XR200 piston in an 85 200x???

[YTZ drew]

Sorry if you all misunderstood my post. I wasn't trying to say that XR pistons would not fit, only that they are not identical to a stock 200X piston. FWIW, I have a stock 10:1 XR185 jug and piston on my 200X. It works just fine. As far as the cheapo aftermarket piston kits, its common to find lower compression height than stock. Its also a common issue with cheap automotive piston kits. Sometimes the aftermarket slugs end up 0.040+ down the hole at tdc!

[mayhem17]

I had spoke to two guys I know on the Honda ATC facebook site that had used the piston I ordered and said that it worked great for them. They used the domed piston which is the one I ordered. I'll check it out once I get it. I figured for that price, and 2 others using it with no issues to date, it couldn't hurt. I will get it and compare to my original first also.

I was wondering if with the lower compression height, but being domed... if maybe being domed which would give it more height, but then being a lower compression height.. if it would somewhat cancel each other out maybe? I'm by far an expert on this. Will be the first time doing it myself.

[barnett468]

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i would have just bought the correct piston . . do it right and you will only do it once.

a compression estimate in your case would be this . . if you have a 10.0 compression piston and you raise the pin by .015", your compression will be 9.5, if you raise it .030", your compression will 9.0 . . if you raise it by .045" it will be 8.5.

[mayhem17]

As stated, was told this was a good option from a few fellow trike riders. Also stated it was a good bang for the buck upgrade. Figured for that small amount of money, its worth finding out myself, and if it doesn't work out, it't only $20 for a good lesson learned.

[barnett468]

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As stated, was told this was a good option from a few fellow trike riders. Also stated it was a good bang for the buck upgrade. Figured for that small amount of money, its worth finding out myself, and if it doesn't work out, it's only $20 for a good lesson learned.

As stated, wrong parts are never a "good" option . . Also since no one has the actual data or has posted compression tests, there is no hard data as to what it will do, however, if shadys info is correct, it will most likely have less compression than a stock piston . . Even if it actually does increase the compression by 1/4 point it’s a totally useless "upgrade" . . The only way to know for sure is to do the math and do a compression test.

According to Honda, the stock compression on that engine is around 163.6 psi . . If you are at 170 or less with the new piston after it is broken in, you have not gained anything relevant other than restoring compression back to factory spec . . If your compression is around 176 or more, then you have made a difference.

One of the problems with the claims of big power improvements from this piston is that their old piston and rings are so worn out that instead of having the factory 164 compression, they might only have around 135 or even less, therefore, even if this piston only increases compression to 150, it is still a big improvement to them even though t is still below the factory 164 psi level.





From post 3.

As far as I know, no, those are different. A friend bought one for his XR200 like it said in the ad.......only the compression height on the oem piston is around 27mm or more and the eBay one is only 22mm.

Using a compression height difference of a whopping 5 mm as shady has stated it is, if it was a 10.0 piston with the correct pin height and you raised the pin 5 mm . . the compression would then be around 5.22, if it was 13.0 with the correct pin height, it would be around 5.76 if you raised the pin 5 mm.

Bore size being the difference yes. That’s not my question. I'm going to have to bore my cylinder anyhow, and was looking at the xr200 piston as many state that its quite the performance increase with much less cost.

Not all pistons measure the exact same size even if they say 50 mm or 48 mm etc . . if you bore your cylinder and do a compression test and find that it is around 140 or less, you need to get another piston and pray that it is the same size or bigger so you can hone the cylinder to size because if it is smaller than the other one, it will still work but it will be loose which is not the best option.

[mayhem17]

Got the piston in yesterday. Spoke with the guy that had used the same piston last night also. Just finished his break in period and is right at 170 psi. Not bad for under $30. So I went ahead and took it and my cylinder to a machine shop out of town today to get them matched up. Said should have it done tomorrow, so hopefully have this thing back together this weekend and I'll let you know what I find. I don't mind learning the hard way at times I guess. As stated, I have a few more cylinders, and this was just a budget build plan for me. I did compare the pistons also. There is a difference in the compression height for sure. Stock is a dished piston, and this one is domed. I'm guessing that the difference there is roughly making up for the difference in compression height. At least a guess from speaking with the other two that have used it. This will be a good learning experience for me either way. Hopefully can put a few hours on it this weekend and I'll get back to you.

[mayhem17]

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i would have just bought the correct piston . . do it right and you will only do it once.

a compression estimate in your case would be this . . if you have a 10.0 compression piston and you raise the pin by .015", your compression will be 9.5, if you raise it .030", your compression will 9.0 . . if you raise it by .045" it will be 8.5.

These measurements in inches I take it?

[barnett468]

These measurements in inches I take it?

yes, those are in inches and they are not guesses, they are exact mathematical calculations, and i would be happy to calculate what your piston should have if you want but ultimately the compression test is the final say . . even if you have a 12.0 piston with the proper pin height, it might only provide the compression of a 10.0 or 9.0 piston etc if your rings leak.

[mayhem17]

So what is the stock compression height for the 85 200x? I'm not finding it anywhere. I believe this one was listed as a 22mm, but domed. Having my cylinder done at a shop I finally found. So all that should be good.

[barnett468]

So what is the stock compression height for the 85 200x? I'm not finding it anywhere. I believe this one was listed as a 22mm, but domed.

I don't know right now but shady said it is 27 mm which is a whopping 5 mm difference.

[mayhem17]

Thats for the xr200 he did say. Wonder if there is a difference.

[barnett468]

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the atc200x piston is purportedly 18.5 mm from the top of the pin to the top outer edge of the piston

[YTZ drew]

I just dug out my worn out original 1984 atc200X oem piston. Has honda cast into it and 965 stamped on top (OEM code for 200X), a flat top and 2 valve reliefs. It measures 17.57mm from the top of the pin hole to the top of the piston. Add 7.5mm for a 15mm wrist pin centerline and you've got a 25.07mm compression height.

[Scootertrash]

So what will the theoretical compression be with the shorter compression height?

[barnett468]

So what will the theoretical compression be with the shorter compression height?

i still need to know the exact pin/compression height and rated compression of the xr200 piston to determine it.