Hi Folks -

So I have a parts car, an '85 928S with about 140,000 miles on it. The car runs fine but the interior is trashed and the body is only in fair condition. There's no sign at all the car has ever been in a wreck but it's a salvage candidate.

I want to pull the engine and re-build it and I'm looking for suggestions. I'm thinking about sending the block out for new nickasil cylinders then building the engine back up from ground zero. The idea is to build a new engine using an old block.

First, does anyone have an opinion on re-plating a block that only has 140,000 miles on it? Good? Bad? Stupid?

Second, can anyone point me at technical procedures for verifying the re-use of engine parts like valves, valve springs, cam bearings, crank bearings & other moving parts that wear out on these engines? I need to know how to decide what needs to be replaced. I have the factory service manuals but they don't (obviously) talk about the replacement schedule for these parts.

Thanks in advance for any suggestions,
Scott.

 

Hi Scott-

An '85 (as well as the 78-84 and 86-95) block was never nikasiled at the factory, and doesn't need it now, unless you're planning on running non-factory pistons in it. Measuring bore wear would tell you whether it needs any cylinder work.

What kind of compression does the engine make now?

As far as determining what can be re-used and what cannot, while there's a core set of things that should definitely be replaced (contingent of course on the maintenance history of the engine) , there will be many opinions about what constitutes a thorough engine rebuild. And the spectrum of cost for what constitutes 'complete' ranges from something like $4K up to ~$15K. Bottom line, though, I'd say it's impossible to say what your engine really needs without having the parts in person, in the hands of someone who actually knows what they're looking at. And that someone sure isn't me....

What are your goals for this engine and is it going back into this parts car, or a different car? Building a ground-up rebuild that's good for the next 20 years is a whole different ball of wax than a reseal and a peek at the rod bearings.

 

Rob it's hard to say exactly what I plan for this engine. One part of me wants to keep it as a spare for my driver, which is also an '85 928S automatic. Another part wants to build the "parts" car into a "full race" track car and thinks of supercharging or turbocharging the engine.

Right now I don't know the compression the engine makes, all I know is it runs and that it has about 140K on it. I haven't really begun the re-build process yet, I'm just considering alternatives. I'm not thinking of non-factory pistons (yet) but I'm used to the idea of replacing cylinders as a first step in re-building a block. My understanding is this may not be needed or recommended for a circa 1985 928 block since the engine was designed using alloys that revealed a high silicon aluminum when the cylinders were machined, though I've also been acquainted with companies that claim to re-manufacture these blocks by performing a nikasil re-plate on the cylinders. I don't have enough experience to know if this is a valuable service for an engine with this wear or even if it's ever a good idea. I wouldn't rule out non-factory pistons in a race engine if that was a good idea.

I'm definite about building an engine good for the next 20 years if I use it as a spare for my driver and I'll keep it stock in that case. The other alternative (full race) has no restrictions on life expectancy other than I'd like it to run hard and fast for as long as possible between re-builds. I have a good shop and I can re-build a race engine every so often once I learn how to do it

Thanks for reading, and thanks for your opinions.

Regards,
Scott.

 

Scott,

Actually most everything is usable. You should use some oil in the pistons and try to get a compression check. This will tell you the condition of the valves. Without oil you will not get an accurate compression test. The pistons and rings will probably go forever - it was one of Porsche's strong points. You will need to pull the heads to check the piston walls. If they are not scored or scratched up too badly then I would not replace the rings.

Look here there is a difference in philosophy here on a rebuild. A rebuilt engine should match or exceed the specs as published by Porsche. So if you measure the end play on the crank and it is with the Porsche spec and not at the extreme then why would you crack the case and replace the main bearings? It only makes sense if you have a lot of money to throw away. The main bearings and rings will go hundreds of thousands of miles probably an easy half million.

Then the next thing to check is the rod bearings. You can use a plastic gauge on one to see the wear. if the crank is still highly polished and bearings are in spec then why replace. Rod bearings are cheap but that are not run in like the ones in the engine.

Of course a lot of wear has to do with the oil used in the engine. Synthetic will make a huge difference. When you pull the cam covers look at the lifters and cams. I have yet to see any cupped lifters or excessively worn cam lobes. The cams run so straight that Porsche chose not to use cam bearings.

The next are the heads. These take the worse beating. Measuring valve guides is important. If they are good then lap the valves and put in new seals ($2 each) and call it good. Check the surfacing of the head and if good re-install.

