Top-end Recommendations - Page 2

HarryD · 02-17-2004, 10:58 AM

Fellow Pelicans,

I think this is great discussion.

I would like to add a bit of spice to the mix.

I think alot of the cost issues relate to the degree of machine work required. For the early engines, the magnesium cases tend to stress relieve over time. If you spilt the case, you need to machine the halves to get the faces to align properly on reassembly. Am I mistaken in thinking that the later, aluminium cases do not have this issue?

Also, as JP notes, the valve guide materials have been improved over the years. I have heard that the ones used in the early 911 had an expected life of 50-60,000 miles. Hence, it is not uncommon for a top end only to renew the guides.

echrisconnor · echrisconnor's Garage

I just re-read Wanye's ealier post commenting that if the engine had been abused badly enough to warrant a top-end at 100k, that there may likely be bigger issues.

For the record, this is a C3, which I believe has the crappy valve guides that were in the 2.7. For it to have made it to 100k in original form, with everything I know about the car, indicates that it was well cared for.

I realize that the engine can contain all sorts of skeletons, and I'm not trying to turn a blind-eye to reality.

One further question:

If I pull P&Cs together and do not separate them, can you still clean carbon off the cylinder heads? If so, how?

Damomma · 02-25-2004, 05:52 PM

I'm not totally familiar with the lingo but what does keeping the P&Cs together have to do with getting carbon off the cylinder head? I don't see why You can't totally r&r the cylinder head without separating the pistons from the cylinder. Does it have something to do with remating them, one clean and one not?

echrisconnor · echrisconnor's Garage

In re-reading my post, I can see how what I was asking could be confusing. I'm not asking about cleaning the cylider heads, I'm curious about how to clean the heads/tops of the cylinders themselves. If they're still surrounded by the pistons, I wouldn't want to blast them off, nor would I really want to do anything to dislodge the carbon and potentially get gook in around the rings.

Maybe I don't clean them at all...

Damomma · 02-26-2004, 03:02 PM

I plugged the holes in the long block with a bunch of rubber stoppers and capped the intakes and exhaust with the old gaskets and blanks that I made and blasted it with a high pressure washer. 1. I wanted it clean for disassembly and 2 if I have the Alusil cylinders I don't want to separate the p&cs but wanted them reasonably clean since the heads will look new after the machine work.

Jim

911pcars · 06:41 PM

I don't see any down side in removing the piston assy. from the cylinder as long as you don't mix them up. Good time to check ring side clearance. The rings can also come off if you want to clean the pistons, just reinstall in the same piston and in the same orientation (not upside down).

Sherwood

Damomma · 02-26-2004, 05:08 PM

I tell you I'm spooked, Wayne's recommendation on this board and in the rebuild book is to leave them together and do not disturb if they are Alusils. I don't know what they are yet because I can't find a 46mm crowsfoot in stock, so I can't tear the rest of the motor down.

Superman · 02-27-2004, 07:27 AM

You're right, JP. I hadn't noticed the engine vintage. My case is AL, so machine work on the case costed exactly $0. I'd also agree that, given the age of the engine, leaving the bottom end alone makes sense.

P&Cs can be removed without separating, but you'll have to use heat to remove the wrist pins. When moist air gets onto the pistons tops, the carbon will flake off. It'll just falke right off, making a mess if you're not careful. Given some thinking and strategizing, you should be able to prevent those carbon flakes from causing trouble.

This engine might be a good candidate for the kind of rebuild many of us try for, and fail. The true budget overhaul. In fact, why remove the wrist pins? Replace the guides and seals, perhaps valves if necessary, and button her up. Perhaps even if the valves are worn, with new guides, button her up and go. If you're just trying to get 20K miles, you should get that.

echrisconnor · echrisconnor's Garage

While I'd be happy with 20k, I of course, would be happier with more... I do want to replace the head studs while I'm in there. So, I believe I'll need to pull P&Cs to have necessary access. We'll see where the budget ends up.

You think the carbon will basicall jump off the cylinder tops and that they'll be clean enough to reinstall without any sort of mechanical or chemical cleaning (enough being a relative term)?

911pcars · 02-27-2004, 10:25 AM

echrisconner,
Okay, I'm amending my recommendations. If you want to save a step, don't remove the rings. After separating the piston assy. from the cylinder, submerge it in a vat of carb cleaner overnight. Don't submerge the con rod big end with the bearing shell (which you will not want to remove either, right? Sorry). The next morning, the pistons should come out completely de-carbonized (the stuff that's going to come off easily anyway). Rinse in hot water, blow-dry, check ring clearance, re-lube, then reinstall. If you want to go to the trouble of removing all remnants of stubborn carbon from the top, follow up by completely masking the ring area and skirt, then have the tops glass bead-blasted. All this is assuming your rings are in good shape (good compression), cylinder walls pass inspection and you can't budget for new rings (maybe save up for this). The cyl. walls won't mind if the mating piston rings loose intimate contact for a few days. Mine were separated for many years with no apparent ill side effects (my extended assy. schedule).

