Question about Yamaha YZ 426 F Motorcycles

1 Answer

YZ 426 F 2000 mi bike is leaking coolant from bottom through this little whole on the right side, I also checked the radiator inside and it's all frothed up. How to fix?

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  • jimcatherina Apr 08, 2015

    When you say frothed up. Do you mean oily of just foamy??? If its oily the head gasket is gone???

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  • Yamaha Master
  • 41,728 Answers

Hi, Jesse and the usual suspects are:
1. Low coolant level.
2. Restricted radiator air flow.
3. Faulty thermostat.
4. Coolant pump or fans inoperative.
5. Vent hose crimped.
6. Air in the coolant and needs bleeding.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
Coolant leaking from little hole in bottom of case YZ 400 426 450
Dirt Rider Magazine
Yamaha YZ426F Owner Service Manual
OEM parts for Yamaha
Yamaha YZ450F Owner Manual Page 3

Posted on Aug 02, 2016

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You may need to ask AAA to put a radiator pressure tester on the resevoir bottle and pump it up to operating pressure(Pressure cap rating) and see if it over pressurises while it is running at operating temp,rev engine up and down and watch what the testers pressure readings do,it should move up and down in sync with the water pump.If the pressure keeps building i would have to believe that combustion chamber gases are over pressurising your cooling system.Also test the pressure cap is functioning within factory specs.

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SOURCE: coolant leak from left side of engine block running down oil pan.

when you say left side are we talking passanger side or drivers side if drivers side which is my guess most likely your waterpump seal is leaking

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Posted on Mar 23, 2009

  • 11 Answers

SOURCE: my bike stopped running and was leaking coolant.

A coolant leak from the bottom of the cylinder indicates a blown base gasket. easy fix if you have a manual and some mechanical knowledge.
If you lost all you coolant, you may have also seized the piston.

you will require a top end gasket set, and most-likely a piston kit (Now is probably a good time to freshen that up anyway.)

If the engine was running good you probably did not get any coolant in your engine which is good.
-here is an idea of what is involved

dissasembly
(label everything and keep it nice and clean)

1) clean your bike good. You do not want dirt in the engine.
2) remove seat, fuel tank, rear subframe, and the pipe. This should give you easy access to everything.
3)drain whats left of your coolant into a bucket, the drain is usually one of the lower bolt holes on your impeller cover . A copper washer might give it away.
4) remove the carb from the boot going into your engine. the carb can stay connected hanging out of the way on its cables.
5) remove the cylinder head
6) remove any exhaust linkage covers if so equipped, and the screw holding the linkage. there may be a hole that will line up with a slot in the arm/clip. Use an appropriately sized drillbit to stop the thing from turning on you. Be careful, these are fragile (on Yamaha's anyway)
7)remove the 4 nuts holding the cylinder on. you should now be able to slide the cylinder off of the piston.

Inspection
& cleaning


Inspect the piston for any rough metal, scrapes or gouges. same with the cylinder. if damaged it will need to be replaced. Iron sleeved cylinders can be bored out 1 size and honed, nikasil can be cleaned of minor aluminum deposits with muriatic acid (don't get this on your skin) or will need to be replaced as a unit. Make sure there is no coolant inside the engine case. Crank should turn over smoothly with the bike in neutral.


Clean the old gasket off of the cases where the new base gasket will go. A plastic putty knife does wonders. make sure you get it all off, DO NOT use metal on the sealing surfaces. gasket remover can be used, but don't get any into the engine, and avoid using it where the bottom case halves are joined. Then stuff a rag in the case to keep it clean in the meantime.

Repeat the process for the cylinder, bottom and top if necessary.

Assembly
Check with your dealer for torque specs.
The piston kit should have instructions. Remove 1 circlip (don't lose it in the engine- (rag is in there right?). Slide the wrist pin out (long socket+ light tapping on it from the opposite side if you don't have a puller). CAUTION: I do not know if the wrist pin bearing is caged or not (check the new one when you get it) if it is not a caged bearing all the little roller pins will fall everywhere if you are not carefull. There is like 25 of them!
Now remove the piston, leaving just the rod. Prep the new piston (gap and install rings...line up gap with ring keeper pin...also, pay attention to orientation...some have an angle on the upper side of the ring. Install one of the circlips, rotate it so the gap does not line up with the hole, gap should be up or down not sideways. Install the wristpin bearing in the rod, slip on piston (usually arrow points to exhaust port...check instructions). now lube up the wristpin bearing and pin, slide pin through, and install the 2nd circlip.
Remove the rag, add a capfull or two of 2stroke into the bottom at this point. use a little break cleaner on a rag to make the gasket surface is clean.Throw down the new gasket. Line up ring in groves, Squeeze with one hand, and slide the cylinder down the piston. Once partway up, rotate the crank so the cylinder lines up with the studs. tighten nuts appropriately. Rotate it slow by the kickstart with the kilswitch held in the off position. Everything should be smooth. With the piston at the bottom throw a few capsfulls of oil in it to lubricate it as you rotate it through slowly. now clean the top, install topend gaskets and the nuts. Reassemble the bike in reverse order, make sure the carb is on tight, and don't forget to ADD COOLANT at proper ratio. Break in mix is gonna be 15:1 or 20:1 somwhere in there, for the first few hours riding anyway. Vary the throttle lots don't be afraid to run it though, just don't hold it WFO for more than a few seconds till everything gets happy. also, Especially when using FORGED pistons. Make sure the first time you start it, only let it idle, don't ride it. Let is get all the way up to temp, then let it cool completely. Do this heat cycle twice.
then continue normal break in.

