Topic: Oversize pistons for my 74' CB 550 K0

[Kelly E]

It's looking like I need to do a rebore on my 74' CB 550 K0. I need some advice on where to buy and which brands to look at. My buddy the machinist has plenty of experience with precision machining. All he'll need is the cylinders, pistons and the correct clearances. He's already been through the head to make sure everything is right. The bottom end doesn't make any funny noises so I'm not going in there.

I don't need anything high performance, just decent quality pistons and rings. The next question is how much bigger can I go with the stock liners without issues.

Thanks

[bryanj]

Cruzinimage in Japan do good piston kits, max Honda overbore is + 1.0mm but you can get 605 kits which are 3.0mm oversize, liner gets a bit thin then though.
Piston to bore clearance is very tight Mark will be best for that question, if your mate does mostly cars he wont believe how tight it needs to be!!

[HondaMan]

Yep, Bryan has a good recommendation: I use a lot of CruisinImage pistons. They start at the 0.5mm oversize, which should work fine. This will also give the engine a future, with the 1.0 oversize, the 590cc kit, and the 605cc kit, also from CruisinImage. I've used them all at one time or another. A caution: the 605cc kit is the last step for the bores, and it does make these engines run hot.

And yep, it must be TIGHT in the bore! The piston clearance for these is 0.0004" to 0.0008" AFTER HONING (that's not a typo: it is LESS than 1 thousandth of an inch!). The bores must be honed-to-size after they were bored 'undersize' a little bit: the shop that does my work bores to -0.002" less than the target and then hones the last (0.0010" + clearance) amount. The honing becomes the finished size.

Don't let your machinist be tempted to 'hone it to size' using a ball-type hone: I have seen when others tried this approach and it was a disaster. A straight hone should be used.

[denward17]

I recently purchased the CI pistons (.5mm over) for my 550 and used Mark's specs above, came out real nice, bike runs good.

Only have about 400 miles on it though.

I also used the CI pistons in my K8, it also runs good, about 2K miles so far.

[Kelly E]

My buddy is very familiar with close tolerance machining. I've seen everything from Subaru heads to Ferrari blocks and even a 1916 Mercedes block at the shop. I'll tell him about all of the machining tips. He's also done a lot of snowmobile, dirt and street bike stuff.
Sounds like I'll go with the .5mm pistons.

[M 750K6]

Get them measured by your engineer. That will tell you how far you need to go. The place I took mine did this and chatted with me about my intended use of the bike and we settled on a fresh hone and rings, rather than rebore, which should give me another 10-15,000+ miles. That coincides with the point I estimate the bottom end, particularly primary chain will be refreshed. I was on a budget and the immediate action required was around the leaking head and renovating the frame, steering, suspension and braking.... Costs add up!

Of course, running beautifully, I now love the bike and am riding it more than twice as much as I'd estimated! But still happy with my decision. Don't mind an engine out in another 3 years time, I'm guessing.

But my point was, your engineering firm should be happy to advise whether 0.5mm is good, or your wear dictates missing out that step. Be a shame to buy the pistons and rings, then find you'll still have wear at that point.

[Kelly E]

I ordered a set of oversized pistons from Cruizin Image that shipped on the 3rd. I forgot to order a head gasket and ordered one the next day. Today I received the head gasket but still no pistons.
So I ran the tracking number and the last location was released from customs in New York. I live 50 miles north of Seattle, why are my pistons in New York? 3000 miles in the wrong direction. The US postal service at it's finest I guess.

Hondaman I made sure that Terry is clear with the piston clearance specs. I guess I clicked on the wrong box and I'm getting 1.0mm over pistons, not really a big deal to me. Once the pistons are done touring the country without the rest of the bike Terry will fit them right away. It's awesome having a long distance riding buddy that now has a full machine shop in his garage. Now he doesn't have to go to work early to do it anymore.

[HondaMan]

I ordered a set of oversized pistons from Cruizin Image that shipped on the 3rd. I forgot to order a head gasket and ordered one the next day. Today I received the head gasket but still no pistons.
So I ran the tracking number and the last location was released from customs in New York. I live 50 miles north of Seattle, why are my pistons in New York? 3000 miles in the wrong direction. The US postal service at it's finest I guess.

Hondaman I made sure that Terry is clear with the piston clearance specs. I guess I clicked on the wrong box and I'm getting 1.0mm over pistons, not really a big deal to me. Once the pistons are done touring the country without the rest of the bike Terry will fit them right away. It's awesome having a long distance riding buddy that now has a full machine shop in his garage. Now he doesn't have to go to work early to do it anymore.

It's OK if you got the 1.0mm oversize: the cool thing about the SOHC4 engines is their lack of wear when bored oversize, so long as the 'cured' portion of the liners is still there. It cures out about 1.2-1.5mm in the 750 and about 1.2-1.6mm in the 500/550 engines, from all the bore-and-build work I've seen. The cured portion will not warp again like the original bores did: the liners (and fins) are heat-destressed ("cured") now and won't shift around. It is this warping (especially on bores 1 & 4) that makes the engines uneven and increases their wear: I have seen many of the step-bores exceed 80k miles with nominal maintenance, running fine. Heck, my 750 went from 50k (1980 rebuild) to 131k on the 1st oversize and still had no measurable wear, which led the machine shop to ask me why I wanted to bore them in 2013: they were still 'straight' and perfectly round to less than 0.0001" (he can measure to even half that much in his rig). I told him I wanted another 100k with even less maintenance.