WillyC4S

Hello again,

I'm almost hesitant to post this question, especially after my previous post about checking for the bent valves. I actually do quite a bit of work on my own cars, past and present, so two potentially junior-type errors during this timing belt/water pump replacement is really embarrasing and frustrating.

Anyways here goes:

I was trying to removing the Woodruf key from the crankshaft extension (the section of the cranshaft where the cranshaft bolt screws into and all the pulleys and sprockets mount on). The key was on there tight so I decided to see if the key would move if I hit it with a punch. Hit it several times fairly hard to loosen it up. I hit it at a 45 degrees angle to the direction of the shaft axis. I couldn't get an angle parallel to the axis due to lack of room in the front of the engine. Anyways, I finally got the key out (the brute force with the punch I don't believe helped any) and I tried re-fitting the crankshaft bolt into the crankshaft extension. The bolt would only turn about 3 full turns and then "seize" up. The bolt's leading threads were starting to wear down after a few attempts at re-installation. This was strange since I remember distinctly being able to hand thread the bolt into the extension all the way up to the head of the bolt, all this without any hand tools. This was, of course, earlier in the day before I started working on removing the Woodruf key from the crankshaft.

Something's changed to cause the bolt to bind in the extension. My worst-case guess is that I bent the crankshaft extension while pounding the Woodruf key with the punch. Is this entirely possible? Am I the only idiot to perform this mistake? I'm not entirely sure if this is the case since I can't spin the crankshaft yet due to the timing belt not being fully installed. I was planning on using a dial indicator to measure any runount after the timing belt was installed to check for the possibility of a bent crankshaft extension.

The only other explanation is that the bolt was bent (some how?) and that this was the reason I couldn't thread it into the extension. But I'm not putting a lot of stock into this explanation since the bolt was relatively undamaged and it visually looks straight when measured against a straight-edge. I've got a new bolt on order and will check to see if this was the issue. I guess this is the lowest-priced way of starting the diagnosis process.

If the crankshaft extension was bent, can I measure the runout and then bend it back with the punch without much significant damage? If I can't "fix" it, am I totally screwed and have to buy a replacement crankshaft and do a bottom-end job on this 951?

Thanks for the help guys.

*****

R.B.

*****, I just got my crank back from my machinist. My crank had a bend in it as well, I had a spun rod bearing. It was out of Porsche spec by several thou. of an inch. The machine shop ground my rod bearing journals and took the bend out of the crank. If it is not too bad, take it in too a reputable machine shop that does crank work and see what they think. Bring in the specs from the Porsche shop manuals as well, so they know what to go by.

Hope this helps.
R.B.

Toolmaster

Whoah...

That must have been an HUGE hammer and punch.

Try cleaning out the threads, and getting a new bolt before worrying here. That front part of the crank is pretty tough.

While I guess it's possible, I'd bet against it in a heartbeat. Leverage in that area is not possible easily.

I ALWAYS use a new crank bolt, and clean out the threads WELL before trying to re-assemble.

A bend in a crankshaft due to a rod bearing failure is a good potential, but with a hammer and punch, I guess not. Kinda like trying to bend 1" think steel with a banana. Besides it's mounted pretty tight in there.

Clean 'er up and try again, slowly. You could get a tap of the right size and run it in there too, to clean it all out well.

HTH!

Tabor

there may have been some gunk in the treads that you nocked loose, but I doubt that you bent anything

WillyC4S

Hello again,

Everybody that I talked to seems to think that bending the crankshaft extension is near impossible. I'll have to check to make sure of that, but it's likely that I may need to chase the threads a bit and use a new crank bolt. I'll keep everybody posted on this as things develop.

Thanks,

*****

WillyC4S

Update on progress:

I went out and bought a 16mm x 1.5mm tap hoping to remove any debris and chase the threads all the way to the end of the blind bolt hole. Turns out that I had a hard time turning the tap. Took it out and some of the cutting threads near the first few threads had chipped and some threads were slightly blunted. I was expecting to screw the tap in easily and maybe pickup some debris and clean up the original thread, but it didn't happen. I started dry and then added some silicone lubricant to make the tapping easier. Used a magnet to pickup any chips on the internal threads.

The bolt went in a bit further, but still no where near what it needs to go into to hold the pulleys and sprockets in securely.

If the crank extension didn't bend, I'm having a hard time explaining why a brand-new tap isn't going in all the way to the full depth of the blind hole or why it chipped.

At this point, I'm afraid to tap further in fear that I might re-thread a bent shaft (so if the shaft is repaired, the threads no longer are any good) or snap off the tap inside the bolt hole.

