New rings, bad compression. Why does it hate me?

'82 XJ550 Seca
So this build has been going on for about 18 months now.
I rebuilt the engine with new piston rings/refinished bores valve lap, new valve guides etc etc sometime last year.

Ive only just picked up a compression tester.
Readings from cold: 1@130, 2@110, 3@120, 4@125

Cylinder 2, four consecutive readings with oil added: 150, 135, 130, 128

So this implies the rings. The new rings. The ones I installed correctly, right way up and clocked according to the Clymer manual.

Presumably I'll have to tear down the engine again, but what then?

 

You refinished the cylinder bores, are you certain they are within spec? Checked for bore diameter, ring gap, square, all of that?

 

Exactly! The correct way to re-ring:

1) Clean up the bores. Final honing not necessary but they should be square (perfectly round holes, no taper).
2) Measure each bore and determine proper piston size (consider the bores will get a bit larger if you haven't done final hone).
3) Acquire new pistons and rings as necessary.
4) Fit each bore to correctly its piston (each bore sized to the piston that will go in it). This is with the final honing.
5) Check ring fit to their assigned bores. File end gap as necessary.
6) Reassemble.

If you skipped any steps you could potentially have a problem.

Having said that, new rings need to "wear in". It's possible they will seal up after a few hundred miles.

 

I don't know if this will be any use to you or not, but 30 years ago I rebuilt my cb350 Honda cause it blew a head gasket. So I thought I'd may as well put in some new rings.Which I did. But after rebuilding it was smoking and no compression. Three time I tore that down and rechecked every thing with the same results. Finally I had mt GranDad have a look at it and one look at the piston he said those scraper rings are installed upside down. I said they can't be I followed the book and the dot impressed on the ring was facing up. The rings were stamped wrong therefore upside and giving little compression. Something to think about.Did you check the ring gap with one of the those new rings in the cylinder bore and was it in spec?

 

Oh sweet jesus.
I handed over the honing/measuring to a speed shop. (Weeps gently)

All I remember is checking ring gap and filing them back. This kinda implies that the rings were tight (I know i know)
I'm sure the speedshop would have mentioned if the bores weren't square (oh geez)
The decent compression numbers on the other cylinders imply that I got the rings right, I did triple check that against multiple sources.

What am I risking by waiting to see if the new rings will seat (say 300mi) ?

 

Unless you provided the speed shop with the pistons they cut a corner.

For future reference: You can check check up on the shop that does the bores by measuring the ring end gap at several depths in the bore. If it changes the bore isn't square.

You didn't do something silly like put in OS rings with a STD. piston, did you?

 

Lol, no to OS rings.
Yeh they had the pistons.
I cant check ring gap now without tearing down the engine and splashing out on a new gasket set, so it's - blow £100 to find out nothing is wrong, or spend £100 to find out I need to spend another £200.
These are not pleasant options, especially if there's a small chance that the rings will seat themselves.

I'm guessing that tuning will be difficult and I'm likely to go through more oil than I should, but I can live with this short term as long as I'm not creating more problems later.
Is there anything else I need to consider?

 

Assuming you didn't break a ring putting them in it shouldn't make you worse off to run it.

If it were mine I'd run it gently a few miles and check the compression again.

 

Yeah - get it running and then worry about it -if it's too smokey/drinks oil . I've been fretting over my top end rebuild (similar new rings etc.. but the damn thing won't start) freezing temps don't help of course. So now I have the carbs off again...

Good luck..