley...its a mark on the accessories pulley..that one has like a half a tooth tolerance when you assemble it.
being a NA i would not worry if the timing is 1 tooth off...but i'd check TDC with a camera and see if the cam lines up.

I doubt that the mechanic messed up your engine timing while doing the oil change. But he may have touched smth else by mistake...or a simple coincidence that some hoose cracked when he touched it by mistake...or a similar situation.

I'll give you an example: my car has an occasional hesitation when turning hard right....not all the time...but sometimes when turning right sharply, it will run on 3 cylinders only for a second or so...after that it goes back to normal.
This started happening after i took the head off for a clean and head gasket change.
In my case i suspect a bad spark plug lead going bad and sometimes sparking on the car body when turning sharply.
_________________
Supercharger and EFI kits
https://www.the924.com

[Eliza]

Thanks Morghen,

I did indeed mean that when set at TDC , the timing dot on the camshaft pulley was out of alignment with the pointer at the cam cover by one tooth. Sorry - my technical English letting me down

Anyways, I am right in assuming that unless the car was driven into the workshop at plus-5k ( or out, after the oil change ), the belt should have stayed where it was.

I have been driving this car almost daily for seven years. I hear you about incidental things ( whatever they are ) causing temporary changes in how the engine performs, but I suppose if something like that were the case here I would have seen the engine run so crappy before which I never have. And mind you, the one-way trip to the workshop is 50 km. The car ran crappy all the way back on Friday, and all the way there on Saturday.

I am not overly worried about the crappy running now I know what caused it, it's more the idea that from where I'm standing, I'd have expected to be told if during the oil change, anything happened. It's such a nagging feeling of, if something went wrong, why not simply own up to it?
_________________
1985 924 NA RoW
1981 931 S2 RoW

[morghen]

You sure the crappy running was because of that one tooth? I think one tooth may be noticeable...but not make the car run drastically worse.
Also, i think you have been running with the one tooth offset since you last had the belt changed.
_________________
Supercharger and EFI kits
https://www.the924.com

[safe]

They did something, the cam belt doesn't slip without reason. It might be from a miss shift during a joyride.

I wouldn't go back there for the next oil change...
_________________
/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

[TJC]

[Paul]

Timing belts are cheap, I always recommend replacing them anytime they are loosened or disturbed. I wonder if the belt in question has 1 or more damaged teeth.

I have always asked my customers and friends to turn around on the way home if they notice anything wrong upon leaving the shop.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[peterld]

Can't speak for NAs, but on turbos one tooth out is noticeable.

Have to agree with TJC.......big chance some foreign object caused the jumped tooth.

Time to find another repair shop, unfortunately.
_________________
80/81 932/8 ROW

[RC]

Check the alignment of the crank pulley / timing gear with #1 piston at TDC and "0" at the flywheel mark.
This timing gear is indexed to the crankshaft by only a 4mm dia pin which can sheer completely or deform along with the gear; especially so if the crank bolt is not torqued sufficiently, and a 50Km trip will permit thermal expansion to losen the bolt further.
_________________
World`s quickest 924 2L slushbox