logan2z

Still looking for a nice 993 and have a few questions about valve guide issues and top end rebuilds:

1) Is it true that the 95-96 MY are more prone to valve guide issues than the 97-98 MY?

2) If the valve guides are worn, I understand that the car will consume quite a bit of oil. Is this an emergency-fix situation or can the car be safely driven indefinitely as long as oil is added frequently?

3) Once the top end is rebuilt, will it ever need to be rebuilt again? Or is it a one-time thing?

Thanks again for answering my noob questions!

goofballdeluxe

OK here are my noob answers. I could be wrong, but most my info about this I read here:

1)No, no one model year is more affected than another.

2)No, it's not an "emergency fix", but on the same token, it cannot be driven indefinitely like this. Sooner or later, it will cause even more problems if it is not addressed.

3)No, it should be a one-time deal.

2ndof2

Every P-car mechanic I've ever talked to says all air cooled 911's "wear guides"

It is possible that you might have the guides done and the car needs it again sometime way down the line but probably not for a very very long time.

Speaking of top-end rebuilds - Hey Philip you have a PM

Bgoldey

If worn valve guides result in a SAI check engine light (MY 96-98) (Code P410) you will not pass smog in CA. You can clean the SAI ports but if valve guide wear is causing this problem, this is obviously not a long term solution. The CEL is probably a symptom of an even larger issue (as in my case). I replaced my valve guides (in 2002) with non-OE guides because my mechanic thought the OE guides were too "soft". I have been trouble free for the last 6 years. It seems as though a top end rebuild on a high mileage 993 is inevitable. I'd be interested to see how many 993s with more than 100k miles have not been re-built. There are probably some exceptions. A 993 with a top end rebuild will yield an additional $5K or so in sale price. Make sure you get a PPI w/ a leak down done by a reputable shop. Hope this helps.

Marv

1) All have the same issue with wear.

2) If the car consumes more than 1 quart of oil every 1,000 miles it is time to get the problem fixed.

If the problem is worn guides, the ultimate end to the problem will be when a valve stem breaks and drops into the cylinder. This will be a catastrophic failure in anyone's book.

When guides wear, the heat from the valve can not be wicked away as efficiently as it did when new. The higher than normal heat will cause the valve stem to fail in time.

3) If you replace the valve guides with OEM guides you will just be resetting the clock, albeit the new guides may last longer, I don't know. Several rebuilders offer improved materials and expert service on the heads that should drastically improve the longevity of the engine's top end.

3)

jim dorociak

The 95 engine is OBDI not OBDII compliant which means the cars computer does not transmit error codes directly to Smog Check computer causing to fail whether or not you are clean out the tail pipe. Jim

Steve Weiner-Rennsport Systems

Hi,

Perhaps I can help,...

1) ALL 911's are affected by relatively short guide life and its primarily due to: poor guide material, excessive clearance from new, excess heat, and a lot of idling (stop 'n go traffic). OBD-I cars (95's) do not report an SAI problem as the OBD-II cars ('96-'98) so the only way one knows there is a problem on the early 993's is by noting oil consumption.

2) Given that oil consumption is the best bellweather for guide wear & condition, thats the way one knows its time to fix it. Generally speaking, its NOT a good idea to continue to drive a car using 1qt/800 miles due to detonation issues and increasing propensity for much more expensive problems.

3) How long an upper-end overhaul lasts depends on many things such as what guides were used (factory or aftermarket), how they were fitted, what other wear parts were replaced, and other modifications for OBD-II cars to reduce SAI issues like enlarging the SAI passages in the heads and cam housings. If its done right, you won't revisit that for 100K+miles.

Hope this helps,

shamrock

Steve , what replacement guides do you recommend? ..
Not meant as a loaded question.

Steve Weiner-Rennsport Systems

We've been making & using our own Phosphorus-Bronze guides for 29 years.

I've grown fond of them for their durability, but they MUST be installed and fitted correctly for maximum success.

logan2z

Thanks as always for the informed responses of the members of this forum. Much appreciated!

logan2z

While this thread is still alive, can someone (Steve?) tell me what exactly is involved in a top end rebuild and why it is so costly?

NP993

The engine is removed from the car; disassembled to the point where the heads can be removed (about 75 percent, maybe more, of a complete tear-down); the heads have to be rebuilt with new guides; and then everything is reassembled and reinstalled. And it's foolish not to do a whole bunch of maintenance while the engine is apart, everything from spark plugs and wires to valve and chain cover gaskets. After the engine is back in, the rear wheels need to be aligned. If you're paying a shop to do it, it's a lot of labor and a hefty bill.

rconnon

Hi Guys,

In all of the posts i've read on this topic static numbers on consumption are noted 1qt<1000 miles etc.. with no reference to style of driving, average trip distance etc and i'm curious of the effects on consumption these factors will have.

For instance a car thats a sunday driver once a week for 200 miles cruising below 3000RPM vs a car that travels 200miles in a week 40 miles / day with many short trips in those miles.

My car has 92,000 miles on the clock and i do alot of city driving as the car is a daily driver, it sees many short trips in/out of the city, in fact for work i do about 7KM to/from work of city driving 14KM total daily (at minimum) this means 2+ cold starts a day, short trips etc.. I realize this isnt the best case for these cars but i made a conscious decision that i would drive my car every chance i got as i have no idea how many opportunities i'll have as we all know life can indeed be short.

in the city i do about 1qt/600-700 miles depending on length of the trips (hwy/street etc) - but when i took the car to Laguna in April i was over 2000 miles per qt of oil and it was a spirited driving all the way down / back. I would guess this is attributed to the car not operating at FULL optimal temperature for the periods of the day to day trips.. for instance in colder climates it would take longer to reach optimal temperature.

From http://www.101projects.com/rebuild.htm - how much of this data applies to the 3.6 in the 993?

" There are two places that the oil can be lost, either past the piston rings, or the valve guides. If the car is excessively smoking, then there is significant oil being burned in the combustion chamber. Air-cooled engines expand significantly when they are run. It’s not uncommon for the entire engine to expand more than 1/8 of an inch side-to-side when heated from stone cold to operating temperature. This means that certain clearances that are designed to be optimum at operating temperature are sometimes not ideal when the engine is cold. Oil seepage when the engine is cold is considered normal. Just about every 911 engine smokes when it’s started, primarily because some oil has seeped into the combustion chamber when the engine was cold. This smoking is not necessarily a sign that the engine needs to be rebuilt. A more accurate test would be to check for significant smoke when the car is completely warmed up."

I found this information interesting, again not sure how much of it applies to the motor in the 993 - http://www.pelicanparts.com/techarti..._rebuild-1.htm

So i'm wondering how to gauge a proper consumption number as the data is drastically different with driving condition temperature etc.

The car pulls incredibly strong, idles smooth, doesnt leak and there is no smoke on startup, WOT, or when doing the redline to 2000RPM in 3rd Decel test.

thoughts?

NP993

Rob -- if you have cats installed, you won't see oil smoke, even with pretty well-worn guides. The cat does a very good job of capturing it.

As far as consumption goes, I would measure it on the basis of warmed-up driving, not puttering around the city on short trips with a cold motor.

shamrock

Thanks for the earlier reply Steve.