I don't think I left anything out. Good luck.

Posted on May 20, 2009

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1 Answer

Steps to taking apart radiator and hoses


Radiator hoses usually only need changing if they leak or are very perished. An '05 should have reasonable condition hoses. If they do need changing or you are putting some crazy colored hoses on:
1. Take off your radiator cap.2. You may need to take the fuel tank off in some cases.3. Get a 2 litre container with a large opening or funnel ready to catch your coolant.

4. Undo the coolant drain plug/bolt on the water pump and use the container to catch the flowing coolant, it may squirt a little.
5. Match your new hose to the same section on the bike and make note of the way it is installed.
6. Loosen the hose clamps on the section you are working on and push them back along the hose a little way.
7. Gently twist and pull the hose away from it's connection points, if it's till tight loosen the hose clamp more.
8. Repeat 5,6,7 for any other hoses in the cooling system.
9. Transfer the hose clamps onto your new coolant hoses.
10. Install new hoses in the same position as your original hoses.
11. Make sure the hoses are fully pushed onto the connection plumbing.
12. Tighten hose clamps with a screwdriver, firm but not super tight or the hose clamp could become damaged.
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14. Fill your cooling system with anti boil / anti corrosion coolant, gently rock the bike from side to side to allow air to escape, top up as required.
15. Install your radiator cap.
16. Start the bike and check for coolant leaks or drips.
17. Re-tighten hose clamps if required.
18. Ride the bike around for a short time and check again.
19. Check the coolant level in the radiator, top up if required.
20. Ride Hard! (Always check the coolant level at regular intervals as a lack of coolant can lead to engine failure). General advice only.

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1 Answer

Oil is leaking from the bottom tie across hose on the radiator on my 2004 yamaha YZ 250F. Why?


Hi, Anonymous for this situation I would call my local dealer or reputable shop's service/parts department and inquire about any possible quick fix, answers, or parts inquiry. If necessary, transport your bike to the dealer or shop and have a professional technician take it for a test drive, if it is in running condition, and give you a written estimate of repairs and answer any specific questions you may have about your problem. For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
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http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals
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1 Answer

I have a Yamaha yz 125 2003 and there is water leaking out the bottom through a small whole and was wondering why it is doing that as it has just started doing it recently


This is telling you your oil and water seal need replacing ASAP do not ride until fixed as you will seize bottom end guaranteed !
there is small seal each side of your water pump impeller when you take the impeller out replace both even if only one needs doing as you will be going back to replace the one left soon after as they always go together..
Most people would not do this repair without replacing the impeller as well - usually the impeller starts to wear groves where it spins inside the seals then damages the seals So you get the theory behind replacing the whole lot as old impeller can damage your new seals
The seep hole is designed to give you warning of burst seal before its way to late as without the seep hole leak you would have no idea you are leaking coolant into the motor
You can do your self its a bit of work but not complicated - if you do your self don't forget to change your engine oil couple of times after first few rides reduce any risk of having coolant inside it where it should not be
good luck regards Jamie

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mixture is to rich not all the oil is being burnt inside the head when you are driving the bike try turning the air screw in by half a turn then try it again you may have to play with the screw to get it in the right place for you bike

Hope this helps

John

Apr 05, 2011 | 2004 Yamaha YZ 250

2 Answers

Coolant leaked out; how do i repair?


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1 Answer

My water pump is leaking coolant from the bottom.


will need a seal, and sometimes a new impellor shaft. dont ignore it and let the bike overheat

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1 Answer

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The passenger right side of the car doesn't have any flanges for cooling system, if that's correct then your radiator has a leak or puncture.

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The middle part of the bottom engine compartment is where your oil/coolant cooler assembly just above the oil filter. A loose oil filter could be the cause 95% of the time and 5% would be a bad o-ring from the oil cooler to the oil filter flange.

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