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924RACR · Posted: Sun Nov 20, 2011 9:28 am Post subject: Back in the game...

Thanks to some willing friends, we pushed the 931 back in the garage (first time it's moved in 2 yrs!) this afternoon.

She's now about 1 hr away from getting the motor pulled out, thence to rebuild... hopefully just a basic, pure stock rebuild... but we'll see how those pistons look once they come out. As it is, the bottom end has a nice knock, so hopefully a polish and balance of the crank and rods will be sufficient...
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Holding breath. Crossing fingers. Praying to the porsche gods...

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

go go go ! there are some of us who have been out of the game for some time...this spring we've got some driving to do

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924RACR · Posted: Sun Nov 20, 2011 11:09 pm Post subject:

LOL... thanks.

Yeah, my biggest fear is having boogered-up pistons - based on others' experiences, not so much anything this motor was doing. Just seems so much like these motors like to eat piston ring lands. I certainly have a good local hookup for pistons, but would rather not have the expense - the DSR needs lots of money spent on it too!
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

924RACR · Posted: Mon Nov 21, 2011 5:20 am Post subject:

Engine is now out...

Have to button the car back up to get it back outside, out of the way; then I can start tearing 'er down and see how bad things are...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

924RACR · Posted: Wed Nov 23, 2011 12:19 am Post subject:

Haven't finished putting the car back together, but started tearing the motor down anyway.

Most embarrasing.

When I pulled the oil pan to reseal, many moons ago (5 yrs?), I popped the #1 rod bearing cap off to check bearing wear.

Looks like I didn't do a very good job with the torque wrench putting it back on. The end was loose, and slapping around, with a spun bearing.

Now I'm hoping to find a) no similar damage from the main cap I also removed, IIRC, to check main wear, and b) no lasting damage to the crank.

So on and so forth...

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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

924RACR

OK, maybe I'm not quite as dumb as I think I are...

Pulled the pistons and rods out this PM. Turns out the offending rod bolt had snapped! Head only was snapped right off... so no more torque.

On the plus side, I don't think the crank needs more than a mild polish to remove some funk on the #1 rod journal.

The mains are definitely due for replacement though, and bores will also benefit from a cleaning - looks like there's some funk left over from when the car sat for a while (before I got it), which can use to be removed. Hoping a vigorous hone will remove that.

Definitely makes me glad to know that I planned to put in the ARP rod bolts (already procured from Dan). Also makes me think maybe I'll go ahead and get the ARP head stud kit too, for further insurance etc (since I do hope to work up to cranking the boost, once she's back together again and broken in).

Also need a clutch - what's the current wisdom on clutch kits for these guys? I'm guessing it's original... flywheel will need a skim, and seems like the whole kit for the clutch including release bearing, pressure plate, and bolts will be needed too.

"Bad" news is that the pistons look in fine shape, only very mild scuffing/scraping. So no hot-rod flattop pistons in my future. But that's really a good thing, as I need to buy enough other stuff (not to mention work on my DSR racecar) that I didn't really need that expense...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

Even though I haven't joined ARP rod bolt group buy and I don't consider them as an absolute necessity when staying withing 7000 rpm, I have never made fun of it.

My point was and still is that if you don't move the powerband up (north of 7000) with some heavy cams, you don't necessarily need ARP bolts, just need to ensure that stock bolts are OK. One can measure the stretch of the bolts and therefore be sure about it.
Using lighter pistons will further redue the need for uprated bolts, for example the flat top VW pistons are lighter than stock pistons and I've revved Gulf engine up to 7200 without any issues.

Raising max rpm on 924 requires several serious things like lighter pistons, rods (+ better bolts!), lighter valves (with 7 mm stem), titanium retainers, lighter (Piper) lifters and cam that breathes better in higher rpm. Note that I did not mention valve springs. It's because if you lighten other valvetrain components and stock springs are not worn out, they work excellent as they have less mass to control. Of course if you have funds, then it is a no-brainer. Unfortunately money is always issue to me even if I have it

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'67 911 2.4S hotrod
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'84 928 S, sold
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924RACR · Posted: Wed Nov 23, 2011 10:39 pm Post subject:

LOL...

Yeah, I should point out my goals too... mainly stock refresh type rebuild, get it running again... but, without making cost prohibitive, plan to put in intercooler, Megasquirt, and bump boost up to 15psi/1bar later on.

So now's the time to put in appropriate, modest tweaks to the guts to hold up well to that. I have the ARP rod bolts and Cometic head gasket, and so seems like the ARP head studs are needed too, and suitable clutch.

Hopefully not too much else...

Pulled the mains last night - they do seem more worn than the rods (makes me wonder if I already replaced the rod bearings?), and will need to be replaced... but that's OK, have those on hand.

I do believe the crank is good, based on preliminary measurements with my calipers...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

emoore924 · Joined: 13 Apr 2004 Posts: 2822

I can't recall if I have a spare set of those ARP rod bolts. Are they still around? Thinking of maybe picking up an extra set to throw on the shelf...

924RACR · Posted: Thu Nov 24, 2011 11:42 pm Post subject:

I believe the last group buy was sold in full. I got a couple pair.

Don't think I'll need any more for the next group buy (ask Dan), but think I may well get in on some more rod and main bearings!
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype