gnosis

In case anyone was wondering what's happened to my engine rebuild, I'm currently waiting on the final shipment of parts including the right size bearings as well as a replacement lightweight flywheel after I found out the one I was shipped previously was not for the 968. I expect the rebuild will resume around a month from now.

I hope the info I've posted on my site so far has been informative.

Clayton

cjeckert

Wow the detail you have put into this rebuild is amazing, i really enjoyed the slide show. Good luck w/t the rebuild !

gnosis

I've finally received what appears to be the right flywheel, ater being shipped the wrong one over 18 months ago. I've posted another update to my site where you can see photos of the new item. It's a SPEC lightweight unit.

I won't be updating the site again until around the end of October, when the final batch of parts for the engine arrive, and I can afford to get the block honed and head serviced.

Clayton

Damian in NJ

If you don't have someone to do the head you may want to contact Raj, he knows someone with talent in that area.

gnosis

I do have a contact to get the head done. It's a company I used to use to do my engine machine work when I was racing a Toyota MR2. Also, the guy who's doing the honing for me can do a range of other machining tasks, so I should be covered.

Are there any other gotchas I need to know about with block honing or head servicing? The honing will be done on the proper Sunnen machine to the proper spec, so that's in order. But if anyone has any horror stories or tips they'd like to share I'd be grateful. This applies even moreso for the head since it'll be going under the knife with potentially irreversible acts committed upon it. I intend to have the valve guides Klined. Has anyone had that done?

Suggesting Raj as a source for an engine machinist is thoughtful but impractical for me, since I'm in Australia.

Clayton

Damian in NJ

Got me on that, I hadn't read your sig.

gnosis

I thought I'd give you all an update of my engine rebuild progress. No updates to my blog or new photos just yet, but the final shipment of parts has arrived and I've handed a bunch of parts over to my machine shop to be prepared before the rebuild begins in earnest in about a week's time.

Here's what's happening right now. I was intending to have the machine shop hone the block and balance the new flywheel and pressure plate. It was decided that in order to do a proper job of the balancing, it would be balanced as a unit including flywheel and pressure plate, crankshaft, crankshaft pulley and associated rotating hardware, and rod and piston assemblies. I've been told that since it's a Porsche, the crank, rod and piston assemblies will be close to balanced anyway (unlike your typical American V8), but since it has to be balanced, treating it all as a single unit will ensure it balances exactly.

I'm also getting the rods serviced to make sure the rods are in as-new order. The small ends are getting new bushes, which will be align-honed to ensure correct fit to the piston pins, and the big ends are getting a trimming and honing process done to bring them to exact roundness, on spec.

I got a bit of a scare when I removed the crankshaft from the block and found some blue colouration around the journals. I was concerned that it might be signs of overheating during use. This confused me because the bearings were all in good shape, and I've never had any oil surge problems or lack of oil, particularly when pressing the engine hard on the race track. The guy at the machine shop was worried when he saw the crank too, and recommended that I have it crack tested, since overheating causes a softening of the metal which can lead to cracking and subsequent catastrophic failure. So I agreed to the extra few dollars and got them to crack test the crank before doing anything else. The good news? It passed with flying colours. No cracks, and the blue marks aren't the result of overheating. They're apparently common on these cranks due to some heat treatment done by Porsche when they're new. And if that wasn't enough good news, they confirmed my journal measurements and found that the rod journals were mid-size (between the top and bottom tolerance) and the main journals were top size. This makes the crank practically brand new in terms of wear. They're going to linish it, balance it all, and hand it back along with a correctly honed block (using Sunnen equipment, as required for all AluSil blocks) in about a week's time. Then the building of the short block can begin, and photos will resume on my blog.

I have yet to commit to having the valve job done on the head. Once I know there are no surprises to be had with the short block parts, I'll hand over my head to be done too.

