Crankshaft seisure?? New rebuild!

[farleyd]

Ive been following this thread. I am rebuilding my 2.7 and am a complete novice. I have Anderson book, Wayne books and usefull advices from this board.

-I measured my case using a straight edge and a feeler gauge using a 1.5/1000 in. and that gauge sticks between every bearing surfaces and the edge
- the #8 bearing sits squarely on every bearing surface

Now would that be a good thing or not to mount (with lube) the crank and torque the case to see IF it turns by hand? The case have had timeserts.

Best to you.

[J P Stein]

To check a case for straightness (or coaxial true position, if you prefer) or to line hone it.... about anything dealing with the case, it needs to be bolted/torqued together. In this state, access to the brg bores is very limited. Using the crank , with the (bearings installed, of course)for a precision mandrel is a good plan, IMO.

When my case was being worked, it was also decked and squared. Once the case is set up on the mill, things become fairly automatic, I was told. .010 is taken off the deck height, kiss cuts in the spigot bores...the mill becomes the check fixture. I inspect machined parts for a living and it made sense to me.

[john walker's workshop]

it could save you a re-do for sure. on the other side of the issue, i've seen several cases where the mainline was beat to hell, allowing the flywheel to be moved a considerable amount, up and down and side to side. obviously, a crank could turn very easily in that situation. just something else to consider.

[biggtbiggt]

The bearings actually show the journals that were cleaned up with the hone. You can see in the journals where the hone cleaned up the case. I think I probably could have gotten away just letting it wear in! But who knows. It took a bit of effort to start the crank moving, but when it was in motion it kept turning with little effort.. I am happy I took apart and honed! FYI When the machinist honed it I had to torque every case bolt including the outside ones! The bearings are not wore down to the copper, they are just polished shiny and the gold tinge in the picture is oil sitting on them!

My advice to anybody rebuilding a mag. case is to have it checked by a machinist with a proper bore guage as shown in Wayne's book. If I would have done this I would not have had to do twice!! With these cases being as soft as they are I see no easy way around this. I did all the unbolting and retourquing of the cases at the machine shop as well as built a case holder to hold it in the machine. It took the machinist about 1 hr of his time off and on, measuring and setting up and honing. He charged me $100.00 Canadian.

[J P Stein]

I haven't seen Waynes book so I can't comment on what he recommends. A dial bore gage is fine for checking for roundness of an individual bore....the best tool, in fact. For a serise of bores in line they can't do anything for you. A boring mandrel with a dial indicator...on the boring mill or a CMM is the hot ticket here. Then you have to plot it out and figure whatcha got.

Or a precision ground mandrel, sized properly and gentle honing till it "goes", but without going oversize on the bores diameters....a tough act, but quicker that either of the former set ups. If it dosen't work......bring money.

If a mag case has pulled studs it's prolly not a candidate for a line hone.
Chances are good that it's warped (overheated) and needs a line bore w/ OS (id) brgs
or the whole enchilada from Competition Eng.

I kinda fell into my 2.7L, otherwise I wouldn't mess with them. Mag cases are a PITA......makes gud power, tho I have gone to some lenghts to keep it cool. I've never seen 100C on the oil temp.

[Wayne 962]

Originally posted by biggtbiggt
The machinist used some sort of long dial guage that went down the bore and measure each journal. The one's that were tight were the ones that had the shiny bearings. By the look of it the journals they must wear into an oval shape. I gues just a quick rub with the line hone is supposed to clean them up. I had to bring the block home from the machine shop and manufacture a cradle to securely fasten it into the line hone as they usually just work on american engines and the mounts are different. I done't think you could measure this with a straight edge and feeler guage as it would be too hard to get acurate! we are taking a very small amount here and with the curve of the journal it would be damn near impossible to get in their.

Yikes, you should run screaming from *any* shop that doesn't have the know-how or tools to work on Porsche engine cases. These puppies are not like big American iron - they are completely different. Read my book (Chapter 3), and if you know stuff about the American cars, you will find a lot different about the Porsche cases.

