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Rex Walter Rex Walter is offline
Registered User
Join Date: May 2005
Location: Bothell, WA
Posts: 239
Uncommon Engine Building Mistakes

My 1975 Porsche 2.7L engine is the first engine I’ve really rebuilt, and I just finished. I’ve watched friends rebuild engines, and have even been allowed to turn a wrench once in a while. There was a Triumph engine that I put together years ago, but that really couldn’t be called a rebuild, better described as making more work for the next guy. There is a thread on the Pelican BBS that is called “Common Engine Building Mistakes”. I would like to add to this thread, but most of my mistakes were not what you would call “common”. Here are some of my not so common, novice engine building mistakes. First, let me thank everyone that has contributed to the Common Engine Building Mistakes, as without that, my list would be much longer. As a matter of fact, since I studied all the hard stuff, the hard stuff turned out to be pretty easy. It was the simple things, that aren’t even worth mentioning in the rebuilding books, which were a challenge for me.

If God had wanted the clutch and flywheel to be at the front of the engine, he would have made Camaros and Mustangs that way. Even Triumph got that much right, although you could argue that a Triumph is not exactly an engineering marvel. Once I got the Porsche engine on the engine stand, I had a lot of trouble figuring out which end went forward, which side was right, and which was left. The following picture actually shows the correct numbered cylinders attached to the correct side of the engine. JW is probably falling over in disbelief right now. (We won’t speak of this in public, will we John?)

Actually dismantling the engine went pretty well, except I took it just a little too far. You see, I was taking the engine apart to send to Motor Miester. They ask you to remove all the studs, in all the parts. This includes the case studs, the chain housing studs, the cam tower studs, the 10 studs in each of the 6 heads…..etc. There were a lot of studs. After a few weeks of stud pulling and packing everything in crates, it was ready to ship. Now I couldn’t get MM to answer the phone to tell me where to send the crates. Doing a search on the web, to see if anyone else had trouble with MM, I found the Pelican BBS. This was definitely not a mistake. At this low point in the rebuild, things began looking up. I contacted Walt at Competition Engineering to do the case, John Dougherty to do the rocker arms and cams, and John Walker to rebuild the heads and inspect all the remaining parts (P&Cs, oil pump, etc).

It turns out that taking all the studs out of a magnesium block pretty much destroys the threads. Walt had to put inserts into all my threaded holes. I now have the strongest magnesium block on the planet (except it’s not shuffle pinned). As I got parts back from different shops around the country, I started putting studs back in. It turns out that the length of the exhaust studs and chain housing studs are critical to getting the engine back together correctly. The length of the head studs is well documented, and wasn’t a problem. Even though my ARP studs look different from the stock studs in that only a small section of the stud top was threaded, and was rounded at the top instead of being squared off. What do I use as the top of the stud to measure to? The top of the threads? The top of the rounded stud? Since there was so much information available, I was able to figure this out by measuring the length of the cylinder, adding the length of the head, and calculating where the barrel nut should be on the head stud. It turns out that the stock stud height is correct when measured to the top of the constant cross section of the ARP stud, just before the rounded top begins. If only I had been as smart with the exhaust and chain housing studs.

I probably assembled, took apart, and reassembled each part 3 times before I was happy with it. So that means I’ve actually rebuild about 3 engines now – right? There was lots of discussion on the Pelican BBS about which cam goes on the right, and which is left. This I got no problem. Rabbit ears on the right, the letter “L” on the left. This is great if you can tell the left cam tower from the right. I grabbed the right cam and the wrong cam tower, and began to assemble. By the time I got around to figuring out how all this stuff would fit on the engine, I realized that the cam gears would stick out the front of the engine, or is that the back? Anyway, I had to take it all apart and do it again.