Clayton

gnosis

I got all my bits back from the machine shop, but the head is still at another shop. It needs new valve guides because all 16 are worn beyond spec. I'll be supplying them within the next few days so they can go ahead and complete the valve job. The rest of the head is in good shape, so things should proceed smoothly in that department. I expect the completed head to be back in my hands before the end of this week.

As for the machine work, I succumbed to the "do it properly while it's apart" mentality, and got everything balanced while it was apart. The result, according to the pieces of paper supplied with the work, is 0.0 grams out of balance for all the reciprocating parts i.e. perfect. But it didn't start that way. An interesting thing to note about the balancing process is that at the start, the crank on its own was only 0.9 grams out of balance, but when the pulley and flywheel were added, the assembly was out by 25.6 grams. This was corrected, and then the pressure plate was shown to be 16.1 grams out of balance, which was also corrected. So for any of you out there who think it will be okay to skip the balancing part of your rebuild, take note. Imagine 30 odd grams of weight spinning around at 6,500 rpm, blurring your vision. Now that I've paid for this extra work to be done, let's hope the result is a very smooth and reliable engine.

I'm holding up the rebuild process a bit myself now, as I want to buy a few more tools to make some measurements before I reassemble everything. The onus is always on the owner to ensure the machine shop did the right thing, and I don't want to leave things to chance. So once I get the measuring tools I need, I'll measure everything that wears and has been machined so I can double check the machine shop as well as have a record to compare to when I do the next rebuild at 350,000km! That is if I don't trade the car in on a Cayman CS before then. Oh, and before you ask, no there isn't a Cayman CS. I just think there should be. If they made one, it would be the first time Porsche had come close to luring me away from my beloved 968. The other requirement would be to change the name from Cayman to something a little less "Gay Man". Not that my sexuality is threatened, or anything!

Anyway, for those of you waiting for more photos, I'll update my site with the pics of the holes the machine shop drilled in everything, as well as the mysterious missing material on a few of my pistons, which they deemed necessary to remove in order to match up the piston weights exactly. I haven't noticed, but I expect the rods have had a little material removed too, since they were weighed end to end to ensure consistency.

Look for an update to my site in a few weeks, as the final fastidious cleaning and reassembly begins in earnest.

Clayton

gnosis

Well, it's been a little more than a few weeks since my last post, but the good news is that I've finally rebuilt my engine! The other good news is that things went very smoothly, with every piece, nut, and bolt falling to hand when needed. I don't know how long most people take to rebuild these engines, and I'd hate to think what Porsche charges to do it, but so far I've clocked up 65 hours in rebuilding the engine. This includes taking photos but does not include getting the engine out of the car (18.5 hours), disassembling it (22.5 hours), and major part cleaning such as the block and machined engine components (6 hours), but it does include cleaning of parts as I needed them for reassembly. I figure another 12 to 15 hours to put it back in the car, cross the t's and dot the i's, and get it running, and I'll be all done! Grand total: Approx. 125 hours. And since I've been rather meticulous, I won't be a happy camper if it doesn't work properly first time!

For those following this thread, I've taken a gazillion photos, and will post them within a week or two. First, I need to get the engine back in the car and make sure it all works as planned. I hope to have the car back on the road by next weekend, and this will free up my time to get the photos on the web. I think a different format to the disassembly photos is required - something more like a "How to rebuild a 968 engine" format, with chapter and index page.

Anyone have any free web space I can use to host the pages? I'll still link to them from my blog where the earlier info is, but if I can find a host it would be better to set it up as a proper website.

Clayton

RajDatta

Get in touch with Bruce ward at bruce@2ward.com . He can host just about any size pictures and is a DIY guy himself who has taken plenty of pictures to help other members out.
Regards.
Raj

gnosis

Thanks for the suggestion, Raj. I've sent Bruce an email. Hopefully there'll be some space available, and I can put the site up there.

