Bradster928

I have been operating under the assumtion that my 1983 928S, as it has 16V, is, therefore, not an interference enigine. This assumption has provided some comfort as I decide how quickily to tackle the timing belt. I have ordered the John Kelly book and Roger is pricing out a kit. I am currently pondering the PK tensioner versus a rebuild versus air pump or no air pump.

Anyway, I was just searching through a parts warehouse looking for a washer reservoir cap (cannot find one anywhere) and happened upon a timing belt. In the description it referenced "interference engine." I am assuming this is a typo or just a general description used for all 928s.

With that said, and since I no longer want to assume anything (ignorance is not bliss) is there a definitive answer to this question? One other clue, Roger has confirmed that I have the round toothed oriented timing belt, versus the square toothed belt. Apparently this conversion happened during the 1983 production year.

My car has only 29K since the dealer timing belt change (60K total), but it was performed in 1991. No doubt it needs changing, but I have been operating on the assumption that it was not urgent. I was planning to take a week off in April for the job and make it a DIY. This is my daily driver.

Thanks!

Bradster928

Jadz928

Non-interference.

Pull covers, inspect belt and tension. Fill tensioner with oil (do search, see WSM). Inspect gears, inspect water pump for seapage. Assess. Button up.

Taking it a step further, replace belt, inspect WP bearings, and replace WP gasket, check tensioner idler for free wheeling. Button up.

Bradster928

Jim,

That's certainly definitive.

As always, thanks!

Steve (Bradster928)

fraggle

Jim is knowledgeable.

pcar928fan

OB-Yoda has spoken! Or Jim do you prefer OB-Wan???

Of course an '83 is NOT, I repeat NOT and OB, it is an S! I love the thread that is currently active that says, I have an OB 'S' Spoiler... Oh, so you have an 'S' spoiler then! LOL!

ROG100

Well I am very much on the fence on this one. I have never seen any proof that the S engine is interference or not. Not questioning Jims knowledge at all but show me where it says "none interference".
I would rather err on the side of caution then assume everything is OK.
Just because we may believe it is not an interference engine do we throw caution to the wind and not follow the proper procedures. Everything should be done by the book regardless.

Nice OB = Old Body 8>) All my pre 87 cars are OB cars. Just a term not a definition. Nowhere did Porsche ever refer to cars as OB's.

Lizard928

I verified an 85 euro S was non interference when everyone said it was.
As well had a fellows 84 euro that broke a camshaft, no valve damage occurred.

Also verified that an 84 US with slightly hotter cams was non interference as well.

However this doesn't mean I would leave it long enough for a part to fail!

ROG100

Colin,
We are in agreement then.
Roger

Mike LaBranche

Right, Porsche never called them that... Herr GoFast Kempf did, and it stuck. 78, 79. That's pretty much it.

86'928S MeteorGrey

I questioned this for years. Then recently, I did the timing belt, wp, and pksnr... I didn't use a flywheel lock, and I purposely spun the cams and crank separately and slowly. No contact. I've been told.. (or maybe ive seen it here somewhere) that if you surface too much off your heads that you can make these 4.7 engines interference... That I don't know. But I'm 100% confident that my '84 4.7 is NOT interference. Also of note... When I pulled the old belt, it was off one tooth. When I got it reassembled in correct timing alignment, it sure seems to make quite a bit more power. I didn't think one tooth effected the 16v engines that much?

pcar928fan

So true Rog, but they DID refer to them as "S" cars... So why do we have to refer to an S car as an OB with "S" spoilers? Why not just "S"... Then you need to call the NON-S cars something... so probably 928 would be best, but since we are all lazy, we do "OB" instead! LOL!

BTW, I agree w/ you Rog on the NOT throwing caution to the wind... Better to get a new T-belt since you KNOW it needs to be done rather than get stranded in the middle of nowhere when it breaks...even if it does not toast the motor that will be a bad day!

brutus

If you have AAA long distance towing having a t-belt jump on the USA 16 valve really is no big deal unless you are too far from home. And just doing the belt is a few hours work for most. If you are concerned about the belt just drive very easy do not rev it and you can stretch the life of the belt.. (pun intended)
If it is your only driver and the belt lets go one "sick day" would be more than enough to put on a new belt to get it running, sure you could do more but with a belt it would be running. Get a replacement belt so you have it when needed or in April as you have planned. You can go back in easily when you have more time to address things like water pump, oil seals etc.

danglerb

My 85 Euro bent valves when the TB broke, I don't recall the condition of the reliefs in the pistons though.

I don't know why people worry so much about the belt, has a belt ever failed without something else being the cause?

brutus

Yes eventually some teeth shear off at the crank and it goes out of time.

NoVector

Dude - 1991 since the last belt change? Congrats! Unfortunately, I see some snapped WP bolts and new cam gears in your future.

I would go with the PK tensioner, but with a non-interference engine, no biggie. I would also leave the air pump just because there's no big difference in engine drag/HP loss. That said, it does look much cleaner with it and its plumbing removed. You'll have to change your belt, but if all your belts are from 1991, they would need replaced anyway. Good luck!