Interesting timing failure...
 

Hi all,

I'm new to this board and hoping to utilize all the experience here. Just got an 87 944 - my first Porsche! So exciting and yet it doesn't run (...how I could afford it...)

Anyway PO said a timing belt failure. I figure it's not that bad of a fix. New head, etc.. Car is absolutely cherry except for that - I couldn't pass it up.

So I take off the front cover and the cam belt is loose but intact. Hmmm. Try turning the crank - balance belt/sprocket moves but the timing sprocket on the crank won't turn! Has anyone had this happen? I've read about plenty of timing belt failures but never because of the cam pulley. I'm assuming either the crankshaft key is shot or the sprocket is just totally spun out. Doesn't seem too catastrophic - am I right??

Oh yeah, and can I crack the crankshaft bolt with a breaker bar and a little spurt of the starter? Don't wanna buy a flywheel lock...

bent valves, almost for sure. sounds like the key went south. buy the flywheel lock. its cheap. arnnworx.com.

Belt lost tension but did not break. Valves hit head and locked up, now the cam can't move and therefore the loose belt just slips on the crank sprocket.

You are looking at a new head possibly, definitely new valves, possibly new pistons if they are gouged. Also check the cam over and lifters while you are in there.

It's not cheap but depending on how much you got the car for it can be a good deal and is always a learning experience.

Also please post your car's year and model in your signature for future reference with diagnosing problems.

Can't turn the cam by hand but the belt is still on it. When I turn the crankshaft I can see that the cam pulley is not moving, while the balance pulley is.

Best way on the head seems to be buying a rebuilt for 500. At least if I have a bunch of busted valves.

What sort of damage to the pistons would be "acceptable"? I would assume they are marked up at the very least. If this car needs lower end work that's gonna get way out of my budget and I'll probably just sell it for parts. What would gouges do in terms of performance?

Gouges in the pistons would marginally lower compression aswell as cause hot spots on the piston heads. More of a problem for a turbo car. It will surely leave an impression but not something to worry about.

Good to know. Apparently this happened while driving at slow in-town speeds, so hopefully the damage is minor. I'll take off the head and see what I can find.

Before taking off the head just try to time the engine and tension the belt correctly. This may just fix the problem. If the timing is out then you sometimes cannot move the crank even if everything is OK.

I was planning on trying to do this first, but I need to figure out the crankshaft cam pulley situation first. Is it possible to have no internal damage from this? Seems like the only way that could happen is if the cam stopped with the valves in the perfect spot - seems highly unlikely...

Anyway though I can move the crank - the pulley is slipping on the crankshaft and not turning. The other pulleys - AC, balance, PS all turn with the crank.

On another note, when this happens will the camshaft seize? Seems like it shouldn't.

I talked to a mechanic yesterday and he said if the timing belt has slack this can happen to the pulley. It will take up the slack quickly and "shock" the pulley if the motor is gunned, and then either the key will break or the key will destroy the pulley.

Well this does not look good, if the crankshaft moves freely it is likely the cam has seized because of bent valves. You can still remove the belt first and try to see if you can unstack the cam. You should be able to attempt to turn the cam without the belt from the cam pulley. Try do this a few times but do not apply excessive force and rotate the crank in a different location at each attempt. If the cam seem to get unstack you may attempt to fit the belt again. Your belt is likely damaged, teeth stripped out most likely, so you will need a new belt to try this.

The timing belt is completely separate than the balance shaft belt. If the teeth are stripped on the timing belt by the crank, the balance shafts will turn with no problems and still be in time. However, the timing belt will not turn because there are no teeth at the crank puley. This happens all the time and bent valves are a definite just depends on how many are bent. A rebuilt head can be bought for much less than $500. I normally get mine rebuilt for less than $150 so if you buy a used head for $100, the total is $250.

As I said before, when turning the crank the cam pulley, on the crank, does not turn. The belt teeth may be stripped too, but the pulley on the crank is not moving and therefore cannot turn the timing belt anyway.

I'm assuming you would pick up a head without bent valves to keep the cost low? I've heard that these heads can be straightened rather than milled. Know anything about that?

How is it possible you are turning the crankshaft but the crank pulley is not turning? When the crank turns, the crank pulley will turn along with the balance shaft gears at the crankshaft.

You should be able to buy a good used head for $100 with no bent valves. The machine shop will charge you about $150 to $175 to resurface, replace valve seals, do a valve job, pressure test it etc so your total cost should be around $250 to $275. If you can't find one, I have a rebuilt one fresh from the machine shop for $275.

Definitely have all pulleys turning except the cam pulley when I turn the crank. I'll be taking it apart soon to find out what's going on in there. A 944 mechanic said he's seen it before. Either the key broke or the sprocket is broken internally.

A have a line on a couple heads, but I may take you up on that offer. Would you do 300 shipped to Colorado?

Andy,

Where in Co. are you?

