worf928

I've been meaning to post this for a while but keep forgetting until subject comes up.

So...

I am of the opinion that the WSM (and spec book) torque spec for the block drain plugs has a translation error.

Short story: it's 26 N-m, not 26 ft-lbs. (So, 26 N-m would be 19 ft-lbs.)

Long story and partial re-post from a current thread:

The very first time, closing-in on 20 years ago, when I tightened the drain plugs on my '91 for the first time, I started the first one with the torque wrench. WAY before the spec was reached I could see the crush ring deforming to the point that it was about to be 'squirted out.'

A couple of years ago I progressively torqued four drain plugs and determined that the crush ring seals nicely at 26 N-m.

Therefore, I'm of the opinion that the WSM spec of 26 ft-lbs is really 26 N-m and that someone at Porsche got confused.

If anyone has access to the German Language WSM or spec books I would be interested in seeing if the same spec is in the original.

I got interested in finding the 'right' spec when one of my customers brought me his 928 on which he had recently torqued-to-spec his drain plugs and stripped the block's driver's side threads. Putting a time-sert in that was too much fun for me to want to do a repeat...

Ducman82

i think some one busted the block before following the book spec....

Mrmerlin

well truth be told my calibrated hand says make it tight, but not too tight.
I dont use a torque wrench to figure this fastener out,
thus it prevents damaged assemblies.

Its funny how when using a torque wrench ,
sometimes the user will just keep pulling the handle till it clicks, beeps, or points.
With no regard for what the fastener is telling you.

If you listen you can hear whats happening

worf928

Maybe. But, note that I considered that spec suspect 18 years ago.

But, give it a try on yours. Torque it to 35 Nm (the spec) and see what the crush ring looks like when your done. Assuming you get to 35 before you strip the threads...

worf928

I think it's important to remember that any set of specs can have errors and to always use the calibrated hand to determine if the spec is right the first few times regardless of the fastener. But, some folks are either incapable of, or don't wrench enough to, develop the calibrated hand.

Ducman82

it would never happen on my car. i am in the "calibrated hand" category.

Mrmerlin

yes, the calibrated hand takes many years of of continued use to stay calibrated

Rob Edwards

Interesting- Here's the 80-84 Tech specs books, English vs. German, the specs are the same (35 Nm, 26 ft-lbs) in both:

WasserablaBschraube-Zylinderblock/ water drain plug




But what's weird is the M12 x 1.5 spec- Are the drains in early blocks really M12 thread? Here's the WSM pic of an early drain plug- Looks like an M10 (17mm) bolt head (maybe even M12 (?)) , compared to the M8 gridle bolts nearby. The S4+ drain plugs are M8, maybe there was supposed to be a change in the torque value and they just forgot?

worf928

Ding! Ding! I think we have a winner. Like I wrote above " someone at Porsche got confused."

Nice sleuth work Rob.

Edit: wait..... my GT spec book says M12 x 1.5. Out to the garage to measure a plug.

They are M12s not M8s.

Sorry Rob. Have to un-ding...

Rob Edwards

So the head of the 'later' plugs is 13 mm but the threads are M12. Always wondered why they chose that arrangement.

mike77

Next time I change the coolant I'm swapping the plugs with taps similar to the oil sump taps 928 motorsport sell. Hopefully no more worries about stripped threads or getting covered in coolant

FredR

Dave,

An interesting observation. I understand quite a few motors have suffered damage to the boss that was [presumably] put down to heavy handed oiks [which it may well be] but perhaps they were not quite as heavy handed as previously assumed.
When I did my first TB/WP job last year the thing I feared more than anything else was a problem with those plugs. I used my "feel gauge" to tighten them.

Rgds

Fred

The Deputy

I knew the torque value was wrong all along...that's why I just drove them in with a hammer.

But seriously, after thirty seven years in this profession, mechanic, the only time I use a torque wrench is on engine internals and head bolts...the rest is by feel.

It's funny...I remember while doing some searching on here I ran across a topic about oil pan gasket replacement...and a member here went on and on about "if he ever went into a garage and the mechanic didn't know the torque value of an oil pan bolt and use a torque wrench...he'd take his car and get the heck out of there". I thought to myself, "personally, if I ever went into a garage and the mechanic said he wouldn't do the job unless he knew the correct torque value and such...I'd take my car and get the heck out of there".

Any mechanic worth a grain of salt doesn't need a torque wrench for such jobs, period.

Brian.

Adk46

Wow, this is an interesting subject - torque wrench or feel.

The experienced mechanic who also appreciates the engineering of a particular fastening system will likely do the right thing. For example, he'll be able to feel a crush ring being crushed (good). The sense that the threads are yielding (bad). He'll be able to judge how tight something must be in order to stay tight and not back out. The difference between a static load and a dynamic load. The difference between a bolt failure that is only an inconvenience and one that means $$$. When "feel" is OK, and when it isn't.

But I'm aware of some bolting situations that defy intuition. Here's the classic case: the bolts for a pressure vessel cap. There is a certain preload that you can put on these bolts from careful torquing such that the stress on them remains constant as the vessel is pressurized and depressurized. This eliminates the possibility of fatigue failure. I don't know, but I'm guessing that head bolts are designed to work this way, too. And lug nuts, perhaps. Intuition may not serve well in these cases.

hacker-pschorr

Agreed, learned that years ago working side by side with seasoned mechanics at the track and their various shops. The only time a torque wrench was ever used was on wheels or in the rare occasion an engine was apart.....and maybe some key suspension components.
I'm no seasoned mechanic by any stretch of the imagination, just sharing what I've observed. There has been a few cases where I was working on my car at my friends shop, time came to tighten a critical bolt and I called over his lead tech to do it for me.

These are sealed with a copper / aluminum crush washer, the bolt only has to be tight enough to crush the washer, just like the oil drain plug. I've seen other thread where people put the white plumbers tape on the threads too.
Who here pulls out a torque wrench when putting the oil drain plug back in? I never have.

That being said, the next time I pull these drains I'll probably ruin my block.......just the way things have been going lately.