New Member RD400C

[EPApolice]

I get my pistons from Yambits along with other parts to save on postage. I also use Yambits crankseals although it seems everyone else says to stay clear and get genuine. I would pull out the crank and check bearings and replace the crank seals for sure at the very least its not a big job on the aircooled bikes and if you have basic tools and skill you will be ok. As you live in Sydney then peak rebores in Peakhurst will see you right for the rebore

[JonW]

Pat, any idea what those guys charge? The place Ive used before in Grnville is gone i think now, they were 77 a bore Incl GST.

[Blue]

I'm goin there tomorrow Jon will let you know.

Col at Peak Rebores won't be around much longer either, by the sounds. "Semi retiring".

Thanks everyone for your kind help.

Blue.

[EPApolice]

Colin is a mates father so does mine at mates rates I can find out for you if you like Jon

[Stankflapper]

Blue, give me a call, I maybe able to shed some light on that.

[Blue]

Barrels at the engineers today. Will be getting the pistons from Yambits as the general consensus is that they're ok...?

See image of the cracked piston.

The thought is that a correct run-in procedure was not followed.

[Greasemeup]

Looks like you pulled it down just in time to avert complete destruction, lucky man..

[EPApolice]

Interesting theory

[BRG1200]

YPVS type piston with the tang still on it. Would it be right that the aircoolers would have a "keyhole" shape port with no bridge, like the LC? Would put stress on that area and I know that would clatter, the LC I bought a few years ago had unmodified pistons in it and suffered chronic and noisy indigestion as a result.

[Greasemeup]

Would it have been ok to keep riding with a cracked piston?

[BRG1200]

better find that chip of aluminium.....

[hybrid]

When you get your new pistons, file off that tab!

[EPApolice]

As Hybrid said that tang should have been removed the last time because that being left on causes the piston to crack right where that one has. Of course the fact the bore was sloppy also will cause piston slap the therefore the post on to crack so either could be to blame. That doesn't explain the sieze mind you an too much clearance will make this more unlikely.
Its not unheard of for the AC bikes to suffer oil starvation if the oil level in the tank is low. How much oil is in the tank and check for dirt in the bottom of the tank. I a always make sure mine is full of oil every time but don't fill to the very top or as the oil can come out the overflow when it expands.
What's the bore on the other side like if its a new bore you will see straight away
, you can ask Colin to check the bore to clearance on the good side and he can confirm if the new bore was too big the last time if its a fresh bore.
If that was my motor I would strip it right down.

[BRG1200]

I think thats what they call "a near miss", congratulations on pulling it when you did.

[Stankflapper]

When you get your new pistons, file off that tab!

This is a interesting modification. As we all know pistons are taper ground so the largest point of a piston is the skirt measured from front to back of the piston, so to shorten the skirt will can cause the piston to rock in the bore. IMO unless the skirt may come in contact the crankcase or crank wheels I truly can not see why this is done? Also that piston has not seized it looks to me like it has ingested some material through the intake, most pistons pick up on the exhaust side of the bore through heat and lack of lubrication.
The crack has been caused from too much piston rattle (clearance) in the bore.
my 2c worth.