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Crankshaft scratches

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Old 05-05-2018, 05:22 AM
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Default Crankshaft scratches

After taking my engine apart recently and i noticed scratches on my crankshaft, i know these are from dirt getting into the engine but i dont understand how it is getting in. I replace by air filters after use and even wrap them in vetwrap after every race, clean the airfilter housing with soap etc. I check the inner filter regularly and no dirt makes it passed the outer layer at all. The scratches are limited to the crankshaft and not my piston and sleeve from what i can see and the bearings are smooth. Could it be my fuel tank letting it in? Its a d817 clunk tank without an external filter.
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Old 05-05-2018, 06:00 AM
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Post pics of the crank. There are “tells” of where it’s coming in. Pop the rubber seal off the front bearing too, and take a look.
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Old 05-05-2018, 08:14 AM
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Originally Posted by SlowLST2 View Post
Post pics of the crank. There are ďtellsĒ of where itís coming in. Pop the rubber seal off the front bearing too, and take a look.
Ive already cleaned the bearing, it wasnt gritty before but i went over everything anyway. I cant take a pic right now but when i had it was like a darker discoloring of the barrel under where the carb is, inline with the intake port on the crankshaft. I couldnt feel them under my finger nail but it looked like tiny scratches for sure
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Old 05-05-2018, 08:21 AM
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Scratches and scuffing below the carb indicates a poorly prepared air filter and/or a poorly fitted air filter system to the carburetor. It’s imperative to have a tightly ziptied filter neck and a properly oiled filter. The stickier the oil the better. It must be well saturated and well distributed. If there was any dirt behind the front bearing seal, replace the bearing. Off-road engines - in my opinion - should never have their bearings cleaned if dirty. They should be replaced.
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Old 05-05-2018, 08:28 AM
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Originally Posted by SlowLST2 View Post
Scratches and scuffing below the carb indicates a poorly prepared air filter and/or a poorly fitted air filter system to the carburetor. Itís imperative to have a tightly ziptied filter neck and a properly oiled filter. The stickier the oil the better. It must be well saturated and well distributed. If there was any dirt behind the front bearing seal, replace the bearing. Off-road engines - in my opinion - should never have their bearings cleaned if dirty. They should be replaced.
The bearings werent dirty i just cleaned my whole engine including bearings, sorry if i confused you. My airfilters are always maintained and zip tied as tight as i can. I used to use RB filter oil (extremely thick) now to motul which is also very thick and tacky
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Old 05-05-2018, 08:49 AM
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Well, a scuffed crankshaft wouldn’t happen if everything was setup and maintained properly.

Was there a reason to dismantle the engine to clean it?
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Old 05-05-2018, 10:03 AM
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Originally Posted by SlowLST2 View Post
Well, a scuffed crankshaft wouldnít happen if everything was setup and maintained properly.

Was there a reason to dismantle the engine to clean it?
Yea it had been sitting for a while and has 15 litres through it, just thought it would be a good idea to check it before i start running it again
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Old 05-05-2018, 11:42 AM
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Originally Posted by Pugg View Post
Yea it had been sitting for a while and has 15 litres through it, just thought it would be a good idea to check it before i start running it again
If an engine turns over smoothly and isnít gummed up, thereís no need to tear it down needlessly. Clean the outside up, maybe peek inside the backplate... But no more. You interrupt the parts fitment every time to disassemble an engine.

As for your scuffed crankshaft? Must be a ghost that did it.
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Old 05-05-2018, 01:49 PM
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There is just 0.05mm up to 0.1mm space (depending brand) between the crankshaft and crank case. Probably you will not imagine it but the crankshaft does flex. With an unbalance by default with a 1 cilinder engine and maybe from the clutch the crankshaft can band that much to touch the crank case. But just keep in mind with foam filters it is possible that dirt will come through.
I know in the large scale with K&N air filters they have a dust sack to put over the filter, maybe something to try.
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Old 05-05-2018, 03:39 PM
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K&N is a great filter. As long as it’s properly maintained. The same goes for foam RC filters...
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Old 05-05-2018, 04:26 PM
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Nothing significant can get through a properly done foam filter.
OP, perhaps just run the engine and enjoy it. It's just a toy, nothing to stress over. If the engine is running fine, then have at it.
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Old 05-06-2018, 05:58 PM
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99% of off-road engines you strip down will have some light scuffing or at least dullness directly under the carb. Unless your seeing some deeper scratching it's nothing to really worry about.
The ingestion of microscopic dust particles is very hard to complely eliminate.
You also have some introduction of dust through the front bearing which gets transported through the vaccum oil return gallery (behind the front bearing) and exits directly into the area beneath the carb.
Even relatively new front bearing will start passing dust after a gallon or so. You can see the result of this as a black oily film behind the bearing when it's pulled. Some of this black film will find its way through the oil return gallery and onto the crank.
Running something like the Buku front bearing cap will stop a lot of this happening.
You can also block off the oil return gallery. All this will result in is a little pooling of oil behind the front bearing which may weep a little after use.
Some believe in doing this - others don't agree.
Something to think about if your worried about the crank getting scuffed.
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Old 05-06-2018, 06:26 PM
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Last week was the third time Iíve had an unusual issue that could be the same as yours but check your air filter carb neck, Iíve had them rip a few times and I believe itís from maintenance usually. This last time I had a log smash threw the body and destroy my gas tank which also hit the neck but in the past it happened very randomly one time being from a screw driver punchering when titening a zip tie. You would never even see the hole without stretching it but it was there.
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Old 05-07-2018, 01:45 AM
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Originally Posted by Matt Piva View Post
Last week was the third time Iíve had an unusual issue that could be the same as yours but check your air filter carb neck, Iíve had them rip a few times and I believe itís from maintenance usually. This last time I had a log smash threw the body and destroy my gas tank which also hit the neck but in the past it happened very randomly one time being from a screw driver punchering when titening a zip tie. You would never even see the hole without stretching it but it was there.
Yes ive had a rip in my carb boots before, those soft losi ones and it was from using scissors to remove the zip tie. I noticed it when i did it at the time though and i got a new one which has no holes. I prepare my airfilters as best as i can so im thinking something got in side when i removed it for cleaning or something. Engine still runs so it could be worse
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Old 05-07-2018, 04:34 AM
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You still might want to post a picture.
If you think about it, if dirt was getting in during air filter maintenance, there might be a scratch here or there. If you have the typical cloudy, smeared fingerprint appearance on your crank, thats not from the occasional speck of dirt from swapping air filters. It's from a long continuous supply of super fine particles getting through the filter over time.
I still say nothing of significance gets through a properly done foam filter, those tiny particles are likely harmless, and you should just run the engine.
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