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Kawasaki ZXR400 Piston Pop Problem...

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Wagman2000
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PostPosted: 13:44 - 10 Jan 2019    Post subject: Kawasaki ZXR400 Piston Pop Problem... Reply with quote

Hey!
My Kawasaki ZXR 400L snapped one of the heads off an inlet valve due to, what I think was the inlet camshaft been in constant contact with the followers as they are heavily worn. All because I had neglected to check the clearances...
The stem has clattered the top of the piston two or three times before the engine inevitably stalled, it was at tick over at the time so it wasn’t totally destructive.
I’ve had it to bits and I think I have been lucky in a way as the damage isn’t too bad, the Con rods are straight and true as are the other valves. The camshaft hasn’t worn either as the hardened surface won over the follower’s surface.
I have replaced the followers and the broken valve.
The problem I have is the piston. I thought at first I could dress the light damage out and reuse it. I had second thoughts as I didn’t know if the top of the piston is hardened and dressing the damage may compromise the integrity of the piston? A NoS piston is not cheap. Any thoughts?
Pictures on Pinterest here...
https://pin.it/2cam62aqmea4u3
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redeem ouzzer
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PostPosted: 14:10 - 10 Jan 2019    Post subject: Reply with quote

Pistons are aluminium. They aren’t hardened. However judging by the photo I think that’s too much to dress in all honesty. Wouldn’t you be better off chucking another engine in?
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Fisty
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PostPosted: 14:39 - 10 Jan 2019    Post subject: Reply with quote

From experience killing several zxr400 engines.

Get a used engine.
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Wagman2000
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PostPosted: 14:40 - 10 Jan 2019    Post subject: Reply with quote

I thought they would be harder than aluminium but now I think about it it does make sense.
The engine has only done 11,000 miles, I’m loath to replace it for something that has higher miles and an unknown history that I would have to strip and check anyway. Plus I already have new parts to sort this motor except the piston.
I’m cleaning it all up next week and I’ll post pics of it all after it’s degreased.
I’ll start checking for the availability of a new piston now though Rolling Eyes
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Wagman2000
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PostPosted: 15:20 - 10 Jan 2019    Post subject: Reply with quote

There were a couple on eBay and I’ve got an original piston from Germany for £46 posted, so not too bad.
I’ll still post the clean up next week and tell you how it goes.
I’ll keep an eye out for replacement motors, just in case...
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Fisty
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PostPosted: 15:43 - 10 Jan 2019    Post subject: Reply with quote

Even at tick over speeds the damage can be tremendous and invisible to the naked eye.

Have you measured the con rod?

Also what damage is there to the head? Having 2 motors drop valves, there was damage to the heads on both.
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Fisty
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PostPosted: 16:00 - 10 Jan 2019    Post subject: Reply with quote

Also is the Reg on yours Y398DJO?
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Sister Sledge
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PostPosted: 16:07 - 10 Jan 2019    Post subject: Reply with quote

Fisty wrote:
Even at tick over speeds the damage can be tremendous and invisible to the naked eye.

Have you measured the con rod?

Also what damage is there to the head? Having 2 motors drop valves, there was damage to the heads on both.


That's my first thought.
I can see some obvious damage to the piston in one place - like a groove but I very much doubt the piece of valve stayed in that place.
I reckon you'll have damage to the head and other valves in that cylinder - damage that can't be seen with the naked eye such as cracks.
I'd hate to see you rebuild it and another valve in that cylinder fail and let go.
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MarJay
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PostPosted: 16:09 - 10 Jan 2019    Post subject: Reply with quote

You can't guarantee that shards of swarf haven't flown around into the bottom end from that stuff, so yeah I also concur that a used engine is the way forward.
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Fisty
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PostPosted: 16:15 - 10 Jan 2019    Post subject: Reply with quote

Fisty wrote:
Also is the Reg on yours Y398DJO?


Im 99% sure I bought that bike as a crash damage none recorded in 2005/6 with 15k ish miles on it.

I repaired it as a track bike and sold it with a new speedo on it reading 0 miles.

I need to do some more digging.
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redeem ouzzer
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PostPosted: 16:37 - 10 Jan 2019    Post subject: Reply with quote

Pass the popcorn
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Fisty
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PostPosted: 16:43 - 10 Jan 2019    Post subject: Reply with quote

So, mileage adds up to what I am saying.

https://i.imgur.com/uavROkK.png?2

I think that engine has a lot more miles on than you think, I still could be wrong but that plate rings a bell. I am sure somewhere I have a picture of it.

I sold it to a guy in Sheffield, are you aroud that way? Do you know the history of it at all?
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Sister Sledge
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PostPosted: 16:52 - 10 Jan 2019    Post subject: Reply with quote

Well this has taken an interesting turn!
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Fisty
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PostPosted: 16:56 - 10 Jan 2019    Post subject: Reply with quote

Sister Sledge wrote:
Well this has taken an interesting turn!


I could be very wrong, but that plate rings bells. Ive broken, repaired and sold so many of the damn things they do blur into one.
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Riejufixing
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PostPosted: 20:48 - 10 Jan 2019    Post subject: Re: Kawasaki ZXR400 Piston Pop Problem... Reply with quote

Wagman2000 wrote:
The stem has clattered the top of the piston two or three times before the engine inevitably stalled, it was at tick over at the time so it wasn’t totally destructive.

The problem I have is the piston. I thought at first I could dress the light damage out and reuse it. I had second thoughts as I didn’t know if the top of the piston is hardened and dressing the damage may compromise the integrity of the piston? A NoS piston is not cheap. Any thoughts?
Pictures on Pinterest here...
https://pin.it/2cam62aqmea4u3


My first thought is that the damage you have is going to be difficult to "dress" out, leading to carbon build-up and pre-ignition, and, much worse, that the top ring land may have been distorted and pinched in the first ring groove which will be most unhelpful. At idle speed it will have received about 17 hits per second. The valve head is what's done the damage, since the stem seems to be in place still.

