RyanPerrella

Agreed,

Now if we could find a new solution for this problem and get a ring set for $300 we would be set.

It used to be that the GTS pistons were crap, but thats only true because of the oil drain holes which is something you can fix with a drill press and about an hour's time, that hardly requires new pistons, but what to do about the rings! Now were talking new pistons to change the ring gaps, a silly reason for new pistons although new pistons would have other benefits.....

I have a theory that the difference in rings is only one of the 2 compression rings. Is this true? I doubt that Porsche changed the upper and lower compression ring width, one is more likely, again this is just an assumption.

However, if my assumption is correct, perhaps the ideal solution for GTS pistons is a hybrid ring pack, lets say 5.0L rings for the oil control and the lower or other compression ring. Having to find a suitable single ring for 8 pistons is much less of a problem than having to acquire an entire ring set.

So what does it cost to have rings produced to fit this mysterious ring gap?

I have a GTS piston that Greg sent me, unfortunately I dont have a way to measure it but I will compare it to an S3 piston and hope that the S3 and S4's had similar ring sets. (again not a given)

How about a combo ring pack of S4 rings for whats compatible and something from another supplier for whatever is GTS specific? Could work?

Cheburator

A lot of myths on the GTS engine as usual...

1. Has anyone actually broken a 1R road? Yes, I have seen the Porsche technical buletin. I have also seen a GTS engine with 1R rods, which has been tracked for 12,500 miles and is still good - dr Nick's old car

2. The GTS oil control ring is different from the one used in the GT/S4 engines - the GTS has one piece oil control ring similar to 944 rings

3. Only someone who has not driven a GTS engined car can say that the engine is crap. Stock for stock, it is the pinnacle of the 928 engine evolution. I have driven a 4.5 Euro, 4.7 Euro S, 4.7 Euro S2, SE, GT, hot rodded GT, S4, stock GTS and finally a hot rodded GTS, which was keeping E60 M5s honest, but what do I know...

928GTSM

Ok so my ignorance of the workings of a 928 engine is showing through here never having worked on one of these engines before. I assumed trhat with the engine out if I dropped the crank with the rods and pistons still attached I could remove the pistons drill and replace them with new rings and replace the main bearings.
Accepting that the big end bearings are likely to have worn then it would make sense to replace these also but I'm now being told that if I split the rods to replace the bearings the rods are effectively scrap and I'll need to change these also.
Basically the engine never misses a beat, pulls like a train and is not making any noises that would indicate any excessive wear in the bottom end.
What it is doing is consuming oil quicker than any other car I've had and belching out an embarassing cloud of smoke either when you come off the gas after travelling at high speed or having come off the gas when you first get back on it.
As previously stated I'd originally planned to fit the Shark Vent when I was told the only proper way to cure this was to remove the engine and drill the pistons.
If this is the case then whilst I don't want to incur unnecessary expense it would be pointless to do a half ar*ed job only to have to take the engine out again later through not doing it properly the first time.
Bit of dilemma to somebody that has no experience of these engines other than getting in turning the key and having fun. So based on the above what are the recommendations?
Rings - likely yes and had planned for these
Rods - am I really like to break one with no S/C and street driving
Main & big end bearings - sounds like a definite yes on both irrespective of rods.
Any thing else thats essential while I'm in there?

Cheburator

the pistons can only come out from the top. the heads would have to come off... £250 for a gasket set

the 1R rods that you have are purportedly weaker than the 2R introduced in 1994... dr Nick in the UK of orange car fame drove the nuts off his track GTS and it still had 1R rods. Porsche UK has 2R rods in stock - about 900 odd pieces at £130 each + VAT. i doubt very much that street driving will break them

given that you will be spending about £1000 on all the parts for the refresh, to save £150 from not changing rod and crank bearings will seem like a daft thing to do. Do not forget to order a set of rod nuts - they definitely need changing if you split the rods

what was the mileage on yout gts lump?

Rob Edwards

If it were my GTS engine that I was rebuilding myself, cost was a consideration, and the goal was a stock GTS engine for exclusively street use, I would:

Buy 8 sets of Porsche rod bearings ($240), new head bolts ($300), an engine reseal kit ($500), valve stem seals ($100), and bite the bullet on a new set of GTS piston rings with the understanding of the vendor that the sets better be in spec/useable. Agreed that there are few (none?) reports of R1 rods actually breaking, but I know people have seen them bent, in running engines. I guess you'll just have to open the engine and see what your R1 rods look like and go from there. I'd also get a pan and oil pickup spacer set.

I'd pull the heads, rods and pistons (but not separate the block from the girdle) make sure the valve guides are ok (and replace if not), skim the heads clean, have the lifters ultrasonically cleaned, decarbonize and drill the pistons, re-ring, and reassemble.

There are a million small gotchas and things to check while it's apart. Pull the engine and start disassembling, get a good digital camera (no cell phone shots!) and make a thread of it- you'll get lots of help and opinions along the way.

Koenig928

Hmm, I'm guessing 3 things possibly:
- you're sucking in oil that's accumulated in the intake from the oil breather
- oil is getting sucked in past the valve stem guide seals (as in my case)
- or a small amount of oil is getting past the 3 piston rings (from the lack of oil return holes)

I'm with Vilhuer and Roger, try modifying the oil breather first.

To try and put it into perspective, unless you plan on applying boost to your engine (S/C, turbo, nitrous), then the GTS rods should be fine. They work now and they'll work when you put them back in. Just put it all back together per the WSMs and ensure the timing is correct. Yes they can be replaced, but it's all at additional cost.

