SOHC.co.uk Forums > CB350/400

CB400F failure

(1/4) > >>

Mr-Gear:
Hi All,

Took my CB400F for a trip along the Pyrenees, Bilbao to Barcelona but unfortunately fully complete the return trip.

The route I took meant the bike covered approx 750mi with a mixture of 30mph and 80mph roads - some riding was enthusiastic and some riding was cruising. The fuel I used was whatever standard e10 fuel as "super" wasn't always available.

At some point, the bike began overheating, smoking, had an unstable idle and would not accelerate past 60mph prompting me to cease riding for the remainder of the trip through fear of damage.

The bike was rebuilt some years ago using a mix of OEM/pattern parts (in particular the rings were aftermarket) and has covered approx 12000 miles.

Bike is back home and currently (slowly) in the rebuild process.

On dissassembly, there appears to be some minor damage to the pistons, rings, bores and head. (see the pictures attached). It appears to be localised to cylinders 2 and 3, cylinders 1 and 4 are visually ok and have good compression.

1. Any ideas on what could have happened or some ideas on what might have caused this situation? it would be pointless to rebuild and ignore this as it could happen again.

2. Are any of these components savlageable? The cylinders are actually smooth, can't feel anything by fingernail but there are a couple of dents. Probably due to the piston rings breaking up. Perhaps a rebore to 0.50 and use the DSS aftermarket piston/ring kit again?

As for the head, it does not look like theres damage (on initial look over) to the valves, valve seats or sealing faces - could this damage be removed with a rotary tool and tidied up? or is a replacement head necessary?

3. other misc information

- Engine oil used halfords petrol/diesel oils with a higher zinc content changed at 1200mi intervals.
- So far, it does not appear that theres been oil starvation. It looks like the head has been recieving plenty of oil but further inspection of the pump etc still needs to be done.
- Carbs have genuine jets and parts, no obvious signs of blockages etc.
- Genuine points ignition which appears to be adjusted correctly (via strobe light) and is functioning.

Alexrayz:
Hey man! That is a sad view, sorry about that!
My first guess would be overheating from an improper mixture?
Did you adjust the air/fuel mixture? At altitude there is less air available so the mixture becomes richer. Without adjustment it can get the balance off kilter and mess with the performance.
What kind of smoke did ya have? And was it struggling to idle or was it hanging revs?

Cheers and good luck for the rebuild.

Johnwebley:
Sorry to hear you have issues

It looks like pre ignition, detonation, or pinking


Maybe the ignition was over advanced?

Or wrong grade plugs,

Or running to lean,

Best wishes

Sent from my SM-A546E using Tapatalk

Nurse Julie:
Broken rings, pre ignition, running lean, very similar damage to the damage I had on my 400

McCabe-Thiele (Ted):
Not sure if it would have prevented the damage  in your cases (probably not as it changes the burn temperature) ,   I've always been a fan of using some UCL like Redex.
It was very popular at filling stations in the 1960's when I worked on an Esso  Petrol Forecourt (no self service back then) even though all petrol was still leaded.

The forecourt had a hand held dispenser, one shot per gallon (2p) or for a tank full of fuel we had a large static dispenser that would deliver a Long Shot for 10p.

Navigation

[0] Message Index

[#] Next page