Top-end Recommendations

[echrisconnor]

OK, I've done my homework and read the assorted texts. Still I have a copule questions, since Wayne's book is really slanted towards a full rebuild. I intend only to do the top end. This is largely for cost measures and trying to avoid all the "while you're in theres."

My car is a 1976 Carrera 3.0 with about 100k on the clock. It smokes like mad and has all the typical symptoms of bad valve guides. It had a good leak down a year or so ago though.

Here's what I intend to do in my top-end followed by questions:

1. Pull engine, clean exterior and pull off heads.
2. Have heads machined and new valve guides/springs/valves (as necesary) replaced.
3. Pull pistons & cylinders and replace lower Dilavar studs
4. Inspect and regrind cam to 964 profile.
5. Replace things like internal thermostat seal & oil pressure sender.
5. Leave the bottom-end alone
6. Reassemble & drive like hell

Questsions:
1. Any more must-dos?
2. Pistons & Clyinders should be removed in order to relace the head studs. Should I pull them together and not pull them apart? Also, how do you do this without contaminating the inside of the case with gunk?
3. Related to #2. Should I simply re-ring at the same time?
4. Related to #3. If just re-ringing Nickasil cylinders, can I just grape-hone them myself? I really don't want/can't replace them.
5. I don't even intend to pull the pressure plate unless the clutch seems really thin. Are there any other accessable seals there are "must-dos?"

Any advice would be appreciated. I am on a tight budget though.

Chris

[HarryD]

Your car, your choice, but a question. Why are you pulling your jugs? Do you have leakdown and compression data to support this extra effort? If you re-ring, you will need to be careful to ensure the rings seat properly. Why take the risk if you do not need to do so?

Assuming you have ok compressio/leak down results, an alternative approach would be to pull the heads and inspect the cylinder bores for evidence of damage. You may find that that you do not need to rering.

As far as other whle you are there's, I think you have a few seals on the crank shaft that you can replace.

Like I said, your car, your choice, but an idea to consider.

[ChrisBennet]

Replace things like internal thermostat seal & oil pressure sender.

You mean "oil pressure switch" right?
The oil pressure sender is the big sensor just to the right of the fan.
The oil pressure switch is the little sensor on top next to the breather hose.
-Chris

[Bill Verburg]

My C3 at 115k miles had similar symptoms. The final straw was the broken head studs. When disassembled the piston/cylinder/ring assemblys were found to be well within spec, as was the bottom end, but valve guides were shot.

If you are planning to keep that engine I would plan on 12 new Manganeese Bronze or Silicon Bronze guides. 12 new valves, use Carrera Clubsport intakes and 930 exhausts, Smartracing valve spring kit, a sportier cam of your choice(talk to the cam grinders), and if budget allows some 98mm ~9:1 piston/cylinders

[echrisconnor]

Harry -- I'd rather not do the rings, but it seems like a prime "while you're in there thing to do" If, at 100k, it shouldn't be necessary, I'd like not to deal with it. However, I need to replace the bottom studs, so I assume I need to pull the P&Cs, but may not need to separate them if I'm not re-ringing.

Chris-- yes, Switch, not Sender (monday morning post).

Bill-- I plan on new valve guides, of course, in the head rebuild. I really don't have the $$ right now for new P&Cs or hotrod valves. Any low(er) cost suggestions?

So I guess my main question is -- is it sensible to be pulling the P&Cs to do head studs and not do rings?

[Wayne 962]

I would recommend doing the rings, and including the bottom end as well. Talk to Noah - his intermediate shaft bearings were toast (I think it was him), when he tore down the bottom end. It's like driving all the way to the grocery store, but not going to the drug store next door because you don't feel like it. The bottom end is the easiest part.

