Honda-SOHC

Is yours the sort of oval shape?

If so have a look at KNHA-0750.

Gather it's a CB650Z? around 1979?

Sell them. Someone will buy them, let them have the problems and use the money to buy a decent set of barrels.

I can understand you thinking that. However experience on this site says that a lot of engineers get the clearance size wrong for Hondas, they either refuse to accept the right clearance and insist it will seize or just plain ignore you and bore to what they think is acceptable.

I suspect you have fallen into this category, the PO has gotten it wrong by the look of it.

Experience also shows that the Yoshi 812 kit wasn't the best idea in the world anyway, it sounded good in practice but didn't really warrant the cost involved or the problems they could create.

Best bet, buy a set of decent second hand barrels and go back to standard, it doesn't sound as cool standing by the bike telling people it's got Yoshi pistons etc but the reliability of the OE system far outweighs any cool factor IMO.

I drilled and tapped my headstock, fitted a grease nipple and it's now completely full of grease. One thing about steering races etc is that you cannot easily regrease them unless of course you do what I did. If you've got tapers fitted it could be the bottom race isn't shimmed out enough, check the bottom of the frame for rubbing marks. Or it could be a lack of grease or the grease has started to dry out in the very warm weather we've had recently.

The O-Ring is a thicker chain than standard so check where the rivet pins go as it goes around the front sprocket, there are some reports of them gouging a track in the crankcase, hitting the chain guard that you're after and on the 500 breaking the clutch push rod. See if you can spot any shiny areas where it might be touching.

Looks like an O-Ring chain, make sure there is clearance for it.

Seal looks ok, looks dry as well.

I've always used Coppaslip but after buying some nickel grease I think it's better than Copper so I tend to use that now.

Not sure if you've done this Mick but it's something you should know about.

Got 2 550 engines earlier this week. Both minus gearboxes and essentially just cases, cranks and primary drive. The clutches were also there but seperate as were the generators etc.

One set of cases still had the barrels on, fins chipped to hell and back, I presumed that the barrels were bonded to the cases so made plans to remove them. Couple of hefty whacks with a rubber hammer and up they popped, some wiggling (and this was them in a large crate in the back of my car) and eventually the barrels came off. Good news I thought except I now noticed that number 2 rod was seized, removed the psitons, top case off (no bolts were fitted) and turned the crank around until I could access the 2 rod bolts. Removed the nuts and split the rod, the oil gallery in the crank feeding that journal was completely blocked with solid white powder, the crank still looked ok, the shells weren't marked but they were contaminated. I got the powder out by just sliding a 3mm drill down and spinning it by hand. I can't think what caused this, it could be water ingress or condensation or something else. I may remove the ball bearings capping the internal oil galleries and running a 3.5mm drill down them or I may try and see if a bottle brush and some brake cleaner will do the trick.

So check the oil gallery opening on that journal, maybe there's a small amount of stuff just sticking up and that's catching the shell, if you've tried yellow and it's still sticking it's not a shell selection issue. Check the rod journal surface for any dents that would reduce the clearance.

Have you tried another rod on that journal?