In terms of progress on the car, the big moment (starting the engine) arrived this weekend, and after a tense Saturday evening mulling over all the possible reasons why I had no oil pressure, I'm pleased to announce that the aforementioned missing oil was just being a little shy rather than suffering from any terminal problem. It was simply a case of ensuring the oil pump was properly primed, and things went smoothly from there. So with 4.5 bar of pressure on tap, I confidently went ahead with the beginnings of the running in procedure.

Impressions so far, after 20 mins of static running and two drives totalling 20km? Wow! It feels like a new engine! Well, I expected that, but it's nice not to have to buy a whole new Porsche for that new engine feel! No leaks, no weird noises, nothing wrong at all. In fact, I'm mighty pleased so far.

The lightweight flywheel is interesting. Sure makes it responsive! But also carries with it a little vibration at certain rev levels, especially coasting in 2nd gear through about 2100 revs. The vibration is currently made a helluva lot worse by my rattling exhaust shield, which I will have to fix very soon! But it seems to me to be prefectly liveable for a road car. As for the Spec stage 2 clutch disc and pressure plate, it's as smooth as silk. I've suffered for a few years with an OEM clutch that shook and rattled and carried on disgracefully, all because our local Porsche Authorised Dealer Service Department seems to think it's okay for apprentices to work on water pumpers. I mean, they're not 911s, so who cares if you forget to machine the flywheel before replacing the clutch, right? Yeah, right. So those days are behind me, both in terms of letting others work on my car, and putting up with a dud clutch. I look forward to bedding the clutch in and running the engine in. I hope my good fortune continues until at least 2000km, where I can change to a synthetic oil and consider the job complete.

Overall, from the depths of no oil pressure despair on Saturday evening with me wondering just how far back into the engine would I need to dig to find the source of the problem, to a Sunday full of wins, culminating in a few excellent test drives.

So far, mission accomplished. Now I have the spare time to get this website together so you can have a look at the photos.

Clayton

BruceWard

I would be very happy to provide hosting.

RajDatta

Excellent job there. Kudos to you!! very very impressive.
Good luck.
Raj

gnosis

Thanks :-) Let's hope it survives the running in process without incident. I guess it has a way to go before I can claim it doesn't leak, doesn't make weird noises, and doesn't lack the all important dose of power I've been missing.

It seems that when my heater control valve blew (the final straw that set this rebuild in process), it not only stripped the water pump's plastic impeller off the shaft, but also seems to have possibly cracked the radiator. It seemed to be leaking a little on both sides after I filled it, but tonight I've given it a shot of radiator leak filler, so hopefully this will keep things dry and pressurised for the duration of the run-in period. After that I'll get the radiator pressure tested and either fixed or replaced.

As you may have seen, Bruce has kindly offered to host any web pages I put together, so I'll be working on that as soon as things have settled down with the car (I have to get it registered, for example). The intention is to offer pages with how-to descriptions and accompanying pictures, with the option to look at full size version of the pictures if you need a close look at something. Once the pictures are hosted, it will always be possible to add more narrative and link to the relevant photos as examples, so other may be interested in writing their own text to go with the photos as well. We'll see how it develops.

More news soon.

Clayton

gnosis

As a teaser for the engine rebuild website, I thought I'd talk a little about my new SPEC flywheel and clutch, and show a few photos of the assembly. Later, this stuff will be part of the complete engine rebuild site, but since I promised some photos and haven't had time to put the proper site together, perhaps these few pics will whet your appetites for more later.

As some of you may be aware, I did away with the standard dual mass flywheel and replaced it with a lightweight unit. I got the unit from Linsdey Racing, who sent me the wrong one at first, but then kindly swapped it over after I realised 18 months later that it wouldn't fit. The only real downside to this issue was that I had to foot the return shipping bill from Sydney, Australia to Oklahoma, USA, despite it being entirely their fault that I got the wrong item in the first place! Still, after 18 months, accepting a return was pretty good. I've read stories of refusal to exchange flywheels before, so I'm not going to gripe too much about the circumstances.