-Wayne

[Eagledriver]

Harry,

You can pull the cylinders with the pistons still in them by not sliding them all the way out-just far enough to pull the wrist pins. I've pulled two engines apart now and both sets had rings and pistons well within the wear limit. You shoul pull the pistons out (or at least one of them) and check the side clearance and end gap. The specs are available in lots of books. The numbers for my 2.7 were .004" for side clearance and something like .030 for end gap. My end gaps were exactly half of the wear limit. My opinion and the opinion of my machine shop is that it is safer to use the old rings if they are well within limits than take a chance on new ring break in problems on the old cylinders. I think you will save a lot of money by not splitting the case (assuming good oil pressure and no leaks).

-Andy

[Jim Richards]

I would recommend doing the rings, and including the bottom end as well. Talk to Noah - his intermediate shaft bearings were toast (I think it was him), when he tore down the bottom end. It's like driving all the way to the grocery store, but not going to the drug store next door because you don't feel like it. The bottom end is the easiest part.

Yeah, I was thinking the same thing when I started reading this thread. Is it a false economy to forgo the bottom end, especially since there's already 100k on the engine?

[HarryD]

Originally posted by Jim Richards
Yeah, I was thinking the same thing when I started reading this thread. Is it a false economy to forgo the bottom end, especially since there's already 100k on the engine?

In absolute dollar terms, I agree it may be a false economy. Much depends on the status of the engine. Like stated earlier, compression/leakdown tests, inspection/measurement of a piston and crank bearing may be prudent to help decide to complete the teardown.

While it can be see to be prudent to do it all, the original poster pointed out that he was on a strict budget. Also, a top end will cost a person $3,000-5,000, if done by a shop. A full rebuild, in a shop, is on the order of $10,000. This is not an insignificant difference. On th eother hand, if you DIY, the cost of parts and machine work for the top end is about $2,000 and about $3,500 for a total rebuild. This may be close enough to justify the additional work.

If he is like me and drives 5-7000 miles a year and gets 20,000 miles out of his top end, he gets 3-4 years of driving before he needs to do the bottom end. At that time, chances are that he will not need to redo the heads. While he will incur the cost of R&R'iong the engine and teardown twice, he gets to spread his cost over a longer time with little increased risk.

Of course, it is a gamble but it may be one he is willing to make.

As always, YMMV.

[Wayne 962]

Originally posted by HarryD
Like stated earlier, compression/leakdown tests, inspection/measurement of a piston and crank bearing may be prudent to help decide to complete the teardown.

All things that tell you nothing about the condition of the bottom end of the engine. 100K miles is a relatively short time to be tearing down a 3.0L engine. If the motor was abused enough to warrant a top-end job at this juncture, odds are that there are bottom-end issues as well. Simply closing your eyes and pretending that problems don't exist is not a good solution.

Originally posted by HarryD
While it can be see to be prudent to do it all, the original poster pointed out that he was on a strict budget.

It's unfortunate, but probably the worst thing for any 911 is an owner who cannot afford to do the proper maintenance and repair on their car. People on budgets tend to short-cut things -reusing parts that are out-of-spec, skipping vital machine work, slapping together parts without the proper tools. All of these issues come back to haunt when it's time to resell, or later on down the line when the engine doesn't perform well or leaks oil.

There really is no such thing as a "911 Engine Rebuild on a budget."

-Wayne

[HarryD]

Wayne,

With all due respect, you points are well taken. As you very correctly point out, you need to know why you are rebuilding to define the scope of your work. As you, and others have pointed out, you are taking a risk by doing only a top end but that may be a risk some wish to take knowing full well it can come back to haunt you later.

I was merely pointing out that you may decide to limit your scope, but you should still do some investigation/testing to avoid any obvious risks. Should you pull a cylinder and measure the ring lands? Yes. Should you pull a connecting rod to inspect a bearing? Sure! These may help you decide if you need to go further or take a chance and stop and wait for a later day.

As you state, there is not such thing as a Budget Rebuild, but you may decide to limit your scope to buy some time. And as I did point out, when it is time to pay the piper, you will incur more total cost by doing two rebuilds than you would have if you did only one.

