1976 CB550F1 (what have I let myself in for) Project

[Nurse Julie]

I've pulled the head again and checked the piston that was hanging up the most.

Without the rings it drops through. With the rings it's really tight, but maybe it's supposed to be this tight?

https://youtu.be/glUKwGO5nxU

No, that is definitely not right.
Edit... Difficult to see on the vid but there appears to be a big gap fore and aft, piston to barrel. Have you tried that piston in another bore?

[eight0]

It looks like there's a gap because of the taper at the bottom of the barrel.
Good to know that shouldn't be like that I guess. I was contemplating cracking the cases again. If I have to get more pistons and another rebore then so be it. I'm this deep in.

[Nurse Julie]

It looks like there's a gap because of the taper at the bottom of the barrel.
Good to know that shouldn't be like that I guess. I was contemplating cracking the cases again. If I have to get more pistons and another rebore then so be it. I'm this deep in.

I would start by taking it back to the machine shop that did the work. They did the work, they can measure everything up again and advise.

[eight0]

Thanks for the advice Julie.

I'll go over there tomorrow. Seems odd that the ring gap is in spec and the pistons fall through without the rings bit it's still binding.

[Nurse Julie]

Thanks for the advice Julie.

I'll go over there tomorrow. Seems odd that the ring gap is in spec and the pistons fall through without the rings bit it's still binding.

Let us know how you get on.

[Nurse Julie]

Just one other thought, have you got the compression and scraper rings in the right way up 🤔

[eight0]

The writing is facing upwards. That's correct right?

[Nurse Julie]

The writing is facing upwards. That's correct right?

Yes, correct.

[Bryanj]

Its possible but very rare that the ring groove is not machined deep enough, try clamping them with a jubilee clip carefully

[Laverda Dave]

Is the oil scrapper ring in three pieces? Sometimes the very thin top and bottom rings don't sit fully in the ring groove due to the centre ring taking up most of the space. This happened to be with the RSA piston, it was very tight in the bore but fine when the rings were not fitted. It turned out to be the lower scrapper ring sitting slightly proud as it was sitting against the centre scrapper section at the back. I think I read it on the forum the best way to fit a three part oil ring is to fit the upper and lower rings first followed by the centre scrapper part. Maybe worth a try.

[Nurse Julie]

There is a Forum member called Ashdowner, Andy, who had exactly the same problem with a set of 550/4 K3 pistons / rings (or maybe just rings, I can't quite remember now) that he bought from Silver. It almost drove him mad as he couldn't get the 'sandwich' together on the oil rings at all. He even sent them back to Silvers and they said they were fine. In the end, he fitted a set from another supplier or fitted the old ones and they fitted just fine.

[eight0]

Ok breakthrough moment.

I tested each ring individually. Top two are fine but the oil rings are the issue. I tried with just one of the thin rings either side of the oil scraper and no difference.

I tried the two old pistons thin oil scraper rings and.. no binding.

Now I guess I could carefully file down the new rings, but can I or should I use the old thin rings, bearing in mind they are not oversized.

[Bryanj]

No complain to supplier that either the rings are wrong or the piston incorrectly machined, if you have bored the block you cant use standard rings without oil burning and mucho smoko

[eight0]

Didn't think so. Just to clarify, I only meant using the old thin bottom two rings not the top thick ones.

What are they going to offer though? All the rings can't have the same issue surely. If they give me a complete new set I'd have to get a rebore done again and probably at .50.

[eight0]

There's still another problem besides this. I test fitted the pistons and barrels to see if, without them binding as much it would turn over ok.

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Both outer pistons are still not centered. On piston 1 The inner side has +.60 clearance and on the other side I can't get a .05 feeler in the gap. It's the opposite with number 4. Gap is on the outside.

Sorry for the flurry of messages over the last couple of days. I took Friday and Monday off work to make some progress and this has stopped me in my tracks. I appreciate all the help.