I would have your case restored to std/std and not bore it larger. I believe that certain machine shops unnecessarily recommend boring oversize because then they can sell you the bearings for extreme profit. The case is permanently "damaged" then, versus bringing it back to std/std. Plus, when Walt does it, the mating surfaces are resurfaced reducing any chance of leakage...

-Wayne

[Wayne 962]

On the crankshaft issue, it's *extremely* rare to see a bent 911 crankshaft, unless the engine has completely destroyed itself. Each rod is supported on either side by a total of eight main bearings. This makes the crank very well supported.

Snowman, in other engines, the wear patterns shown here may indeed also indicate a bent 911 crank. But in real world practice, that almost *never* happens. The magnesium cases are much weaker and tend to deform a lot easier. 99.5% of the time, the crank is fine, but the case needs to be remachined. I'm of course referring mostly to the mag cases here.

-Wayne

[Wayne 962]

Originally posted by snowman
Unless you have some kind of super race engine, with an all out racing cam, you probably do not have to worry about valve clearence. If you have machined the thing so much that the valves have any chance of interfering with anything you will more likely have a problem with the tensioners not being tight anymore.

Not true, the clearance on the 911S engines is very tight. Read page 70 of the Engine Rebuild book - it's surprising how all of these small machining processes can add up. Mix that in with the natural tolerances of the engine, and you could have intereference problems...

-Wayne

[Wayne 962]

Originally posted by snowman
PS after looking at the bearings some more I do not think you had any problem here. The reason is that there is still some tin flash showing at the wear points. This flash is so thin it almost cannot be measured. This means that there is NO wear of any significance. I would have those injectors or carb floats checked.

Jack, you appear to have quite a bit of book knowledge about American motors, but you are *way* off base here. I have seen engines come apart with 200,000 miles on them, and the bearings looked better than these. This engine was clearly headed for disaster, because the case was not properly treated prior to assembly (I emphasize this in the book).

There are people who have been working around these engines for year, and they know what works and what doesn't work...

-Wayne

[emcon5]

Originally posted by biggtbiggt
Here are the pictures of the wear on the bearings after 250 miles about 6hrs

And:

Originally posted by snowman
PS after looking at the bearings some more I do not think you had any problem here.

Compare those bearings with 250 miles, with this bearing from Leland's engine with 220,000 miles:




Tom

[Wayne 962]

Thanks Tom for the photo evidence to back up my statement. I have indeed had people tear down engines, spec the bearings, find them to be in spec, and rebuild the engine without replacing the bearings. I don't really recommend this, although technically, I can't find anything wrong with it. Perhaps metal fatigue could cause some problems that you can't measure? Either way, it's best to use new bearings.

biggtbiggt, make sure that you do use a new set of bearings in there...

-Wayne

[snowman]

Well ,
I do not think all engines wear in the perfact manner that you have shown here. Nor do they need to. What makes you think that after this initial wear in that accelerated wear will continue? Onece these bearings are bedded in I think they will hold up for a very long time. Thats unless the initial wear is more than seems to be indicated by the photos.

As to valve clearences to pistons. Unless you do something radical there is a whole bunch of margin for any stock Porsche engine. I run my race engine with 0.080 inches clr for valves to piston and 0.035 inch piston to spark plug. Thats tight. And it runs to 8500 plus rpm no sweat, time after time.

The reason for being worried about float levels or injector leakage is that it fits the symptoms, exactly. IF you have an engine that will turn over ok but after setting for a while will not. it may be hydrolic lock up. That means that enough gas has leaked into the cylinder to stop it from turning over freely. This can even result in a bent connecting rod if the case is extreem and you try to push start it.

[snowman]

PPS

I do not think that anyone with real engine experience that sees these pictures of bearing wear would be worried in any way. Try it on for size with anyone like CE.

