SOHC.co.uk Forums > CB350/400

CB400F failure

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K2-K6:
A thread about this type of problem here

http://www.sohc.co.uk/index.php/topic,14609.0.html

 :)

K2-K6:
It would be interest to hear which spark plugs were in use too.

Can you post binman?

Bryanj:
Timing slipped or "over enthusiastic" riding from cold, possibly ring groove to ring clearance too large you will need at least 1 piston but what does 3 look like? And before any decision on that a light hone on the cylinder(s) in question plus very carefull inspection and measurement, by the time you have 2 piston kits plus rings it can be as much a 4 piston kits, oversize is same cost as standard so only extra is a rebore to be "as new"
At what altitude did the problem start as possibly weak from thin air

Mr-Gear:
Hi all,

to answer some additional questions

1. My own suspitions similar to others is lean condition and detonation which deteriorated the pistons and ultimately the piston rings. since the top ring is gone on cylinders 2 & 3.
Cylinder 3 has damage to the same type and extent as cylinder 2. Cylinders 1 and 4 seem ok and no visible damage but do look like they have been hot. All pistons will be replaced and all cylinders will be inspected and reworked.

2. Thank you for the link K2-K6. I have read that post before and I think even replied to it. I'd like to think I learned from the information provided and It did influence my riding style but perhaps I didn't adjust enough. I try to keep the rev range a bit higher and not roll about on the throttle too much accelerating in high gears.

3. The colour of the smoke was blue, which I guess tracks.

4. The spark plugs used were NGK D8EA, the plug caps were the NGK ones DSS sells.

5. Timing was configured with the help of this video https://www.youtube.com/watch?v=3933ouJ1wrI and I used a timing light. (this isn't to say that I didn't make a mistake of some sort, of course.)

6. I didn't adjust the mixture dependant on the altitude I was at. I can't say I was being that observant about the altitude. a quick google suggests the highest I got was probably about 900m elevation.

K2-K6:
Doesn't it get too rich at altitude if set correctly at sea level  ?

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