The flywheel is very much lighter than the dual mass unit. I weighed both but then promtly lost the numbers, so I can't say exactly how much lighter. But it might give you an idea if I say that I could carry the SPEC flywheel around with one hand without giving it much thought, but I had to brace myself and ensure I kept my back straight when lifting the dual mass unit. Seriously! The dual mass unit weighs a huge amount.

The clutch and pressure plate package was also supplied by Lindsey Racing. It's a standard Sachs solid centre disc with custom linings, and a standard Sachs pressure plate with adjustments to the clamping force. It's referred to by Lindsey's as a SPEC Stage 2 kit. I got the standard weight one rather than the lightened one because I figured the flywheel was going to be a big enough change over standard. After all, this is my road car and occasional track car, so I have to live with it in Sydney (read: pathetic) traffic.

Here's a shot of the new and old flywheel side by side. The dual mass unit is dirty, but I doubt it would be as pretty as the SPEC unit even if I cleaned it.



Note how both flywheels have bearings in the centre. The first one I was sent didn't have a bearing, and had nowhere to put one. It just had a big hole. My guess is that it was a 944 flywheel, but I can't be sure since all I have to compare to is a few photos from the Haynes 944 Repair Manual.

Here's the new flywheel mounted on the newly rebuilt engine.



It's a direct replacement, so it uses the same mounting bolts as the dual mass unit. However it's decidedly "wasted" on the mounting side. Instead of being filled with metal (and rubber in the case of the dual mass unit), there's a gentle curve of aluminium back to the mounting face of the crankshaft, leaving a big gap through which you can see the rear main crank seal. That'll be useful if mine leaks!

Here's a shot looking side-on, where you can make out the gap between the timing ring gear and the block. It's all empty space except the curve of the flywheel as it meets up with the crank.



Now, I did this rebuild by myself (apart from the machine work, which was outsourced to two different machine shops). Sometimes I had to be creative with the tools I had to get the job done. In order to assemble the release bearing onto the pressure plate, I had to compress it enough to open up the groove for the large circlip. I rigged up some G-clamps and a big old shifting spanner to push the pressure plate down towards the release bearing.



You can see the footprints on the face of the pressure plate where I first took the advice from the Clark's Garage site to stand on the pressure plate to complete the job. But this pressure plate has too much force, and I'm too light (73kgs) to make much of an impact by standing on it. Thus the elaborate setup with the G-clamps.

Now I was ready to assemble the clutch components on the engine. I installed the new clutch plate, using the tool supplied in Lindsey's kit to centre it.



You can see the custom surface on the disc. Although not having separate pucks, the surface itself for all intents and purposes acts the same way. Note that there are no springs or rubber pieces in the disc.

Next came the pressure plate, complete with release bearing.



It had been balanced at a machine shop before assembly, so it had to be oriented correctly to maintain the balance. There are three possible ways to bolt it up, so I had to ensure I picked the right one. I was aided in this task by the marks the machine shop put into the flywheel and pressure plate, making it a simple task of lining up the marks before bolting things up. You can see in the following photo that they've drawn some white lines, and also used a small punch to permanently imprint matching pairs of marks into each component.



You can also see quite a few holes where they drilled weight out of both the flywheel and the pressure plate. I have the piece of paper that ensures me they got it balanced to within a tenth of a gram by doing this.

One nice part of clutch maintenance on the 968 is a moveable sleeve on the driveshaft.



This sleeve retracts, allowing clutch and subsequently flywheel removal while the engine is in the car. Unlike 944s and earlier, there's no need to drop the rear suspension to remove the clutch. It takes a 16 hour job down to a 4 hour job, apparently. But this was irrelevant in my case since the engine was conveniently located right in front of me. However I took a photo of the central shaft sleeve as it would sit in position in the car. There was also another reason for putting it into the assembly at this time. I wanted to check fit everything so there were no surprises later when I was under the car attempting to slide this item into place while positioning the bellhousing to the torque tube. It's only after correctly mounting the engine and engaging this assembly that you can tighten the bolts to the torque tube. This ensures everything lines up properly without imposing any lateral forces on components that shouldn't be there.

