Often just reringing the pistons works...you need to set the piston ring end gap in the cylinders...use the piston upside down to get the rings square in the cylinder and find the tightest section of the bore. The ring gap is a factor of pi (3.14159...) times the cylinder bore variation, so if you have a bore taper of say .007" you'll have a ring gap variation of approximately .021", which IMHO is excessive. The rings work too much and will fatigue and crack or simply wear out...blowby may also be an issue. Childs and Albert MAY make a zero-gap piston ring setup (actually a pair or trio of overlapping rings for gap-free operation) for your piston, but you'll have to check. FWIW, they can offer superior sealing over the stock rings.

Another two issues with used pistons are (1) piston to cylinder wall clearance...tighter is better for oil control, worse for high rpm/friction. Case in point, stock Triumph 650 Tiger turns 7500 rpm with one carb at 113mph (1970) and piston/wall clearance of .007"...same engine with new hepolite pistons fitted by #$@%#$ BMW bike shop fitted at .002 lost 1000 rpm and 10mph...but my was it quiet and didn't burn any oil unlike the OEM setup. Also had to break it in for 1000 miles gently whereas the OEM Trump setup was ready as Freddy from the get-go. And (2) ring land to piston ring clearance, less is better, too much and the ring twists too much and can either cause blowby or excessive scraping/wear. Yes there are specific L-ring sections that are designed to twist for improved sealing, but they're not stock to this engine, I believe.

Heck, the more I think about it, replace the #$@%@#$ pistons and be done with it. Also have the conrods sized, honed, etc. and consider replacing the con rod bolts with new high quality ARP bolts. I personally like floating piston pins (gudgeon pins to the UK members!) Use a stretch measurement device for torquing the rod bolts.

Chris, while you've got the head off, it would be a good idea to get hardened exhaust valve seats installed, then you won't have to worry about valve recession from using unleaded gas. Any good machine shop can do it and it should not be expensive.

you'll have to pull the engine apart to check the wear on the cylinders. otherwise, it's hard to say.

on my 68 1800, i was able to re-use the stock pistons. i purchased a re-ring kit from ipd and, 40,000 miles later, it still runs great.

when you have the engine apart/at the machine shop, check the wear on the cam. these tend to wear out faster than the block. if the lobes are worn, get a cam from ipd, you won't be disapointed.

Rebuilt a b-20 with the same pistons, got about 50k before it started blowing oil. Did a 200k b-21, 70 k with no problems.

As ever without looking and measuring you can't tell. However from experience I would say that your engine needs a re-bore. Usually with those symptoms what has happened on a B20 is that you have a broken ring or two. Likelyhood is it will have scored the bore and no amount of re-ringing will cure that.

The pistons are excellent quality, if you find a late B18 engine block you could have that bored to 2 litre, re use the B20 pistons with new rings. Drop straight into your car no mods, B20 head will go straight onto it. Usually if you can find one they are pretty cheap , at least here.

Just make sure you get one with the mounts for your alternator or you will be fabricating, '67 on should do it. The other big but is that it is only easy if your B20 is a six bolt crank engine ie 6 bolts holdng the flywheel to the crank, the later 8 bolt crank is metric and the pistons won't readily fit the earlier block

Regards

I like the previous post. I have had some experience at re-ringing pistons, but not as much as him. The issue I have run into is the ring lands being worn out when the piston and bore measurements are satisfactory. When the ring lands are worn past specifications, the rings will work up and down in the ring lands, and your overhaul will not last as long as you would like.

I have put new rings (along with bearings down below) on LOTS of old pistons for everything from Minneapolis-Moline tractors to Porsches, but you can't just stare at a piston and decide whether it's ok with your eyeballs -- you have to get someone with good machinist's measuring equipment to judge the piston skirt wear, the roundness and taper of the cylinder bores, etc. If the bores are good, but the piston is just a bit below spec for diameter across the skirt where it matters, it can be knurled, too: this consists of using a special tool to raise bumps to bring the diameter back to spec., and it's a lot more durable solution than many would imagine.

But none of this is possible without the right tools and experience. When I was 40 years younger, I wouldn't have been afraid to slap in a new set of rings and bearings on my own machine (and only my own) without all these concerns and then see how it worked out on the track, because I had the energy to redo it properly for myself all over again if necessary, but that was long ago.