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

[stownsen914]

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

[Alan L]

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

[bigred23]

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...

[boyt911sc]

Originally Posted by bigred23

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...

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

[bigred23]

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

[boyt911sc]

Originally Posted by bigred23

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

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

[bigred23]

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

[boyt911sc]

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



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

Tony

[Flat6pac]

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

[boyt911sc]

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

[VFR750]

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.

[Flat6pac]

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

[strictly]

Originally Posted by boyt911sc

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

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!!