Had a go today with a small Dremmel tool recommended in another thread to drill a hole in my snapped engine stud in order to try and remove it with a stud extractor (Easy-out). No luck. I have a hole about 4mm deep and probably 3mm wide. It isn't cutting any deeper now so I will have to think again. These Dilivar studs are extremely hard. Anyone know of a drill bit that will work?

My only other choice is to get it done professionally which will probably mean splitting the crank. I wasn't planning on going this far though.

Premature valve guide wear is very common since Porsche historically uses very soft valve guides.

Just tore down my 993 3.6 at 107 k miles and every exhaust guide was terribly worn. The good news should be that you should be able to not touch the bottom end of the motor which should be good for 200k miles.

Project is now going from bad to worse. My two broken head studs have beaten me. Neither the dremmel tool or locksmiths tungsten carbide drills will successfully remove the stud and now I have broken off an easy-out in the hole.....bugger!

So my new plan is to remove the other side of the engine, cylinders 4, 5, and 6, so I just have the crank cases left on my stand. I have fitted to engine stand on the wrong side as I had a stripped thread in one of the transmission stud holes. I will now repair this, replace the stud, move the stand to the other half of the crank case and split the crank. When done, I will get the broken studs removed professionally, maybe by spark erosion (EDM).

So I have a few questions. I would like not to disturb the inner workings of the crank case but some messing about is inevitable. I plan to remove the crankshaft and measure the journals. Assuming they are within tolerance, I could either refit the original shells or replace them with new standard ones. I am not planning to remove the conrods as there is no wear in the big ends and they are all free moving. I guess I should do the same with the intermediate shaft bearings?

Any advice here would be greatly appreciated!

Try welding a nut onto the remaining head studs to create a "bolt" to remove. The heating of the stud during welding will help to loosen them also.

Today I have had some long awaited success with my engine. I have given up any idea of getting the two broken studs out of my engine casing after having tried most things, so I have decided to get them professionally removed. This has meant splitting the crank cases. Very luckily, the three studs that were broken on the other side of the engine all came out with a stud extractor. Good news because the only side needing work is the side you lift off. This means the crankshaft and secondary shaft/oil pump can all stay in place!


http://forums.pelicanparts.com/uploa...1381605155.jpg

http://forums.pelicanparts.com/uploa...1381605171.jpg

http://forums.pelicanparts.com/uploa...1381605202.jpg

The main bearing shells from the removed half are sitting on the crankshaft in this picture below.
http://forums.pelicanparts.com/uploa...1381605389.jpg

This is the side with the offending broken studs. All nice and clean for a casing just lifted from the engine.
http://forums.pelicanparts.com/uploa...1381605460.jpg

Splitting the cases was a bit of a challenge as the original sealant was not keen to part. Quite surprising really as there is actually very little sealant used on the joint. I believe that this is from the factory in 1978 as there are no signs my engine has ever been apart before.

Once I have had the broken studs removed, I will reassemble the crank cases as they are. I am not getting any crankshaft rework done as there are absolutely no signs of wear anywhere. Not even any scoring lines on the main shells.

Just realised I started this thread and hence engine rebuild on 27th May. That means I have been at it for almost five months! I have had a few delays here and there but today I hit a major milestone.

I have all my broken studs removed!
http://forums.pelicanparts.com/uploa...1382386244.jpg

http://forums.pelicanparts.com/uploa...1382386269.jpg

http://forums.pelicanparts.com/uploa...1382386286.jpg

I also have three of the cylinder heads back having been cleaned and with new valve guides fitted.
http://forums.pelicanparts.com/uploa...1382386329.jpg

http://forums.pelicanparts.com/uploa...1382386351.jpg

This is all good because (except for the other three heads which will need valve guides) I have got to the turning point where I am no longer dis-assembling the engine, but rebuilding it! Hopefully this will not take me five months, but with the winter, kids, family, Christmas (9 weeks away!) etc. don't count on it!

Good Progress!!
 

How were the broken studs removed?
Was it using EDM (& was it expensive)?

I hope your garage is warm enough in winter to keep up the momentum. :D

Peter in Melbourne

Congratulations! Unfortunately, you need to be realistic on what lies ahead of you. I dropped my 3.6 motor in January of this year, and it is just now ready to go back into the car. Many of the delays for me were in turnaround times on components that were sent out for rework. Then there are the inevitable issues discovered when you realize that you do not have all the small parts needed for re-assembly.

Also, keep in mind that you have to assemble the cases with bearings and crank and rods installed to check bearing clearances. And, then disassemble them again. And, then there are the challenges of building the engine stack so that all the dimensioning is correct. The list is long. Not complicated, but long. It just takes a lot of time to do it right........especially if you haven't done any or many of these motors, which was my situation.

