Hi mate can a crank bearing/ seal cause a bike not to start have got a kmx and it has good compression have taken head off and barrel and piston and rings look good I even taken it to a shop and they said my top end looks fine so anyway I have checked my fly wheel and it has movement when I pull it up and down not loads but its there will this be the problem do u think

I have a yz 80 i haven't ever been able to get to run properly. Kicks over first time almost everytime. Wont rev up. Tons of oil coming from the pipe. Any ideas?

André Welser, thank you very much indeed for taking the time to write your comment. It really does motivate me to keep going with these videos. Thanks again, Craig

That is a brilliant idea actually.

A two stroke engine has a total loss lubrication system and not a wet sump like a four stroke. There are three things in a two stroke sump, mostly air, and then fuel and 2-stroke oil. Leakage around here is not very prominent unless the engine has been flooded.

That is absolutely correct. A telltale sign of failed crank seals is black, oily residue around the seal area.

@@TonyLing Baloney! Read my comment.

Thank you so much 👍👍

It can cause it to over revv and starting problems mainly. It can be very temperamental with trying to set the carb as well. Almost impossible to get the settings just right depending on how advanced this is

@@TheRepairSpecialist Thank you sir,my crm 250 won't stay idle but when choked, it idles,I think this is the problem or it should be a air leak,do you have any idea?

Russell Booth thats a four stroke engine, did you check your valve clearance after lapping? To adjust the clearance you have to grind the valve stems a little bit at a time, with piston at tdc on compression stroke, check the clearance with springs removed and feeler gauge inserted in the gap between the cam tappet and valve stem. Clearance should be .006 for intake and .009 for exhaust. Grind a little at a time until proper clearance is met.

Briggs Stratton ? 4 stroke then you plumb

Left hand crank seal or your pilot jet is blocked dirty sort that out before crank seals

Depends how bad the leak is at the seal. If it's a large leak, the amount of air from the carb will be small in comparison

Actually measure the compression with a tester...I had same problem w/ mine died while running, wouldn't start back up even w/ starter fluid, EVERYTHING else checked out... I then measured the compression and it could only muster 35 psi! Took the top-end off and piston had a huge crack & the rings were stuck solid, pretty new engine so I think it sucked in some dirt or something 🤷‍♂️

i think so but dont spray too long or you will seise ur engine

You have a point Sir, so any other suspect to look around ? Assuming oil seals are both ok

@@sunflxwergamer303 bogging can come from bad seals, bad reeds, dirty or damaged carburetor, incorrect carburetor adjustment, bad fuel. 2 strokes are finicky, I’ve seen bad spark plugs cause it as well as sheared key on flywheel and even a weak magnetic field on flywheel. I tend to look at case leaks last as the leak would have to let pressure out but not leak on vacuum to cause a bog, it it leaks on vacuum it generally will cause the engine to rev uncontrollably. It is nearly impossible to diagnose without being able to test the engine all we can do is tell people how to diagnose by themselves but it will not replace experience in knowing the sound of the bog, what point it starts and so on. I turn down a lot of work on small 2 strokes simply because the diagnosis cost and repair could exceed replacement cost and quite often I will not get paid for the hour or two it took to figure it out

Steve R, i personally have used WD40 on my machines.

TheRepairSpecialist thanks!

Steve R m- thought most crank seals are located inside the case, not easily accessed

Propane works also. Non chlorinated brake clean also. Non flammable brake klean is worthless as tits on a boar hog.

@@Community-Action mostly the early engines

James Blake main bearing, and both crank seals.

nope

@@integrationofmanandmachine4714 Wrong, totally wrong! Spark plug hole adapters are made for this exact purpose!

Many tools are sold for this. The most well known is MityVac.

It has Zero effect on compression. It causes a lean fuel mixture with a leaky crank seal

@@chrisheffernan7540 Primary compression is not the compression on the compression stroke but on the down stroke to pressurize the crankcase, with leaky seal the primary is affected.

@@UpInSmoke54 that's not what he asked

@@chrisheffernan7540 who?

@@UpInSmoke54 you asked how is primary compression affected, it is not affected. Crankcase pressure is less due to the leaky crank seals, which will lean your mixture.

So 3 years later what did you end up doing?

Bennie Coetzer They might have been installed incorrectly. You can also try adjusting the carb.

Most light oil spray cans have a straw that fixes onto the spray end of the can, which direct the spray to the main seal area much better and without contact with the clutch. Thanks. Craig

@@TheRepairSpecialist nice

your main jet is too lean

yup sounds like bad crank seals symptons

William Isen a small book

Dod you fixed that issue? I am having that problem with my 2 stroke now 😔

A very common thing with two stroke engines, that I have seen more than once, is that most people put the clutch side oil seal in backwards, which would be right on a four stroke engine, but on a two stroke engine you are try to keep oil out of the crankcase, because it gets it's oil from the gas mix. If the seal is blowing out of the holder it's because it is trying to keep pressure in the crankcase, and not the oil out, I know it looks backwards, just remember that the part of the seal with the little spring on it goes toward the fluid that you are trying to keep in, or out, whichever the case may be.this is part of the reason for the vent tube on a two stroke, and also the reason why the tranny oil should be changed more often, on a two stroke.