Cam timing! For all of you losing sleep over cam timing – it was simple. Some of the language used to describe cam timing is a little strange. I still don’t know what “intake valve stroke in overlapping TDC” means. All you do is measure the amount that the intake valve has opened when the piston is at TDC on the intake stroke. I had to re-do the cam timing 3 times, and I even checked it once after the engine was in the car. I don’t think I’ve ever read this anywhere else before, so let me say it again. I double checked the cam timing with the engine in the car. It took me all of 5 or 10 minutes to check it with the engine in the car. If you are contemplating a rebuild or a cam change, and are worried about the cam timing, just whip out your dial gauge and give it try on the engine while it’s still in the car before you take anything apart. It only takes a few minutes, six intake rocker arm cover nuts, and you will sleep much better.

Why did I do the cam timing 3 times? The first time I set the cams to the 5 deg ATDC mark on the crank pulley. I realized my mistake while lying in bed at 2:00am, thinking over what I had done the previous evening. I went down to the shop in my bathrobe and slippers, and reset the cam timing correctly to the Z1 mark. This took only a few minutes as I was practiced now, and then I went back to bed. Z1 is now painted with bright white paint, along with the corresponding mark in the fan housing. After doing the valve to piston clearance check, I had to redo the cam timing again, to get the proper amount of valve clearance. Good thing I checked – thanks for the warning Wayne. When this was all done, I borrowed the cam gear tightening tools from a local Pelicanite, Al Kosmal, because I am too cheap to spend the $117 to tighten 2 nuts – thanks again Al.

From here on out, things weren’t too bad. I had to install and remove the heat exchangers 3 times – once to get clearance for the oil tube (even though the book warns you to put the oil tube nut on first), and once more to get clearance for the exhaust cross-over pipe. I had to install and remove the distributor 3 times to clear the hydraulic chain tensioner oil lines, and again for the fan housing strap. While the distributor was out for the oil line installation, I managed to drop one of the crush washers down the open distributor hole. Tink, tink, tink – tink. Tink, tink, clunk. Great. After fishing around with a magnet in the bottom of the case, I removed the right chain housing oil lines, and cover, and there it was - whew. Then reassemble everything again – one more time.

I put the distributor back in according to the book, forgetting that I had the wires rotated a couple of spots. Once I fixed the timing issue, the engine fired right up, and I ran it at 2000 RPM for 20 minutes. But it wasn’t happy, and ran rough. After double checking all the typical novice mistakes (again, well documented, so they weren’t a problem) I discovered that my Pertronix Ignitor magnetic rotor had come apart, and only 4 of the 6 magnets were in their correct location. I finally got my new Pertronix Ignitor from our host, and it still didn’t run well. I drained the old fuel, put in new plugs, checked my cam timing, checked my distributor, re-did my valve adjustment, tried to set my fuel mixture, had the injectors cleaned, nothing worked. I finally towed it to John Walkers and within an hour, he discovered that I had reversed the wiring harness for the cold start injector and the WUR. They both have the same two prong plug. Now you could argue that this should have been marked when I took the engine wiring harness apart. But marking them both with something generic like “cold start system” doesn’t help. Who knew, when taking the wiring harness off, that there were two identical plugs that would drive me crazy for 4 weeks.

So now, thanks to the folks on this forum (and especially John Walker), I now have a running rebuilt Porsche 911 with the infamous 2.7L engine. Would I do again? Yes. I wanted the experience of doing it myself, and I learned much more than I would have if I just had someone else do it, and I met some great people along the way. Sometimes the frustration was too much, and just having it done would have been great. I think I only saved about $2000 over having a professional shop do it – and a good professional shop would have done everything right the first time, and given me a guarantee. You’ll have to decide for yourself if you want the learning experience, along with the frustrations, delays, and inevitable mistakes of DIY engine rebuilding.

Thanks again for this wonderful site and all the information that is available here, and I would like to especially thank John Walker - as the few minutes he spent showing me how to do things saved me countless hours.

1975 911s
1997 Saab 900s
Old 10-21-2005, 04:12 PM
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