[MB968]

Doing a major rebuild, and yesterday I measured the rod bearing clearances (plastigage). Expected to be changing rod bearings, as the engine has ~155k miles on it. Don't know history to know if rod bearings had been changed in the past. Anyway, I was pleased that all surfaces looked and felt great. It's hard to get real accurate numbers, but #1 was clearly a bit over .0015, and all the rest were a bit less than .002. So, I estimate the clearances as #1 ~ .0016, #2 ~.0018, #3 ~.0018, #4 ~.0018.



I think it was from Lindsey R. posts that I read they like to build up their engines with rod gaps close to .002, and use 15w50 weight oil. So, unless I can be convinced otherwise I'm planning to get new nuts,and just button up the bottom end and call it good.

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[Cloud9...68]

I'm a little confused. What do you mean by a "major rebuild"? Rob bearings are very cheap, and if you've already gone to the trouble of removing the bearing caps, why not pop a new set in? How's your oil pressure at idle, FULLY warmed up (I mean after driving a good 30 minutes, preferably on a hot day)? If it's below 2 on the gauge, I'd defintiely replace the bearings. Heck, I'd replace them no matter what the reading was. I'm doing a complete, down-to-the-bare-block rebuild, and new rod bearings are a no-brainer. Also doing the main bearings (that's probably overkill, but as long as I have everything disassembled, I figured I might as well), and the balance shaft bearings.

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[sydneyman2007]

replaaaaaaace!!!!!! <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />

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[flash]

lol - funny - i'm preparing for doing this right now. the whole bottom end is getting done.

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[DaveN]

The whole bottom end? You gonna get an @ss like J-lo? <img src="/forum/images/smilies/968/tongue.png" class="smilie" alt="" />

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[MB968]

OK, guess my "major rebuild" probably doesn't qualify compared to what some of you are doing. I'm doing a "major overview" of the whole car. I'm more in the mode of making sure that the car is in a reasonably dependable and safe state for some day trips on fun roads, a little autocross, and maybe even a track day or two but nothing too serious.



I have a leaky engine, so it's all the main seals, new belts and idlers, replace the very heavy clutch (and a few worn parts in that area). I've also found some hoses that arean't in the best shape, the front brake lines show cracks if bent into a tight radius, the main vacuum line pulled right out of the manifold when I tried to remove the hose to the brake booster (would've been scary if it came out during some spirited driving). And I also have a new upper timing belt reat casting to replace the one that corrodes behind the distributor cap at the friendly price of $960 from Sunset. And, before I've finished going over the car completely I'm sure I'll find more things that want replacing.

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[flash]

no worries. going through the car is a good thing

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[Cloud9...68]

Leaks on this engine are a very "slippery" slope, if you'll forgive the expression. Many of the seals are in places that are VERY hard to get to with the engine in the car. I went through the same thought process as you, when a very knowledgeable neighbor of mine said, "You know, if you're going to go to that much trouble, you might as well pull the engine so you can take care of everything all at once." So that's what I did. Was it the right decision? Probably, as I found many leaks from seals I didn't even know existed, plus I discovered that my valve guides were pretty badly worn (even though the car wasn't consuming much oil). But it is a huge job, and it always takes about ten times as long as you expect before you get everything back together - at least that's been my experience. Best of luck.

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[MB968]

Problem is, even though I have mine out and on an engine stand, its still a little hard to tell what's leaking. I think the front main crank seal has been leaking for a long long time, and so it has oil and grime all over the bottom half of the engine. Some things are clear, but then there are seals close to the ones I know are an issue, and can't tell if its carryover oil, or if they are leaking also. I'll address all the ones that would be hard to get to later. I've been under Eric K's race car, and I'm envious of how clean it is.

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[Cloud9...68]

If you already have it out and on an engine stand, why not just replace all the seals? They're not very expensive through Sunset Porsche, and that way you'll know you've got all the leaks taken care of.

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[MB968]

I guess in my almost 4 decades of working in manufacturing around machinery, I've seen a number of new seal installs leak more than one that wasn't leaking or was barely showing signs of leaking. Even with highly trained technicians, removal can scratch a surface that later weeps, installation can abrade a seal, or I've personally run into new seals that didn't fit quite as snug as a seal that I replaced and wasn't leaking, etc. It might be unusual to have these kind of issues, but I'm of the school if it isn't broken, don't fix it.



So, for instance the cam seal that is on the front of the engine is a good candidate for not replacing. I don't see any signs that it is leaking, it feels pliable to the touch (doesn't show any signs of age hardening), and if it ever starts to leak, it'll be an easy fix. On the opposite side, because of the difficulty in fixing leaks on the two cam seals on the firewall side, I'll definitely address these two.

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[Cloud9...68]

Actually, I agree with you to some extent. Wiper seals, like the ones at the front of the balanced shafts, do pose some risk upon R & R. They weren't leaking when I did my last belt job, but I replaced them anyway, and fortunately they're still not leaking, so I'm not replacing them as part of my current rebuild. But what I'm primarily referring to is the myriad o-rings throughout the engine. These are cheap, easy to replace, and are prone to leaking.

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[MB968]

I have the front end seal kit from Paragon. O-rings are cheap and very low risk if replaced, so I'll look for others I don't have. Thanks for the tip.

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[MB968]

So, isn't there anyone on this forum that sides with my plan to keep the old bearings?



I understand that replacing the bearings is the easy answer, but I’m not sure it is the best. I still have good oil pressure when hot at idle, and with even minor increase in rpm, oil pressure goes up between 4 & 5 bar. If I were to put in new bearings I might end up with a tighter fit than the ~.002 that I'd like based on Lindsey R's comments. And I'd have to "seat in" the new bearings, not knowing how it turned out. I just don't see the value in replacing bearings that are well seated to the mating journals, have happily lived that way for over 150k miles and are now just getting to the clearance values for good oil flow under competitive conditions.

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[flash]

too inexpensive to buy for me to guess wrong and have to go back in to do it over again. a couple hundred bucks is good piece of mind for me.



there are three different sized bearings. they are yellow, blue and red. yellow is smallest, red is largest). the hot engine builders say that you want to run yellow on everything but #2 and red on that one. you can try glyco, but they tend to run tight because they assume they are being used on rebuilds, which would mean the crank was being turned, but these cranks are really hard, and don't generally wear. oem tend to be matched bores, but you may have to sort through a few to get the right ones.

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[MB968]

[quote name='flash' timestamp='1330175445' post='122373']

but these cranks are really hard, and don't generally wear. [/quote]



Can anyone confirm, looks to me like the journals on the crank were flame hardened. There are some telltale signs on the crank that would indicate to me that this method of increasing the hardness was used during manufacturing.

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[vliegwielolaf1234]

PORSCHE 968 Workshop-manual 13-34



Upper & Lower big end bearing inserts ALWAYS REPLACE USED BEARRING INSERTS

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[MB968]

Never reported back in after getting my car back on the road some months ago. As mentioned earlier, I did not replace my rod bearings due to their good condition and desired clearance. I didn't post any info previously on the prior to teardown idle hot engine/oil pressure. I knew it was OK, but never really made a note of what it was. Now that it is back together I can report that my hot engine/oil pressure at idle is between 2.5 and 2.75 bar.



Edit: Forgot to add an important fact, I'm running 20w50 oil.

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