plaining a 200X head????

[oldred95]

Can a 200X head be plained to raise the compression slightly? I just got an '84 and I'm redoing the topend with a .040 over WSM stock compression piston, and I cleaned up and smoothed the ports today on the head. I'm just looking at a cheap easy way other then the 100+ dollar wiseco piston to get a bit higher compression out of it. If it can be plained slightly, just enough to get say 10:1 that would be cool otherwise I'll just leave it as is. Not looking for a racer or anything, just wanting it to be plenty stout for what it is.

[Beardoh]

I don't know if machining the head on a four stroke would affect the valves (maybe they would scrape the piston at TDC) it works okay for 2 strokes but you should only get maybe .010" max taken off. Also, when you increase the compression you may have to run higher octane fuel. maybe a race gas/pump gas mix. All in all it's $$$$ any way you look at it.

[oldred95]

Yea I was wondering about valve to piston clearance. I did some reading here on the site and learned that the 10.25:1 wiseco piston lives longest with around 93 octane and 91 is the highest we can get out in my area. I was just wondering if there was a simple easy way to get a bit more compression but it doesn't look like it, at least not keeping things practical anyway. I'm sure the overbore and the porting will help stuff a little more air in the cylinder as well.

[deathman53]

why not get a 12:1 piston???? you will have to use race gas, but it will do the same thing as cutting the head.

[oldred95]

why not get a 12:1 piston???? you will have to use race gas, but it will do the same thing as cutting the head.

Practicallity. I read up on the 12:1 and honestly its not worth it for what I want out of the bike. The high octane gas I could deal with but the part where the kicker mechanism starts to give out because of so much compression just makes me think its not worth it. I think the overbore, port work, K&N filter that came with the bike, and the bassani muffler I have should make it plenty stout for me. We'll see. I've never even ridden a 200x before and I'm not sure what to expect.


Can the head gaskets be left out on 4 stroke engines if the mating surfaces are plained and are a perfect fit? I know two strokes just use a little shim for a head gasket, or at least some of them do but I wasn't sure if that applies to 4 strokes as well.

[deathman53]

most aftermarket pistons are 10.25:1 , most stock pistons are 9:1, so if you get a aftermarket piston you are raising your compression.

[oldred95]

most aftermarket pistons are 10.25:1 , most stock pistons are 9:1, so if you get a aftermarket piston you are raising your compression.

Its says right in my 1983-1985 200X book that stock compression is 9.6:1 and the WSM piston kit I ordered says its a stock compression piston so I would think it would still be 9.6:1 which is pretty good.


Since this thread is discussing head work I have a few valve questions. The old valves were cupped a little bit on their seats and I went ahead and got new ones. I want a perfect seal with the new valves. Can the valve seats be ground for a proper fit of the new valves? Then lap them in to make a perfect seal?

Here's the auction for the piston.

http://cgi.ebay.com/ebaymotors/ws/eB...7205&rd=1&rd=1

I found one that was .050 over but it was a no name piston and I didn't feel like chancing it.

[deathman53]

every piston I've ever gotten is 10.25:1 or 12:1

[oldred95]

every piston I've ever gotten is 10.25:1 or 12:1

Even a WSM piston? That would be great if it was 10.25:1 but I highly doubt it is as it said it was stock compression. Just have to wait and see what comes in the box.

[200x Basket]

no you can not do that. you will cause the cam chain to loosen.

[oldred95]

no you can not do that. you will cause the cam chain to loosen.

I completely forgot about what it would do to the cam chain. Good point there.

[TimSr]

I guess Im not following here. You dont want a high compression piston because its over $100 but you are ordering a new piston for stock compression anyways. Is there much of a price difference between stock compression and high compression? If you have to get a piston anyways, why not get the 10.25:1? Seems to make more sense than machining your head and doing something that can never be undone.

[oldred95]

I guess Im not following here. You dont want a high compression piston because its over $100 but you are ordering a new piston for stock compression anyways. Is there much of a price difference between stock compression and high compression? If you have to get a piston anyways, why not get the 10.25:1? Seems to make more sense than machining your head and doing something that can never be undone.

Yea I went ahead and orderd a stock compression .040 overbore piston. Because the 10.25:1 was more then I'm wanting to spend. Yes it does but I didn't know if you could simply leave the head gasket out and up the compression some or not or machine the head but apparently not. I'm going to have about 150 in the engine and it should be fairly strong even with stock compression. I've read good things about port work and I didn't do anything wild, just took care of that nasty little ledge right before the valve seat on both intake and exhaust and smoothed things out nicely.

[dufrain]

I dont know why you couldnt plane the head a few thousanths but im not sure raising it for 9.6 to 10 would make much difference.The cam chain tensioner would take out the slack as long as its a new enough chain and if a 12.1 piston will work without the valves hitting then you wouldnt have to worry about them hitting a stock piston planing only a few thousanths

[Jason T]

We have skimmed heads on 4-strokes many times to raise the compression, and had excellent results.
As stated the tensioner takes the very small amount of extra slack out of the cam chain.
You will have to use the head gasket, theres no other option.
Ideally you will need to work out what your CR currently is, and from there work out how much to take off the head to give the required CR.
Or you could take a bit off, do a dry build of the engine to check the valve/piston clearance, and then take some more off if you are happy to.
You can't reverse what you are doing, but 200 heads seem fairly available, so give it a go

Jason