Full rebuild as a result of piston slap?

[aseem]

Hi.

EDIT: Happy ending on the next page :-)

I'm about to do a mild upgrade on my less than 70K miles 930 (1980). The plan is a new GT35R turbo, Turbokraft IC, RarlyL8 headers and muffler, new TiAL WG (.9bar) and BL adjustable WUR. I have also installed a Zeitronix logger to monitor A/F ratio after the build. To make sure the engine is sound prior to upgrades, I took it to my shop for a leak down test and diagnose of a ticking/clanking noise that have developed recently (maybe valves). The plan was for this to be a enjoyable DIY project and to get a more responsive engine with a bit more torque and HP, and lower RPM boost. To make it more drivable and enjoyable, not to make an extreme engine.


The conclusion from the shop after inspection was piston slap, and they recommended a top end rebuild with new P&Cs. We would also do 964T cams while in there. I now have a proposal for the job, and I found the job recommended bigger than anticipated and the price very high. It has also turned into a full scale rebuild from the initial talks with them of a top en job. I need some advice from the experienced crowd here at PP, not that I don't trust my shop, but a second opinion never hurts. Also, I don't know how serious it is to keep on driving with piston slap, and whether piston slap neccesitates the full rebuild described below.

Here is the extent of the rebuild I have been recommended: Polish crank, new bearings, new rod bearings, new rod bolts, balance rods, new bearing on oil pump shaft, new oil return tubes, 993TT stretch bolts, new 964 P&Cs, full overhaul of cylinder head (polish/grind seats, valves, new valve guides), machine heads, head porting , porting of intake, new cam chains and rails, new seals everywhere, new 964 cams. Mind you, some of this has been initiated by me, as the engine was going to be opened anyway: I asked for new cams (I actually asked for SC cams, but were recommended 964 cams), and also asked about porting which they initially didn't think would make that much difference in this performance range (375-400 RWHP with CIS). The shop is aware of my modification plans, and are in tune with my wishes for a fun, and drivable street car. I'm looking for more fun in the mid range, not top end. They will also install the "fun-parts" mentioned above, so in a way they are taking over my project, but I see the advantage when it comes to tuning the fuel delivery.

Of course, I don't want to start modifying an engine that isn't healthy, but this is just becoming very expensive. I am on a budget for this project, and now I'm looking at 3.5 to 4 times my initial numbers. The shop has a good reputation, and has a very! good engine builder. I understand their attitude, to make the engine 100% when they are responsible, and do it right while they are in there. But I don't know if they over-medicate the patient. I can see myself in the future while on the operating table for new heart valves, being asked if we shouldn't replace the liver and lungs also while we're in there. They will tell me that this will give me a complete overhaul, and provide a 100% sound mid section for at least another 15 years. Who would say no to that other than the bank. I guess its like that with our Porsches as well. We all want the best for our cars, and we like the idea of a 100%-engine; as new.


Some other background info: I was swapping the gear box a while back for a "new" one, and the new tranny had a different pivot for the accel linkage. The engine had been sitting for a long time without oil (over a year), so I was going to crank it with no ignition to get the oil flowing. The starter wouldn't crank and I was doing a lot of bug tracing as we say in the computer industry. In that process I reconnected the ignition, and forgot to remove it again. When triggering the starter with a wire directly to the battery, the thing fired right up and went directly to WOT (funny how this car fire up so fast even after a year without running). The linkage pivot was different, and the throttle was initially at WOT. I managed to stop asap, but only after what felt like an eternity. Had to jump into the car to switch the ignition off, en even then it took tree-four loong seconds before it stopped. Not good, but at least it wasn't a newly built engine. However, the clanking from the engine developed after this. I have driven the engine from time to time after this, but not as much as I wanted to. When driven for a long period, like two hours, the engine has no noise to speak of. But if I run it shorter to operating temperature, it's still noisy.

Sorry for the lengthy story, but I wanted to explain all the details and I hope for some valuable second opinions and insights from the collective knowledge of the PP forum

Thanks

[pkracer21j]

If your spending all the money do build it right, I would ditch the CIS and go megasquirt EFI. you'll be able to take full advantage of your upgrades/mods and you will be much safer fuel wise at high RPM's. a few members here as well as myself have done megasquirt conversions with great success.

[aseem]

Thanks for taking the time.

My idea was to keep a basically stock engine, with only bolt on mods. Target was in the 375 RWHP area. With the piston slap (if that is what it is) I first need no make an educated decision on weather the full rebuild is necessary.

Of course going EFI with 3.2 heads and intakes would be interesting but an entirely different project. I guess it would add some cost, but probably not that much.