Any more ideas or comments as to what I can do or what's causing this issue.

Is removing the crankshaft something that requires the engine to be removed from the vehicle or can the crank be removed with the engine still in the car? I'm afraid that I'm running out of ideas and I might have to remove the crank to seek professional help at a machine shop.

Thanks,

*****

Hans

*****
Are you sure the original thread is M16x1.5?
Normal (industrial standard) would be M16x2
This would explain the chips and the difficulty you experience while screwing the tap in.

A new tap in "old" thread might give some problems since the production tollerances of the tap are differing from the one used to cut the original thread.
It might tend to scrape the original thread a bit more than ecpected. Cutting chips (= forming new thread) should however not occur.
TakeCare

WillyC4S

Hello Hans,

Thanks for your post. I'm very sure it's 16mm by 1.5mm pitch. The Porsche parts CD indicated this size for the crank bolt. The full size is 16mm diameter by 1.5mm pitch by 60mm in length. I also did a very careful visual inspection of the threads between the tap and the bolt and they are identical.

However, you are correct on 2.0mm pitch being the standard bolt pitch for industrial usage. I had a hard time finding a replacement bolt other than at the dealer or a salvage yard. Home Depot had a class 8.8 bolt but was 2.0mm pitch, likewise with other sources like Grainger and McMaster.

*****

Hans

[quote] I'm very sure it's 16mm by 1.5mm pitch. <hr></blockquote>OK, than just run the tap through it.
You can not damage the crank further.

Just be carefull not to snap the tap off in there.
Use a lot of oil, take the tap out after each full turn to get the dwarfs out and clean with compressed air (both tap & hole) and re-oil.
Use the typical tool to turn the tap [looks like a clamp with two handles (one on each side) dont know the English name for it, you know what I mean when you see it] to apply an straight torque without bending.
An ajustable spanner wont do the job right!!
Take your time doing it.
TakeCare

WillyC4S

Hans,

You've been reading my mind. I also got the exact same advice from a trusted mechanic here in San Jose (CT Automotive) ... take it slow, use cutting oil, take chips out, blow out w/ air ...
whatever time is spent here and done correctly, will save the engine removal and R&R on the crankshaft. We suspect the shaft is bent a thousandth or so, enough to cause binding of the bolt. Good advice from both you and him.

I was using an adjustable wrench and will migrate to a tap handle (T-shaped tool where tap goes into the middle, perpendicular to the wrench).

Thanks,

*****

WillyC4S

Update on the crankshaft bolt problem:

Tonight I decided to proceed and use the tap again to see if I could improve the situation of the binding bolt. Took some clean motor oil and dipped the tap into this and then started the process of re-tapping the crankshaft extension. The tap was binding up again but I turned it a bit past the last point it was stuck at; little improvement, but only incrementally so. I was thinking for sure this wouldn't have done much. As a last futile check before calling it a night, I screwed the crank bolt back in the extension and tightened it up. This time the bolt just kept on screwing in, without any binding! I couldn't believe it. I thought for sure that at some point it was going to lock up like before. Kept turning and turning until the bolt head was flush with the outer edge of the crank extension. Holy Cow!!Looks like the combo of the tap and the motor oil did the trick! I'm thinking that the oil probably did significantly more than the tap.

Lesson learned: if the bolt binds, use oil to see if this will make the binding go away. If not, then tap it with the oil and that should fix the situation.

Thanks to all the good advice on this board, saved a myself a bottom-end job and R&R on the engine! I thought I was screwed for sure on a simple belt job! No more nightmares now.

*****

Hans

*****
Glad for you it worked out fine.
BTW: I use channellock cutter to get woodruf type keys out. The cutting edge is slightly "circular" and gives an perfect lever.
<a href="http://www.all-spec.com/cgi-bin/fccgi.exe?w3exec=showitem&w3site=ALLSPEC&w3path=vend&w3product=CL436" target="_blank">http://www.all-spec.com/cgi-bin/fccgi.exe?w3exec=showitem&w3site=ALLSPEC&w3path=vend&w3product=CL436</a>
TakeCare

Peckster

Just read this, it sounds to me like either a big piece of junk somehow got caught in the threads, or the bolt was crossthreaded, the latter being the most likely. For a bend in the shaft to lock the bolt after only three threads, the bend would have had to be enormous.

Whenever I start to encounter unexpected resistance while handtightening, I try to resist the urge to reach for a wrench. It took me several times to learn that.

Bri Bro

*****, glad it all worked out in the end, it could have become expensive. I was following this thread thinking how sick I would have felt if this had happened to me. Thanks for a good follow-up report, so many people forget to do this.