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Discussion Starter #1
Hey everyone! New to this forum hope to get some good advice from some knowledgeable people! So I have a 2001 Rancher that keeps blowing oil out crankcase breather I bought it from a guy who had 4 experienced mechanics try to fix it but it puzzled them all so now me being a mechanic I dove right in first I checked the compression which it was not good at 60 psi but the motor has a fresh rebuild? I was curious why and I came to find the valves were partially opened at TDC so I readjusted the valve clearance to spec (.006) and now it has 100+ psi so I thought that had to be the reason it was building pressure in the crankcase blowing what gases are supposed to stay in the cylinder out into the valve cover and down the pushrod passage into the crankcase? Much to my surprise tonight I took it out after buttoning it back up and wouldn't ya know it the same problem just pumped damn near a quart which is half the oil capacity into the airbox and she had one hell of a cloud of blue smoke behind her haha. Just curious if anyone else has run into this issue and if there is something I'm over looking here? Also btw I took the cylinder/ jug off and inspected the cylinder and piston/rings which was all basically brand new with out a scratch, another thing I noticed when taking the rings on and off..............the piston had no alignment pins for the rings? They are not supposed to be in line they should be staggered 120 degrees which if isn't done correctly could effect compression and would cause some blow by? If anyone else has encountered this issue any tips to save me a little time would be greatly appreciated!
 

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Discussion Starter #3
Ok so your thinking the timing chain is stretched enough where it's throwing the valves out of time and causing low compression? Makes sense I will look at it tonight and keep you posted thanks for the advice!
 

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do you know why the new top end was done?
as its common these days for folks to sink these things and then to a top end, which only tends to lead to motor issues shortly down the road?
correct way to fix a sunk motor is splitting cases and cleaning! , not just a flush and a a new top end!

and also, any chance the motor is over filled with OIL? that will cause it to pump out vent into air box!
there is a right and a wrong way to check oil levels on these things?
and HAVE top made sure the oil filter is installed correctly , putting it in wrong will cause oil to be pushes into wrong places and worse!
 

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I bought it off a 71 year old man who just drove it around his cabin never mudding and he was original owner, he had it rebuilt because of the oil just one day started pumping into the airbox and rebuilding it did not fix the problem. As far as oil goes I just changed it so I knew it had 2 quarts in it so I could rule out the overfilling. Wheeler has about 1900 miles on it also
 

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I bought it off a 71 year old man who just drove it around his cabin never mudding and he was original owner, he had it rebuilt because of the oil just one day started pumping into the airbox and rebuilding it did not fix the problem. As far as oil goes I just changed it so I knew it had 2 quarts in it so I could rule out the overfilling. Wheeler has about 1900 miles on it also
I’d assume something is amiss with the rebuild, a cut corner somewhere or cheap Chinese parts.
 

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1900 miles and needing a new top end is odd , unless the owner used to let the motor idle for hours, or something just went wrong*anything can happen)
but honestly most honda atv motors are good for a LOT more miles than 1900 before needing motor work, that is very odd to me
 

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The previous owner had a mechanic look at it and he replaced the top end assuming the piston had to much blow by I'm thinking and in doing that it didn't fix the problem. The cylinder kit is a Namura and I tore it all down and made sure everything is correctly installed. The wore out timing chain is what I'm thinking the problem is so I am planning on replacing it.
 

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I may be wrong but I always thought Namira was Chinese.
 

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Ahh ok. A quick google search shows nothing but issues with Namura pistons unfortunately, poor quality it would appear. Sorry to be the bearer of bad news.

I know guys here use Wiseco or OEM, I haven’t had to do a top end yet on my ATV’s but I would follow suit and use known good parts.
 

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Ok the piston and rings are brand new but the bike only has 60 psi of compression and when I reset the valves yesterday and did a compression test immediately after it had 120 psi so I'm thinking fishflies has a good guess with the timing chain but the Rancher only has 1900 easy miles on it so I just find it hard to believe the timing chain is shot and it runs like a million bucks, before I tear into it is there anyway I can check it beforehand? Thanks a ton for the input!
 

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The 350 Rancher motor is a dry-sump oiling system design. It has a two-part oil pump... a scavenge pump to sweep oil out of the sump into an oil tank (integrated into the crankcases) and a pressure side pump that feeds oil throughout the motor & trans, some goes through the oil filter & oil cooler before returning and some goes directly through the primary & secondary shafts to lube the trans.