Question for now is:
- how serious is the condition of the engine (or how serious is piston slap)
- does piston slap normally require an engine rebuild

[s5uewf]

I'm not an expert, and perhaps one will chime in, but my impression is the 930's pistons and cylinders were designed for same rate thermal expansion - so there should be no piston slap. You could get piston slap from putting in aluminum pistons during a rebuild, for example, but not using the stock set.

If it was piston slap it should go away when warmed up. Does the noise go away?
Also, I do not think piston slap in itself is dangerous to the health of the car.
I think GM makes V8's that slap from day 1 and they run forever.

You may want to call Turbocraft or other rebuilders and talk to them and see what they have to offer in terms of advise or opinion.

Good luck!

[pkracer21j]

no need for a 3.2 manifold or 3.2 heads. xbmwguy here on the forums has done a megasquirt EFI on his 930 using 930 heads and his 930 manifold with turbokraft's injector blocks and fuel rails

[aseem]

The noise does not go away after say 30 minute driving. I took it for a two hour drive a while a go, and then it had almost no noise at all at idle. I hear it mostly at idle and lower revs, but then there are so many other sounds at higher revs, so its much harder to detect.

pkracer: I know, I was just summing up some ideas for how I might want to do it if I was to go the EFI route. For now I'll stay on the CIS path...

[gsxrken]

You might have hurt your timing chain rails with your unloaded ride to redline and that's your noise. Tapping can be a valve or broken rocker (compression test?) or an exhaust leak that sounds like a tap. I don't buy the piston slap either, but I guess it's possible. I'd get another opinion.

At 70k, you could reasonably trust that the bottom end is still good. With good oil pressure and no rod knocks (perhaps get an oil analysis done to inspect for bearing material), I would try a top end overhaul first.

SC cams sound much better for your mid range power goals than the top end of the 964s.
And EFI is a topic unto itself. Not for the faint-hearted but in either case I would get all sorted out mechanically and budget wise before I went there.

[911nut]

Classic piston slap is a result of manufacturing tolerances not being what they are supposed to be for a variety of reasons but the bottom line is that when the pistons heat up and expand to their working diameter, the noise stops. This will happen pretty quickly (5 - 10 seconds) and it's really just an annoyance.
Sounds like you have a different issue. If your shop has a borescope they could look into the cylinder to look for evidence of valve-piston contact or ring/cylinder wall issues before launching into a teardown.

[Miguel Antonett]

After a WOT for few seconds, right off crank, stone cold, with NO OIL for over a year... it doesn't sound favorable for a healthy engine. IMO, you should open that engine top & bottom checking for damage before making any firm plans.

[MikeD930]

Originally Posted by Miguel Antonett

After a WOT for few seconds, right off crank, stone cold, with NO OIL for over a year... it doesn't sound favorable for a healthy engine. IMO, you should open that engine top & bottom checking for damage before making any firm plans.

+1

I would not drive it anymore. I would take the engine apart and check everything. It only takes a few seconds of "no oil" to damage the bearings (crank and connecting rods) among others especially when revving engine at start up. These problems won't manifest until later. At the least I would replace all main crank and connecting rod bearings. As for the noise...it could be valves or timing chain related that was caused by sudden over-rev without any load on the engine.

[aseem]

Thanks for the valuable input. We are talking about putting half the value of the car into the an engine rebuild, in addition comes the parts I have purcased. I guess this is the way whan you own an old performance car; pay up and smile, but don't tell the wife or anyone else without P-car experience.

After reading through Lincoln's thread, I suppose I should be happy that I have such a cheap car ;-)
Project 930 The Resurrection

[T77911S]

if the noise developed after the WOT, i would be more concerned.

me, i would budget for a complete rebuild. upgrade to a 3.4 with SC cams then add the other stuff later. if i opened it up and found the noise was inthe top end, i might consider leaving the bottom end alone and look at doing it in another 70 to 100k.

[Speedy Squirrel]

What RPM was reached at WOT? Was there a leak down/boroscope done to confirm if the piston is loose in the bore?

WOT with no load is the worst condition for pistons/rods. You need to be sure that the rod bolts aren't stretched. Don't drive it any more.

[aseem]

I don't know exactly the rpm but I have a rev limiter, and I'm sure it kicked in. It all happened so fast. This happened a couple of years ago, and I have put maybe a thousand miles or more on it since then. But no serious driving, since I always had this nagging feeling I should have the engine checked out.

AFAIK the shop only did e stetoscope check listening to the engine. I put it there for a leakdown test, but I don't belive they did it beacuse of their diagnosis of piston slap. They never mensioned that they used a boroscope to look inside.

The engine builder in this shop has 17 years of experience from RUF , so I don't question his qualifications. But I know from my own industry that sometimes the MBA people get in between in the dialog and recommend more parts and work than strictly required. Every business wants more sales, and every person with a quota wants to fill it up. The fact that from their first guestimates to the final quote, the price has nearly doubled, makes me want to ask for a second opinion.

