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Discussion Starter #1
Ok, I posted on another post below regarding top end noise.Moose, you suggested I check the valve clearance.I just got done doing that, and it is a little better, but still way too much noise.As it was running, I removed the front valve inspection cover, and it seems like there is pressure under there, like the exhaust valves arent sealing, and allowing compression to leak by them, into the valve cover.I dont know if that would make the noise I am hearing, but I'm pretty sure there should be no pressure under the valve cover.It seems to be getting plenty of oil though, so that's not an issue.Any input on this before I pull the valve cover\head off ? Thanks! Mike

PS This thing starts right up, and idles\goes great.I'm just trying to fix whatever is making the noise to avoid my daughter breaking down in the trails.
 

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Discussion Starter #3
Thanks Mud - I am headed into the garage to remove the valve cover.I will look for any vent hoses, but am not holding my breath.The noise seems to be coming from the front of the very top of the motor, right where the exhaust valves are.I'll pop off the cover and get a visual, and will report back.Thanks for you $.02!!
 

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Discussion Starter #4
Ok, So I removed the rocker cover.Once that was done I did a compression test.It maxed out at 45psi, which is waaaay low.The factory manual calls for 185psi. No biggie, now I know.I pulled the head and inspected the valves, they are good and tight.I will do a quick valve job before reassembly anyway.The jug has some very light scoring, I will drop it off at a machine shop and see if it needs to be bored out, or just honed.My guess is they will need to bore it .030 or so.The only thing I question at this point, is when I reassemble, how do I know where to set the cam, when the piston is at TDC. How do I get the timing exactly right????
 

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When you are ready to install the cam install it with the lobes facing down tighten the cam mounting bolts down and the when you slide the gear and chain on there are 2 little lines or tick marks on the back of the cam gear they will allign with the top of the head. Make sure all or the slack is out of the chain towards the front of the engine then release the tentioner all your marks should stay alligned the marks on the cam and on the crank--- there is a line just above the "T" that alligns with the knotch in the flywheel inspection hole on the shifter side cover, good luck.
 

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Discussion Starter #6
Thanks Moose! I will follow your instructions to the "T". I'll drop the cylinder off at a machine shop this week, and have them hone or bore it,whichever it needs.I'll have them get the piston too, since they will know what size I need if they end up boring it.The bike went good at 45psi, I bet it'll scream when the compression is back up to 185psi! Once the motor is all set, I'll go looking for tie rods, the headlight plastic assembly, and the front chain guard.If anyone has any of this, I'm open to offers! Thanks again, I'll post back soon!Mike
 

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Discussion Starter #7 (Edited)
So I ordered a piston set from Dennis Kirk, part #1311326 if you want to look at their website.No, it's not a wiseco, but I have to make my dollars count as much as I can.I have a 74.5mm bore, so does this look ok? Can I just bring the cylinder to the machine shop and tell them I need a 75.5mm bore, or do I have to wait till I have piston in hand?
 

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a stock 250X/300ex is 74mm bore not 74.5 where did you get that number? it's best to have the piston and rings so the machine shop can match the bore to your new piston specs no matter what the box says they will mic it out and make the necessary adjustments in the cylinder.
 

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I agree with moose. You should take the piston, because the piston my read 30 but it can be a few thousands of a inch bigger or smaller
 

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Discussion Starter #10
OK Guys, I'll wait till I get my new piston before having the cyl. machined. I measured MY cylinder, and got 74.5mm, which Im sure is why I only had 45psi of compression.It is pretty worn out, way overdue for this! Again, as always, thanks for your input!
 

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as far as your top end noise goes. mine was making a lot of "racket" also. i pulled the rocker cover and my rocker arm faces were worn, one of them badly. i replaced the rockers and shafts with some that looked like new from one of my parts engines. it made a unbelievable difference. you can hardly hear any clicking at all now.
 

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Discussion Starter #12
I put it all back together last night, with the newly bored jug, and new piston.It is now pushing over 180psi compression, and fires up immediately.However, there is still alot of racket, although much less than before, coming from the top end. Raciea, I think you may be onto something.My rocker faces look badly worn also, and I suspected those before I popped back in to update the status for the forum.I am glad to see your post.I am going to look for a set of rockers, but am wondering, should I bother to change the cam too? I am going to go with used parts, since I am a single pop on a budget, but am willing to do what's best if I can.

Moose - Thanks for the info on setting the timing.Your info matched just what the factory manual said to do, and it started right up.It sounds very tight now, other than the very top end racket, which is much less than before.Just wanted to thank you!

Does anyone happen to have a valve cover with the rockers installed, in good shape, that they are willing to let go cheap? I will look on ebay, but thought I's ask here. Is the 300ex valve cover the same? I had someone email me with 2001 300ex parts, and am wondering if the top is interchangeable with my 88 250x......





as far as your top end noise goes. mine was making a lot of "racket" also. i pulled the rocker cover and my rocker arm faces were worn, one of them badly. i replaced the rockers and shafts with some that looked like new from one of my parts engines. it made a unbelievable difference. you can hardly hear any clicking at all now.
 

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I would say if the rockers are worn, the cam is too. Just inspect the lobes on the cam. You should be able to see any wear. The lobes should be flat and smooth all the way across.
 

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I agree with Helmut as far as the 300EX is concerned yes the heads are the same.
 

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i don't think that the 300ex rocker cover has the hole drilled out for the decomp. shaft. but if you can get the rocker cover cheap and it has good rockers in it then you can change them out. i am pretty sure that even though the 300's do not use a decompression the rockers are the same, meaning that the 300ex exhaust rocker has the tip cast into it that hits the decomp. shaft when you kick it. i agree with the guys, if your rockers are worn then your cam is also. just check it out, it is pretty noticeable if it is worn. changing the rockers are easy if you have a slide hammer. what i did was take a half inch rod and drill the center out big enough to fit over the pins that hold the rocker shaft in place. then drill and tap a hole near the end of the half inch rod for a screw. take a good file and file a slot near the end of the pins on your rocker cover. then you can put your half inch rod over the pin, align the slot that you filed with your screw that you tapped and tighten it up. fix your half inch rod to connect with your slide hammer and pop them out. it works great. i cannot tell you how many rocker covers i have seen where someone tried to take the pins out with a pair of vice grips and were unsuccessful. if you use the slide hammer and do it correctly you can reuse the pins over and over. when you get the pins out, use the small end of a allen wrench to push the rocker shafts out enough so that you can grab them and pull them out. there is a hole at the end of the shafts to stick the allen wrench in. if you get the 300ex rocker cover and the rockers are good then i would use the shafts out of them also. it will take all the noise out of your top end.
 
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