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Project Yamaha R125 Engine Rebuild


Classickid21
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Hi all,

So lately i have been commuting too and from different jobs usually doing about 150-200 miles a week, well finally got the job i have always wanted Happy days!

i worked out my miles just to and from work, 350 miles 5 days a week. The R125 i brought it with 34k its now coming up to 35k, i started hearing a top end noise so i did the usual checks oils smelt it very runny and stinks of fuel (rings are worn). so i have changed the oil and oil filter and i also did a Compression tester witch came up 50 psi Standard they are around 78psi. i went on to fowlers website and all i could find was std parts no over size rings ? does this mean i can fit a STANDARD piston and rings in the current barrel or do i need to buy whole new top end complete ? witch is about £450 .... give or take on Vat estimate,


started browsing the internet found various silly kits 150cc (read up cane have lots of problems as i expected) then i saw polini/malossi 180-182-183cc kits... £457 ... £20-30 more then the usual price, id love the extra power but i should be back up and mobile in 6 months time with the land rover, this is just great for commuting to and from work (when everyone is stuck in traffic its a great feeling riding past) :D :up:


if any one can help me with this bit advice i would really appreciate it, YES GET A BIG BIKE DO YOUR TEST ! WELL i know these answers will come up, BUT I DONT HAVE A LOT OF ££££ until i start the new job :D :angel12: i have just forked out and had my forks seals done and brand new front tyre :(


i need this as my work horse! i am looking to rebuild it my self i have brought a manual for it do i need any specialist tools ?

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Try a compression test as normal .. then pour oil down the bore ( small amount ) then do one . If it goes up ( compression) then rings/bore are suspect

 

yes standard barrel as far as i know, its a great work horse i will take it apart tomorrow and try this trick thank you

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Try a compression test as normal .. then pour oil down the bore ( small amount ) then do one . If it goes up ( compression) then rings/bore are suspect

 

yes standard barrel as far as i know, its a great work horse i will take it apart tomorrow and try this trick thank you


no need to take apart . Pour down spark plug hole

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Try a compression test as normal .. then pour oil down the bore ( small amount ) then do one . If it goes up ( compression) then rings/bore are suspect

 

yes standard barrel as far as i know, its a great work horse i will take it apart tomorrow and try this trick thank you


no need to take apart . Pour down spark plug hole

 

i know that, i need to take the fairings back of to get to the fairing :D

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After agro with forks and front wheel, managed to get a nail in my tyre :( so just had that repaired today new rear pads. All my top end goodies arrived it was like early xmas pressy :)


This friday ill remove the engine, this weekend i will dismantle the top end and rebuild/sunday refit and put back together and test. Then 600 miles riding in.

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Do you need to drop the engine to do a topend rebuild?

 

Not entierally sure, i have just purchased a haynes manual, so i can have a look, id imagine it would make my life easier with the engine out. Ill see what clearance i have once i remove the fuel tank :)

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Don't forget to stick a rag down the crankcase hole or turn the engine on it's side before you drift out the gudgeon pin just in case you've got loose needle bearings. You really don't want those dropping in to the crank.

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Don't forget to stick a rag down the crankcase hole or turn the engine on it's side before you drift out the gudgeon pin just in case you've got loose needle bearings. You really don't want those dropping in to the crank.

 

I might cry if that happens lol. It would be game over, i had to ride the bike to work today, it made it 15 miles and cut out ended up having a coffee hoping i can coach it to work and then load it in the works van to take it home and pull it apart poor bike was so sluggish, i kept the revs just under 6k :)

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Sooo took the engine out in the dark friday night saturday cleaned and took head and barrel off done. Today try fit piston and it back together and hopefully back in the bike later on.



I am having a few difficulties there is no room for a piston ring tool ? Tried pinching the rings and pushing up the barrel nut still no luck and it moves the rings from there postions.... HELP PLEASE

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The piston ring compressor doesn't have to fit into the barrel.

Push the piston all the way down, put the compressor on the piston so the rings are compressed but the tool is sitting on top of the barrel, then a quick tap on the top of the piston with a plastic hammer and the piston will slip down out of the compression tool and into the barrel.

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The piston ring compressor doesn't have to fit into the barrel.

Push the piston all the way down, put the compressor on the piston so the rings are compressed but the tool is sitting on top of the barrel, then a quick tap on the top of the piston with a plastic hammer and the piston will slip down out of the compression tool and into the barrel.

Ive tried this there is annoying groove at the botton of the barrel that the rings ope on and the piston so diddy i have to push that far to alline with a the conrod, i am close to defeat with it. I feel like giving up with bikes just seem to end up with lemons i over paid for this one from a friend. I fewl doomed! To be road legal so stressed in the bike for work never expect any of this for a 6 year old bike

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Barrel off engine

insert piston from top of bore ..

As described above method

Push piston to bottom of bore so little end gudgeon pin can be re inserted (small bits of wood as supports between cylinder barrel and crankcase to allow hands free )

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Are you trying to push the piston up from the bottom??

Don't.

Remove the gudeon pin, and push the piston down from the top then re-attach to the conrod.

And don't be afraid to use a good bit of oil to help it slide in.

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after a cuppa tea and fresh head the engine is timed and built...


the funny groove at the bottom i pushed the piston rings against and slipped straight, i tried previously twice trying to slip it down the bore, had no problems until the pinion would not fit so in the end i worked out the groove happy days.


everything back together and timed up, lesson i have learnt walk away if its stressing me out, have a brew and come back to it. sorry for the little rant earlier on, felt like i was going around in circles.


now just need to look up the head bolts and barrel bolts torqing nm

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quick question how long shall i need to run the piston in for and do i need to retorque the head down?


some people have said 100 miles and when i read online some people ran them in at 600 miles ?


i am going to have a read through the manual today and have a little browse.

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