[Doug Zielke]

We have some *genuine* experts contributing to this Forum.
One would be extremely foolish not to take their proven advice.
Anything else is just nonsense.

[john walker's workshop]

hydro-lock is not the issue here. when i first started rebuilding 911 engines, i found out about tight cranks in 2.7s. it's been an issue since the beginning. with the case torqued up, the initial effort to get the crank moving was considerable, and once it was turning, it still had some drag, but was a lot easier. when you stopped turning it, and tried again a few seconds later, the crank was tight again. these engines are too expensive to take a chance with, and hope it frees up later. there are plenty of folks out there who are going to let it go, even though that voice in their head is telling them that it's not right. but stopping when you find a problem and correcting it makes you a better mechanic than the guy who lets things go and hopes. this ain't no stinkin' ford!

[Trevor Long]

Think of the additional frictional power losses with a crank that is binding.

Under operation, crankshafts flex both torsionally and axially.

Add in a misaligned crank bores and the friction goes up bigtime.

[john walker's workshop]

correct. i was going to mention that the oil temp would increase because of that, too. it's just wrong!

[Wayne 962]

I would seriously doubt that Walt (Competition Engineering) would say that those bearings look okay. Too bad, I was hanging out with Walt last weekend, I should have asked him. Wait a sec - no need to, the answer here is obvious - that's why I didn't even think of it...

-Wayne

[snowman]

Well I personally think its a lot more sensable to rule out something like a leaky injector before tearing down an engine. Another clue that was presented is that the engine turned ok if the plugs were removed, even after sitting for a while. If it were indeed the crank it would seem likely to still have the problem.

As to the bearing wear, what I can see, and with the photos its less than a certainty, is that only the tin flash is worn off. The tin flash is only a couple of millionths of an inch thick and is there to protect the bearings from corrosion during storage on the shelf. If the wear were more, say the oil clearence increased from 2.2 thousands to say 3.2 thousandths or there was copper showing, I would say there is a problem. Also if the crank is truly in a bind you tend to get galling of the bearing material onto the crank surface and everything looks pretty crummy, nothing shines anymore. After this galling starts there is no more oil film to seperate things and it gets real bad real quick.

I have torn down my race engine, many times, with very few hours (25 to 30) on it and seen wear like this (on the original porsche crank) I checked the oil clearence with plastiguage and found that the original clearence of 2.2 thou had increased to 2.5 thou, not a problem in any way. The almost perfact scat crank I use now dosen't do the same thing but then again its a billet crank and everything is perfact as humanly possible.

Ps I have taken apart and repaired more euro cars than american. I used to like chrysler products, and GM products but then after breaking many of them and seeing the crapy quality I got turned off to them. By the way there is NO difference in the way a quality crank and bearing works, no matter who makes it. Theres good steel, and theres junk steel. By the way a chevy V8 is an engineering marvel. If its built with quality parts its very very good. What makes it a marvel is that it works with junk parts, poor quality workmanship, and 1/3 the parts in a porsche and makes the same power. The chevy will also go 100K miles at a fraction of the cost. Trouble is that if you hot rod it , it will break. When you put the same quality parts as Porsche uses in one it will smoke the Porsche easily. My basic gripe is that it no longer is really a Chevy at this point, its all aftermarket stuff even the block. Anyway its true Chevys are junk and Fords and Chrylser are just as bad. A little off subject but somone mentioned chevy and somehow associated me with one, DON'T, please.

Another off subject- why dosen't the spell check work with this browser? Mozilla (in other words Netscape)?

[Wayne 962]

Don't know about the spell-check?

The problem is not with the crankshafts here - you are correct - they are very similar. The problem is the magnesium cases, which are very susceptible to warpage, and have a tendency to pinch the cranks like this. As you know, main bearings are not really bearings, but merely metal supports that flow the oil. Theoretically, in a perfect world, they would see zero wear because they are always insulated by a layer of oil. A well maintained street engine's bearings should look like the ones that came out of Leland's engine.

-Wayne