911SC engine disassembly going great, until...crank's not turning
 

I'm nearing the end of engine disassembly for an '82 SC, 207k miles, and will be ready to split the case once I remove the last two pistons (#1 and #3). Unfortunately, I can no longer get the crank to rotate enough to gain access to the wrist pins; the resistance feels similar as if there were a set of cam locks on the engine. The crank rotates maybe 10-15 degrees, at best.

All hardware is accounted for (nuts, washers, circlips). Not to say one of my kids could've "slipped" something in there! Anyways, in the little travel I do have, it doesn't appear any of the rods are getting hung up on the case. In addition, the cam chains do not appear to be bunched up, and are still engaged around the intermediate shaft sprockets...

Anybody encountered this? Any ideas?

Double check the cam chains. I had something similar when disassembling and it was one of the chains overlapped on the gear.

yeah, I've checked and double checked the chains. They don't appear to overlapping...I've contemplated just cutting them, though...

A pic would help. Have you got the chains hanging outside the case on the sprockets?
Can you move all the other 4 rods freely when it binds?
Have you been able to spin it 360 deg before this point? (I have had mine bind on the engine stand).
Alan

+1

Cam chains can easily half jump a tooth and do exactly what you are feeling. You have to pull the chains outward and rock the crank back and forth to get the chain back on the sprockets.

Also: get used to it.

This will happen multiple times during assembly; When installing the pistons, cam housing and finally just before you time the cams.

One of the rods is binding in the dropped back stroke, or the chain is binding on the gear.
Bruce

Agree with Bruce/others...my guess is rod(s) binding in bore.

I was dis-assembling a 2.7 yesteryear and while rotating the crank to remove the pistons, i had the crank rotation stop several times.....it was a chain binding every time. When the rotation stops......pull on a chain and rotate the crank slowly in the opposite direction you were originally rotating it. If it was a chain issue you will feel it free up.

regards,
al

On chains I built a simple fixture (X2) that holds out the chains so they can't bind. There is a Porsche fixture that I copied but I don't have time to look right now.

Thanks for the input, guys! I hesitated to post this topic b/c it's like, "what the hell am I missing here?". Rods are free of obstruction, chains appear to be fully extended and riding on their sprockets, etc. Perhaps with the promise of fresh nitrile gloves, I can coax my better half out into the garage tonight for assistance while I muck around with the chain :)

So, while it is bound, the 4 other rods are totally free to move? They can and will bind inside the bottom of the cylinder housings. But if totally free then really only chain or engine mount - depending how you mounted it. As stated above - rock the crank and pull on the chains - you may be able to peek down inside. But they are notorious for binding if you don not keep them outside the case. Again - not sure how you have it mounted - but with the sprockets providing weight in the ends of chain, outside case, usually avoids this.
You should be able to do this on your own - socket on crank pulley, lean back/forth, pull on L/R chain. Something should come free.
Alan

Standard setup i.e. Porsche engine yoke, engine stand, etc. Yes, with the 1-3 cylinder bank orientated towards the ceiling (and 4-6 facing the ground), all 4 piston-less rods can be wiggled freely while rocking the crank. One nuclear option I've considered is to just cut the chains and remove (they'll be replaced anyways...). But as one previous post pointed out, this can/will happen on reassembly, so I need to just work it out

Most likely the 1-3 chain.
turn the crank back 5-10 deg and yank on chain. If nothing pings free, go back another 5-10 deg etc. Try the bottom chain too - just in case it bound before you flipped the engine.
Alan

Just to be clear, while the crank is rotated until you feel it "lock" the the other 4 rods wiggle freely? WHile gentle pressure is applied to rotate the crank? I have had this happen on every single motor I have disassembled, its totally common. In every one of my cases holding the rods perpendicular to the caseline made rotation easy. The old "elastic band through the rod and on the studs" usually works but sometimes you need to hold a particular rid 'just so' while rotating the crank.

You could also just skip ahead and take the chain housings apart so the chains are slack.

aye..no luck tonight. Both chains appear to be fully engaged in their sprockets (no bunching), and the piston-less rods are wiggling freely. While my wife managed crank duties, I went around moving the rods, attempting to keep the piston pin bushings centered in the bore

Interesting finding, though, one of the the four interior chain ramps was only be held on with one of the bolts; the other side had cracked around the other bolt and a sizeable piece was missing. I'm thinking that plastic piece has found its way around one of the intermediate shaft gears and is wedged in such a way to prevent crank rotation. Possible?

Yes, possible. (but you should be able to rotate in one direction I suspect - so it is spitting the piece out of the gears rather than trying to trap it.) Presumably you have the cam chain covers off. have you had a good peek down there with a torch.
Have you tried to move the ramps, or is this old?
is it now totally locked or do you have some movement?
Alan

Thanks for the response, Alan. Yes, engine is two pistons away from splitting the case. Reason I'm not thinking chains, is that you can look through the bottom oil plate and see the 4-6 chain is engaged; likewise, you can look through the distributor hole and see the 1-3 chain appears to be engaged as well.

As my wife rocked the crank (ha, there's gotta be a better way to say that), I couldn't see any obstruction with the rods, and with the chains appearing unbunched, I'm thinking some interference with the intermediate shaft gears (maybe between the gear and case?). I should jury rig some clothing hanger to try and sweep in that narrow region....

Right now, I have about 10-15 degrees in crank rotation, and all chain ramps are removed.

If you haven't tried already, try flipping the engine over, maybe the piece of ramp will dislodge if that is the culprit. If not then I would cut the chains and get them out of there just to eliminate that possibility.

Typical problem........
 

