Author Topic: YZ125K Rebuild  (Read 37844 times)

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Offline sleepy

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Re: YZ125K Rebuild
« Reply #225 on: November 29, 2017, 10:38:04 AM »
Using the BTDC method for the stock ignition is the most accurate method but you still need to check that the retard at the top end is working as it should or you could have another failure. Simple check for that is aim a timing light at the marks and if they don't line up at 9k it is faulty.
With the PVL until you know exactly what the timing curve is with your 5000 wind stator any sort timing check below 8 or 9k is asking for trouble.

Interesting how you had the same failure with a cast piston as you did with the Wossner, guess that it wasn't the fault of the Wossner after all.

Online alexbrown64

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Re: YZ125K Rebuild
« Reply #226 on: November 29, 2017, 11:45:02 PM »
Thanks for all the input guys. I'm working away for a while so I've had to put the bike aside. I did achieve a bit though. I reassembled the engine with another new piston kit, and took the lot up to get measured and checked over.
Also ordered a genuine stator and coil, and have a spare Yamaha cdi.
Will do leak down test, timing light check and use my new standard size carb with Yamaha spec jets. The newer Mikunis may be a whisker different, but I am sure I will be in the ball park.
I will do all these mods, together with the recommendations and mods that Ray Easson is doing in regard to squish and compression.
Hopefully I will have a runner in the new year..

Updates later...
Cheers,

Online alexbrown64

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Re: YZ125K Rebuild
« Reply #227 on: April 30, 2018, 04:43:30 PM »
Just a quick update.  Will be putting her back together soon.. just had a million and one other projects on the go..
Anyway, according to Ray Easson she was detonating, and the reason he believes is because she was built for high octane race fuel by Eric Gorr. He measured everything up and has added an extra base gasket.  Still wants me to check ignition etc..

I have everything to take her back to stock.  Stock size carb and jets, stock ignition etc.  I will put her back together with all the stock parts and slowly go from there..

Cheers,


Online alexbrown64

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Re: YZ125K Rebuild
« Reply #228 on: May 20, 2018, 06:47:53 PM »
The Curse Continues...

There was a ride day at Coastal Park today.
I quickly cobbled the Euro YZ back together with a new 2mm oversize 58mm head gasket and new base gasket and some other fresh parts and got her running last night.

So me and a mate hit the track this morning.  About 100 bikes there by the time the fun started..



Bike is running like a champ for the first half of the warm up lap, but i do notice it feels a bit weak in 4th at high revs..
Then after 1 lap i hear a pop and she comes to a stop....
I push her back to the pits and notice that the radiator hose has popped of and no fluid.  I have cooked her. I obviously forgot to really tighten one of the hose clips, as it was hanging off.

Damage has been done..



I think the cylinder is OK, as there are no scratches, just light scoring..



OK, so i know i am up for a new piston kit, gasket kit, hone etc.. But... is it a tear down motor job.  Will i need to tear it apart and rebuild the big end, replace main bearings etc..
Or is there a shortcut? There was some small aluminium pieces around the edges of the cylinder.

Cheers,


Offline Hoony

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Re: YZ125K Rebuild
« Reply #229 on: May 20, 2018, 07:36:25 PM »
its a total tear down i reckon. its not worth the risk NOT replacing the big end and mains.
i think you know that anyway but are hoping for the impossible.

it they let loose they you are back in the same boat.

thats a very tidy K you have there.
Long time Honda Fan, but all bike nut in general, Big Bore 2 stroke fan.    http://www.youtube.com/watch?v=XJoKP6MawYI
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Offline GMC

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Re: YZ125K Rebuild
« Reply #230 on: May 20, 2018, 08:27:38 PM »
While I agree with Hoony I did have a KX 250 that melted a piston twice in 2 years (Curse you Sea Lake)
A flush out and new piston and it was fine for several years.

You been a bit quiet of late, are your projects ramping up again now?
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Online alexbrown64

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Re: YZ125K Rebuild
« Reply #231 on: May 21, 2018, 08:06:34 AM »
Thanks for the input guys.  I might not risk it, and just order some new parts and rebuild her properly.
Yep, work and other projects have been getting in the way. I am fifo, plus i am separated and have my kids the whole time i am home.. bit of a juggling act.
I have the yellow YZ engine ready to go back in, and a timing light to check out the ignition.

I also have the G 125 project going, so hope to strip down the engine soon. Then hit you up Geoff for the pipe...

Cheers,