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SOHC.co.uk Forums => CB350/400 => Topic started by: Dolomite_ on April 11, 2024, 07:16:35 PM

Title: Big end bearing help
Post by: Dolomite_ on April 11, 2024, 07:16:35 PM
My green and brown sets of big end bearings have arrived and I have measured them up, and once again its not going to be as easy as I hoped.

Im not sure if I've read it wrong but my con rods are C2 C2 C2 C2, my plastigauge measurements are 0.050mm 0.050mm 0.050mm 0.038mm. And to throw more confusion when measuring with the micrometer I get a clearance (32 - the diameter measured) of 0.0138mm 0.0163mm 0.0163mm 0.0087mm.

I measured with the brown bearings first and was surprised at the big gap. 0.050mm is too big what is the tolerance? The connecting rod chart is a bit more confusing than the main bearings chart.
Title: Re: Big end bearing help
Post by: Nurse Julie on April 11, 2024, 07:20:07 PM
Did you measure the crank Lukas, it may well be very worn.
Title: Re: Big end bearing help
Post by: Dolomite_ on April 11, 2024, 07:30:54 PM
Did you measure the crank Lukas, it may well be very worn.

If I'm reading the wear tolerance on the graph correctly, the wear is within the tolerance. All below 0.016mm
Title: Re: Big end bearing help
Post by: Deano400 on April 11, 2024, 08:07:07 PM
When you say 'my con rods are C2 C2 C2 C2', is the C and 2 on either side of the conrod or have you got the Cs from the crank?
Title: Re: Big end bearing help
Post by: Dolomite_ on April 11, 2024, 08:12:44 PM
When you say 'my con rods are C2 C2 C2 C2', is the C and 2 on either side of the conrod or have you got the Cs from the crank?

Yes, the C and 2 are on either side of the conrod, I don't know if they're relevant to the graph. My web codes are 1 1A 1A 1A 1A and the crankcase codes are BAAAA.
Title: Re: Big end bearing help
Post by: Deano400 on April 11, 2024, 08:20:27 PM
The Cs on the conrods are the weights, the only thing that matters about that is they are all the same.
Take the As from the webs and your conrod shells are A2, A2, A2, A2 which is Yellow.
Using Green or Brown should give you tight tolerance. Are you just tightening them or torquing them?
Title: Re: Big end bearing help
Post by: Dolomite_ on April 11, 2024, 08:29:09 PM
The Cs on the conrods are the weights, the only thing that matters about that is they are all the same.
Take the As from the webs and your conrod shells are A2, A2, A2, A2 which is Yellow.
Using Green or Brown should give you tight tolerance. Are you just tightening them or torquing them?

Im torquing to 14.75 lb ft.

It says 14.5 - 15.9. Should I bo going higher? I always go middle to lower end of the range.
Title: Re: Big end bearing help
Post by: Deano400 on April 11, 2024, 08:40:02 PM
I always go middle but I can't see that 14.75 would be a problem.
If they are new shells then it should come in spec no problem.
Title: Re: Big end bearing help
Post by: Dolomite_ on April 11, 2024, 08:48:12 PM
I always go middle but I can't see that 14.75 would be a problem.
If they are new shells then it should come in spec no problem.

Yeah new shells just a big clearance.

Im just surprised at the clearance. The Haynes manual says 0.018mm to 0.048. I might need to go to black.
Title: Re: Big end bearing help
Post by: Bryanj on April 11, 2024, 09:00:38 PM
I think you are missreading the plastigauge chart or the micrometer ifvit was the gap you say you would probably feel play
Title: Re: Big end bearing help
Post by: Dolomite_ on April 11, 2024, 09:08:29 PM
I think you are missreading the plastigauge chart or the micrometer ifvit was the gap you say you would probably feel play

I'll give it another go tomorrow. The measurements for the mains went fine, unless it was just one of those days today.
Title: Re: Big end bearing help
Post by: McCabe-Thiele (Ted) on April 11, 2024, 11:00:02 PM
When you check the big end bearings iirc the two slots for the bearing shells are on the same side plus the weight code marks will then be in alignment. Have you fitted the big end cap the wrong way round when taking the Plasitgauge readings.

For reasons that seem contrary to common sense the axis for mains & big ends are transposed the number code for mains are on the vertical axis with the letters on the horizontal axis.  For the big ends (con rods)mits letters vertically numbers horizontal.

My big end tollerances were all pretty much the same at 25 microns each a lot tighter than the mains clearances that were 38 microns. I had Green shells in all four of my big ends the codes on my crank were mostly illegible.
Title: Re: Big end bearing help
Post by: Dolomite_ on April 12, 2024, 11:25:37 AM
measured again and the clearance looks like its more along the lines of 0.038mm 0.050mm 0.050mm 0.025mm. I might order a set of black and see what that shows.
Title: Re: Big end bearing help
Post by: Deano400 on April 12, 2024, 12:54:10 PM
Not sure going to Black is going to help.
You’ve posted two sets of readings and got different results, so not consistent readings.
Set 1         0.050mm 0.050mm 0.050mm 0.038mm
Set 2         0.038mm 0.050mm 0.050mm 0.025mm
Are you giving everything a clean between readings? No remanence of oil, plastigauge or anything else that may affect your results.
Conrod and cap aligned with the C and 2 always matching?
Conrod installed with shell tabs to the exhaust side?
Torquing progressively on both bolts i.e. not torquing one up then the other?
Title: Re: Big end bearing help
Post by: Dolomite_ on April 12, 2024, 01:24:59 PM
I took 2 measurements each time. Cleaned them in between and made sure it was the correct direction. I've ordered some blacks anyway as I need to do an order at DSS. Just need to wait for that and some more plastigauge. I'll take pictures next time too.
Title: Re: Big end bearing help
Post by: McCabe-Thiele (Ted) on April 12, 2024, 09:29:48 PM
I did wonder if the big end journal looked okay visually when you bought the replacement crank, presumably if you could feel a wear ridge you would not have fitted it out for mains.

As you know I have a spare 400 crank so if the Black Shells do not fix your problem let me know.
Were the new shells in Honda packaging?
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