Lock up near TDC?

Hi

Yesterday, one of the flyers had a norvell .15
that is fairly new but has run some.

It turns over freely but every now and then, it locks
up at TDC where there is normally no resistance.
We found we can get it to do this by reversing rotation
near TDC. This is a ringed motor. Any ideas what might
cause this?

Look real close I bet you will find that the ring is missing:)

Ken,

completely normal for a Norvel .15, I have four of them and each has been very tight up near the top at the beginning of life. Just keep running it! It will eventually become a very well mannered motor.

I'm told that the empty "ring grove" near the top of the piston is there for oil retention.

Ta

I'll let him know it's normal.
Was not easy to see if the ring was there or not.
Even if it's normal, I don't understand why it's normally
smooth at TDC but locks real bad occasionally.
Any explanation?

It does not seem to be compression related as it's the same with
the plug removed.

Ron B.
F4Fguy

They are fitted very tightly at the top. Enough so that if you turn them over too slowly you'll wipe all the oil film off causing the piston and cylinder to lock together. If he still has the factory instruction sheet,he'll find a warning about this. The factory instructions are to wash out the assembly oil,re-oil with a good lube and allow to set overnight before the first start. A short break-in after this is all that's needed. These engines should never be turned slowly by hand,but always flipped vigorously through compression.

This is completely normal for a norvel engine. If you turn the prop by hand very fast you will notice it turns over just fine. If you turn the prop slow it will lock up. When you turn it slow it give the oil time to squish out from around the very tight close fitting piston and cylinder wall and metal to metal rubs and locks up.