CB400/4 ENGINE STRIP, ASSESSMENT AND REBUILD BY JULIE - NOW COMPLETE

[K2-K6]

I was just thinking the same as you hairy,  the amount of carbon visible in the number 1 piston looks like it happened some time ago. Don't know if it's fallen out of the others as you've cleaned them. Seems to have done a decent job of holding compression up though,  guess it's a bespoke shape to fit it 

I'd guess at it happening some time ago. Detonation (yep,  pinking)  that sounds like if you dropped a M8 nut into a porcelain hand basin from about three feet up so it rattled around. Likely this was previous owner.

Hairy,  it understand that piston centre melted is not detonation but pre-ignition that gets the centre of the piston bouncing up and down like a trampoline as it gets hot enough to melt through like you've attacked it with a cutting torch.

[Nurse Julie]

Haha, yes, I remember 'pinking' very well, I had a Vauxhall Chevette that did it in every gear under load !!!. What my concern is I suppose, is if it were something I have caused, how can I rectify it to make sure it doesn't happen again? Now, if it was the PO that had it set up wrong thus causing the damage and then me just being the one owning it when it presented it's problems, then I can't change anything to prevent a further failure.

[K2-K6]

I messed that up,  I should have said dropped from a metre as I was working in metric with an M8 

You may have just invented carbon piston rings,  could call them graphene in a honed fossilised matrix and claim design rights.

Those Chevettes where quite a nifty chassis with double wishbone front suspension and panhard rod location for a coil spring axle at the rear. Escort owners would kill for something so good,  they're still welding bits on them nowadays to get them that good.

[Nurse Julie]

The engine blew up on my Chevette going up the old A21 at Polhill in 1982. Got my Dad to come and pick me up, left the car and never, ever went back for it. Could still be there in the undergrowth for all I know but, doubt it 

[paul G]

Mind boggling how that was still running 
Good luck with the rest of it Julie in at the deep end with this one

[Nurse Julie]

Mind boggling how that was still running 
Good luck with the rest of it Julie in at the deep end with this one

Just my luck Paul. I thought a new set of rings, new cam and primary chains and a cam chain horseshoe would do the job a treat.....never mind, keeps the old grey matter active 

[Rozabikes Tim]

Mind boggling how that was still running 
Good luck with the rest of it Julie in at the deep end with this one

Julie, if its any comfort - mine WAS running rough when you saw it at the Crich do - what will that look like?? Watch this space

[paul G]

Look on the bright side, if you crack this one then any other should be a doddle.
Ask Graham if that is the worst piston damage he has seen on a decently running engine.

[Nurse Julie]

Mind boggling how that was still running 
Good luck with the rest of it Julie in at the deep end with this one

Julie, if its any comfort - mine WAS running rough when you saw it at the Crich do - what will that look like?? Watch this space

I think every 400/4 owner on here should strip their engine at the same time as me Tim, hopefully someone has worse problems than me 

[Nurse Julie]

Look on the bright side, if you crack this one then any other should be a doddle.
Ask Graham if that is the worst piston damage he has seen on a decently running engine.

Graham says No, he says he has seen alot worse than that!!!. Hettie's engine was running perfectly even with the pistons in that state. She also only burnt about 100-200 mls of oil every 1000 miles. She was a flying machine.

[Johnwebley]

yes,she did run well,

 my 500 had that issue about 5 years ago, 1 piston was damaged and top ring vanished ,2 piston just had cracked top ring and no damage,3 and 4 were ok.

 new piston and 4 sets of rings sorted it,

  luckily no damage to the bores,

  used a demel to smoth out the head,

 the reason given by others more expert than me,was revving to hard when cold

hopefully the filter will have trapped the small debris ,as you say,the cam looks ok



 

[Nurse Julie]

yes,she did run well,

Yes John but I couldn't keep up with you 

[Trigger]

The damage is very old, down too much air either from a pervious air leak or not been set up right. The problem is the damage is too old and maybe the cause will never be found. It is unbelievable as this engine started first time every time and not even bad compression. It is still strange that number 4 is perfect. Julie has forgot to mention how many times it has been taken through the red line, when her head is in race mode

[Johnwebley]

yes,she did run well,

Yes John but I couldn't keep up with you 

  well,mine has 65000 on the clock,nicely run in,so spins over well !!!!

[Nurse Julie]

yes,she did run well,

Yes John but I couldn't keep up with you 

  well,mine has 65000 on the clock,nicely run in,so spins over well !!!!

So with mine at 47000 miles, do you think I should put my pistons back in for another 1000 miles and see if they bed in any better