ZX6R...Piston slap

1762 Views 9 Replies 5 Participants Last post by Kllongbrake, Apr 12, 2017

10Arghh

Discussion Starter · Apr 10, 2017 (Edited)

So as part of my ZX6R engine strip down, I've found that no.1 cylinder bore and the corresponding piston's skirt is scored.

As per pics.

All other pistons and cylinder bores are smooth and fine.

I think this is what was causing the loud engine ticking which prompted me to look into the motor. I already bought a manual cam chain tensioner and that had no effect so I thought it was time to look.

Anyway, I believe I'll need a rebore and a new piston to repair, but I was wondering if there are further problems at the bottom end with maybe the conrod bearing as there's no good reason why a piston should slap.

Would be greatful for any knowledge.

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R/T Performance

· #2 · Apr 11, 2017

WOW!!! That for sure needs to be bored and new piston. year and miles? I am not a bike mechanic but a auto mechanic. not sure if the zx6 has an oiler on the rod where it sprays oil on the cylinder but if it does and got blocked off this could happen. good call pulling it down

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michael4012

· #3 · Apr 11, 2017

Its relatively hard to judge the bore from the picture is it rough to touch with the finger? Nikasil seriously is tough mate, if its smooth just get some wire wool and see if those marks come off that looks like dirt to me (crap of the piston skirt) & may clean up but only if its smooth. There is a jet next to each crank main journal which lubricates the cylinder wall take that out for a look i think you may get away with replacing that one piston as Nikasil takes serious punishment mate, pop in one of the other pistons and rings and check the piston to wall gap i reckon itll be in spec.

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10Arghh

Discussion Starter · #4 · Apr 11, 2017

Thanks guys

My boss who races cars and builds engines reckons this is caused by oil starvation.

He said to check for scoring on the conrod bearing also, and that it'll probably need a rebore.

I will check what you say though Michael.

Unfortunately, I suspect the bike at some point in it's life, has been down on track (found lots of gravel around engine bay) and maybe was run whilst on it's side.

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Kllongbrake

· #5 · Apr 11, 2017

I'm also not a motorcycle mechanic but a class 8 truck mechanic. I have rebuilt quite a few multi cylinder snowmobile engines. My only advice is that at this point of tear down, for me anyway, it would make sense to re-nic the cylinders and put new pistons and rings in. In the long run you'll be better off if you plan to keep the bike. Only my opinion though. Take it for what it's worth. -Edit- millennium technologies does great work with fast turn around times.

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michael4012

· #6 · Apr 11, 2017

Well there's no doubt oil starvation caused it, but reasons are many, yes it could be a blocked oil jet, yes it could have been over whilst running. Without seeing pictures of all the piston crowns & spark plugs, it could also have been caused by either, an excessively hot temp in that cylinder possibly a blocked injector or low pressure causing it to run lean and then the heat burns oil of the cylinder wall & causes that also it could be over fueling & unburnt fuel diluting the oil on the wall. Are all the pistons & plugs the same colour etc. Are the exhaust valves from that chamber dark grey or white. If you are lucky you wont need a re bore & Nikasil coating (bout £500) maybe a new rod & piston with pin rings & clips (bout £250) but you well have to without doubt plastigauge that big end. Its a choice you make but a rebore with all new pistons & rings is gonna cost a grand plus and if your doing that you had may as well refresh the whole engine new crank shells rod bolts oil strainer pressure valve oil pump it all starts to add up its your choice. But without doubt you must sort the problem so it doesn't happen again.

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10Arghh

Discussion Starter · #7 · Apr 12, 2017

michael4012 said:
Well there's no doubt oil starvation caused it, but reasons are many, yes it could be a blocked oil jet, yes it could have been over whilst running. Without seeing pictures of all the piston crowns & spark plugs, it could also have been caused by either, an excessively hot temp in that cylinder possibly a blocked injector or low pressure causing it to run lean and then the heat burns oil of the cylinder wall & causes that also it could be over fueling & unburnt fuel diluting the oil on the wall. Are all the pistons & plugs the same colour etc. Are the exhaust valves from that chamber dark grey or white. If you are lucky you wont need a re bore & Nikasil coating (bout £500) maybe a new rod & piston with pin rings & clips (bout £250) but you well have to without doubt plastigauge that big end. Its a choice you make but a rebore with all new pistons & rings is gonna cost a grand plus and if your doing that you had may as well refresh the whole engine new crank shells rod bolts oil strainer pressure valve oil pump it all starts to add up its your choice. But without doubt you must sort the problem so it doesn't happen again.

Thanks mate.

All piston crowns and plugs are same tan colour colour except spark 1 is oily.

Just totting up minimum parts needed if bearing shells were ok...

I can get used cylinder bore and pistons for £50
1 x 11060-1667 -GASKET,HEAD COVER - £ 29.38
1 x 11004-1303 - GASKET-HEAD - £ 35.65
1 x 11060-1844 - GASKET,CYLINDER BASE - £ 19.28

Have to replace conrod bolts after checking shells
2 x 92150-1683 - BOLT,CONNECTING ROD,7MM - £ 4.25 = £8.50
2 x 92015-1527 - NUT,CONNECTING ROD,7MM - £ 2.89 = £5.78

I also wanted to throw in a new cam chain
92057-1397 - CHAIN,CAM,92RH2015 - £ 31.54

I should probably also replace valve stem seals, new piston rings and cylinder head bolts as the motor has about 42000 miles on it, but I could get away with not doing that.

So with taxes and postage I'm looking at over £180. Even minus the cam chain tensioner that's still over £140

Seen used engines for £250, and I know you don't ever really know the history, but some come with a warranty.

I think I'll just get down that route.

I'll keep the damaged one to learn with.

Might rebuild it one day and make a Super Kart or something

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michael4012

· #8 · Apr 12, 2017

Thats not too bad there not too bad at all:smile2: i should have paid attention to the "2004" title :lol:

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gazx10

· #9 · Apr 12, 2017

u can wipe that scored cylinder wall area with sulfuric acid, will dissolve alum from piston smeared on wall without harming wall coating for a better look at actual cyl damage. coating very tough stuff. however, agree used probabley best choice.

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Kllongbrake

· #10 · Apr 12, 2017

gazx10 said:
u can wipe that scored cylinder wall area with sulfuric acid, will dissolve alum from piston smeared on wall without harming wall coating for a better look at actual cyl damage. coating very tough stuff. however, agree used probabley best choice.

Very true. Though you must be careful around the ports. The acid will crawl up under the Nicasil and cause it to peel.

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