Go back to the leak-down test. Did the rings pass muster?

Misc. thoughts:
Comparatively speaking, the main bearings should last longer than the rod bearings. If your observations of engine history and condition look okay (oil changed regularly, engine not abused, etc.), leave the crankcase alone. But if you're going this far, you might as well check what's happening inside the cylinder.

Mind you, this is not my definition or version of an engine rebuild; it's just a version.

Sherwood

HarryD · 02-27-2004, 10:34 AM

Quote:

Originally posted by Superman
You're right, JP. I hadn't noticed the engine vintage. My case is AL, so machine work on the case costed exactly $0. I'd also agree that, given the age of the engine, leaving the bottom end alone makes sense.

P&Cs can be removed without separating, but you'll have to use heat to remove the wrist pins. When moist air gets onto the pistons tops, the carbon will flake off. It'll just falke right off, making a mess if you're not careful. Given some thinking and strategizing, you should be able to prevent those carbon flakes from causing trouble.

This engine might be a good candidate for the kind of rebuild many of us try for, and fail. The true budget overhaul. In fact, why remove the wrist pins? Replace the guides and seals, perhaps valves if necessary, and button her up. Perhaps even if the valves are worn, with new guides, button her up and go. If you're just trying to get 20K miles, you should get that.

Jim,

I'll let you know as I went for the "budget" rebuild in hopes of decent life extension on my old gal.

FWIW, I have had several respected experts tell me to expect not more than 10-15,000 miles but our inspection revealed no issues beyond worn valves and guides. I am at 3,000 miles and no signs yet. Ask me again after AutoX season.

Bill Verburg · Bill Verburg's Garage

I would replace all the head studs w/ the latest 993.101.170.51 Porsche list ~$20. If you are concerned about one you should be concerned about all, age and corrosion arn't limited to only half of them.

echrisconnor · echrisconnor's Garage

I've read so many stud posts recently, I don't know what to think any more. I was thinking about doing just the lowers since they're Dilavar.

I've heard Wayne's recommendation for using the original Steel ones. I've seen another recommendation to use the 993 steel ones, now this recommendation for a different one still... Not sure what to think.

Bill Verburg · Bill Verburg's Garage

993.101.170.51 are used on the 993tt/99RS and are the ones the Porsche Motorsports and most respected builders will recommend and use for their own projects.

I currently have several build sheets form different houses in front of me, everyone of them used 24 of those studs.

I agree that there seems to be a lot of conflicting opinions on this topic you will just have to separate the wheat from the chaff by yourself.

Damomma · 02-27-2004, 12:21 PM

I'm in the same situation but I decided to go with the OEM steel. And after reading that 17 page post on Alusils I'm going to rering as well.

markwemple · 03-01-2004, 03:16 PM

CE and Ollie's both said that my SC w/130k should only need the top end which I am doing due to a little smoke and broken head studs. CE was very certain about this!!

garibaldi · 03-01-2004, 04:18 PM

To respond to eagle driver post on his ring end gap, boy that is a lot. .030 for end gap is huge. So I guess you carry around some extra quarts of oil with you since half of it is coming up from that case past that gap. .030 ! thats spark plug gap , not piston ring gap!

markwemple · 03-01-2004, 06:59 PM

I'm sure this has been discussed a million times before but, what is the opinion(s) on pulling the pistons/rings out of the cylinders. I believe you can take them off the rods w/o sepapration. Is this good/bad/indifferent? Have had many takes. Tell me yours!

Doug Zielke · 03-02-2004, 07:22 AM

Quote:

Originally posted by markwemple
I'm sure this has been discussed a million times before but, what is the opinion(s) on pulling the pistons/rings out of the cylinders. I believe you can take them off the rods w/o sepapration. Is this good/bad/indifferent? Have had many takes. Tell me yours!

Yes it has.....

Sure you can do it, but what's the point?
You can't measure and inspect the pistons (and more importantly) the rings for wear.

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by jgparker
SuperMan,

Not to be argumentative, but my last bill from the machine shop for case work was almost as much as Chris has budgeted for his entire rebuild. Between the line-bore back to Std, case mods, case savers, spot facing, spigot boring, rod reconditioning, crank inspect and micro-polish, Plus round trip shipping from Florida (or Bolder) to California, my rebuild cost just about doubled. Now, if you skip all the machine work, then the cost of cracking the case is close to nothing, but I think that is ill-advised. I believe there are plenty of cases where a top-end only rebuild is a reasonable choice, especially given the short life of the valve guides from this period of 911s. Given Chris's situation, it may be a reasonable choice for him. Just my two cents.

JP

You can't compare machining costs on a magnesium case to machining costs on an aluminum case. Typically the aluminum cases require nothing but a cleaning.

-Wayne