Turning crank with jug off

BruceW · #1 10-21-2019, 11:11 PM

Pulled #3 jug due to bad intake valve (another story) with A&P assistance.
Now pulling pin for the piston. Cant get pin out due to obstructions.
Realized the crankshaft is not quite at TDC.
Need to turn it about 30-40 degrees more to get TDC.
Should be able to get piston pin out then.

Is it OK to turn the crank this much with jug off and nuts off thru bolts?
What are chances of "turning the crank bearings"?
Should I put thru bold nuts back on and tighten half way to prevent?
Other suggestions ???
Thanks.

N804RV · #2 10-22-2019, 12:03 AM

Had to go back and check my class notes to be sure. But, it is possible the bearings could move or get "cocked" slightly.

Wonder if, in your case, you could put washers over the through studs to the approximate same height as the cylinder deck, and then torque the cylinder nuts up?

Flyhud · #3 10-22-2019, 12:11 AM

Nothing to worry about as far as spinning a bearing, leave the cylinder base nuts off. The primary thing you need to be careful of is protecting the case, rod and piston from getting boogered up. Take a clean rag and place it between the bottom of the rod and the case. Just keep the rod and piston from bumping around on anything as you slowly turn the prop/crank in the desired direction.

JET14 · #4 10-22-2019, 03:58 AM

Can you get a torque plate on it? That is the safest option in my opinion. The through bolts maintain the correct bearing crush.

https://www.youtube.com/watch?v=3-3pkRLqoGw

JET

lr172 · #5 10-22-2019, 07:18 AM

Quote:

Originally Posted by Flyhud

Nothing to worry about as far as spinning a bearing, leave the cylinder base nuts off. The primary thing you need to be careful of is protecting the case, rod and piston from getting boogered up. Take a clean rag and place it between the bottom of the rod and the case. Just keep the rod and piston from bumping around on anything as you slowly turn the prop/crank in the desired direction.

+1

Bearings can't spin, as they have tangs that prevent any rotation of them (Nose bearing is the exception, but the bolts compressing it aren't loosened to remove any of the cylinders and it is held captive with two pins though they have a bit of clearance slop). Not sure how this rumour keeps propogating. Bearings are also a few thou larger than the bore so that they are compressed into the bore with the case together. There will still be some light tension on the bearing shells even with the nut off. Hand spininning with one set of nuts off is safe and is routinely done during your engines assembly or any top o/h.

Larry

Ted RV8 · #6 10-22-2019, 07:37 AM

This “rumor” comes directly from Lycoming. Your safest procedure would be to follow the Lycoming methods. As others have said it’s not that the bearing could spin but that you’re affecting the crush on the bearing which could lead to early bearing failure.

If the jug is off get a torque plate, install and torque it. Other option is put the jug back on and torque it. The larger through the case studs are the ones that need to be torqued. Then rotate crankshaft.

Would think your A&P assisting you would be aware of Lycoming procedures.

You might be ok not following the recommended procedures as I’m sure it’s been done many times in the past. Why chance it?

rocketbob · #7 10-22-2019, 08:27 AM

Bearings are tanged and most engines have dowel pins as well. At this point I have had hundreds of cylinders off and on and never had a bearing spin.

BruceW · #8 10-22-2019, 07:49 PM

Thanks all for the replies.
Since I am a greenhorn, went with a middle recommendation.
Washered up on the thru bolts and torqued to 70% of book.
Got the piston pin off going low instead of high.
All packaged and off to the shop.

Now the wait and hear how much for the damage to the intake valve.
Figure my tipping point is $800. Above that, and I will just get a new one for $1200.

Ironflight · #9 10-22-2019, 11:10 PM

Quote:

Originally Posted by BruceW

Thanks all for the replies.
Since I am a greenhorn, went with a middle recommendation.
Washered up on the thru bolts and torqued to 70% of book.
Got the piston pin off going low instead of high.
All packaged and off to the shop.

Now the wait and hear how much for the damage to the intake valve.
Figure my tipping point is $800. Above that, and I will just get a new one for $1200.

Just so you know, using washers on the bolts is considered a no-no by Lycoming because if they spin they can scratch the mating surface for the cylinder. That why they have the torque plates. Alternatively, you can make a steel strap with holes that pick up two bolts at once - that can?t spin.

Paul

rocketbob · #10 10-23-2019, 06:06 AM

I've mentioned this here before but in the Continental IO-550 overhaul manual there is no mention of torquing of bolts until the entire engine is put together. If this were such a problem as the design of the thru studs and bearings are similar to a Lycoming why would they not be concerned about it?