I'm up in Conifer (west of Denver off of 285).

I have an eary model head that I pulled off of a hydrolocked (cracked cylinder wall) engine. The block, other than the damned cracked wall, was in excellent shape so I don't have any reason to believe that that the head would be in need a valve job. I also have a set of pistons, rods, crank, cam tower, etc. out of the same engine. I also have good info on local outfits in Denver that could do the work on this for you if it needed a valve job.

I'm down in north Denver (62nd and Washington) every day helping a friend start up the local franchise of Big Box Storage, so if you're close by to that area and want to stop by the warehouse just let me know what day and I'll bring it down and let you look at it. I could also bring my mic's and dial indicator so we could check the stems and valve play to be sure as well as a straight edge to check for any warpage. If it's all good you should be able to bolt it right on although I would replace the stem seals as it's been stored dry for about 3 years now.

I'm thinking no more than $100 if everything checks out and then less if it's going to need work.

Wow d.a. that sounds awesome! I might have a line on a head with a pretty recent rebuild but I think I would rather deal with locals :) I get paid on August 31st so I wouldn't be able to get it before then. Maybe that weekend I could cruise down?

I'm in Fort Collins so that's close enough for me. Do you know if that head will work with my 87 block?

BTW I love this board!!

I'm showing the same part number for the cylinder head across the years of '83-'87. (part. no. 944-104-033-06). I think the only difference to the heads over the years is the actual sensors. Someone correct me if I'm wrong. You should be able to take these sensors off of yours and use them on any head during those years.

However, here's an intersting thought;

. . . before you start pulling the heads off fix the crank pulley problem first, then pull all the spark plugs and turn the crank to where the all the pistons are at the middle point of their travel in the cylinder bore.

Once you've done this, see if you can turn the cam one full revolution. If you have a small pen-light you should be able to look into each spark plug hole and see at least part of the intake and exhaust valves as they rise and fall when you turn the cam.

If that all looks good in each cylinder and you don't see any obvious bent valves then try to set your valve timing with the new crank pulley parts in place. (you might have to to turn the cam independent of the crank to keep valves and pistons from hitting.) Just set enough tension on the timing belt to keep it from slipping while turning the engine with the starter.

After you've done this, see if you get a full 2 rotations of the crank (1 full cam rotation of course) without feeling any mechanical interference. If that works and seems fine then squirt just a little oil into each cylinder and do a compression check. If the compression check works out then try adjusting the belts and seeing if it will run. Who knows, you might just get lucky.

Knowing what I know about this engine you'll still probably taking the heads off and fixing valves, but wouldn't it be a slap in the face to take them off first and find out that just by chance nothing bad happened in there!!!!!

BTW, when checking the valves with the with the pen-light you should be able to turn the crank a little and bring a set of pistons (#'s 1 & 4 or 2 & 3) high enough to see their tops to try and check for damages.

This is a good idea. I also considered that if I pull the cam housing off and all the valves are at equal height I may be okay. What's the best way to get the cylinders in position? Just pull the spark plugs and watch them? I don't want to hit valves...

Has anyone in the history of interference engines ever lost a timing belt or chain and not messed up the valves??

Another question - I'm looking at an 88 head for this car. My parts manual does not list a cylinder head for an 88 944. Anyone know if it will bolt right up?

d.a. autry - if my head won't work I would like to pick up your extra. Would you be able to PM me an email address or phone #?

I think I recall, maybe, one person on the board here not having any real damage.

My bent recently slipped the timing (3 teeth fell off due to oil contamination). I was doing 30mph at the time. I was hoping I'd be "that guy" that cheated an expensive repair bill.

Bent all 8 intake valves. (Gonna make a valve wind chime when I get around to it).

D.A.'s plan of attack sounds pretty solid. I got up to the "try adjusting the belts and see if it runs" portion before I eventually had to replace the head.

Best of luck.

EDIT - BTW, '87 944's had a fuel rail recall. Call a dealer with your VIN# to see if the work has been performed. I purchased my '87 in 2004 and it had not been done. Something about leaking gas and flaming engines if I remember right.

That's what I'd try to do (just look to see a piston coming up) once you remove the plugs you can pretty much feel any major mechanical interference as your rotating the crank by hand.

Look to see a piston coming up and then back off until you see that piston go down far enough to rotate the cam and actuate the valves.

Like I said, usually interference engines will suffer, but then someone, somewhere ends up winning the lottery eventually. You've got to fix the crankshaft pulley problem anyway, and it only takes a few quick checks after this is done to see if you might possibly be a winner.

As far as in the '88 head I don't know. I do know that parts lists show a different # for the '88 (944-104-033-08) and the '89's have a different # too (944-104-040-02).

I do know that since cylinder head # 944-104-303-7a (this # is per the service manual, don't know why there is a difference in the 3rd set of #'s) that one difference is how the spring seat is machined. The spring height was the same but I don't think the later ones needed shims when new.