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Discussion Starter · #1 ·
On my third Gen4 (the previous two lasted ~100,000 km before being taken out in accidents) and after 206,000+ km (128,000 miles) yep, one of the outlet valves snapped on #1 cylinder, snapped the spring retainer, bent another exhaust valve, bent an intake valve then embedded itself in the top of the piston, smashing into, splaying, and destroying the spark plug. Several parts of the failed valve went through into the headers (made a lovely rattling sound when I removed them!)

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After much work, the engine is out of the bike and the crankcase split. I don't have the gear needed to check the trueness of the crank and the head will need machining (valve seats). So, what are my options?
  1. Sell the bike for scrap
  2. Part out the bike (easy to do as it's already in many parts!)
  3. Replace with a second-hand engine - none so far found in Australia (or the world)
  4. Get the crank checked for trueness
  5. Replace crank bearings + big end bearings
  6. Replace 4 cylinders (?) + rings + replace 8 con rod bolts (designed to stretch)
  7. Get the head machined and
    1. Replace 16 valves
    2. Replace 16 valve guides
    3. Replace 16 sets of collets
    4. Replace 16 valve springs
    5. Replace 16 valve spring retainers
    6. Helicoil the spark plug thread
  8. Replace the entire head with a second-hand unit
  9. Sob quietly to myself :)
Who has rebuilt a motor like this, what tips, tricks, traps, and advice can you give? I'm happy to invest the time myself (it's kind of Zen working on a motor like this). Is there anything else I should look at, are there other options? I can get parts at wholesale prices (a rough estimate for the retail parts above is ~US$4,000). The #1 cylinder wall looks A-OK, still showing signs of honing. Cams and upper head are in an almost pristine condition with no visible signs of aging, scoring etc. Bike has been going through a very small amount of oil between regular 6k services (but I've been playing with first gear a lot: very high revs).

Rest of the bike is in mint condition - gearbox replaced ~15,000 km ago, clutch replaced ~20,000 km ago, new radiator, new gas tank, new fuel pump, new stator, new head stem and wheel bearings, panels in pristine condition. I also have three sets of stock exhausts with two cats, three sets of OEM levers, two sets of OEM pegs, a spare front and rear with new bearings.

Sure, I've been looking at a brand new '21/'22 ZX-10R too. The MY22 model is awaiting homologation - should be available in late January.

Thanks for your advice,
Arc.
 
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FFS mate, that's sad to see. We can get incredible mileage out of these but at the end of the day its a motor built for racing and there are compromises with that. Certainly not the first iv seen like that and not the first iv re-built. Considering the mileage of the bike i would be looking at getting repaired correctly but as cheap as possible and then trade her in for your MY22. The cylinder heads alone are becoming more common as the G4 ages and reaches the breakers so i am +1 with badassjake on buying a guaranteed low mileage head preferably complete with cams, yours have done incredible mileage. There is a good chance that the conrod is now out of round and possibly deformed small end! So i would be looking at getting a set of 4 second hand pistons and rods with guarantees, you can use G4 11-15 and G5 upto and including 19. If the price is comparable buy 2016+ as the pistons are a tatge better! But whatever set you buy in spend the cash on 4x ring set. The cylinders can be cleaned well with hot soapy water and scotch brite. The danger is the crank on the G4, with the higher mileage they are known to spin bearings. For the cost of sending it out for inspection you could buy yourself a dial gauge and 2 V blocks, a decent micrometer (not vernier) will be needed to check the journals. If your lucky just replacing the main bearings will do. If its FUBAR then you will be hard pushed to find a good replacement so repair will probably be the cheapest option. You have an immense clean up on your hands now, little bits of that shite are everywhere so meticulous cleaning of all parts is essential as is a new oil pump and strainer!! Even if your going to trade this in, be meticulous and replace the rod bolts and nuts, all the crank main and big end bearings, with a good second hand head and good rods and pistons with new piston ring sets you will notice a stronger sweater running motor but above all you will sleep at night knowing whoever takes it on is safe.
 