So, my guess is that at mid-October, you still have about 60 to 80 hours of work ahead of you. That will be a challenge to complete by end of year. Just being realistic. So, don't set your gates too high......only to be disappointed. In the end, you will have a nice project that will run for years.

The only reason I split the cases was to get the studs removed. I haven't disturbed the crankshaft or secondary shaft and I do not intend to. As all is exactly as it was when it came apart, reassembly should be just a case of bolting it all back together. This will save a huge amount of time. The engine has only done 74K miles and there are no signs of wear to anything inside. Even the main bearing shells from the half I took off are completely unmarked, so any further rework is not necessary at this time.
Removal of the two broken studs including a check of all the stud hole threads cost me £140 in the UK. They were both broken about 2mm proud of the surface. The guy who did it only commented that they were very hard material!

Great progress! You are certainly setting new standards on how to "minimize" wisely that temptation to do other things "while in there".

As with the several motors I have done, I am amazed at the condition of the bottom end of these 911 motors when you do split the case. Built like the proverbial brick ***** house! The bottom end of most of these motors that have had religious oil changes can usually go at least 200k miles without attention.

Having said that, the IMS bearings appear to not have that life. Mine were visibly worn, though there was still babbitt on the inserts at 107k miles. But, if you review other high mileage rebuilds, builders usually comment that the IMS bearings show wear. Since the IMS bearings are cheap and can be replaced without pulling the IMS or the crank out of your motor, I strongly suggest that you consider replacing just them. The mains look fine. And, of course if you touch the crank, then you have to do the chains and all of the reassembly adjustments to assure cam timing, etc.

old school
 

I am by no means an engine expert, but to my experience, whenever a case is split all the bearings MUST be replaced. I understand the thought behind this is the fact of the bearing clearances cannot ever be set as to the same position as prior to splitting the case. I am not sure of the bearing clearances, but I will bet it is less than .002.

Personally I would spring for all new bearings. Cheap insurance, in my opinion

I am not sure what you mean by bearing clearances being reset? There is no setting. You clean them, and their seats and reinstall the shells. The process for fitting new ones is identical. In the case of my engine, there is absolutely no signs of wear on either the shells or the crankshaft so replacing them as far as I can see, is not necessary....unless anyone else has a different opinion (Preferably based on some factual data!).

During my engine rebuild I have thought long and hard about what to replace and what not to. Rebuild companies tell you to replace everything and there is a certain amount of 'preventitive maintenance' sense in that, but there is also a huge associated cost to doing work that just isn't required. I have decided to replace the exhaust studs on the cylinder heads however as they are a bit rusty and breaking one just after rebuilding the engine would be a killer!

On another note, all six of my exhaust valve guides displayed the same wear as shown below:

http://forums.pelicanparts.com/uploa...1383053333.jpg

The end of the guide is wafer thin but the wear is only in the end 10mm, not all the way up the guide, which means the valve couldn't rub on the worn area. So ho did it get like that? I did find that when a new guide was installed the valve would not slide into place due to deposits on the stem near the valve head. I can only conclude that as the guide begins to wear, a gap apprears that allows a carbon depost to start accumulating on the lower end of the valve stem which eventually wears away the end of the guide....Just an idea!

All new
 

I would bet the farm there is wear on the bearing shells and the crankshaft, the amounts may be small, but wear. Again, in my opinion the issue is not the wear but rather how the components fit together. These are close clearance, high performance machines, I would make the investment in new bearings across the board.

Inspection Findings
 

You are being extremely prudent. Having gone through three engines myself over the years, there are some generalities about 911 motors.

First, Porsche has historically used very soft valve guide materials. And, they usually are in need of replacement at 100k miles........almost guaranteed. Being an air cooled motor, there are only two avenues for dissipating the heat of combustion.......you either radiate it through the finned appendages that are in an air stream, or you pass the heat off into the oil which then goes through a cooler to remove the heat. BOTH of these mechanisms require that heat travel down the valves for transfer into the valve guides and then the heat travels through the alloy of the cylinders and heads to cooler air.

As the guides wear, the clearances between them and the valve stems increase. That clearance is an insulator that prevents the flow of heat. So, the engines then begin to run hotter which is a death spiral.

Bottom line: you really need to consider a full head refresh if you are going to keep the car.

Regarding bearings, I am with you. As long as the bearings were arranged so that they fit in exactly the same location as from which they were originally installed, you can have a high certainty that they can be reused and you should expect a total life of these bearings of about 200k miles.........IF they are perfect when you first inspect them.

