Neils 1978 CB550 F2 Project - Newbie Let Loose

[Oddjob]

I can find 2 sets of 0.5 oversize rings and 2 genuine 0.5 oversize pistons. However Cruzinimage will be much cheaper, I'm personally not a fan of Cruzinimage as I hear bad things being said of them on the USA site amongst others, especially on ring quality.

Oddly I'm going through the same as you. I have a 500 engine which I'm converting to a 550 set of barrels, I had one set of barrels ceramic coated and then found a mark on the bores that meant I had to consider a rebore. I decided to go 0.5, got new rings and for some reason I ended up with more 0.5 pistons than I needed. Hence the extras I mentioned before. Then I found a set of NOS 550 barrels going cheap, so I bought them and had to then source a set of genuine standard pistons and rings, which I did. I now have to decide which set I'll fit, the ceramic coated set need a bore but I can't work on the bike just yet due to health problems so no rush. I may keep the NOS barrels for spares, they'll only go up in value.

[Neilw]

I can find 2 sets of 0.5 oversize rings and 2 genuine 0.5 oversize pistons. However Cruzinimage will be much cheaper, I'm personally not a fan of Cruzinimage as I hear bad things being said of them on the USA site amongst others, especially on ring quality.

Oddly I'm going through the same as you. I have a 500 engine which I'm converting to a 550 set of barrels, I had one set of barrels ceramic coated and then found a mark on the bores that meant I had to consider a rebore. I decided to go 0.5, got new rings and for some reason I ended up with more 0.5 pistons than I needed. Hence the extras I mentioned before. Then I found a set of NOS 550 barrels going cheap, so I bought them and had to then source a set of genuine standard pistons and rings, which I did. I now have to decide which set I'll fit, the ceramic coated set need a bore but I can't work on the bike just yet due to health problems so no rush. I may keep the NOS barrels for spares, they'll only go up in value.

I guess I need some more information. I'll put an existing ring in each bore and measure the gap. I assume that if they are within tolerance, then replacing the pitted piston and the chipped pistons with std pistons and rings is an option?  i feel out of my depth here :-)

[Oddjob]

If you use a used ring and it's within spec then yes stay standard. Change the pistons though. However you'll normally find it will be out of spec, then you're left with wondering if it's the rings which are worn or the bores or both. Only with a set of new rings can you be certain. I did this test on my NOS barrels and you'd expect them to all be at the bottom of the spec range but in fact they were around the middle. Wasn't best pleased by that but what can you do. If you were local I'd pop round with a NOS set of standard rings and we could see what they measure up at. However check the bores first, with that amount of damage on the pistons I'd expect some on the bores as well. Maybe post some pics of the bores.

[Bryanj]

There are several firms selling piston kits, Dave Silvers has 0.25 os kits BUT nearly all the 500 bolcks i have bored did not clean at o.25 and had to go0.5 due to "barreling"

Cruzin only sell 0.5 and 1.0 as does an English firm i have bought from.

I know Trigger used Cruzin and i have done a few 400 recently using their kits, the us problems i have read about all seem to be 350 four and they are VERY critical on bore to piston clearance.

Cruzin piston kits usually arrive within 8 days and i have had uk parcels take longer

[Murf]

When I opened up my 550 engine I found the piston tops had score marks that look like they have come from a belt sander with 60 grit abrasive. I have to assume that is exactly what it is and that some tosser ‘cleaned’ the pistons on a belt sander!!!??.

Anyway I decided to replace the pistons and after looking around I got these IMD ones which look OK, the company is in the U.K. www.imdpistons.com and were very helpful on the phone, the pistons are made in Taiwan and look good. A lot of pistons are made in Taiwan. The pistons come complete with rings, gudgeon pin and circlips.
I have got standard size as my bores seem ok.

If you do change your pistons, and I would, then you need a full set.   If you stick with what you have and just change the damaged pistons then you will need genuine Honda pistons so that the weights match.

You say you are a bit overwhelmed with it at the moment, don’t worry this will just become normal life after about a month🙄

[Neilw]

If you use a used ring and it's within spec then yes stay standard. Change the pistons though. However you'll normally find it will be out of spec, then you're left with wondering if it's the rings which are worn or the bores or both. Only with a set of new rings can you be certain. I did this test on my NOS barrels and you'd expect them to all be at the bottom of the spec range but in fact they were around the middle. Wasn't best pleased by that but what can you do. If you were local I'd pop round with a NOS set of standard rings and we could see what they measure up at. However check the bores first, with that amount of damage on the pistons I'd expect some on the bores as well. Maybe post some pics of the bores.

Here are some pics of the bores. To the touch, they feel smooth, but one cylinder has a slight vertical indentation about an inch long, about halfway down.

I used the second ring from each piston to check the gaps at the top and bottom of each cylinder (since I broke the top ones), which should indicate wear.

• Top 1- 0.55mm, 2 - 0.63mm, 3 - 0.65mm, 4 - 0.35mm
• Bottom 1 - 0.70mm, 2 - 0.75mm, 3 - 0.70mm, 4 - 0.55mm

Looking at the book, these are all outside the standard range of 0.15mm to 0.35mm, assuming I'm reading it correctly.

BTW, Thank you all very much in helping me sort out what to do.

[mickwinf]

I would go with a rebore to .5 oversize then you know its right. I have used IMD pistons on a 550 with rebore done by Trigger and all seemed well. I think they do rebores as well, worth asking.

[mickwinf]

just had a look and IMD are £167 per set plus P&P also do rebores from £35 per bore.

[Murf]

I am not sure your readings mean a great deal because it sounds like you used a different ring in each bore, the rings may have different degrees of wear or even gaped  slightly different when first used.
At The very top of the bore,  top 1 to 3mm, there should be virtually no wear.  Use one ring for all bores, take the reading at the top most edge, then about 3 readings down the length of the bore. The variation between the reading at the top and those further down the bore will indicate bore wear. As the same ring is used in each bore an indication of difference between the bores can also be seen.

All that said, having seen the photos of your bores, plus the fact you need new pistons anyway, I would just go for a rebore.
The piston to bore clearance are very small 0005 to 0008 thou as I recall, there is plenty of past posts about this on the site, so Get someone that knows about boring these engines to do the rebore if possible. If not, then tell your machine shop what you want and don’t be dissuaded when they try to tell you the clearance are too small.  Check this out further though.