oldmxrider

Maintenance times on motocross race bikes We use easy to install hour meters. They are cheap and work great !

I have been rebuilding motocross crankshafts for 19 years. I have a 35 ton press and a jig for assembly.. A 20 ton press was not enough to get them apart.

Been a while since I repaired this one. Best I can recall is someone had played with the shift adjustment and it started jumping out of gear but they kept pounding on the unit and I replaced some gears that were worn. The machine also needed a few sensors and a initial setting done to make everything work as it should.  The machine was treated VERY bad and lived in water and mud.

Will it move at all when in the forward gears ?  Might be a sub transmission problem !

I only played with one hondamatic it barley tried to move lots of grinding noise. The repair was just the simple sub transmission used parts were bought from eBay and it worked like a new one when done..  I did not pull the engine for the repair pulled the swingarm and rear end was able to do the repair with the engine in the frame.

Does the machine move in reverse normal with no noise or clattering?

On 12/8/2022 at 6:40 PM, Harleydavidson said:

And check crank seals 

I think the old engine is a four stroke and crank seals will not be involved.

I would also check for air leaks.

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On 11/30/2022 at 11:07 AM, toodeep said:

It's not very common but I have seen the bolts work loose on the stator/flywheel and cause this. Where your getting complete revolutions one way but not the other I'm going to guess the problem is in the bottom end, not the top. Everything is just a guess though until the problem is found. Did you happen to get the story of what they was doing when it quit? 

The bolts coming loose might not be very common but I have seen it more than once!

What did You end up doing with it?

www.jetsrus.com

Looks like You have some gouges and worn nikasil on the exhaust port and some aluminum stuck to the nikasil on the intake side. Does not look pretty.  What does the piston look like ?

Muriatic acid removes aluminum from nikasil plating.

I was just going to ask for an update!  Hope it goes well!

Is the crankshaft centered in the case ?   I take a feeler gauge to both sides and center them.  I do have a press.  Though as to deep said are You sure the main bearings were completely seated ?

Should go on with no problem. Sometimes the seal is a bit tight a little lube and a tap or two should do it.

On most cases there are hollow steel dowels at the very rear and possibly front, Heat that area with some pressure on the seperator tool and with right side down crack the counter shaft with a plastic dead blow hammer.   

They all come apart just did a KX250 last week new main bearings and seals and rebuilt the crankshaft with new rod, pin, bearing and spacers!     Good Luck !

Yes, it can work have repaired several over the years. I have never tried to pin them did not need to, did embed stiff short wire into the jb weld. Years later it is still working !

20 hours ago, Harleydavidson said:

On the fly wheel the mark says TDC and right after it says F will it fire on any stroke or how do I figure it out

What are You trying to figure out ?  The ignition will fire the plug every revolution one is a waste spark as it is not on the compression stroke.

Sorry put the pictures are not that great to troubleshoot online, can say I specialize in race bikes MX.  If one is torn down that far it gets new piston and rings. I am not there to check ring end gap, piston ring groove dimensions and the like.  I also cannot see the wear on the nikasil cylinder it will happen at the bottom and top of the stroke.

Just trying to help and it can be very hard to do online .

Sounds good, just last week had a bike that lost compression while kicking it over, failed the leak down test big time could hear the air blowing out the carb, gas down the head a valve leaked big time.  Bike had sucked in a small bit of plastic from the filter ?  Was smashed in the valve seat, I removed the valve saw it wiped it off put it back together and all is good !

Now that the head is off did You pour a little gas down the intake and exhaust to see if it held the liquid or did it run out the valves ?  I have the tools to do a leak down test before it is torn down.   Is there a problem with the automatic compression release ?

When You turn the engine over slowly ( counter clock wise )  and You see the intake valves open with the cam lobes the next t on the flywheel is top dead center on the compression stroke.

At this position check Your valve clearance.

I cannot blow up the pictures enough to see You timing marks on the sprockets. The intake cam lobe looks to be in the correct position cannot see the exhaust lobe because the auto decompression works are in the way.  The lobe should be in about the same position pointing outward as Your intake cam lobe.

These twin cam bikes can jump time for various reasons they can also spin a cam ( sprocket that is just pressed on, spins on the cam,) lobe timing is them WAY  off.

Just repaired a 2021 KX250 with 19 hours on it that spun the cam and bent a valve.

Can You get a picture of Your timing marks left side cam sprocket and fly wheel on the compression stroke ? Then without turning it a picture of the right side of Your cam lobes ? 

2005 KLX300? If it was in My garage the very first check would be cam timing.

Hard for Me to believe, that Your cylinder will only need a bit of honing with the looks of that piston !  Just My opinion !

1 hour ago, _Wilson_™ said:

what was the builder thinking ??  

Might have been drinking not thinking !