1998 honda 450 foreman S oil leak and smoke problems. - Honda ATV Forum
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post #1 of 12 (permalink) Old 08-13-2019, 03:04 PM Thread Starter
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1998 honda 450 foreman S oil leak and smoke problems.

The oil is leaking around where the cooler lines go into the engine. I have put teo sets of orings on them and they will not leak for about 20-30 mins and then go right back to leaking.

Also it fuel smokes a little bit, but recently i have noticed it has a slight oil smell along with the smoke now. Could it be rings or valves seals? Any suggestions?
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post #2 of 12 (permalink) Old 08-13-2019, 04:00 PM
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well it could be a LOT of things
motor ever been sunk?
could have crap in motor wearing things out and need =more than rings
how many mile and hours on motor?
any mods to it?
have you cleaned fuel SYSTEM lately, tank, peacock, line, carb?

have you done a compression test on motor?
whats the plug look like?
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post #3 of 12 (permalink) Old 08-13-2019, 05:54 PM
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I would check the oil pressure relief bypass valve operation. Perhaps there is junk caught in the spring between the valve and the cap (or a broken spring jamming the valve) causing the pressure relief valve to be jammed closed, which could result in the oil pressure going very high when the RPMs of the motor are brought up. That could explain the blown oil cooler hose o-rings and likely cause some oil consumption too.

See the attachments... first pic is the retainer cap (allen head hole in it) inside of the front cover that holds the relief valve and spring in. Bypassed oil under pressure exits that allen hole returning to the sump.

The 2nd pic is the relief port (circled in red) inside the oil filter housing in the front cover. You can remove the oil filter and use a small L-shaped allen wrench (or bend a short piece of stiff wire) to depress the relief valve in a bit... you should feel the spring tension on it and it should push in about 3/16" and return freely with no binding. Careful don't bugger up the aluminum... just check for free movement and spring tension and get your wire out of there.

If your bypass valve is stuck you'll have to take the front cover off the motor, remove the cap and fix or replace the valve & spring.
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Last edited by retro; 08-13-2019 at 05:57 PM.
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post #4 of 12 (permalink) Old 08-13-2019, 08:26 PM
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wasn't this atv sunk awhile back, and you did not split the engine to clean it, just rebuilt the top end ?, if so ?, well..all I can tell you is..i told ya so !.

'89 trx350D foreman 4x4...'85 vf700c magna, '03 trx450fm foreman 4x4 , 2015 Yamaha waverunner fx cruiser ho, '08 vt750c2 shadow spirit
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post #5 of 12 (permalink) Old 08-13-2019, 10:34 PM
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You have a 350 Rancher oil cooler on it?
https://www.hondaatvforums.net/forum...ml#post1257778

Check the hose fittings they might not be the same length/diameter as the 450 fittings. That would explain blown o-rings better than a stuck bypass valve.


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post #6 of 12 (permalink) Old Yesterday, 04:30 PM Thread Starter
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Its not the one that sunk, the rancher that was sunk is tore apart right now with the cases split waiting for my crankshaft to come in.
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post #7 of 12 (permalink) Old Yesterday, 04:30 PM Thread Starter
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It does not have a 350 rancher oil cooler. It has the oem 450 foreman oil cooler on it.
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post #8 of 12 (permalink) Old Yesterday, 04:40 PM
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Great advice above that shouldn't be ignored..

What condition are your cooler lines in? Clean and corrosion free? Where did you source the replacement O rings from?

As for the smoke.... Could be rings or valve stem seals, either way you need to dig into that top end to fix the issue. Don't cheap out on the build, if that top end is off then replace everything while your at it.

A week's work and a few hundred dollars on a Honda will see it last another 10 years or more, reliability and affordability at its finest ;-)

98 300 Fourtrax 4x4

Custom built mud bike - Now sold.

2004 Foreman 450S

Fully overhauled (nut & bolt rebuild), 2 lift kit, 28 mega mayhems, ITP delta rims, ES floorboards, 22 LED lightbar, Pyle Bluetooth sound system.
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post #9 of 12 (permalink) Old Yesterday, 08:33 PM Thread Starter
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The lines are a tad stained from over the years but besides that everything is clean. I got the orings from a kit i have that has all assortment of o rings.
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post #10 of 12 (permalink) Old Yesterday, 08:38 PM Thread Starter
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When i put the piece of wire in the bypass valve hole i can feel the spring and it seems like its stuck closed
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