993turboplease

How do I know when my 993 needs a top end rebuild? 65,000 miles, increasingly smelling like a boat. No smoke or oil coming from the exhausts. How do you tell?

goofballdeluxe

Oil consumption. If using more than 1 quart every 600-800 miles, you are due.

pp000830

Some 993 consume excessive oil if the oil is topped off. If left a quart down these same cars stop consuming oil. Overfilling a 993 is very easy to do and an easy to fix
​leaking valve cover gasket can lead to bad smells and oil on the floor. Opening up the engine should be a last resort and rarely needed but commonly done, go figure?

user 723923490

+1
65,000 is not high mileage. If you are worried, have some testing done. Compression, leak down, oil analysis by someone who knows these engines. You can also clean out the aluminum and silicone pipes on the underside of the engine. These can get pretty nasty from oil leaks and oil over-filling.

vjd3

Can't imagine worn guides would cause the smell. I did the top end on my (former) 97 C2 cab at 58k miles. Exhaust valve guides were fairly shot even at that mileage but the car ran great. Only did it because of the SAI issue at the same time and figured, just fix it -- especially since I got it done at a very reasonable price and it needed a clutch anyway. I would not worry too much about it until you are using a lot of oil but I suspect any 993 with the stock guides probably has significant wear. But as long as it's not fouling the plugs it's fine. After my guides were replaced with the phosphorus bronze ones the car did not use a drop of oil.

C4inLA

That's great line, not funny to OP I'm sure...

pp000830

All the above indirect diagnostic analysis is good in conjunction with gross operating issues such as fouled plugs causing the check engine light with related ignition diagnostic codes present. If your car idles well, is not throwing ignition codes after clearing them to seeing if they come back, has good power and is not consuming large quantities of oil, don't look for an issue that is probably not there.

Andy

Steve Weiner-Rennsport Systems

Right here. Nailed it.

When you hit 800 mil/qt, its time.

Churchill

This is advice best ignored. Compression/leakdown won't reveal worn valve guides (unless they're extremely worn). 993's had poorly reamed guides from new and many consumed excessive oil from the day they were driven off the lot. A healthy 993 motor will not consume any measurable oil between changes. The engines that have had the guides done absolutely needed it.

As knowledgable folks said above -- oil consumption is how you know if the guides need to be done.

mgianzero

Well, Steve having so much knowledge when it comes to 993 engines, I'd hate to argue. But isn't it, perhaps, a combination of things that leads one towards needing a top-end rebuild?

For me, I've owned two 993's and one was throwing the SAI code which I couldn't get rid of, but needed to fix in order to pass California smog. The second 993, (and my current one) did consume a bit of oil (not as much as stated above ... maybe 1,100 miles per quart) with the usual common oil leaks. But I pulled the engine for several reasons. When I had heads rebuilt, the machine shop couldn't believe I only had 78K on engine and exhaust valves were so worn. Didn't throw any codes but did have misfires which we attributed to either worn-out DMF or bad lifters. Everything replaced, engine runs beautiful now!

trophy

I am local to you if you want I can have a look at the car... Happy to help out.

trophy

The smell as mentioned above can come from a number of things, lower valve covers leaking oil onto the headers (burning smell), over fill and extra oil goes into the intake (burning smell), spilt oil when filling slowly leaks down onto the headers (burning smell)....

Lots of things to look at before thinking the top end needs doing and the only indicator of that really is the oil consumption.

Churchill

You answered your own question. It's not a combination of things. The DMF is not the heads, and lifters aren't valve guides.

mgianzero

You seem to have misunderstood my comments. I was merely explaining how I came to discover my valve guide were gone. Let me explain ....

My first car was ONLY throwing SAI codes and did NOT burn much oil. The car was evaluated by Andial, when they were around, and said it needed a top-end.

My second car was burning a bit of oil, but not what Porsche (and Steve W.) were saying was the lower limit of normal. I had pulled the engine since it needed a DMF, a clutch (was worn out too) and valve lifters were extremely noisy. So I was able to take care of "usual" oil leaks (case stud through bolts, valve covers, intake leaks, and a cylinder sleeve) while engine was out. The misfires we attributed to either bad lifters or DMF. Either cause, the misfires went away after they were replaced. But that's just a side-note.

My point is ... when engine was pulled, I decided to also do a top-end since everything was out. Turns out that the valve guides were very worn by comments made by machine shop. Don't know what the exact measurements were, but shop told me they were very worn.

So, I guess there can be several reasons to do a rebuild (massive oil consumption) and also throwing SAI codes, which to us living in California, can be critical because the car will not pass smog. So the engine almost has to either be rebuilt to remain drivable, or we get exempt for high cost of repairing (not a satisfactory solution to me). My first 993 had about 65k on the clock and my present one had 79K.

A third case was a very good friend of mine who also had his 993 top-end redone, not because of oil consumption but because it was leaking oil everywhere. Again, oil consumption was not alarmingly low since there's an expected amount of oil burn with these flat-six engines. But when that shop (also very reputable and known very well on this forum) rebuilt it, they noticed exhaust valve guides were worn out of spec.

So, in each case above, there were different reasons for going ahead with a top-end, but each car proved the need to do one was necessary due to the amount of valve-guide wear at time of teardown.

But, after all these experiences with worn guides, it makes me wonder what the true end-point is to rebuild, which is what 993turboplease posted as the topic of this thread. If we continue to drive these cars with worn out valve guides, not really knowing how extensively they are worn until we take apart the engine, what would happen? I haven't really heard any true horror stories ... do these engine fail by eventually bending a valve or something worse if we do not rebuild them? I'm sure Steve W. can give us a story or two about this.

Churchill

I can tell you a story about a 911 I owned many years ago that developed severely worn guides. The oil consumption became significant -- a quart every 400-500 miles, and lots of oil smoke out of the tailpipe (this was an old 911, so no cat). Soon thereafter it developed a tapping noise. When I disassembled the motor it became obvious why: one guide in particular was so worn that the valve head was no longer seating correctly on the valve seat (this is why they're call valve guides). It was pounding the seat like a hammer. Hence the knocking/tapping noise. If you keep driving it at that point, you'll get catastrophic failure, such as a valve head breaking off in the combustion chamber.

Valve heads have to fit precisely onto the seats -- in fact they are lapped together when you rebuild the heads.