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What does a "Top End Rebuild" really mean?

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Old 06-06-2007, 01:02 PM   #1
Texas993
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Default What does a "Top End Rebuild" really mean?

I am in the process of buying a 993 (pending PPI) that has had a recent top end rebuild. Valves and valve guides done by Otto's and the rest of the rebuild done at a UT dealer. I have the receipts and understand the parts used.

But my question is: Does a top end rebuild mean that you have a fresh engine? What about the bottom end? (Silly question, but I am serious.)

I understand the CEL and SIA issues with these cars and the fact that the top end fixes this along with excessive oil consumption.

But is a car with a new top end rebuild and 82k miles have a stronger engine? Are the other engine internals worn out?

See what I am asking?
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Old 06-06-2007, 01:23 PM   #2
Edward
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Top-end "rebuild" means valves, seats, springs, requisite machining, checking tolerances (with care!!!); depending on how else it's "defined" it also includes re-ringing and, with more enthusiasm, p's and c's. As for bottom end, no self-respecting shop or builder would do a full top end and NOT check the bottom. 911 bottom ends are renown for their strength and longevity, and going 300K on the bottom is not unheard of. That said, if you are "already in there," it would only be far more expensive to deal with a main bearing later than at that point.

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Old 06-06-2007, 01:27 PM   #3
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Top end rebuild means redoing just the heads. That means valve guides, check/replace valves and valve springs. Piston, cylinders, rings, crank bearings, etc. are left in tact. On the 993, this also and usually mean clearing out the SAI passages in the head and also in the cylinder head housing.

I just went through this. While you have the heads off, it's also a chance to re-ring which is what I did. Top end are usually due to valve guides and/or SAI, from what I've heard, the bottom is pretty strong. The car should be making stock power after you are done.
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Old 06-06-2007, 01:28 PM   #4
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Couldn't live without, eh Patrick??

The simple answer (because that's all I am really "qualified" to give anyway): the engine is mostly fresh with a top end. The bottom end (bearings, crank, pistons, anything in the case) have not been freshened with a top end rebuild. Doing a bottom end rebuild requires opening the case, which is not only expensive, but likely unnecessary at low mileage. The bottom end in our cars stands to live for many hundreds of thousands of miles without need for a re-fresh.

When I did my top end, I "freshened" all top end bits, but also rod bolts and bearings, which are "bottom end" bits. The bearings are a wearing item on the bottom end, but they can be accessed without opening the case.

Verify that the oil pressure at idle is sufficient. Ask the folks doing the PPI about that.

Glad to hear you asking the question though. I think Marc still has your car. Maybe you could buy it back!!
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Old 06-06-2007, 01:35 PM   #5
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Thanks everyone. Good news and comforting to know what is done and that the bottom end lasts a long time.

On the receipt, I only see the valves, guides and various gaskets, washers, screws and a temp sensor. So it looks like they strickly did a top end and nothing else. (Besides total tune up, fluids, brakes, rotors, new top, top motors, etc.)

Ooo, just saw a 997 GT3 RS drive by my office window. Black/orange. Sweet.

Yes, Adrienne. It only took me 6 months of pcar withdrawls to need my fix. And Marc can keep the Targa!
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Old 06-06-2007, 02:09 PM   #6
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Patrick,

You already got the answers to your questions, so I only have one word for you at this point:



"YEHAW".

Welcome back to the party!
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Old 06-06-2007, 02:43 PM   #7
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Ditto on the Yeehaw!! Keep us updated on your search!
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Old 06-06-2007, 02:49 PM   #8
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"no self-respecting shop or builder would do a full top end and NOT check the bottom. "

Huh? That is a misinformed statement as is the recommendation to re-ring the engine simply because you are in there. You should never install new rings in a cylinder without preparing the cylinder for the new rings. You need special honing tools to hone a Nikasal cylinder to get the specified RA value which is require to properly wear in the new rings. Simply taking out your honing ball, installing it on your drill and running it up and down the cylinder is the wrong approach.

Also, the bottom end of the 993 engine is not as robust as the earlier engines because the bearing surface area has been reduced. We are seeing a higher number of 993 engines having rod bearing failure when tracked.
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Old 06-06-2007, 03:24 PM   #9
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Patrick,

Best of luck on the PPI... and we'll be waiting to hear some good news.
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Old 06-06-2007, 07:54 PM   #10
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Quote:
Originally Posted by Geoffrey
"no self-respecting shop or builder would do a full top end and NOT check the bottom. "

Huh? That is a misinformed statement as is the recommendation to re-ring the engine simply because you are in there. You should never install new rings in a cylinder without preparing the cylinder for the new rings. You need special honing tools to hone a Nikasal cylinder to get the specified RA value which is require to properly wear in the new rings. Simply taking out your honing ball, installing it on your drill and running it up and down the cylinder is the wrong approach.

Also, the bottom end of the 993 engine is not as robust as the earlier engines because the bearing surface area has been reduced. We are seeing a higher number of 993 engines having rod bearing failure when tracked.

Well I will concede that in my haste typing that this morning, I should have added that a good shop would check the bottom end *IF* the p/c's are being done. BUT, I NEVER said that I recommended re-ringing. Moreover, I also said depending on how a shop defines "top end rebuild" will the the p/c's even be touched.

NOR did I EVER raise the issue of honing ...let alone going at one's cylinders armed with a power drill. Check my post there, sir. Not exactly accurate to go putting words in another's mouth. Perhaps you "read in haste" as I typed in haste, eh?

Additionally, I never made any comparison of the 993's bottom end to any other 911. My *generalization* of air-cooled 911 robustness in their bottom end (I implied "aircooled," though admittedly failed to state that explicitly since the topic was, after all, initiated with regard to the air-cooled engine) is a generalization that holds "true" in so far as the numbers of high-mile 993 cars are mounting. Are they *as* robust as earlier cars, especially of say the 3.0? I don't have that answer, and as such I never even tried to make a specific claim of knowing.

And checking "while in there" is defined by how deep one is "in there" ...if the p/cs are not cracked open and all else was well beforehand, then no, I would not recommend one cracks them open ..but if one has already gotten into the p/c's then yes, I believe it would be cost effecient to check the bottom as you truly are already there.

There is my clarification. Please excuse the hastiness in which my original post was conceived. But consider, too, that I did not say all that was purportedly said or implied to have said.
Anywho, peace.

Edward
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Old 06-06-2007, 09:06 PM   #11
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"Check that oil pressure is sufficient at idle"...what is sufficient?
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Old 06-06-2007, 09:47 PM   #12
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well..... looky here..... hello again Patrick..... scratch the itch my friend, scratch the itch....

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Old 06-06-2007, 10:56 PM   #13
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Quote:
Originally Posted by mrsullivan
well..... looky here..... hello again Patrick..... scratch the itch my friend, scratch the itch....

He's been scratching... look at his new avatar.
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Old 06-06-2007, 11:02 PM   #14
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Quote:
Originally Posted by Air Kuul TT
He's been scratching... look at his new avatar.
Oh yes, scratching and scratching. And it isn't the TX bug bites.

Mr. Sullivan. I have emailed and left you a VM. Where you been?
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Old 06-06-2007, 11:12 PM   #15
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Oil pressure @idle depends on the viscosity spec of the oil and operating temperature. I use "thin" 0W-40 Mobil1 and with hot engine I am happy with 1.5 bar. I think the manual states you should have at least 1 bar per 1000 rpm which would mean about 1 bar @idle.

Erik
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