Piston ring replacement

[12jslater]

I've just bought a set of piston rings for my big seven will they be pre gapped (old stock hepolite)

And what's the easiest way of removing a ridge from the cylinder bore without a specific tool for the job?

[Alan]

They may or may not be pre gapped. Best to check anyway and should be 6 thou or a little more. You can take the ridge off with a half round file if you are careful but better to use a hone if you have access to one.

[Stuart Giles]

If they're Hepolite replacement rings, the top ring is usually a "Ridge Dodger" style ring with a step on the outside of the ring so that the new ring never actually reaches the ridge.

If I didn't have a ridge reamer, I'd be inclined to use a sharp bearing scraper to blend out the the ridge once the glaze has been removed.

I always check ring gaps when I rebuild an engine, only takes a few minutes, stick the piston 'upside down' down the bore to ensure the ring isn't crooked which would exaggerate the gap.

[Colin Swinbourne]

Definitely don’t assume they are gapped....I did once with the obvious consequences!

And the other obvious things- take care when checking the gaps and adjusting them, they break easily, and whilst you’re about it, just make sure that when the rings are fitted to the piston and inserted into the bore they haven’t bottomed out in the groove and gone tight ...I got lucky with that one!

[12jslater]

Well just checked and the rings are all gapped evenly, but around the .020 should be okay? granted the gap is a lot bigger than standard .006 but if I remember a bigger gap shouldn't cause too many issues... I hope ?

[Bob Culver]

Wiith the block removed so you can roll it about on a bench, using a fine parallel chain saw file with a few trurns of tape around the end enables the lip to be removed with precison. The ridge remover tools require great care and can easily extend into the worn area. Also operate at a comsiderable taper giving a larger top land clearance than necessary, esp on other makes. (A source of carbon debris)

[David Stepney]

Well just checked and the rings are all gapped evenly, but around the .020 should be okay? granted the gap is a lot bigger than standard .006 but if I remember a bigger gap shouldn't cause too many issues... I hope ?

Yes, Jake, you will be all right at that.  I fitted new pistons and rings to my RP a few weeks ago and the ring gaps were of the order that yours are. just make sure that, when you fit the pistons, don't align the gaps. I set mine at 120 degrees from each other for 3 ring pistons and 90 degrees for 4 ring ones.

I used a honing tool to deglaze the bores and to take off the (slight) ridge at the top of the bores. Alternatively, if your top ring is stepped make sure the step is to the top and don't worry about the ridge. Big Sevens don't suffer from crank whip like ordinary Sevens.

[Zetomagneto]

.004” per inch of bore diameter

[12jslater]

Well... Managed to break two rings getting them into the bore with my dodgy piston ring compressor not sitting flush against the head.

Does anyone have a recommendation where to.het a single oil ring from for a big seven?

[Zetomagneto]

What bore size? I have some 2.2” plus .80” oil rings spare