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honestly I'd just sell the parts (said with self interest) and get a 21/22, there have actually been a lot of changes from 2011 till 2021 they are subtle but there are many, as someone that has studied the parts diagrams extensively they are fairly different from 2021 onwards. Also importing an engine would be crazy pricing atm due to supply chain demands.

The time spent and cost prob wouldnt be worth it unless thats an area of interest... building engines i mean.

If you do part let me know about wire harness and ecu + keys
 

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Jesus christ if my math is right you have about 400.000km worth of gen 4 riding. You sure do love that bike :p
I think you can save a few bucks fixing the engine yourself but if you want the easy way out you can get this engine with 17k km.
It's from a Polish ebay-like site. I live in italy and have bought many times from this site and from this seller in particular. The site also has a buyer protection system if you pay with mastercard/visa. Had trouble with an akra pipe that was damaged during shipping last year so I appealed to the site and got all my money back and got to keep the akra pipe which I then fixed by replacing the carbon cap for 70€ lol.
12k PLN is roughly 2900 USD. Suppose it would cost you several hundreds extra to ship it to AUS. I'm half polish so I could help you contact the seller to organize the shipping.
 

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Discussion Starter · #6 ·
Thanks everyone for your suggestions. I will get pricing for checking the crank later this month when folks return to work in Australia. So tempting to rebuild the engine myself. A replacement head though will be a big $ saver. I'm surprised how pristine my buckets and cam are vs zooming in on photos I've seen on eBay of heavily scuffed buckets.
 

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Discussion Starter · #7 ·
...Even if your going to trade this in, be meticulous and replace the rod bolts and nuts, all the crank main and big end bearings, with a good second hand head and good rods and pistons with new piston ring sets...
Many thanks for your reply. I'm torn between repairing and parting her out and have until the 17 of Jan until head/engine specialists reopen. Even as a repaired engine I think I'll get next to nothing for her with such high mileage, I have Ohlins carts and their mechatronic rear too. If the crank is true I'm inclined to repair and defo replace the con rod bolts, all bearings and oil seals. If it's not true then I guess parting her out is more of an option.

Structurally the #1 rod is potentially suspect so I'd also replace that and defo replace all rings and #1 piston, but do you think I should also replace the other three pistons and rods while she's open?

I've been meticulous with oil & filter changes every 6k KMs with Motul 7100 and only did an oil change the night before the valve failed, there's no visible wear on the cams/buckets. Replace the cam chain while she's open too?

I read that the metal head gaskets should they be replaced as they're designed to crush through tightening and shouldn't be reused (and wow are they expensive!)..

The more I think about it the more parting her out seems to make the best financial sense :/
 

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You'd prob want to do all 4 pistons and rings rods etc, otherwise you have 1 brand new that isn't worn VS 3 others that are. Kind of like changing only the rear sprocket and using the front and chain from original yes you can do it but your mileage may vary as they make a complete system. The clearances should be quite different between the old and new especially given the 100k km unless you just coasting everywhere like less than 8k rpm.
 

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yes, g4's run solid right up to the valve failure; indeed, right before failure bike hits peak experience as in totally jumping to command. So, where am I going here? '11 10r valve failure (not confirmed, but still have the bike, but I'll get to why that was a valve) at 50k miles. NOT under warranty. I NEVER needed an extended until this bike; Thought it a fluke, so bought the '13 10r. 70k, valve blow out and same racket as the '11 problem. Dealer fixes, under extended, then valve blows out AGIAN, just past 80k miles or a bit more. if I recall. Under warranty. So, this time dealer did what you're thinking, just rebuild everything that Kawa wants to rebuild. When I got the bike back, service manager said 'this is basically a new bike.' Bike now has close to 110,000 miles; would be far far far more but wife took ill so can't ride until she can get around the house on her own. Bike's been sitting since May, 2020; I just warm it up every couple days.

So, yes, if you have the tech skills, buy the parts from Kawa. They don't sell complete engines but simply have their techs replace any worn parts. I respect all tech people!
 
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