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Discussion Starter · #1 · (Edited)
Where should I go from here?

Hey guys,

I bought a 98 300ex off a guy that ran pretty good but it was knocking from the top end like a tink-tink knock didn't bog or anything when I was test driving it. It needed new clutch plates and he had some that came with the quad that were brand new EBC Dirt Racer brand... also had the clutch cover gasket.

Took it out riding that weekend all was great ran fine just the knocking was still going and the clutch needed some new plates but wasn't bad.

So a couple days later I drained the oil changed and took the cover off and found quite a bit of metal shavings down under the oil screen so I checked all the bearings and they were all in good shape and went ahead and changed out the clutch plates and put it all back together and as I was putting the nuetral switch on it sheared off and I had to get it out and get a new one so I finally got it all back together. and it started up and ran good and the clutch was now fixed.

Anyways I took it out riding that weekend and was doing some trails and I pulled in the clutch to check my battery to see if it had fallen out because it's only held in by zip ties and the engine just died on me. So I tried to start it back up again and it wouldn't start... the starter motor was turning but the engine was not.

So I got home and checked all the fuel lines and such and it was all clean no obstructions checked the spark plug and it looked ok nice blue spark... put my fingers over the plug hole and checked the compression and it blew by fingers back so now I'm stuck... Any ideas?
 

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Maybe your carb is stopped up. Is it getting gas to the cylinder? Try removing the spark plug and pour about a teaspoon of gas down in the cylinder and put the plug back in, quickly, before the gas evaporates. Now, try to start it. If it will start and run for a couple of seconds, then your carb is stopped up. If it don't, then you have eliminated the carb as a problem.
 

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^^^^^I agree with Helmut. sounds like a fuel problem with what you have said.
 

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Discussion Starter · #4 ·
I happened to have an extra carb sittin around and switched them out the old carb had a ton of gas in it when I took it out (flooded?) it wasn't leaking out the overflow tube or anything but there was alot of gas in it.

So I tried to start it with the different carb and still nothin... then I tried to start it with starting fluid sprayed down the plug whole though I don't know if I got it on fast enough and then tried to start it and nothin... starter still turns but no engine...
 

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Is your spark blue or orange when you checked the plug if it was orange you might have a bad plug or an elect. problem.
 

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Is your spark blue or orange when you checked the plug if it was orange you might have a bad plug or an elect. problem.
Yeah, and make sure it has a strong, bright blue spark and make sure it's jumping from the electrode to the electrode ground and not off the edge of the plug. You should be able to hear it making a distinct clicking noise every time it fires.
 

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Discussion Starter · #7 ·
It was definitely blue... :confused:What do you mean by jumping from the electrode to the electrode ground? Do you mean just jumping that gap to the bottom metal piece? Cuz I think mine was jumping off from that to the engine casing.
 

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It was definitely blue... :confused:What do you mean by jumping from the electrode to the electrode ground? Do you mean just jumping that gap to the bottom metal piece? Cuz I think mine was jumping off from that to the engine casing.
I don't think it would matter as long as it's jumping the gap, too. Try it with the electrode ground of the plug(the main bottom of the plug) directly tipping the engine firmly. Also, listen for the distinct clicking sound as the engine turns over. If you can hear the distinct clicking and you have a strong bright blue spark, then it's probably OK. If it tries to jump from the electrode to the edge of the plug threads, then it's too weak.
 

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Discussion Starter · #9 ·
Ok, my brother's an idiot (he's the one that put his fingers over the plug whole ot check for compression) So I did a true compression reading today and was only getting about :icon_eek: 45 PSI with a dry test about to try a wet test...

Keep you guys posted!

Thanks for your guys' help. :)
 

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Discussion Starter · #10 ·
So I did a wet test I got 70 PSI... so that means either rings, cylinder or Piston?

Any thoughts? I mean the engine was knocking...
 

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Since you have low compression anyway, I would just go ahead and tear it down and inspect it visually. Sounds like you may have worn rings. You'll probably need to bore the cylinder and get an over sized piston and rings. As for the knock, check for a bad rod bearing. Also, check the cam and rockers for wear. Someone may have run it low on oil.
 

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Discussion Starter · #12 ·
So I tore the engine apart today and didn't find much wrong with it found a few more metal shavings and they all look like crankcase shavings when I opened the top end head the cam chain was loose from the lower gear... it was still on the cam chain sprocket though so the chain was just loose in general.

Also noticed some chunks out of the crankcase on the wall where the cam chain is located (see pics) and the cam chain tensioner guide was also beat up pretty good so I'm thinking maybe it has been loose for a while?





I checked out the piston, rings, cylinder walls and rod not really sure what I should be looking for there as far as the rings go... but the the rest seemed all fine no scoring marks of any kind and the rod looked to be in good shape also.






So do you think it was just the cam chain? Also any ideas on the knocking? What should I do from here?

Thanks again for all your help!
 

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If the chain had that much slack in it I would replace the chain and chain guides your low compression could be some of the cams fault but more than likely it need a top end rebuild.
 

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I agree. I would bore it to the next size over and get new piston, rings, timing chain and timing chain guides.

Did you check the rod bearing for up and down play?
 

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Discussion Starter · #15 ·
I don't really have the money to bore it and stuff and I don't really see any point to do it... so I'm just gonna replace the cam chain and the cam chain guides then adjust the valve clearance and timing and go from there... The rings look good and there are no score marks whatsoever on the cylinder walls so there's no point. Maybe if I had the money it would be a nice mod to have. :)
 

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Was it smoking at all out the exhaust? Cuz if you dont have any smoke i wouldnt change the piston or rings either. I just took mine apart and it looks pretty much like yours my cylander walls are smooth but deffinitly check the rod for up and down play mine moved like an inch up and down. Oh and another thing i know this isnt a common problem but make sure you check your oil pump because i put mine all the way back togeather and the oil pump failed causing my rod bearings to go that bad. So while your there check it. It will save you headaches down the road.
 

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Discussion Starter · #17 ·
Ya I didn't have any smoke whatsoever. By checking the rod for up and down play that will tell me if my rod bearings are shot? Which I don't think they are cuz the only knocking I heard was coming from the top end somewhat but I'll definitely check.

As for the oil pump... how do I check that?

Thanks man!
 

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Take it off and check the oem specs do you have a chiltons or clymers book for your quad? And yes if the rod moves your rod bearings are going. Prolly not but better to check while your right there then find out later. And if you dont have a book ill scan my page for checking the oil pump. Mine was pretty easy to figure out tho the main gear right on the front of it moved a bunch in and out. It should move like a couple millimeters at most. Mine moved like 1/4 to a 1/2 inch.

Oh and those marks in the side of your block look like either your cam chain was really loose or it came off at one point in that quads life. Not a big deal tho.

Oh and another thing you should probably check the cam chain tensioner. Its prolly bad and that would be why your chain is loose or your chain could be stretched? Tensioners are cheap and a good insurance policy.
 

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When you get the engine back together, before you start it, loosen the bolt at the top of the head that holds the oil line on. Now, with your kill switch off or your spark plug wire off and grounded, crank your engine over a few times until you see oil run out around the bolt. If oil doesn't run out, then it's not pumping oil.
 
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