Paul,

This happens a lot specially during engine teardown. To avoid getting into this predicament, I leave the chain sprockets hanging on the chain itself. The weight of the sprocket on each side provides some sort of tension preventing the chain from getting off the gear teeth.

Turn the engine up with one side up (example: 1-2-3) and side 4-5-6 down with the chain sprocket sitting on the chain (hanging down). Next pull up the chain loop for 1-2-3 and at the same time turn the crankshaft pulley slightly left and right until the impediment is removed. Now, try to turn the crank pulley clockwise and see what happens.

Rotate the whole engine back to horizontal position and let the left side chain hang with the sprocket in place. Keep us posted.

Tony

A borescope might help you see inside the case where the naked eye cannot. It might help you see if broken chain ramp (or something else) is jamming things up in there. I bought a cheapo borescope off eBay for less then $100 a few years ago, or see if you can borrow one.

Scott

If you can't free the issue, I am getting the impression you plan on splitting the case. Slightly unconventional, but I am not sure why you can't split it as it is now. That way the problem should be come obvious, and it may not be necessary to spend any more time looking for it.
Alan

Alan, I thought that too, but the inaccessible piston wristpins are #1 and #3 i.e. the case side that needs to be lifted off the other half. I would only be able to separate the case maybe 1" or so, before the bottom of pistons 1 and 3 would interfere with the main webs. But maybe that would be enough to gain access and clear any obstruction around the intermediate shaft gears...

Transfer the engine yoke mounting........
 

Paul,

In this case, move the engine yoke to cylinders 1-2-3 instead of the regular 4-5-6 mounting. With engine yoke installed @ 1-2-3 position, you could split the crankcase and remove 4-5-6 half. After you have separated the crankcase halves, you got all the time in the world to investigate the culprit of your crankshaft problem.

Have you tried using the weight of the chain sprockets to relieve the pinching of the timing chains between gears? Turn the engine on its sides with the timing chain hanging with weight and repeat the other side if you are not able to release the chain restriction. The timing chain is being pinched by the timing gears.

Tony

Hi Tony,
Yeah, the switching-the-yoke-side "epiphany" hit me about 10 seconds after posting the previous message.

Try this technique first........
 

Paul,

Before switching the engine yoke, try to apply the sprocket weight technique on the hanging timing chains. I've been in similar situation before and it gets scary when you could not turn the crankshaft after a rebuild. I was able to free the timing chain except when I dropped a nut inside the engine.

Have you read my other post regarding cylinder head studs removal? That was posted because of your inquiries and to others planning to do similar project in the future. Keep us posted.

Tony

disassembly = complete
 

Disassembly is done. And I'm not sure what caused the crank to stop rotating. But between convincing myself a broken chain ramp piece had wedged itself between the intermediate gears, and ensuring the chains were fully engaged on the internal sprockets, it was probably the chains!?!

I mucked around with the chain some more Friday after work; tensioning the chains by using the weight of the removed sprockets. No Dice. Crank still wouldn't budge. Ok, moved on to removing the head studs. I switched yoke positions Saturday (going from 4-5-6 side to 1-2-3), and began to split the case. As soon as I had about 1/4" gap between the case halves, I saw the #1 piston move. I'll be...momentarily rejoined the cases, and tapped out pistons 1 and 3. Crank had full rotation; fully expected to see my unicorn chain ramp piece in the space under the intermediate gears when I removed the 4-5-6 case side...nothing. What the...

Disassembly complete; moving on. Keep those chains tensioned by whatever means, as I may not have fully appreciated the extent to which loosened chains can jam things up (even though they looked fine around the chain sprockets

Timing chains under tension.......
 

Always keep the timing chains under tension or you would be getting into same trouble when you do the assembly.

http://forums.pelicanparts.com/uploa...1462813491.jpg

The weight of the suspended sprockets keeps the timing chains under some tension and preventing the chain getting kinked or pinched between gears.

Tony

Tony, the picture is nice but they have a car waiting on them?
Bruce

Owners waiting for them.......
 

Bruce,

I wished I could finished these engines quicker like you do. I am old and slow. The year 2015 was not a good year for engine rebuilding. I had two eyes operated, found a problem with my heart, traveled to Europe and Asia for several months, got all these weird CIS problems never encountered before and never seen electrical anomaly, and so on. However, I am back and refreshed after visiting NZ and AUS this year to continue the saga.

I just brought up a complete engine yesterday from my basement, out of the kitchen, through the deck, and finally to my garage all by myself. It is amazing how an old guy like me with a bad back and bumped knee (arthritis) could do such activity safely all alone. Yes, all these engines are disassembled outdoor and re-assembled down in my basement. The engine weighs about 350 lbs. and I exerted very little effort to slide them up, and out of the basement. And finally out of the house to its final destination, garage.

Bruce Abbott is my mentor. He has given me sage advises and saved me from troubles many times. A real gentleman and a good friend although we have not met in person. Thanks you and other nameless PP members. I am really enjoying my retirement years doing engine rebuilding and traveling around the world with my wife, who is still in Australia at the moment. I am lucky and blessed.

Tony

Paul

Yes it was the chains. It can be very frustrating to get them back on. You can't see where they get caught. Rotating the engine in the stand is just as effective as dealing the yoke. As you found out they suddenly are back on.

Tony, I'm playing with you....
Bruce

Tony,

is it safe to rotate the engine like that (with the sprockets in the chains, hanging side by side) like in your garage photo on the 2nd page - or must you always have one half of the engine in the air (like 1 to 3 straight up) and holding the sprocket in your hand, with gravity holding the 4-6 side chain down (with sprocket inside).

I havent had any issue with the chains getting caught, but im going to pay alot more attention now!!