There are several screens (3 or 4, I think, maybe 5?) in those cases too, to catch, hold and filter debris.

This is a long shot guess... but its possible that the integrated oil tank has the drain and the overflow ports both plugged up. Its also possible that one or more screens are plugged up. I would suspect the screen for the scavenge pump might be compromised.

A couple things could explain these if any prove to be true.... If the cases were ever split for any reason the person doing the work may have reassembled using RTV silicone gasket maker? Chunks of cured silicone would then plug off those drain/overflow ports and/or the screens. If the person never changed the motor oil, the rotten (saturated with carbon/contaminants) motor oil would have broken down and decayed many years ago... plugging everything up as well.

One or more of those conditions might explain why the motor started blowing oil through the vent in the first place. You'd be surprised how poorly many folks maintain their stuff.... well, maybe not, yer a mechanic after all.

I'm interested in what you find out, regardless. Have fun!
 

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Discussion Starter #14
Ok that could very well be it I'm giving it a valve job and a new wiseco top end gonna try that out and if it still blows oil I'll pull the motor and split the cases just to inspect every square inch of this engine and find the culprit. Thank you for the detailed response! I will keep everyone posted what I figure out
 

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Another thing to remember is the compression is low around 60-70 where I believe it should be around 100 which is telling me it has to be A-timing issue B-sticky/improperly seating valve C-faulty piston/rings so I am having a machinist check the cylinder bore and piston clearance to see if they installed the wrong piston for the cylinder which appears to have been bored prior. I just don't know what other issues could cause low compression and excessive crankcase pressure on a fresh rebuild? One thing I haven't done is a leak down test which I will have to do after I get the top end back together. As far as the timing goes after running it for several minutes I checked the valves at TDC they are still perfectly set with proper clearance.
 

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I rebuilt a 2002 for my neighbor, and by "rebuild" I mean I tore it down, cleaned out the bottom end, put a new timing chain on it, and reassembled. He cut corners on the top end, having me simply hone they cylinder and put new rings on the existing piston instead of having it bored with a new piston. I figured if it didn't work at least we would know the bottom end was good and could just pull the cylinder and do it right.

His burps oil in the airbox too, but doesn't smoke while running.

I extended the crankcase vent line to about 3 feet, and looped it around the carb a couple of times. That helped with the amount of oil being burped into the airbox.
 

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Another thing to remember is the compression is low around 60-70 where I believe it should be around 100 which is telling me it has to be A-timing issue B-sticky/improperly seating valve C-faulty piston/rings so I am having a machinist check the cylinder bore and piston clearance to see if they installed the wrong piston for the cylinder which appears to have been bored prior. I just don't know what other issues could cause low compression and excessive crankcase pressure on a fresh rebuild? One thing I haven't done is a leak down test which I will have to do after I get the top end back together. As far as the timing goes after running it for several minutes I checked the valves at TDC they are still perfectly set with proper clearance.
You are doing the right thing for sure, by having the bore measured, checked for straightness and true-ness with properly clearanced piston/ring gaps etc. The hone finish is important too, but you're on top of all that.

The reason the cylinder compression jumps around is because the 350 motor has an automatic centrifugal compression release cam (it holds the exhaust valve open slightly at low/cranking RPMs below 450-550 RPMs) built in to the end of the camshaft. They are pretty crappily designed and don't provide any operation consistency... its common and expected to see low compression test readings on perfectly fine (& properly freshened) motors. Don't rely on compression tests and you'll be fine.

Others have reported oil entering the air box in varying amounts with 350 Ranchers, so I'm interested in learning the cause(s) of yours. Thanks for this thread!
 

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Little update I checked to see if the oil filter was put in backwards and it wasn't but I noticed there was only a couple drops of oil in the filter housing which was very surprising when none came out after I removed the cover usually it's not much but a lot more than virtually just a residue especially not even a day after the engine was ran, anyone else run into this before it's got me wondering if the oil pump/screens actually are plugged which could very well be?
 

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Yeah, it sounds like either the screens are plugged or the oil pump is shot. Maybe both... There should have been an oil mess to clean up after you took that filter cover off.

The service manual shows where all of the screens are in those cases. I'd remove & flush the oil cooler & lines as well, while you have it apart.
 

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I would think that compression is by-passing the rings is causing excessive crankcase pressure and that is what is blowing oil thru the crankcase vent tube -----if the vent tube was disconnected from the air box and run into a clear water bottle and hung on side the frame while taking a ride might show if that is where it is coming from or direct you in another direction
 
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