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Markopolo400

Ugh, I Feel Like I own a crf250..

6 posts in this topic

...In terms of reliabilty. :applause:

I just got finished checking my 1999 yz400fs valves in my garage. My middle intake is too tight, and the other 4 valves are right on the edge of being too tight (Barely still in spec). Now, this will be the 2nd time that I've had to shim them in the past 6 months.

What should I do?

Should I just bite the bullet, and install all new valves and springs? I am already going to throw in a new timing chain for good measure. Even though the one in the engine is still fine.

Here's some history on the bike.

-Bought brand new in '98 by a guy who had nowhere to ride it, wife got unexpectedly pregnant, sold to who I bought it from.

-Bought buy a dad coming off a 125, rode it for a while, then decided to go back to a 125 (The 400 was too much for him)

-Then I bought it with very little time on it after my 125s crank went last April. The paint was barely worn off the frame.

I changed the oil every 2 rides. I checked the valves in July, had to reshim all 5, the stock shims were still in the engine. I checked the valves again in September, and they hadn't moved.

So, at this point, I think I am going to shim the one intake, then watch them like a hawk, and if they move I'll overhaul it. What do you think?

Also, how much play should be in the timing chain when the adjusted is full tight? Barely any right? I have a pic of how much is in mine, but I can't find the cable to upload them right now.

Thanks.

Edit: After looking at my title, I feel it's a little much...LOL. I know that these bikes are supposed to be as reliable as rocks, and I am kind of dissapointed that mine isn't. At this point I am considering getting a 250 2-stroke too. So I don't know. Help me out.

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Well it is an 8 year old bike. Put some valves in it and it will be good for another 8 years. :applause:

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When the valves are getting tight it is because of wear on the valve face or value seat I believe. You are getting close to time for a head job. If the valves seats or faces get to far worn you are risking the valve being pushed to far down in the cylinder by the cam and possibliy striking the piston. If this happens you can bend a valve, or break one off. Both of those will not be nice. I do not have any experience first hand of valves in these engine tightening up, so I can't give you any advice of how long you can go, but summer is coming up and for me that is prime riding/racing season. I hate to break down during that. Just my 2 cents. I am sure others can offer advice also.

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Well it is an 8 year old bike. Put some valves in it and it will be good for another 8 years. :applause:

Very true.

Do you reccommend throwing in a new piston in there while I have it all apart? Because I think I am going too.

Oh the best part? $50 at the TT store gets me all 5 valves, and all 5 springs. :applause:

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Very true.

Do you reccommend throwing in a new piston in there while I have it all apart? Because I think I am going too.

Oh the best part? $50 at the TT store gets me all 5 valves, and all 5 springs. :applause:

In your situation I'd replace the following: valve springs, valve seals, valves, head gasket, base gasket, tensioner gasket, piston, rings, circlips (2), piston pin and cam chain. Its also a great time to do the 450 DCM if you haven't already. And be sure to have a machine shop touch up the valve seats before you install the new valves. :applause:

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Very true.

Oh the best part? $50 at the TT store gets me all 5 valves, and all 5 springs. :applause:

well with prices like that you'd be a fool not too:thumbsup:

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