Next came refurbishment of the contents of the bellhousing.



New bearings were inserted into the clutch release fork in the place of the old very rattly sounding ones. I used my trusty wood vise, which is super strong and has nice big flat faces. It was the perfect tool for pressing bearings in and out of things. I also used it on the only other part of the engine build that required bearings to be pressed - the front balance shaft mounts.

The bearings were subsequently greased with a long life extreme pressure (EP) grease, as were the other contact areas on the fork. This was installed into the bellhousing, along with a new guide sleeve, and the bellhousing was bolted to the engine.



But not before checking that the hall effect sensor was located the correct distance away from the ring gear on the flywheel. I didn't change the position of the mounting bracket during the rebuild by leaving it bolted in place throughout, but since the flywheel was a new item, I measured the gap to make sure the new ring gear wasn't a different height to the original one. As it turned out, the measurement was good, and the item didn't need to be repositioned.

So with all that done, the last thing to do was to replace the little plate that blocks off the lower space in the bellhousing. I took a photo before putting the shield in place that clearly shows the pretty new flywheel's last look at the real world before being shut away out of sight to do its job. Note how much space there is in there now that the dual mass unit is gone.



And that's the story of my flywheel and clutch installation. So far, after 200km on the road, it's proving to be just what I wanted. My goal was to allow faster gear shifts. I'd always thought the dual mass unit let the engine spin for too long between up-shifts, and this new unit seems to have dropped the time just the right amount to allow shifting to occur the way I want. I wouldn't recommend doing this conversion if you drive around town (lazily), but if you track your car, or drive it fast on the road, then I'd say it's an excellent upgrade. I must say that unless you practice proper rev matching techniques, blipping the throttle on downshifts and heel-toe braking, you won't like it, because as soon as you remove your foot from the throttle, the engine is heading for idle in quite a hurry.

One fear was that it would mess up the idle by making it lumpy, or worse, stall the engine when the throttle was closed, but it's not doing that. It can overshoot the idle point a little if you're not careful, for example if you're coming up to a light at 3000rpm and you just dip the clutch, so simply adjust your driving style to accommodate it. I'm certain the benefits are going to greatly outweight the disadvantages.

The only real downside is that the damping effect of the dual mass unit is no longer present, so the noticeable vibrations that occur off throttle in gear (mainly 2nd gear) at between 2000 and 2300 revs can be a little annoying. They're exacerbated by the fact that the flywheel amplifies the noise of the vibration and sings a little. It's only a minor thing, though, and as with the idle overshoot issue, you can quickly learn to drive around it.

What about the clutch? It's supposed to have greater clamping force, and this is clear through the clutch pedal, but it's not fatiguing at all. In fact, it feels close to stock, and very solid at the same time. The clutch isn't shuddering at all. In fact, it's the best clutch feel I've ever had in the car, easily beating the woeful one I had in last time which was installed onto an unmachined flywheel and consequently chattered like crazy much of the time. This disc, despite being a solid disc with a pucked surface, is wonderful. I won't know how grippy it is until I run the engine in completely and can give it a few hard launches, but I don't expect to experience any problems.

All up, this flywheel and clutch package gets very high marks from me. I'll give you an update once the car's run in, and once I've had the chance to lean on these components a bit harder.

And soon, I'll document the rest of the rebuild, in a fashion similar to this, I guess, but on web pages instead of a dialogue in a thread here. I'd appreciate some feedback on the conversational style of the writeup. Good? Bad? Informative? Ambiguous? Instructive? Pointless? You decide.

Clayton