YZFR125 suspect low compression

[stuartadair]

Hello all,

I think I know whats wrong with this bike, however am hoping someone will tell me I'm wrong.

2009 Yamaha YZFR125
Riding 2 weeks ago in torrential rain. Bike cut out. Engine turns over but wont fire.
1. Plug looks fine and there's a strong spark.
2. Took fuel injector out and lay on top of bike on a cloth. I can see fuel squirting out.
3. Took air cleaner cover off and found about 1 cup worth of dirty water.
4. I can feel some compression in the plug hole, but I can keep my finger over the plug hole. When I try this on my sons 125 I cant keep my finger over the plug hole without it blowing off.
5. Tried firing up with Bradex but no sign of life.
6. Water level is fine and no sign of bubbles in radiator when bike is turned over.

I suspect that rainwater has been sucked into the cylinder and done some sort of damage, however I cant reconcile that with the fact I can feel some compression.

Any advice is welcome.

Thanks Stu

[Ariel Badger]

If water has entered the chamber it can hydraulic... bending valves, breaking rings and bending con-rods. Time to take the head off I had it happen on a 500cc Armstrong, all it had done was loosen some carbon that held the Exh valve open
____________________
Bikers make great organ donors, get 115 on your licence today.

[lihp]

How wet was the air filter? I can't imagine pulling that much water though a filter and air intake system to water damage the engine?

How is the bike treated? I'd do a proper compression check or remove the head?

[stuartadair]

thanks for the reply. I've resigned myself to taking the engine out later this week and stripping it down. Its going to be much easier then messing around in the bike.
I've downloaded a workshop manual and it should have 78psi so there's no way I should be able to keep my finger over the plughole - So definately low compression.

stu

[stuartadair]

[lihp]

On the filtered side of the bo?

[stuartadair]

[moonzoomer]

The owner of this identical yamaha had the same problem, he also complained about difficult starting and high oil consumption LOL .
https://i1142.photobucket.com/albums/n604/mawlarky/MVC-003F-1.jpg

[prawny1]

It seems these engines are failing quite often I can't say it's bad manufacturing because we see them generaly with no oil in and given the fact that they only take about 1 litre of oil (yes thats for engine clutch gearbox everything) added to the fact that none of the owners complained of smoking of oily exhausts it could just be down to normal oil consumption and the owner not checking the oil level between services.

Some condensation in the airbox can be expected on most bikes and given the recent rain i would say you probably have drownd electrics more than anything, do you get a good spark?

just re read your first post and noticed you say you have a strong spark so probably not electrical, did you check with the plug out of the engine or a different plug?
____________________
hellkat wrote:

Some people are only alive cos its against the law to kill them.

[stuartadair]

Hi,

Yes, plug out of the engine and its a really strong spark. It was more than a bit of condensation in the airbox though. What made me initially worried was that it wouldnt even show any sign of life with a squirt of Bradex. I know we have fuel, we have spark. I also know that the compression feels very low and am suspecting a bent con-rod, hence the piston is not fully moving to the top of the cylinder. Will know more when I take the head off.

Have you taken the head off this engine in the bike before or would you recommend removing the engine ?

stu

[moonzoomer]

You can remove the head and barrel with the engine in the frame, its a bit fiddly but can be done. Check all 4 valves for bends and sealing once the head is removed. Every one of these engines I have seen stripped have all had chewed pistons and/or valves.

[stuartadair]

Hello all

I've just got chance to start looking at this engine. Took the crank cover off to see the crank timing mark and the water pump off to see the cam mark. According to the manual I have the mark on the crank aligns with a fixed mark on the cover to show TDC, and at the same time a mark on the cam aligns with a mark on the cam cover.
I found 2 marks on the crank, a single and a double mark so I'm not sure which is the correct one - Can someone please advise.
However, when the single mark is aligned the cam mark seems to be off its mark, and its worse when I align the double mark.
This photo is with the sinle crank mark aligned. The cam mark should be in the V on the cam casing cover.
Has anyone had these engines to bits before and can advise on the crank marks and if its normal to see the cam aligning in this way ?
Have a compression tester coming tomorrow to be 100% sure I've got issues in this area.
https://i997.photobucket.com/albums/af99/stuartadair123/IMG-20120705-00073.jpg

[stuartadair]

Bit more info...
Timing chain tensioner feels ok. Turn the screw to the right and I can feel the spring tensioning so I dont think thats the problem. It looks like the valve timing has jumped a notch though.

Not sure if 1 notch would be enough to kill most of the compression ?

[P.]

get.
the.
head.
off.

Saves ALL the guess work You'll soon see if a valve has been introduced to the piston.

[stuartadair]

I know you're right Paddy, I'm just trying to find any possible other solution in the hope it all goes away

[P.]

[moonzoomer]

Best thing is to remove the head for a look, but before doing that try backing of the valve clearances and check for tight clearances that could account for low compression and the bike not starting on the bradex.

[stuartadair]

[moonzoomer]

Once you have removed the head leave the sparkplug fitted, turn the head upside down and fill the dish with petrol/turps /white spirit to check for leaks around the valves and seats.

[russell210276]

just a quick 1 from me 1 simple thing has been missed but im no expert you said water was in the air box what about cleaning the throttle body incase the fuel has water mixed or am i thinking wrong with me been use to carbs if so ignore me

[stuartadair]

Thanks for the suggestions gents.

I've taken the air cleaner completely off and tried to fire with Bradex. The bike's fuel injected and the injection system is working fine.
Stu

[stuartadair]

Here's an update for you. Took the head off today...

Barrel and piston both knackered. My biggest worry is that 1/2 the piston is missing and there's only one place it could be, down in the depths of the engine.

So, I'm either looking at splitting the crankcase to find the missing bit, full gasket set, barre and piston or a replacement engine. Am speaking to the lad that owns the bike later today to give him the good news

https://i997.photobucket.com/albums/af99/stuartadair123/IMG-20120707-00001.jpg

https://i997.photobucket.com/albums/af99/stuartadair123/IMG-20120707-00002.jpg

[ThoughtContro...]

[stuartadair]

Hi,

The only mod thats its had is a non-standard exhaust. Rest of the bike is standard. If I could have found the missing 1/2 piston I'd be happy but I cant take the risk of it jamming something up when the bikes running.

[P.]