The sad truth about the 928 engine is Porsche made an almost bullet proof motor but then covered it with sub standard junk. The things that fail are all the gaskets, hoses and wiring harnesses. If Porsche had used good gaskets, locking hardware and decent rubber the engines would need far less attention.

For me to put money into a rebuild I leave the internals alone if they are in spec and work on creating a miracle and not having the engine leak oil. Using better rubber and non Porsche seals is a good start.

 

Dan, all I can say is that I've heard and understood everything you just said.

Thanks,
Scott.

 

Dan -

Alright, I didn't ask your opinion on racing engines. The advice on stock engines was spot on (near as I can tell) But what about race? I'm still not sure which way to take this block.

Regards,
Scott.

 

I'm thinking you must not have had a 928 long if you have to look for places to spend money.

Regards racing, you want to have fun and test your skill against other drivers, then you need to think about what sanctioning body you plan to race in and what the rules are. Generally speaking anything that takes you out of a fairly stock motor is going to be wallet racing.

My view ... (see if you can guess) .... do a nice stock rebuild, replacing things that are worn, not just old, and drop it in and enjoy, then take your time with whatever strikes your fancy in a project. The stock engine is likely only going to be 10 to 20% of a real hot rod motor cost, so you won't even notice the cost and have something reliable to drive as the project crawls along.

 

You need to do some more research about what it really costs to rebuild a 5 liter 928 engine. Even a stock rebuild when you actually replace all the wear items like head studs and lifters to name just a couple.
And as was mentioned thinking about building a race engine without KNOWING where and with whom you plan to race is not going to end well. As you modify the car and engine wheels tires to get faster most groups it pushes you up into higher classes with faster cars and suddenly your competition is $150,000 Factory race cars or $250,000 specials.
Unless you have years of on track racing experience the limiting factor for racing is YOU. Start out with a cheap rather stock low power car and learn to race it. Once you are faster than the car then consider spending the money to improve the car.

 

why bother spending the amount of money you will on just having a slightly fresher 85 engine when the same amount of money would buy you an entire 85 928 in good condition? especially since you already have 1 that drives well.

Do a search on the screen name of slate blue and read some of his threads or find the thread about mike's engine or posts from Gregbbrd. Anything less is a waste of time and money, imo

 

Sigworthy.

 

It would be easier to get a barrel and throw a bunch of money and gasoline in it then throw in a match.

Seriously, without information (evaluation of the old motor) who can say. Leave it in the car and do a compression/leakdown to see what the internal health of that motor is. If you are determined to rebuild you still should measure compression, endplay, and things like that. These motors were meticulously assembled in clean rooms by people that just assembled 32V motors all day. Most of the time people ruin a perfectly good motor by pulling it apart then trying to reassemble it with the same precision.

As was suggested, you would be in the win column by just pulling it out (after confirming the compression and end play on the crank are within spec), freshing up the seals, gaskets, belts and hoses and storing it as a spare if you need a spare.

Dont destroy a complete engine with an incomplete rebuild. No bueno !

 

Ah but there you'd be barking up the wrong tree. What you must have meant is I haven't been driving a 928 very long. I've owned one since 1985, two since 2009. I just never drive them.

The only groups I know in my area are SCCA and PCA, I'm pretty sure PCA requires stock. I've been completely out of racing since the 80's. The nearest track is Laguna Seca, I also did some runs at Sears Point when my car was new. For the past 12 years I've been in Wyoming and the car hasn't been driven much at all so I'm exploring my alternatives.

I guess what I'm really asking is, how much life should I expect out of a 32v engine (mileage wise)? My driver has a little over 60K on it so I don't really know what 140K means to one of these in general.

 

The block is alusil. So the block bore prep is different than nikasil. They are finalized with felt pads and a paste that wears away the aluminum and leaves the silicon crystals.

The Manufacturer workshop manuals have many specs for wear limits, including bores, pistons, rings (replace anyway), bearings (replace anyway), valves, etc.

140k is going to start to get tired unless worked on previously or very well kept, inside. I have seen 130k engines look spotless and 78k engines with sludge in the sump and coke on the valves, etc.

 

Thanks for the leads TV, I'll check them out.

 

Thanks, it's the list of "replace anyway" that I'm looking for. It gives me a way to figure the minimum cost of rebuilding the engine.

So is there a cylinder "refresh" for alusil? I had been researching nickasil since that's what I thought the cylinders were made of. Now I know the right term I see it all over in discussions of 928 blocks. Great hint!