Most of the crown here at Pelican are not professional engine techs, but you all have aquired expensive and valuable experience over a collectively very long Porsche ownership. Also there are pros on this forum that chime in from time to time, sharing their hard earned experience. That is what makes this forum great, and also why this is the first place I would turn to for an opinion.

Again, thanks for taking the time...

[66cal912]

He's not in Norway, but it would be worth a phone call and a second opinion, good guy, great work, see for yourself:

Sports Purpose Engines - Matthias Hoeing Sportmotoren

I m quite sure there is reasonable sea freight from your area to Hamburg, where the shop is.


Good, luck, sounds like a full teardown is in order after your description, minimal for a full inspection, be sure whoever does it, goes with the 993 case to cylinder to heads stud, they, are what any of the good Euro builders are using, I think a set will be definitely be between to 2000 Euro unfortunately, but you get what you pay for on those. Also on your build dont forget cost of new upgraded turbo and intercooler to match your new internals, be another 3000 to 5000 euro.

Regards

Ben

[aseem]

Originally Posted by 66cal912

He's not in Norway, but it would be worth a phone call and a second opinion, good guy, great work, see for yourself:

Sports Purpose Engines - Matthias Hoeing Sportmotoren

I m quite sure there is reasonable sea freight from your area to Hamburg, where the shop is.


Good, luck, sounds like a full teardown is in order after your description, minimal for a full inspection, be sure whoever does it, goes with the 993 case to cylinder to heads stud, they, are what any of the good Euro builders are using, I think a set will be definitely be between to 2000 Euro unfortunately, but you get what you pay for on those. Also on your build dont forget cost of new upgraded turbo and intercooler to match your new internals, be another 3000 to 5000 euro.

Regards

Ben

Yes, it looks like we're heading towards a full rebuild. In the first post, you see the parts that are waiting for installation, turbo, IC, exchaust etc. The engine builder is only using 99TT studs. Prices are not that bad, and not in the range you are suggesting. I've also checked Mahle prices from our host, and I get the same prices from my shop. Supprisingly, since i livce in a very expensive country where a pint of beer usually set you back a cool 14 bucks.

[66cal912]

yeah, I left out the 1000 to 2000 sorry on the studs, but I know they are pricey, as I did two rebuilds about 3 years back in Germany, and I think they were at least a 1000 EU at the time for 24 of them, so knowing that Porsche keeps raising parts prices in Germay, is why I put a range on them. I m sure you ll get it sorted out, what ever way you decide to go.

[slyguy]

If it was me I would be pulling the valve covers, checking the rockers, inspecting the cams/rockers for odd wear patterns and give it a valve adjustment if all looks good way before I would or have someone else tear into my engine. A rocker out of adjustment can make an awful l lot of noise and this piston slap diagnosis seems very unreasonable for me. If there's a frozen rocker or flats on a cam or rocker then it's top end rebuild and cam upgrade time.

[aseem]

Ok, so the engine is on the table in pieces.
Piston slap was not the problem, but the wristpin side of #3 rod. Discoloration is proof of high heat, and deformation as a result. A disaster in the comming.

The guy who is doing the engine, has 17 years experience from RUF, and more years at other places. He wants to do it right, or not at all - which is going to cost me, but also give me a "new" strong engine to last a long time as long as I treat her well. I have had The Turbo for 12-13 years now, and always wanted more. Now it is happening....

The case have been split, everything has been cleaned, measured and machined. Polished crank, new bearings and seals every where of cource. New 996Turbo oil pump. New 964 Rods, 965 P&C's, ported heads and intake plenum, new injectors, 964RS cams (same as 964 but without the servo drive, to avoid machining), valve guides, seats and machined valves. I'm keeping the stock airbox, but with a slight modification to fit with the Turbokraft LNIC. The studs were already 993tt, and they looked excellent after many years of service. New cam chains and rails. And I'm going to need a new clutch.

In addition comes what was to be my bolt on project with parts from RarlyL8 and Turbokraft: headers, muffler, IC , Tial WG (0.9) and GT35 Turbo. Yes, and Leask modified WUR.

This ought to be a really fun car to drive, and I have been aiming for mid-range madness. Its a street car, daily in the summer, so top end is not 'that' interesting.
I'm throughing out the old and heavy R12 AC, so that will lighten the car some 75-100 lbs. New 935 carbon seats from dP. Everything is black, no real bling except the Lindsey P2 wheels that I already have. Treated the engine to a new carbon air shroud (semi bling) from Autobahn Extreme. Expensive, but that bill will disapperar together with the rest of the stuff.

[M5guy]

Total awesomeness.