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Old 08-21-2011, 01:41 PM   #1
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Default OS .28xz help

I recently purchased a 28xz that supposedly has only one gallon on it. The motor looks the part but I noticed it would topple over within 2 seconds holding the flywheel. All my OS .21 engines will hold themselves no problem and they have over 2 gallons on them.This is my 1st .28xz so I don't know the characteristics of this mill. It does not have the compression it seems that the .21's do either. The main thing I notice it when having the cooling head off, there is no metal pinch. My .21's still have tons. I was told the engine was bench broken in professionally and like I say, the motor is clean on the outside.

I don't want to accuse the guy of selling me a motor with a old piston/sleeve but it looks like this is the case. Can someone tell me if a 28xz looses all metal pinch unlike the vspecs etc.? Pinch & compression are two different things. This mill has no pinch but has decent compression. Comparing to the vspec, it feels like it has much less but most of what I feel in the vspec is a combination of both pinch and compression so it feels tighter. This motor seems to smoke a lot more the vspecs I have with the same tune. Let me know if you can shed some light on this. Thanks
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Old 08-21-2011, 08:28 PM   #2
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Originally Posted by easydoesit View Post
I recently purchased a 28xz that supposedly has only one gallon on it. The motor looks the part but I noticed it would topple over within 2 seconds holding the flywheel. All my OS .21 engines will hold themselves no problem and they have over 2 gallons on them.This is my 1st .28xz so I don't know the characteristics of this mill. It does not have the compression it seems that the .21's do either. The main thing I notice it when having the cooling head off, there is no metal pinch. My .21's still have tons. I was told the engine was bench broken in professionally and like I say, the motor is clean on the outside.

I don't want to accuse the guy of selling me a motor with a old piston/sleeve but it looks like this is the case. Can someone tell me if a 28xz looses all metal pinch unlike the vspecs etc.? Pinch & compression are two different things. This mill has no pinch but has decent compression. Comparing to the vspec, it feels like it has much less but most of what I feel in the vspec is a combination of both pinch and compression so it feels tighter. This motor seems to smoke a lot more the vspecs I have with the same tune. Let me know if you can shed some light on this. Thanks
You wouldn't really be able to tell how good it is until you have it running at temperature and then give it the best possible tune to see how much life it has left in it.

It could be that the p/s is worn out too much and has low compression once it has the proper amount of heat inside it, but you wouldn't really be able to tell unless you are actually running the engine.
If you turn it over by hand and it still pops, then I would say it's still good to use, but how good? I don't know.
Track test it, and see it it behaves.
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Old 09-01-2011, 01:52 PM   #3
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Default 28

I have that very same motor in my Late model, and on my dirt oval track it is without a doubt the fastest, torquest motor I have. I run all O.S. 21 VZ-b's and the 28 running at 240 -245 degrees is a beast, I think you need a pinch or new P&S. hey thats just my opinion.
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