how to check for a bad bottom end (preventive maitnence)

[jrooster]

I have an 86 250r project im finally getting into. Story was that it ran and then sat 7-8 years. Since ive bought it i got it running and riding fairly easy. Cleaned the carb and took the rat nests out of everything. All seems well. One weird thing about it though. When i bought it it had very little gear oil in it. Like barley enough to drain from the motor. So i fill it up and leave it sit for a month and it doesnt leak a drop. A new top end is going to happen for peace of mind. But how can i check if i need some lower end work? What parts would be worth looking at? What bearings would all need checking? If the bearings are bad, how do i know if the crank itself is good or bad? Thanks for any help, build thread coming soon, as of now its down to the frame and have tons of parts i have to take to work for sandblasting.

[deathman53]

only way is to split the cases. If everything is good, it should only cost you gaskets and 2? hour labor.

[Dirtcrasher]

Like Da man says, you should just split the case (providing you know how to) and inspect the lower rod bearing, countershaft housing holder (often just waiting to fail - ESR has a nice set up) as well as the tranny clutch etc. I bet your trans is just fine but you can put new main bearings and C-shaft bearings in and you won't have to worry about it for quite awhile!! I'd only use Barnett or OEM clutch plates and file the notches out of the clutch basket if it has them and the 89 update clutch rod/bearing/thrust bearing upgrade in my mind is a "must do!!".

The 250R is really an easy motor to work on, you'll just need a couple tips if you run into something not covered.

I haven't done one in awhile but I think there isn't a center case gasket so "anything - BOND" is applied to both sides with a nice thin even coat on both sides and then the instructions may tell you to allow it to get tacky before bolting them together. I am a huge fan of cleaning the bolt threads and using a thin coat of grease on near every case bolt. I clean and grease all the dowel pins as well. Bel ray waterproof or equivalent. On my 350X, I run grease all over the clutch and ignition side gasket and I find I can re use them if I missed something.

Something else I do on the 85/86 250R lower case; The thin cylinder base gasket area just next to and above the main bearing oil holes, I use a punch with a good sharp tip and put maybe 4 to 6 dimples into the aluminum on center. Not deep, just a bit. I've seen that gasket get sucked in and lean out the lower end.
But, it's a fun easy motor to work on. Years ago I could post ALLOT, but there is just a vast amount of incredible guys on the board now with tons of experience under their belts. It's important to have a clean well lighted work bench and I like to use a small hard flat stone and WD-40 for gasket mating surfaces, you can watch prior repairs damage smooth right out as you run the stone over it and it makes you a better and more aware mechanic.

I always chase threads with bottoming taps and other little extra things that give me confidence on what I'm working on. Couple cans of brake/carb cleaner and an air nozzle get allot of use from me. Other guys just tear em down, clean them up, replace worn parts and slap it together. But I have found that using good bearings and some extra stuff not defined in the manuals allow allot of people to put YEARS on a rebuild (especially the bottom end). Do it once, do it right and be confident in it!!

This is just me and some things I like to do.....

Don't sweat it, post here and use a service manual and realize that if you have to force something apart, your over looking something.

[shortline10]

When the tranny side crank seal leaks the motor will suck the tranny oil into the crank cavity and burn the oil .
Probably time for a rebuild .

[atc300r]

The liquid R does have a center gasket I use a little hondabond on mine .

[Gearheadtom]

Never owned an R, but from my experience with 2 stroke sleds, you gotta watch for any rust pitting on the crank or rod bearings on any engine that has sat a while. That can take a bottom end out in a hurry.

[oscarmayer]

with 2-strokes, the biggest thing I ran into racing is the piston pin bearing set. they always seem to wear out faster than the piston pin and can cause pre-mature slap (shut it guys :P this is series slap talk not that joke slap talk ;) ) the crank bearings should have no up and down play when you push and pull on the rod itself. I typically replace a piston every 10-12 hours of racing and riding hard, but not everyone does this. if your trail riding it a lot, then you can do 30-40 hours.
in my mind a piston is cheap compared to a motor and the minimum of a ring is a must on a used bike you know nothing about.

[barnett468]

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If you take it apart, I would accelerate it really hard and speed shift it to see if it pops out of gear or if the clutch slips . . This way, if there is an obvious prob, you know what to look at to replace.

