200x valve seat

[83_200e_rider]

Hey guys, I have a spare 86 200x motor that has been laying around for a couple years, I tried starting it and it smoked like a train and had no power did a compression test a while ago and did not pass. Just recently decided to open it up to learn the engine Incase I ever have to rip the one I actually ride apart. I do want to get this engine back to running condition just to learn. I was suprised how clean the piston and bore were. Basically I have 2 questions. First, the piston is actually pretty decent. Measured the od and it’s out of spec, to small. I don’t have the right tools to accurately measure the bore but I assume it’s worn too. Is it usual for engines to wear out piston and bore in a clean way? The bore is nice with no scoring you can feel. Next question is the valves. The intake valve seals good but the exhaust valve is leaking and seat looks enlarged. Seat spec is 1.4mm and exhaust seat is 1.5m I’m getting. Also the exhaust valve itself is kind of flat looking, no angles left on it (there should be 3 noticeable angles) Is my only option having the seat recut? Or can I possibly just put a new exhaust valve in? I’m not looking to completely restore this engine as the cases have some chain rash, and it’s just a spare. But would like it running good. Just looking for some thoughts. I’ll add some pics when I get off work

[83_200e_rider]

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[yaegerb]

Engines sometimes have no visible signs of wear. Get an oversized piston and have the cylinder bored/honed to match. You could also fill out a 4 stroke order form from L.A. sleeve and they can get the piston and bore/hone it for you. Put the old valves back in with the springs and keepers, flip the head over and pour some marvel mystery oil in the combustion chamber. Watch for leaks and seeps. It is likely it will seep and you will need to get new valves. Get some lapping compound and hand lap the new valves In place. After a new top end gasket kit (with valve seals) you should be good to go.

[Dirtcrasher]

Usually the valve seat can be re used either a new valve and lapping, but they can just cut the seat, even just one if that's all that's needed.

I can usually find those heads pretty cheap on FaceBook.

You need an inside telescopic bore gauge to check the cylinder, yes they often look nice, but the cross hatching will be all gone aside from where the piston rides.

If it's that worn and the seat is toast, how is the cam, rocker shafts and rocker pads?? Those are all hard to find new parts but lots of use ones out there.

I probably have a good head I'd sell after you get an idea of a cost on your parts and see what will work for your wallet.

Do it once and do it right, keep it filled with oil and warm it up properly. It will last your forever...

Biggest issue I find with motors is a lack of changing the oil, and running low on oil, that's what ruins these otherwise bulletproof powerplants.

[83_200e_rider]

Usually the valve seat can be re used either a new valve and lapping, but they can just cut the seat, even just one if that's all that's needed.

I can usually find those heads pretty cheap on FaceBook.

You need an inside telescopic bore gauge to check the cylinder, yes they often look nice, but the cross hatching will be all gone aside from where the piston rides.

If it's that worn and the seat is toast, how is the cam, rocker shafts and rocker pads?? Those are all hard to find new parts but lots of use ones out there.

I probably have a good head I'd sell after you get an idea of a cost on your parts and see what will work for your wallet.

Do it once and do it right, keep it filled with oil and warm it up properly. It will last your forever...

Biggest issue I find with motors is a lack of changing the oil, and running low on oil, that's what ruins these otherwise bulletproof powerplants.

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[83_200e_rider]

This was the filter, yes that is a quarter inch of crud. Worst I ever seen haha. When I clean the filter out in my bike there’s nothing ever in there. The cam seems to be in spec. The right way to fix it would have the seat cut back to spec. Has anyone got machining services done from g&h discount atv? About $140 for a complete head service. Kinda out of my range as this is just a spare motor with that and a new bore I might as well buy a new engine. It would be nice if I could just find someone to recut the exhaust seat for like 50 bucks. Lol It’s really not terrible shape. Have also been looking at neway cutters. Anyone have experience with them? I know exhaust valves are mostly the problem valves. I figure for what i would pay for a cylinder head service I can probably get the 3 angled cutters for around the same price and have the tool forever, and fix more.


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[83_200e_rider]

Engines sometimes have no visible signs of wear. Get an oversized piston and have the cylinder bored/honed to match. You could also fill out a 4 stroke order form from L.A. sleeve and they can get the piston and bore/hone it for you. Put the old valves back in with the springs and keepers, flip the head over and pour some marvel mystery oil in the combustion chamber. Watch for leaks and seeps. It is likely it will seep and you will need to get new valves. Get some lapping compound and hand lap the new valves In place. After a new top end gasket kit (with valve seals) you should be good to go.

I tested it with compressed air through the ports with water sitting in the combustion chamber. Exhaust valve itself is pretty toast. You think my chances are good of just lapping a brand new valve and it sealing? The tolerance is 1.1-1.4mm seat width. I’m getting 1.5mm on my caliper


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[83_200e_rider]

Engines sometimes have no visible signs of wear. Get an oversized piston and have the cylinder bored/honed to match. You could also fill out a 4 stroke order form from L.A. sleeve and they can get the piston and bore/hone it for you. Put the old valves back in with the springs and keepers, flip the head over and pour some marvel mystery oil in the combustion chamber. Watch for leaks and seeps. It is likely it will seep and you will need to get new valves. Get some lapping compound and hand lap the new valves In place. After a new top end gasket kit (with valve seals) you should be good to go.

https://uploads.tapatalk-cdn.com/20200318/eb9cf76d9daa7129505e89325f3ae64a.jpg
https://uploads.tapatalk-cdn.com/20200318/036b01a791d24b67c8c536eb66ea1e99.jpg
Here is the intake valve and exhaust valve


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[yaegerb]

I tested it with compressed air through the ports with water sitting in the combustion chamber. Exhaust valve itself is pretty toast. You think my chances are good of just lapping a brand new valve and it sealing? The tolerance is 1.1-1.4mm seat width. I’m getting 1.5mm on my caliper


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It doesn't hurt to get 2 new valves and try to hand lap it. The other option is to send the head off and get the seats re-cut.

[yaegerb]

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That's not that bad. You should try your hand at a motor that's been used as a boat anchor...…

[BarnBoy]

I just got my valves/ seats ground on my ATC200M by an old school local machinist for $20. Just make sure they know what they are doing and have the right size pilots/stones and a jig to hold it.