The bearing shells themselves are a little longer than the cavity in which they reside in the engine. So, when you bolt up the two case halves, you compress the bearings, very slightly. Theoretically, once crushed (initial install).....they will change shape upon disassembly and you will not be able to duplicate the same crush as the initial install. I think that was what the previous poster was alluding to. Having said that, my guess is that if you do not disturb the bearings and they are returned to service to exactly the same location......you are probably going to be fine. Another consideration in support of reusing your bearings is that Porsche bearing quality has declined over the years......so, new bearings will probably not be of the quality of what is in the current motor.

My one exception on bearings is that you should absolutely replace your IMS bearings. They are cheap.....and they normally show a lot of wear at 100k miles.

You should also consider replacing your rod bolting. Not sure about your engine.....but, Porsche uses materials that actually "stretch" when torqued up. Which you would expect. But, materials not only stretch.......they yield meaning that the stretch results in a permanent deformation of the bolt. The next time you torque the up.......they will stretch another increment.......and will eventually break.....whcih is not a good thing.

Just my 2 cents.

Thanks for the comments. I am replacing the IMS bearing shells as they do show some signs of wear. I am not planning to remove the rods as there is no play in any direction to talk about. I understand the stretch bolt theory, but as an aircraft stress engineer it does puzzle me slightly. In my trade, if a material goes 'plastic', ie. deforms and goes beyond its elastic limit, then it is scrap. A stretch bolt has gone beyond this point and can no longer carry any additional load before ultimate failure. I suppose it is a way of ensuring a certain preload on the bolt, but I am surprised that they can sustain their torque setting. It does work in practice though so there is something going on there I don't fully understand!

declined
 

Ernie,

I find it hard to believe Porsche bearing quality has declined. I doubt Porsche manufactures bearings and I would put five on the fact the quality of bearings today are better than 30 years ago. Again I am no expert, but to my understanding we are talking about "thin shells" with build up of slippery stuff with lots of new technology behind it.

It I split the case on an engine it would be an automatic to replace the "shells"

I just rebuilt the 3.6 in my 993. It took two sets of bearings to get a proper clearance fit. Both sets made by Glycol. One was after market. The other was Porsche. They look to be identical. But, apparently Porsche holds tighter dimensional tolerances than does Glycol.

Also, if you do some research on this board you will find where poor packaging of of bearing pieces results in damaged bearings.....right out of the box. I was advised to use a magnifier to examine every bearing shell for damage and imperfections. Granted, I did not find any visible damage; however, on install, the Glycol brand was apparently out of tolerance on dimensioning.

In talking to several folks who make their livings building up Porsche engines, I got similar comments about a degradation in bearing quality over the last several years. An explanation for this is apparently around the fact that there has been a consolidation of manufacturers and quality has suffered.

So, basis the above, I have been advised that if the OEM bearings are good, consider reusing them in the motor.

I get your point. And, my caveate is that I do not know Porsche's design criteria, but the common statement about Porsche rod bolts and flywheel bolts is to use them once and then toss them. My guess is that Porsche designed them to stretch with loading to push them elastic. But, for any number of reasons they must be going into the plastic area of the curves. It's pretty cheap to replace rod bolting with some of the aftermarket stuff like Raceware. I did that on my 3.6 just to eliminate the bolting as a weak point in the engine.

I would of course always replace a stretch bolt if removed. it is a requirement.

I have stripped and rebuilt quite a few engines over the years and I am always quite surprised how fragile these 911 engines seem to be considering the SC 3.0 is always quoted as being 'indestructible'! I have only ever replaced parts that are noticeably worn, damaged, or out of tolerance, when rebuilding an engine. I am not trying to make it a new engine and I have done substantially more than just replace the broken head studs which was my one and only reason for removing the engine in the first place! The problem is that parts for the 911 are so extortionaletly priced compared to other makes, it doesn't make sense just to replace things unless it is really needed. As an example, a set of main bearings for the 911SC will cost me in the region of £150. A set for my 1970 Rover 3500 V8 is around £30!

Interesting discussion. The high cost of Porsche parts may explain why you see folks putting American V8's in a Porsche chassis. Some of the German engineering is suspect. I will grant you that. But, when you look at the fact that these "fragile" engines will go 200k miles without wearing out main components.......I find support for the term "indestructible".

The end argument is that this is all about power to weight ratios.......and being "indestructible". I don't know of many machines out there in the price range of Porsche that are competitive in those areas. The Chevrolet Corvette comes to mind. Lots of horsepower for relatively little money.......great straight line acceleration......but, on a road coarse not much of a competitor. There are also not to many Corvettes running around with 200k on their bottom ends.

Porsche does have flaws. Chain tensioners and poor designs of things like IMS bearings in their water cooled motors come to mind. But, in the main, German engineering is very good. But, they are "lazy" engineers, which explains why they will perform a hundred revisions to a bad design before electing to start over. I get that.