Made some progress tonight. Removed cylinders and pistons 1, 2 & 3.

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Used a small head flat screwdriver to remove circlips. Wristpin pushed right out.
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Rings looked okay for pistons 1 & 2. Piston 3 middle compression ring was broken.
Checked cylinder for damage, does not appear to be any scoring of cylinder wall.
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How to check pistons and cylinders are within spec?

You need a bore gauge or even a set of telescoping bore gauges to check the cylinders. You can check the ring lands of the piston with feeler gauges and measure the piston with a micrometer.

Except for the feeler gauges, it would be much cheaper to send them out to get measured.

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Looky there, you've got 993TT cyl head studs (top of the line/latest and greatest dilavar) and you still had cylinder head leakage...... :( That's a shame- expensive studs!

Best you can do to check the P&Cs is measure for clearance, ovality, taper. A bit harder to check them for wear limits since there aren't published specs for oversize P&C sets. Meaning, the nice little Porsche spec books give you info for the stock 97mm P&Cs. 98mm stuff isn't in there since it wasn't "factory" parts so to speak. Need to find those wear specs from Mahle or maybe some of the pros with many years of experience have that info in their files.

Need a 3-4" micrometer and a bore gauge to measure them accurately. The snap/telescoping gauges are a good guide but lack some precision. With a bore gauge it is self-lengthening as you rock it in the bore to see the smallest measurement on the dial indicator. With telescoping snap gauges you have to do a bunch of measurements to ensure you're getting the smallest. Can get rather tedious.

$150-$200 will get you a decent mic and bore gauge. Fowler makes a decent one good enough for occasional use. Victor Machinery Exchange in NY has a nice selection of mics and bore gauges. Nice people with a nice selection of decent quality equipment.

Victor Machinery - Metalworking tools and supplies

Goodson also has good stuff for reasonable prices. Their $200 set of mics is a very good value.

GOODSON : Measuring Tools : Micrometers : Economy Micrometers

I bought the stuff because I occasionally build engines. But for someone doing just one build with no intention of doing any more, its not necessarily money well spent to invest in the precision measuring tools.

Thanks for the info guys. Do you think these head studs are history? Or should I replace them with Supertec Head studs? Should flame rings be replaced as well?

I would replace the flame rings and the head studs to give you the best chance of cylinder and head sealing. Obviously they weren't sealing very well based on the pictures. Henry's studs are very good.

Thanks Kevin.

Where to get new flame rings? Are these the sealing rings off a 964? I will post some pics and dimensions tonight.

Thanks Again guys.

J

Rest of the cylinders and pistons have been removed. Happy to report no other broken rings.

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Flame ring measurements 103X4.9X2.2. Contacted Henry @ Supertec about replacement flame rings.

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Need to concentrate on cleaning the engine case. Still pretty dirty.

Heard back from Henry. Flame Rings are very expensive to replace.
He said that flame rings are re-useable unless damaged. Mine are not damaged so I will be re-using them. Thanks Henry.
Will be getting the heads studs on order this week.

Still trying to decide if I should redo the bottom end? Car only has 42,000 miles on the odometer. Barely broken in. I decided to redo the top end due to the head leaks.

How much extra would the bottom end cost me? Top end checked out not to badly aside from the one broken ring. I will be getting the heads redone.

I would like to keep rebuild under $5000.00

Any input would be appreciated.

J

Bottom end may cost you nothing more than some time, sealant, gaskets. Might find all the bearings look just fine and you just clean the case and reseal it. Is the case itself or any of the thru-bolts leaking?

Bottom end gasket kit is relatively cheap. Gives you some peace of mind to look inside and see conditions, plus avoid any future problems should there be something that doesn't look right. Allows you to look at bearing wear, oil pump seals, intermediate shaft bearings (always seem to wear a lot), timing chain sprockets on int. shaft, and so on.

Can also get a look at the crank journals and flush it out. Also allows you to put a THIN coat of 574 on the main bearing saddle mating surfaces to stiffen up that surface which tends to wiggle a tiny bit and fuzz-up the surface.

If your rod bolts are original Porsche stretch-to-yield then you'd have to replace those. That is usually the deterrent for most people because it feels like a waste of money to remove the rods and find nothing needing attention.

Hi Kevin

You are right. Case is not leaking, all thru bolts are dry. Rod bolts appear to be original.
I guess I will get my feet wet, and crack the case open.
This is my first Porsche engine rebuild. Do you remember your first time (Porsche engine rebuild)?

2006. Did the top end on my '87 Carrera. Still remember some of the worries vividly:

-Head nuts screeched like crazy coming loose. Was worried about broken/breaking head studs too.

-First cam housing just would not come off the heads. Rapped on it with a rubber mallet a bunch of times, just wouldn't come off. Missed removing a couple of M8 nuts....... duh.

Still learning as I go. Building a mild racecar engine now and it's slooooow going rounding up parts to recreate the engine that spewed a bunch of bearing material. Finally got all my parts together and just need to get the case back in my hands to start working on the bottom end. Should get my butt in gear and at least start cleaning the crank and then hang the rods.

Yes if you notice Dilivar studs have a black coating on them. This is to prevent them from getting wet and subsequently failing due to stress cracking corrosion. The ones you have pictured the coating is coming off. So most likely they will fail in the near future if re used.

Hi Ken

Yes, going to replace these with the Supertec studs.

J

Reusing bearings
 

What is the current professional opinion on reusing, assuming all appear "good" unscarred or "unworn", the existing rod or main bearings? I thought once you relieved the original tension of the bearing seat that they were no longer suitable for use due to a high risk of moving or spinning? I'd rather not waste good bearings, especially considering some of the reported QC issues with glyco bearings, but also do not want to risk destroying a case, crank, or both, while trying to save $400.00. I must make this decision twice over this winter and want to get it right. Anyone have success or horror stories to tell?

Reusing bearings is common practice on heavy equipment. Bearing wear only happens from start up and abuse, under normal operating conditions there is no metal to metal wear. So if the oil has been changed enough to have not caused chemical damage there is no gain with new bearings. I reuse bearings on all my personal high end engine rebuilds. For customers I use new.

What about spraying the existing bearings with Molykote 321?

You can check the fitment of the bearings pretty easily by feel. They must be "sprung" and you have to shove them out of the bearing saddle. If they come out loosely, they'd best not be reused.

A trick to also ensure bearings grip the saddles well, in addition to the built-in spring effect, is to lightly scuff the back side of the bearing to roughen it. Do not coat the back side of the bearings if you coat them. They need to "bite" the saddle to avoid spinning. Coating gives them additional opportunity to slip. That's not to say that regular uncoated bearings don't get oil underneath them. They do. Just don't want to add any additional means of allowing them to slip.