Author Topic: 1976 CB550F1 (what have I let myself in for) Project  (Read 31110 times)

Offline Nurse Julie

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #225 on: February 28, 2021, 12:31:10 PM »
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.
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Offline eight0

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #226 on: February 28, 2021, 12:46:00 PM »
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.


Offline Nurse Julie

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Re: 1976 CB550F1 (what have I let myself ine for) Project
« Reply #227 on: February 28, 2021, 12:51:29 PM »
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.
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Offline Nurse Julie

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #228 on: February 28, 2021, 01:58:24 PM »
Just one other thought, have you got the compression and scraper rings in the right way up 🤔
« Last Edit: February 28, 2021, 02:06:45 PM by Nurse Julie »
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Offline eight0

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #229 on: February 28, 2021, 02:48:15 PM »
The writing is facing upwards. That's correct right?

Offline Nurse Julie

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #230 on: February 28, 2021, 03:00:51 PM »
The writing is facing upwards. That's correct right?
Yes, correct.
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Offline Bryanj

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #231 on: February 28, 2021, 06:27:34 PM »
Its possible but very rare that the ring groove is not machined deep enough, try clamping them with a jubilee clip carefully

Online Laverda Dave

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #232 on: February 28, 2021, 06:49:36 PM »
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.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Nurse Julie

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #233 on: February 28, 2021, 07:34:47 PM »
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.
« Last Edit: February 28, 2021, 07:36:37 PM by Nurse Julie »
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Offline eight0

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #234 on: March 01, 2021, 10:46:03 AM »
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.

Offline Bryanj

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #235 on: March 01, 2021, 11:26:32 AM »
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

Offline eight0

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #236 on: March 01, 2021, 11:30:49 AM »
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.

Offline eight0

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #237 on: March 01, 2021, 11:48:52 AM »
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.
« Last Edit: March 01, 2021, 11:51:25 AM by eight0 »

Online Laverda Dave

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #238 on: March 01, 2021, 11:51:42 AM »
Have you tried swapping the oil rings around between the pistons? This will tell you if it's the piston ring gap not having enough depth or if it's the actual rings at fault. The 250RS piston I had a similar issue with was a pattern part from DSS. I can't remember the actual make but it was pattern but not IMD or Cruzinimage. I remember it was in a blue and white box though.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Online Laverda Dave

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Re: 1976 CB550F1 (what have I let myself in for) Project
« Reply #239 on: March 01, 2021, 11:54:48 AM »
I would also try swapping the outside pistons with the inside pistons for a comparison and to confirm if it's the bore or the piston at fault. I'd also swap the con rods over for the same reason. Obviously don't run it like that it's just for comparison purposes at this stage.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

 

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