As far as intervals for replacing the piston, I can tell you this, we never changed pistons at Kawi during 100 hour endurance tests, and when I tore the engines down, both the 2 and 4 strokes had extremely little wear and were still well within spec . . I raced in the in the 125, 250 and 500 pro class in Motocross, and rarely changed pistons, and when I did, they didn't have much wear . . I also raced in the 250 Pro 3 Wheeler class and never once changed my piston OR rings and my engine's compression never dropped more than maybe 5 psi and it had stock pistons and rings on a cylinder that had 100 hours of testing on it.

My point is, for just recreational riding, I personally wouldn’t worry about checking the piston until you have reached 100 hours of riding time . . There is absolutely no difference between an ATV or MX piston, and a piston that goes in a street bike, and if one can ride a 2 stroke street bike for even just 20,000 miles before it needs a new piston, I certainly would hope that a 2 stroke dirt bike one could make it at least 100 hours . . Actually if you calculate it, using an average speed of an ATV going 40 mph x 100 hours, you only be 4,000 miles which is far short of 20,000.

This being said, if an engine is tuned properly, the biggest enemie of a piston is sand, so unless you are a pro racer, I would not do things like put air holes in the air box.


CRANK SEALS

Since it was low on oil, it may have a bad clutch side seal as shortline10 suggested . . This can be checked by buying a pressure testing kit and pressure testing it, however if you take it apart, I would just replace the seals as was suggested.

Here’s a leak test video . . If it has a seal leak, you need to remove the clutch and flywheel to see which is leaking but again, if you take it apart, you should do both anyway.


CRANK BEARINGS

If you grab the end of the crank on one side at a time, and try to lift it up or wiggle it up and down, then afterwards, try to move it in and out, and there is virtually no play, they are most likely good, but unless you are on a budget, it might be best to replace them anyway, but only use Japanese or US made bearings . . If there is a tiny bit of play, it will likely be ok for a while and just lower speeds.


LOWER ROD BEARING

Only a very experienced person can tell if this is worn, so you might find an old guy to check it . . It can be checked by hand.


TRANSMISSION GEARS

It’s nearly impossible to describe what to look for, so it is best if you have it inspected or post close up photos of the cogs and slots on the gears and both sides of the shift forks.


CLUTCH

You can measure the plates for thickness and the springs for length, however, even if the plate thickness is within spec, they still may be bad . . You just have to try them and see, however, if I were to reuse the metal plates, I would put a piece of 400 sand paper on a polished granite counter top, or polished marble floor, or tape it to a window next to a the frame and spray WD40 on it, then move it around in a big circle for around 5 seconds only to “deglaze” the surface.


AIR FILTER

If you can pinch a piece between your fingers then pull on it and some comes off, it is junk . . I would buy an original replacement style from Uni Filter.

Here's the filter.

http://www.unifilter.com/atvs/honda-atv/


Here’s free online manuals.

http://www.oscarmayer.net/atc/manuals/
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[barnett468]

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ok, I was bored so I made a gear inspection chart for you in case you ever take and ATV or Motorcycle engine apart.


These gears have slight pitting on the face near the ends . . This is wear from cheap oil and/or oil that is too thin . . As long as the cogs, which are located on the side of the gears, are ok, minor pitting like this will not present a problem.

...............................................htt p://www.infineuminsight.com/media/1340/sumo-gear-spalling.png



The corners/edges on the top of this gear are moderately rounded from wear . . This gear may or may not pop out of gear, however, when they look this worn, it’s much better to replace them.

.................................................. .....http://www.aswracing.com/pictures/worndogs2.jpg



This is one of the types of gears that the gear above would engage with . . This gear is mainly worn [rounded] on only one side of the engagement slot . . The opposite side is virtually like new. . . Both sides should have almost sharp edges . . This gear is worn well beyond the point of being useable.

.................................................h ttp://www.themechanic.co/wp-content/uploads/2015/04/shifter1stgear.jpg



This is a new gear . . They only have a very small radius on the edges on top of the cogs.

.................................................. ..................http://images.cmsnl.com/img/products/gear-top-transmission_medium23431023010-01_822d.jpg



This is an ideal example of a bent shift fork . . Notice the shiny wear spot on the curved area . . If you turned this fork over, this same area would look normal but the tips of the fork might also look shiny . . Anytime you see ANY shiny spot on this area, the fork should not be reused. . . One way forks get bent is when the gear “pops” out of place . . The sliding gear can disengage from the gear it mates with when the gears become worn like the ones shown above . . When this occurs, it is typically under acceleration, so the force of them disengaging is extremely high and this puts a sudden, high, side force on the fork.

.................................................. .......http://i41.tinypic.com/2rgjk7s.jpg
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