968's, 928's Timing belts. same trouble?

Grog · 01-14-2006, 11:08 PM

Just woundering if the 968's and 928's have the same 30k timing belts replacement interval? or the same belt breaking trouble?

Steve

AaronM · 01-14-2006, 11:45 PM

IIRC the 968 has the same interval. Don't know about the 928, but would assume so. Both are definitely interferance designs and will suffer the same issues as a 944 if a belt does break.

That said, 944's really don't have problems with belts breaking. Provided that service is followed the belts are incredibly reliable. They are no less reliable than the timing belts used on millions of Honda interferance engines. The reason that more is said about them is because if the timing belt breaks on a Honda and it totals the car, it's not too much of a loss; Hondas are plentiful and it's easy to find another car just like it. The 944, on the other hand, is becoming rarer, especially in good condition, and is much more difficult to replace.

pokey · 01-15-2006, 03:45 AM

928s are non interference, iirc. But should have the same belt sched., but not the danger of bending valves if you go beyond...

CJFusco · CJFusco's Garage

Quote:

Originally posted by AaronM

That said, 944's really don't have problems with belts breaking. Provided that service is followed the belts are incredibly reliable. .

Yes and no. Both Wilk and I changed and retensioned our belts within the recommended interval, and both of us have had belt breaks.

WaA420 · 01-15-2006, 08:15 AM

Quote:

Originally posted by CJFusco
Yes and no. Both Wilk and I changed and retensioned our belts within the recommended interval, and both of us have had belt breaks.

Exactly, I've had a couple break for no reason within the mile range and the were correctly tentioned and retentioned with the P9201 tool. WTF?

SoCal Driver · SoCal Driver's Garage

Belts were too tight. Take the top section off of the front covers, drive around till the engine is hot (at op temp) and check how tight the belt is. Just might be a good idea to tension the timing belt on a hot engine and not a cold engine.

CJFusco · CJFusco's Garage

Well, that just goes to show you - the best way to ensure against problems occurring is correct maintenance and service... but that is just the best way to ensure against it, not to stop it completely. These things happen, just imagine how much more often they would happen if we DIDN'T replace and retension within recommended intervals.

Eldorado · 01-15-2006, 09:56 AM

exactly..
with moving parts, any number of variables can affect belt life. And sometimes it just boils down to the manufacture process - everyone spits out a bad product once in a while.

gadgit · 01-15-2006, 10:22 AM

SoCal, I'm sure you meant the other way round. Tension it when its cold not hot?

If you did it when its hot, it will get tighter when cold and more likely to break if been in a freezing garage all night when started!

Eh!

livewirevoodoo · livewirevoodoo's Garage

Quote:

Originally posted by gadgit
SoCal, I'm sure you meant the other way round. Tension it when its cold not hot?

If you did it when its hot, it will get tighter when cold and more likely to break if been in a freezing garage all night when started!

Eh!

Wouldnt it get a little looser when cold?

If i recall correctly from high school physics class, heat causes expansion and cold retraction.

Thats why you run the pickle jar under hot water so the metal cap expands and you can open it.

AaronM · 05:58 PM

Quote:

Originally posted by gadgit
SoCal, I'm sure you meant the other way round. Tension it when its cold not hot?

If you did it when its hot, it will get tighter when cold and more likely to break if been in a freezing garage all night when started!

Eh!

It's not the belt expanding, it's the engine. The pullies get farther apart when the engine is hot because the aluminum expands a good bit. So even though the belt itself expands a little when it heats up, the engine expands much more (relative to the belt) and therefore the belt is significantly tighter when the engine is hot than it is when the engine is cold.

gadgit · 01-16-2006, 03:38 AM

Got it!!

thanks for that>

gadgit.

legion · 01-16-2006, 05:03 AM

Quote:

Originally posted by pokey
928s are non interference, iirc. But should have the same belt sched., but not the danger of bending valves if you go beyond...

Some 928s are interference, some are not. It depends on the year and model (S3, GTS, etc.).

adrian jaye · 01-16-2006, 06:30 AM

944 s2 engine = 1/2 928 engine ergo, interferance

re: hot and cold.
OEM's and Indies check tension with engine cold
(at least in the UK they do)

AaronM · 01-16-2006, 10:34 AM

Quote:

Originally posted by adrian jaye
944 s2 engine = 1/2 928 engine ergo, interferance

Wrong. While the 944 engine is based on half the 928 engine, it is not exactly that. The 928 engine was, first of all, only 4.5 litres when the 944 engine first came out. 2.5 litres is more than half of 4.5 litres. Also, only a few parts are actually interchangeable between the engines and compression ratios differ between the two.