Like I said, no disrepsect, just a different view on a common problem/issue.

[HarryD]

BTW,

Not to think I am toatally foolish. On tear down, bad news has been found. I could not find the one Wayne refered to but another example:

Heads and Cylinders Off: Things could be worse

[Wayne 962]

Originally posted by HarryD
Like I said, no disrepsect, just a different view on a common problem/issue.

No offense taken...

-Wayne

[Bill Verburg]

Any low(er) cost suggestions?

Obviously evaluate upon disasembly, but based on my experince a well maintained C3 bottom end will be fine w/o any unusual wear at 100k.

The valve guides and headstuds are the vulnerabilities.

At a minimum in addition to guides replace all 24 head studs w/ the 993tt version. 993 101 170 51

[jgparker]

FWIW, head studs can be replaced without disturbing the P/Cs. Some will advise against it, but it is doable. If you can break the red locktite without heat, you are home free. Replace the studs one at a time, and keep pressure on the cylinders at all times with the hold-down tool.

No comment on the wisdom of not touching the bottom end, but it will almost double your rebuild cost if you do crack the case, and the 3.0 carrera bottom end is fairly robust.

Good luck,

JP

[Superman]

Nope, it sure will not double your cost. In fact, part of what Wayne and others are reporting is that the engine's bottom end is clearly the simplest part of the engine. Not much there to replace in fact, except the hardest working parts in your engine. The bearing shells. Measure (machine if necessary) the rods, and measure/inspect the crank, and you're into it for another $500, maybe.

Or you can wiggle the rods while the pistons are off, and see if there is play. If you split the case you will find some wear on the intermediate shaft bearing shells, and some wear on the main and rod bearings as well. The bottom end will survive, probably, if you don't split it. But if you do split it you will see, visually, the wear you are correcting.

But these are tough decisions. Re-ringing is dicey. Sometimes the new rings won't seat. Or maybe the P&Cs are out of spec. Then again, refreshing the valves brings things out of balance. Valves that seal real well....rings that don;t.

Like all who have gone before you, you'll have to make these decisions on your own, with no guarantees. The greatest guarantees are with the highest prices. The budget strategies have more risk. It works like a laxative. Wait'll you turn the key and start it up after reassembly. Makes bungee jumping seem tame.

[echrisconnor]

I'm a little disappointed that there seems to be no inbetween when doing an engine rebuild. I know that Wayne's book is "How to Rebuild..." your engine, not "How to Screw Up your Porsche Engine on a Budget" but there have got to be acceptable varying degrees of commitment.

I'm not necessarily looking to cut corners and do this in a half-assed manner. However, there are realities of $$ at hand. It does cost more to go into the bottom end. The extra dollars involved make it cost-prohibitive for me to do anything otherwise. Still, I'm budgeting $3k to this and a few other well-needed upgrades. It'a amazing how quickly it goes when trying to do some things right.

If I can get 20k miles out of this top-end rebuild, I'd be very happy. Then I'll do it again-- right. I also expect to be very happy with doing this myself. It's been great fun just finding my machine shop and talking to the people I'll be working with.

That said, If I inspect things and don't find too many gremlins lurking within are there any more *must* do things?

Thanks for the advice so-far.

Chris

[ChrisBennet]

It has been common practice to just do the top end on 911 motors for many years. The valve guides simply wear out before the rest of the motor. There is a good argument to be made for doing the bottom end "while you are in there" but I am not convinced that sky will fall if you don't. Sort of like your Dad telling you to stay away from red heads. He's probably right but still...
If this car will be going to the track I would either add racing valve spring to your list (more $) or skip the 964 cams. The 964 cams increase the likelyhood of valve to piston contact during a missd shift.
-Chris

[echrisconnor]

Thank you Sir Bennet. Previoiusly, I was under the impression that there are top-ends done all the time. They seem to be the soft spot in otherwise solid engines.

c

[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