Is there any chace of no damage

flmont · 09-09-2010, 08:23 PM

I just bought a 86' 944 NA with a snaped timming belt,..I have heard that there is a slim chance that the head or pistons were'nt damaged due to the belt breaking at idel(sitting in traffic)...could that be possible,....Thanks Frank

porsche4life · porsche4life's Garage

There is a chance of no piston damage.... I would put money on toasted valves tho....

flmont · 09-09-2010, 09:08 PM

Crossing my fingers..Thanks

porsche4life · porsche4life's Garage

FWIW when my car crunched the valves before I go it the pistons were unharmed... Or at least thats what I was told... And it runs like a champ so I'm inclined to believe them.

Porsche-O-Phile · Porsche-O-Phile's Garage

There's a chance the Tooth Fairy might magically fix it for you too.

John_AZ · 09-10-2010, 04:26 AM

Quote:

Originally Posted by flmont

I just bought a 86' 944 NA with a snaped timming belt,..I have heard that there is a slim chance that the head or pistons were'nt damaged due to the belt breaking at idel(sitting in traffic)...could that be possible,....Thanks Frank

Hi Frank,

When the car is at idle the rpm is about 900-950. Enough to cause damage.
Usually 2 to 4 valves are bent, maybe no damage to the pistons.

The HG (Head Gasket) on a 25 year old 944 usually needs replacing at this point.

Get a cam/timing belt and try to get the timing marks aligned when you install it. You should feel resistance if the valves are bent.

If the PO did not keep up maintenance on the car, it is time to do the work.

GL
John

Porsche-O-Phile · Porsche-O-Phile's Garage

I would bet money you're buying new valves. I'd recommend checking the piston crowns very carefully. Same with the valve guides in the head - they're cheap to replace "while you're in there".

Most likely you can get away with keeping the pistons but I've also heard of a broken t-belt busting the valve and causing enormous damage to the piston/cylinder. You probably don't have that situation but until you open it up and look, who knows?

Assume the worst, hope for the best.

Absolute worst case you're looking for a new block (or rehoning), pistons, valves and a head. Most likely just valves.

FLYGEEZER · 09-10-2010, 07:31 AM

No damage ????? I would say you have two chances......slim & none. Sorry my friend.

Slam · 09-10-2010, 08:44 AM

Does Many944s still offer heads? He'd be a good source for a replacement.

flmont · 09-10-2010, 02:47 PM

Yea,.. the guy said it didnt make any bad sound just shut off ,...here's the thing if the valves move at a pre-determined distance,and the belt snap's then the cam wont turn to action the valves how do they hit the pistons.???? Thanks Frank

John_AZ · 09-10-2010, 03:18 PM

The 944 has an "interference" engine. The valves that end up "OPEN" when the belt snaps get slapped by the pistons and bend.

John

flmont · 09-13-2010, 07:19 PM

Ok, But why,..if the cam quits spinning. why would the valves still move,..???I know some engines are interference and some are not,..how would the valves get pushed into the pistons... Thanks Frank

Gordon Rankin · 02:02 AM

Ok.. I am going to take a stab at this..The cam is pushing the valves and moving in tune with the pistons... When the belt breaks, the pistons keep moving until they collide with the valves..Hence, instantaneous damage. Its all very, very quick..-

And yes, the 944 IS an interference engine,

Does this make any sense?

flmont · 09-14-2010, 06:59 AM

as usual I dont explain myself well enough,..I understand the collision part, I dont understand why the valve's go past there pre set distance,if they dont hit the pistons while the engine is running at any other time why do they hit when the belt snaps...the valves only move so far up and down,the belt breaks and they move farther into the pistons ?????? Thanks Frank

looneybin · 09-14-2010, 07:06 AM

the valves don't go past the "pre set distance" but when the belt snaps & the cam stops turning, some of the valves are in the open position.
When the piston comes up to TDC, the valves are still open & they collide, bending the valves

Slam · 09-14-2010, 07:21 AM

And a flywheel's job is to help crankshafts spin...

flmont · 09-14-2010, 07:33 AM

Ahh.....Out of time...I knew I was missing something....LOL Thanks FM

Gordon Rankin · 07:53 AM

Normally the closest the piston and the valve get is when there is combustion in the cylinder when they are in "sync". At this point the valves are "closed" or fully distended and the piston is extended to the max. But when the valves and the piston are out of "sync", the valve is fully extended and the piston is likewise fully extended. Sorry, but this is as simple as I can get it..And is just another way of explaining what Looneybin explained above.

Remember that it is called a timing belt for a reason, to "time" the explosion and exhaust of gases. If the "sync" is not timed, the piston wants to compress at the same time the valve wants to open or exhaust.

txhokie4life · txhokie4life's Garage

If you are willing to pull the heads yourself

you can order the parts here including head gasket
and have someone do the valve job.

Parts will cost you ~$400 and the valve job cost shouldn't be too bad.

1.5 to pull the heads, 3 hours to put them back on, taking your time and
letting the heads settle.

It's not that difficult to do.

Mike

John_AZ · 09-14-2010, 02:42 PM

I agree with Mike.

The "basic" head machine work will cost about $150-250 plus parts. If you need valve guides because yours are out of spec add about $10 per guide-part and install.
Call more than 1 machine shop. They want you to bring it in to make sure they can do it! This is dumb. It is a simple 3 angle head job and face machine work. Call more than one.

While you are waiting on the machine shop---usually a week---spend 8 hours getting the gasket material off the parts. Well, 6 to 10 hours should be OK.

Then there is a LONG list of WYAIT---while you are in there -----jobs. Yes many. $200 to $400 for parts.

But it is a fairly easy job and satisfying if you have the basic hand tools and follow Clarks information.

GL
John