I would be very much inclined to replace the piston, even a used one would be a big improvement.

Question: Has the bore suffered damage?

Edit: Not sure I like the look of the inside of the combustion chamber/valve seat, either. Still, it's hard to know from a photo.
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Wagman2000
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PostPosted: 21:47 - 10 Jan 2019    Post subject: Reply with quote

Fisty wrote:
Also is the Reg on yours Y398DJO?


It is yes.
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Wagman2000
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PostPosted: 22:17 - 10 Jan 2019    Post subject: Reply with quote

Fisty wrote:
So, mileage adds up to what I am saying.

https://i.imgur.com/uavROkK.png?2

I think that engine has a lot more miles on than you think, I still could be wrong but that plate rings a bell. I am sure somewhere I have a picture of it.

I sold it to a guy in Sheffield, are you aroud that way? Do you know the history of it at all?


I did buy it off a guy from Sheffield Neutral about 7 years ago. I assumed it had been in an accident due to the respray and one of the lock stops was missing off the bottom yolk but it was cheap and otherwise looked pretty sound to my untrained eye. I thought it could have been dropped binned at a low speed so didn’t really worry at the time.
There is some of the original paperwork and the original receipt of sale. I would have to dig it out to check it though.
Your story would line up with the valve clearances being destructively out of tolerance. The rest of the of the bike is tidy though and the bottom yolk replaced now. I did about 1500 miles on it in France over a few days just before it packed in.

There doesn’t seem to be any damage except to the piston and the valve. The head looks good too but if the damage could be invisible to the naked eye that means nothing. Embarassed
I’m going to strip the removed parts and throughly clean them and check for damage. I have access to NDT kit at work to check for cracks and measuring gear to check everything is straight. I may strip the bottom end down too if the mileage isn’t accurate, if only to make sure there are no bits of metal floating about in it Mad

What a bummer...
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Wagman2000
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PostPosted: 22:19 - 10 Jan 2019    Post subject: Reply with quote

I would say the original colour scheme was the Black/Purple one judging by the wheels and the inside of the fairings too.
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Fisty
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PostPosted: 22:25 - 10 Jan 2019    Post subject: Reply with quote

Wagman2000 wrote:
I would say the original colour scheme was the Black/Purple one judging by the wheels and the inside of the fairings too.


It had a low speed front end crash, forks, front wheel, yokes and RHS fairing.

I sold it with a full fiber glass fairing and beet rearsets. The orignal colour was green/white, those fairings you have are not the ones I sold it with.
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Nobby the Bastard
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PostPosted: 22:54 - 10 Jan 2019    Post subject: Reply with quote

Tick over speed was enough to visibly bend and twist the conrod when the eggcup valdez dropped a valve.
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Wagman2000
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PostPosted: 23:07 - 10 Jan 2019    Post subject: Reply with quote

After today’s chat it’ll be getting a good coat of looking at Shocked

It’s going to NI in May if it kills me! Which by the sound of it, it might...
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Sister Sledge
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PostPosted: 23:10 - 10 Jan 2019    Post subject: Reply with quote

Well you have access to some awesome gear for checking things so hopefully it'll will work out for you.
Bit of a bummer with the history thing but it could happen to anyone.. me included!
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Wagman2000
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PostPosted: 23:14 - 10 Jan 2019    Post subject: Re: Kawasaki ZXR400 Piston Pop Problem... Reply with quote

Riejufixing wrote:
Wagman2000 wrote:
The stem has clattered the top of the piston two or three times before the engine inevitably stalled, it was at tick over at the time so it wasn’t totally destructive.

The problem I have is the piston. I thought at first I could dress the light damage out and reuse it. I had second thoughts as I didn’t know if the top of the piston is hardened and dressing the damage may compromise the integrity of the piston? A NoS piston is not cheap. Any thoughts?
Pictures on Pinterest here...
https://pin.it/2cam62aqmea4u3


My first thought is that the damage you have is going to be difficult to "dress" out, leading to carbon build-up and pre-ignition, and, much worse, that the top ring land may have been distorted and pinched in the first ring groove which will be most unhelpful. At idle speed it will have received about 17 hits per second. The valve head is what's done the damage, since the stem seems to be in place still.

I would be very much inclined to replace the piston, even a used one would be a big improvement.

Question: Has the bore suffered damage?

Edit: Not sure I like the look of the inside of the combustion chamber/valve seat, either. Still, it's hard to know from a photo.


The bore is surprisingly good condition. From my initial brief look it looked as healthy as the other three with no scoring or embedded metal.
I have also ordered a new piston.
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Nobby the Bastard
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PostPosted: 00:04 - 11 Jan 2019    Post subject: Re: Kawasaki ZXR400 Piston Pop Problem... Reply with quote

Wagman2000 wrote:


The bore is surprisingly good condition. From my initial brief look it looked as healthy as the other three with no scoring or embedded metal.
I have also ordered a new piston.


Have you measured the new length of the conrod and whether or not it's twisted?
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Wagman2000
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PostPosted: 09:45 - 11 Jan 2019    Post subject: Re: Kawasaki ZXR400 Piston Pop Problem... Reply with quote

Nobby the Bastard wrote:
Wagman2000 wrote:


The bore is surprisingly good condition. From my initial brief look it looked as healthy as the other three with no scoring or embedded metal.
I have also ordered a new piston.


Have you measured the new length of the conrod and whether or not it's twisted?


Not yet. They’re not bent by eye. Is there a method of checking them while the bottom is still built up? It would save me a job if it turns out they’re all twisted...
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