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HectorC74

Honda Rancher 350 Low Compression?

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Hi Everyone, I recently noticed that the head valve cover gasket on my 2000 Honda Rancher 350 ES is leaking. So I know I have to replace it soon, but since I was there checking it I decided to do a compression test just to see how the engine was doing, well the compression I got was 52 psi, I did it several times and it always topped out at that number. So I decided to do a wet test and still, all I got was 52 psi. I am baffled!!  The atv runs great, it has no reason for me to believe there was something wrong other than the leaking gasket. It idles great, runs great and there are no weird noised coming from the engine.  Any suggestions on how I need to proceed?  


Thanks, 
Hector

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Your holding the throttle wide open while doing it correct? It's on the low side but just an improper tappet adjustment can cause that. Personally I go by the saying "If it ain't broke, don't fix it". I would replace the gasket, set the tappets to spec and retest.

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2 minutes ago, toodeep said:

Your holding the throttle wide open while doing it correct? It's on the low side but just an improper tappet adjustment can cause that. Personally I go by the saying "If it ain't broke, don't fix it". I would replace the gasket, set the tappets to spec and retest.

Yes, throttle wide opened, that was what I was thinking of doing, just replace the gasket order a tappet tool to adjust valves and keep riding it... doing the regular maintenance on it. I checked the spark plug to see if it had any oil residue and it was completely dry as well, so I dont think that oil is passing through the rings. 

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52 psi compression is about average on the 350 Rancher motor.... There is a reason for that on motors in good condition with properly adjusted valves. The camshaft has an automatic compression release built into it that holds the exhaust valve open slightly longer than normal while the motor is being cranked over by the starter below 450 RPMs. The compression release works by centrifugal force so once the motor starts the cylinder pressure returns to normal.

 

To get an accurate compression test measurement on Honda ATV automatic compression release motors you must loosen the exhaust valve adjustment up about 2 turns (valve lash set about 0.040") temporarily while you perform the compression test. After you've gotten your test measurements readjust the exhaust valve back to spec.

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20 minutes ago, retro said:

52 psi compression is about average on the 350 Rancher motor.... There is a reason for that on motors in good condition with properly adjusted valves. The camshaft has an automatic compression release built into it that holds the exhaust valve open slightly longer than normal while the motor is being cranked over by the starter below 450 RPMs. The compression release works by centrifugal force so once the motor starts the cylinder pressure returns to normal.

 

To get an accurate compression test measurement on Honda ATV automatic compression release motors you must loosen the exhaust valve adjustment up about 2 turns (valve lash set about 0.040") temporarily while you perform the compression test. After you've gotten your test measurements readjust the exhaust valve back to spec.

Thanks Retro!! So then I shouldn't worry about it and just replace the leaking gasket and that's it.  This surely made my day!!  I have heard about this on some ATV's, but didn't know this year rancher had the auto compression release.  Again thanks for your info. 


Hector

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Ya fix the oil leak and readjust the valves while the rocker cover is off. You'll be good to go.... precise valve adjustment performed periodically is very important.

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if for some reason you can't afford to purchase a new rocker gasket ?, you can buy a can of copper spray from autozone, advanced auto parts, give the old gasket a couple coats on each side, re-use it, done it many times, it works !.

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7 minutes ago, shadetree said:

if for some reason you can't afford to purchase a new rocker gasket ?, you can buy a can of copper spray from autozone, advanced auto parts, give the old gasket a couple coats on each side, re-use it, done it many times, it works !.

Thanks Shadetree, I ordered the gasket yesterday, it was like $9 for an oem gasket on ebay, but I will keep in mind the spray on copper gasket for future repairs. 

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Just now, HectorC74 said:

Thanks Shadetree, I ordered the gasket yesterday, it was like $9 for an oem gasket on ebay, but I will keep in mind the spray on copper gasket for future repairs. 

your welcome !. good to have ya here, your in great hands !!.

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Hey Guys, so I replaced the leaking valve cover gasket and I adjusted one of the valves, it had a little more gap than the other one, here are some pics of the "T" on the flywheel and the valves. Everything turned out good, I even noticed that it started faster than before?? maybe just me??? I dont know if the slight adjustment on one valve would cause it to start up faster when cold??

 

The only thing left for me to do to it is change the diff fluid, which I will do today. 

 

Thanks

0224202008.jpg

0224202014.jpg

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yep, if the valves are out of adjustment ?, it wont crank and run very good at all, it will run , just not as good as an engine that is adjusted right !.

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now that you got it fixed ?, do you think your just gonna run off into the sunset ?...I don't think so !..lol.

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@HectorC74 are you doing the compression test hot? Gotta be hot to read right, if cold you'll get squat lol. Please retest after a good hot ride and report back what the new reading is. And loose valves can do it, if they aren't up tight it won't bump the compression release. 

 

But strangely enough I seen 300 Fourtraxs that never had the valves adjusted fire and run n good, don't ask me how lol.

Edited by F250 guy

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