DaveK

That's a good point - because apart from the noise, John said it ran fine (I think) - which it surely couldn't have done if the pin had dropped out and the cam wasn't turning.

John Boggiano

Absolutely right, Dave.

That was WHY I drove it home. Naturally, I didn't use a lot of throttle but, from what I could tell, it all felt perfectly normal. Either that, or I must be totally mechanically insensitive...

Indycam

Drives over big bump , plastic thing jumps into chain , cam timing gets messed up ,
pistons bend valves , drives home and parks car , then the pin gets stressed out and takes a hike ?

I don't know but I do not think the pin is a drive pin . I think the bolt and washer clamp the cam sprocket to the cam and the pin sets the timing . Is it possible that the pin was never in place ?

John Boggiano

That's exactly what I was just wondering...

Jeff Curtis

If that pin falls out or otherwise gets sheared in half, etc. it's possible for the engine to keep trucking along as the bolt actually tightens the cam sprocket in place. Now the pin does ensure that the sprocket will not change locations in relative to the camshaft, but it's still possible for the engine to run properly without the pin, although not adviseable.

My guess is that the pin was missing for awhile, be it a day or a week...or a month for that matter...and sudden jolts, acceleration or deceleration re-oriented the cam sprocket position, changing the timing for that cam...the cam could've moved just ONCE and would cause damage to those three valves...tolerances are fairly tight in a flat six in regards to valve to piston clearance, but there is some "wiggle-room".

I can post more pics relative to my explanation here soon, as I currently have my engine disassembled for a reseal.

DaveK

I think it's hard to believe that the pin was never there. At slow speeds, I'd believe the bolt / washer would keep the sprocket clamped to the camshaft - but at 6500rpm I'm sure it would have let go before now. (I'm assuming John doesn't drive like a 75 year old grandmother).

Jeff's explanation sounds pretty good.

Atgani

Davek, the 993 uses precisely the method you describe to secure the drive gear to the cam, ie no dowel. The only difference was the 993 used a concave/convex ? washer to apply more clamping force onto the gear( in place of the woodruff key) When it was found this method was causing cam timing slip on the 993 Rs engines they reverted back to the earlier 964 type vernier setup................. For the "cooking" 993 engines a special finish was applied to the clamping washer to give it a non slip effect.
What we really need to know John, is whether or not the pin is still intact.

DaveK

Interesting.

Of course, this means that if I'd been working for Porsche when they were working on the 993 engine I would have said "that won't work" - and I'd have been right!

Sal 965

John,

Any updates? I saw Colin Belton at the Autosport show where he, whilst talking about some upgrades to help me keep up in Wales, said your car was still in bits in the workshop.

rodders

John - any smoke - a bearing would bring smoke - if you run the engine and it is a bearing you will spread shrapnel throughout the engine and any where the oil goes, tank, cooler, lines, thermostat.
I lost my first engine!! a few years ago - 100% maintained by OPC - and on Mobil 1.
Cruising on the M! back to Stratstones in Wilmslow for a 12k service - no warning and it sounded like a tensioner letting go - or a cupple of rockers broken.
It turned out to be 2nd main breaking up.
I had a subsequent incident on engine no2 which resulted in a strip down for top damage - checking the bottom end we found no2 wearing!
Its seems there is an issue with the oil squirters sticking open and causing occasional drop in oil pressure and wear to the main bearing - no warning.
You have good people in Cheshire - Allan Dyde was at Stratstones and managed my work - he is now with Phil Hindley in Warrington
Dont run the engine - get it into your preferred shop and sweat, I dont like the sound of it !
Look at the Jan issue of Porsche 911 World - you have the saga of my TBK 373

rodders

Apologies to John and everybody who given such good insights and advice.
- my contribution total bollocks - only just picked up the thread and had not read what went before.
but after my own experience does not make me feel better !
Any one any conclusions on oil
- dump the 0 - 40, back to semi ??

rodders

John - any smoke - a bearing would bring smoke - if you run the engine and it is a bearing you will spread shrapnel throughout the engine and any where the oil goes, tank, cooler, lines, thermostat.
I lost my first engine!! a few years ago - 100% maintained by OPC - and on Mobil 1.
Cruising on the M! back to Stratstones in Wilmslow for a 12k service - no warning and it sounded like a tensioner letting go - or a cupple of rockers broken.
It turned out to be 2nd main breaking up.
I had a subsequent incident on engine no2 which resulted in a strip down for top damage - checking the bottom end we found no2 wearing!
Its seems there is an issue with the oil squirters sticking open and causing occasional drop in oil pressure and wear to the main bearing - no warning.
You have good people in Cheshire - Allan Dyde was at Stratstones and managed my work - he is now with Phil Hindley in Warrington
Dont run the engine - get it into your preferred shop and sweat, I dont like the sound of it !
Look at the Jan issue of Porsche 911 World - you have the saga of my TBK 373

kris

What year was your car again Rodders?

foxford

With all of the spun bearing stories, I've been wondering if there would be any warning by way of a fault code showing that the squirters have stuck in the open position. I don't see how it would trip a warning light unless the oil pressure dropped below acceptable range. Would a "hammer" reading then show that the oil squirters are malfunctioning?

Is there ANY way to know if the squirters are functioning properly short of bearing damage?

John Boggiano

Hi, all.

The only update is 'nothing happening'. 9M say the engine should reach its turn for rebuild next week. I'm going to start pushing them a bit from Monday. As it is now, I don't think I'll ever know what became of that locking pin...