Topic: #2 ring groove too tight, no carbon buildup

[1976ssport]

My 76 750f was going back together fine.  Put the rings on 3 pistons and all was well. The second ring on piston 4 is very tight to where i have to force it into the groove. All the carbon is removed. 
The old ring is a little better but there is no room for a feeler gauge to check the side gap. I lightly sanded the sides of the old and new ring with 600 grit to remove any burr, no help.  Is it new piston time?  The old ring has an acceptable end gap, can i sand the side and use it? 
Thanks in advance

[bryanj]

I would be more likely to suspect a burr on the edge of the ring groove on the piston.

[Tracksnblades1]

Was this engine a runner or was she stuck....?
Honda piston and rings...?
Have you checked ring thickness against the other three that weren't any trouble...?

[Jerry Rxman Griffin aka MuthaF'er]

All of the early Super Sports used the pre 77 K rings ie -300 part number. According to my F parts manual there were a few late 76 F's that used the later pistons with the top 2 rings 1.2mm vs the earlier 1.5mm rings. Double check what you have there.  Engine number 2551567 was the change over.

[1976ssport]

Thanks for your thoughtful responses.

The new #2 compression rings all measure 1.43mm.
The engine wasn't running but turned over well with the starter.
Original Honda pistons.
I did lightly sand the ring grove with #220 sand paper to address any burr issues, also broke an old ring in half and scraped the groove, the result is minimal improvement.

I think i will try to carefully sand the groove without deepening it or rounding the top edge. 
What do you think about sanding down the sides of the original ring, the end gap is within spec. It is slightly better fit than the new one.

[Tracksnblades1]

-1 Grost Rider.  I would look closely at the bottom ring land of the top ring groove. If the top ring encountered a hydro-lock or siezure situation it may have more clearance by closing up the clearance on the 2nd groove. You could stack feeler gauges up to measure what you have comparing the top ring groove with the troublesome 2nd. My personnel opinion would be to replace all four with a weight matching set. I don't believe you'll be able to maintain an effective seal on the 2nd ring in question by hand sanding. On other engines there has been debates wether new rings ever seat on used rings lands, but we've all done that before.

Thanks for your thoughtful responses.

The new #2 compression rings all measure 1.43mm.
The engine wasn't running but turned over well with the starter.
Original Honda pistons.
I did lightly sand the ring grove with #220 sand paper to address any burr issues, also broke an old ring in half and scraped the groove, the result is minimal improvement.

I think i will try to carefully sand the groove without deepening it or rounding the top edge. 
What do you think about sanding down the sides of the original ring, the end gap is within spec. It is slightly better fit than the new one.

[1976ssport]

Was able to get the sharp end of my calipers in the grooves to check the size.  That piston has definite damage to the 2nd ring land.  First groove is to large second one too small.  Never thought i would find that.  Oh well, i guess ill have to replace look into pistons.

Thanks again for the comments

[Tracksnblades1]

Glad you found it. Obviously a good wrench...  To bad you already have a new set of standard rings, 836......??

If you haven’t owned it forever it’s hard to tell what the PO had done. 

I’ve seen old antique tractor engines  that had been seized for years. The owner modifies a spark plug by tapping and installing grease jerk in it. An old style bucket air grease gun hooked to it will unsieze it instantly, or it will pop the head studs, break the pistons/ring lands, bend the rod, or push the crank out if it’s not turned right.

[754]

 Sand the ring not the piston.. it should stay flat.
 
Good luck trying to sand a ring groove accurately.

On top fuel cars, they often recut the ring grooves, as they get closed up.

[1976ssport]

Ordered 4 used pistons for "F" model, same year off of Ebay.  I'll pick the best one. 

[Tracksnblades1]

Ordered 4 used pistons for "F" model, same year off of Ebay.  I'll pick the best one.

👍  ,  Best one + compare them on gram scale for closest weight. 

[1976ssport]

I thought about working on the #2 ring groove to increase the size, but the size is not consistent and anyway the #1 ring groove is too big.  Good to know other engine builders have done it.

[Tracksnblades1]

And Don R knows..... them little NitroHammers can pound everything down in short order......shhh...top secret Don R has 1000hp NA engine @ his place....😎