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Thread: atc200s top end rebuild?

  1. #1
    Join Date
    Sep 2018
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    Ga
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    11

    atc200s top end rebuild?

    Well another hump in the road trying to save this 1985 atc200s. A compression test resulted in around 75 before and after a teaspoon of oil in the plug hole. So.... does this mean a new top end? I have not checked my valves, so do I need to look into the valves or something else. It has spark but feel like it should be better. If a rebuild is eminent, I need some advice about where to find the right parts for this rebuild. Is there a kit that includes the piston, rings and gaskets? Or am I getting too far over my head. I've never done this but I have the shop manual and the internet ha ha. Any suggestions?

  2. #2
    Join Date
    May 2006
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    Bowling Green KY
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    Quote Originally Posted by Sperdue View Post
    Well another hump in the road trying to save this 1985 atc200s. A compression test resulted in around 75 before and after a teaspoon of oil in the plug hole. So.... does this mean a new top end? I have not checked my valves, so do I need to look into the valves or something else. It has spark but feel like it should be better. If a rebuild is eminent, I need some advice about where to find the right parts for this rebuild. Is there a kit that includes the piston, rings and gaskets? Or am I getting too far over my head. I've never done this but I have the shop manual and the internet ha ha. Any suggestions?
    Yes you'll need to check the valves and seating, the bore, and the piston and rings to locate the compression leak.

    It's not something you should attempt being a first timer without a proper bore measurement and the instrument that is required to measure correctly. If you're really good with your hands and you want to learn to do it correctly, then by all means jump in but be prepared because there is a science to these things and it's hardly a matter of just replacing parts. There are no shortcuts. I hardly ever have had that little of compression and it only required a hone to cleanup and correct. When it's that bad, you probably need the bore recut. Most shops I've encountered charge between $50-$100 for the measuring and machine work which is well worth the price. The piston and rings will probably run you $120-$150. The piston needs to be purchased first so that the machine shop doing the work can match the bore to the piston actual size rather than the other way around. Sometimes the ring ends need filed or ground in order to correct the ring gap. If you fail to do this right, you're in for a possible catastrophic failure with all those new parts

    There are some kits for some machines but I'm not sure if there is a kit that includes everything you need for a topend or not and even if it does, it probably doesn't have the valves and head stuff included if you need to do that as well.

    There are guys here in the forum who can rebuild your topend for you or there's a place on eBay called G&H ATV that offers rebuild services. I've used the member shortline10 recently and had his shop rebuild a 200X head for me with new valve guides installed and I've used F.A.S.T. Racing for a bore job on a 250R. I recommend either one of those two for sure. I think yaegerb also is doing engine work so you might contact him. He has very positive feedback as well. There are others I'm sure I'm missing

    Sent from my Z958 using Tapatalk

  3. #3
    Gabriel's Avatar
    Gabriel is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    I can tell you G&H does a great job. You can send your cylinder in and they'll bore it and send the proper piston, rings, a gasket kit, timing chain and new tensioners. You also get a new set of valves. I recommend sending the head in too. It's more money but you'll get a $20 price cut since you won't need the valves from the cylinder kit they offer because they're included in the head service price.

    They do top notch work and it's worth the extra $20 fee they charge to bead blast the entire cylinder. You'll NEVER get it that clean at home. There's much to be said for getting everything from one place too. AND, when you get them on the phone, you get to talk to someone who actually knows what the heck they're talking about. Not some flunky taking orders and shuffling paper.
    Amateur Resurrectionist

  4. #4
    Join Date
    Apr 2014
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    Since your compression didn't change at all when you added a little bit of oil to the cylinder, I'd suspect the valves. It could have major cylinder damage, but for now, just assume that it's for sure the valves. The first thing that you want to do is check your valve clearances. I worked on a 200S for a guy that had a "rebuilt" engine. I couldn't get it to start, but it kept spitting gas back out of the carb. It turned out that the intake valve wasn't closing all of the way. After adjusting the clearance, it started up pretty quickly. It also turned out that it smoked like a freight train so he got rid of it pretty fast. It could be something simple like this. Always check the simple/easy things first before tearing into the engine.

  5. #5
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    Sep 2018
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    Ga
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    Yeah I need to check the valves for sure. Gas was spitting out the back of the card when trying to crank it. I tried the compression test again and got around 95 this time (before & after teaspoon). I may have had a small leak the first time as it was late on a friday night after i had a few. I got a feeling I will end up calling G&H though. I don't need to try and tackle this with two kids at home and no time. Thanks for all of the advice.

  6. #6
    Join Date
    Apr 2014
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    Edmond, KS
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    It may be the same thing as the one that I mentioned. If the intake valve isn't closing, then it will have low compression and will spit gas back out of the carb.

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