Ring end gap?

**328FTW** · 10th July 2013, 17:17

Posting from my phone so semi brief. Screw my tired old never starts vt250 motor. My new one the rings are here (oem honda). But my manual doesnt have the gap for new ones. Just the old ring max wear spec. I know how to stagger rings etc but id prefer having the clearance number.

Anyone have it or a good rule for the small 60mm bore ive not done a motor this small cept lawnmowers where it matters less. Weisco etc come with spec sheets. The oem does not

**Katman** · 10th July 2013, 18:14

The general rule of thumb is 4 thou per inch of piston diameter.

**Akzle** · 10th July 2013, 19:12

Originally Posted by Katman

The general rule of thumb is 4 thou per inch of piston diameter.

personally i'd go with 3.5
....

**328FTW** · 10th July 2013, 19:43

I just wasn't sure if general rule of thumb applied to something with higher compression and smaller bore than I'm used to. Now I'm on my desktop I really scoured the depths of the internet, hidden deep in an almost forgotten torrent I found what I was looking for. It's taken a few hours but here we go. I worked out in my head about 0.2mm or ~7 or 8 thou seemed a safe bet. The general rule posted above gives between 8 to 10 thou or 0.2-0.25mm.

The service manual I found is pretty damn broad with what it says but it said between 4-12 thou for your top gap, same for second and a max gap of 20 thou before replacement. So given this I was thinking of running with 6 for the top, 8 for the second. It's not the tightest you can run but it seems like an alright combo by my reasoning. I like the second gap bigger in general, plenty of theories but I've found it to help with buildup between rings; might be placebo but keeps me happy.

The block is already honed, I washed and prepped the pistons all purdy, cleaned the grooves etc. Just want to finish it.

**gammaguy** · 10th July 2013, 21:05

Unless you rebored it and fitted oversize slugs it will probably still burn oil

**328FTW** · 10th July 2013, 23:04

Bores measure fine. Not oval. It had low compression, I had to take it to bits anyway. Skirts aren't collapsed, minimal marking. Things are looking fine in my eyes

If all else fails I can carry it into the university, scan it and then secretly using the CNC machine to make a V6 block. VTNZ will wof it easy.

**MotoServ** · 11th July 2013, 18:21

Hi 328FTW,

Just a quick note, glad you found the ring gap spec. I would also suggest you complete a cylinder leak down test once you have the motor together to ensure the valve train is seating/sealing correctly as well.

Cheers & Happy riding.

**328FTW** · 12th July 2013, 00:15

Oh I'm an engine builder kinda, I'm pretty ok with that stuff usually

I'm going to flip the heads and put petrol in them and see if any of them spew fluid into the ports, if any do remedy before bolt down. Get it together, then test compression and leakdown. Once it checks out I have bench balanced some carbs for it ready to go. Put in the bike and break it in.