The GTS rods are not as stout (thinner & lighter) as the earlier S4 rods, hence the problem some have experienced.

Please don't misunderstand, I'm not against replacing the rings, I do think it's a good idea while it' apart. (btw, I found my replacement GTS rings at $50 per hole). I'm just saying it gets expensive very quickly. From my rebuild experience, you never know what you'll find when you open up an engine, even a good running one. I tore into mine thinking I'd just find a cracked head, but found a laundry list of other stuff that needed attention also.

Just my .02 worth. Good luck with whatever direction you choose, we're all here to help

RyanPerrella

1) R1 rods reportedly bend into S's. Porsche also specifically states that no R1 rod shall be reused once its been separated from the crank. Luckily the R2's are reasonably (for porsche's sake) priced at $160 each or $1280 plus tax.

2) Oil control ring being 1 piece or 3 isnt what i was talking about. I was referring to the size of the ring gap in the piston. S4 rings do not fit, I was assuming that only one ring was thicker on the GTS. GTS and S4 bores are the same 100mm +/- so if you could use a partial set from an S4 and then find a supplier for whatever is to thin, that was the idea behind my hybrid ring setup.

3) When people say the GTS is crap, it has nothing to do with output, but rather the parts used to create them. Off the top of my head on a 1993 engine 1) they burn oil and ping because porsche didn't drill oil drain back holes in the pistons. Apparently they did this to lessen cylinder wall wear which ive found to be nonexistent in the GT and S3 engines ive personally torn down. 2) the rods are garbage 3) the rings are now incredibly expensive, thus this thread 4) the car is reportedly under "cammed" if you wanna call it that. If your tearing apart the thing, you would benefit from different cams. The crank for all intents and purposed is just as good as any other. but those 4 items could all use attention, and the 2 are really nearly necessary, 3 is a price issue and 4 is just the while your at it thing to do I suppose.

I have no idea why porsche made so many changes with the GTS production. I suppose with the longer stroke, when new rods and pistons had to be produced anyway, they went cheaper on both. Apparently now the 8cw crank of the GTS is neither a good thing or a bad thing, its just different, opinions ive lately seen vary on the benefit of 8cw's.

allot changed in 1992, and most of it has proven in time to be less than ideal. I dont think there is any denying that.

ptuomov

Here's one opinion from a person who helped get Bryant's shop started:

http://speedtalk.com/forum/viewtopic...239863#p239988

RyanPerrella

So there we have it

all the components in the GTS are somewhat compromised due to cost of manufacture. Porsche made the engine bigger, but the components are of lesser quality.

We know this is true of the Rods, we know this is true of the pistons (at least in case of the extra machining not being done on them) and now the crank possibly.

If anything it shows what was really left on the table and we now see the real potential of these engines with the developments and improvements that are built into the Greg Brown strokers. (sounds like a porno film series) I haven't felt acceleration before like i did in Rob Edwards new blue monster. He said it best when I asked why he doesn't drive his GT anymore.. "Its to damn slow" Or something to that effect.

blown 87

You go in to build a motor and do things half assed, that is exactly what you end up with, a half assed job.

928GTSM

Cheburator I was planning on pulling the heads anyway in case there are in gremlins lurking within the valve train. I shall also do the big end and main bearings and atempt to source rings from my OPC on a sale or return basis if these are not within specification.
As the answer to my original question concerning the rings appears to be that the price is pretty consistant where ever you source them I'll have to accept that. This now leaves the main question to be whther or not the rods really are of that poor a quality that they would also need replacing?
Mileage on my car is 137k which is verified by the service history that came with the car.

Rob Edwards, what are the benefits of the oil pan and pick up spacers that you mentioned? Would I need a longer dipstick or and if these are considered beneficial where can I buy them please. Sorry for so many questions but I haven't seen these mentioned elsewhere.

Koenig 928, when you say about oil being sucked into the intake are you referring to ahead of or after the MAF? When I recently changed the CPS and had to remove the MAF there was no oil at all accumulated in there. Presumably I'm not going to know about the possibility of worn valve guides until I get the engine apart.

cold_beer839

The stock GTS breather system pulls crank case air in behind the MAF. But due to design flaws it also can pull oil from the heads and dump it into the intake as well. The SharkVent re-routes the breather system into a catch can that dumps the oil back into the crank case. It has a filter that you can open and inspect, and I was completely surprised by how much oil used to get into my intake. Sooner or later I also plan on having my motor opened and overhauled to fix all the known issues, but due to lack of funds and at 49k miles it is still running great, it'll have to wait.

Rob Edwards

For an exclusively street driven car you don't NEED the pan spacer, it just moves the oil pan 3/8" farther from the crank, decreasing the amount of oil aeration that is generated. This really only becomes a problem under racing conditions at sustained high rpm. But if you're going to do any significant numbers of track days, it might be relatively cheap insurance. Spacers are available from a number of the U.S. vendors. Your dipstick is fine as it is.

Vilhuer

Yes. Two out of three rings have all the same critical dimensions as S4 etc 100mm rings. IIRR its 2nd compression ring which is 0.1 or 0.2mm different. In any case its one of the compression rings.

There is cheap option of using S4/GT/951 sets and only use two of the new rings and one original used GTS compression. I have tried it on one engine build but do not have long time results. In any case I can't see why it wouldn't be ok as long as remaining original GTS rings are good enough to be used.

John Speake

Don't spoil his fun ! Fitting a provent is too easy. .. he really wants an excuse to pull that motor :-)