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| Piston height above deck http://www.kawi2strokes.com/forum/viewtopic.php?f=13&t=14902 |
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| Author: | Never2Old [ Mon Aug 14, 2023 3:11 pm ] |
| Post subject: | Re: Piston height above deck |
Cliff, I posted the same question to another group and got a reply from a reliable source. He measured 106.92mm on a NOS H2B cylinder, that's 2mm taller than my shaved cylinder. Makes sense that someone was playing around with performance they might take off a relatively even number. Now to find a 2mm base gasket. I've made plenty of gaskets with a ball peen hammer before but 2mm is a little thick. I tried Cometic but their site sucks, keeps erroring when I try to register. I'll have to do it the old fashioned way and give them a call. Dave |
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| Author: | Evans Ward [ Mon Aug 14, 2023 3:25 pm ] |
| Post subject: | Re: Piston height above deck |
^ I would recommend calling Cometic. I had those same issues a couple of years ago with their website and needed a head gasket for my GT750. I called them and the representative was extremely helpful and I ordered what I needed over the phone. |
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| Author: | Hawaii-Mike [ Tue Aug 15, 2023 3:01 pm ] |
| Post subject: | Re: Piston height above deck |
Never2Old wrote: Cliff, I posted the same question to another group and got a reply from a reliable source. He measured 106.92mm on a NOS H2B cylinder, that's 2mm taller than my shaved cylinder. Makes sense that someone was playing around with performance they might take off a relatively even number. Now to find a 2mm base gasket. I've made plenty of gaskets with a ball peen hammer before but 2mm is a little thick. I tried Cometic but their site sucks, keeps erroring when I try to register. I'll have to do it the old fashioned way and give them a call. Dave https://coppergaskets.us/ |
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| Author: | ALTERED IMAGE [ Wed Aug 16, 2023 2:09 pm ] |
| Post subject: | Re: Piston height above deck |
Maybe in the resource page but, does anyone know the cyl. height on a H2? I got a 106.92mm reluctantly. What is reality? cliff |
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| Author: | Never2Old [ Wed Aug 16, 2023 8:47 pm ] |
| Post subject: | Re: Piston height above deck |
Well, after a lot of hemming and hawing and advice from around the globe, I've narrowed it down to two options. I really believe the cylinder were shortened by 2mm, taken off the top. I need to bring the cylinders back up to height so the pistons won't rise above the top of the cylinder and hit the head. I found good sources of custom 2mm gaskets, one for a replacement base gasket and another for a replacement copper head gasket. If I go with the 2mm base gasket it will throw off the timing, but I've heard some opinions that it might not be a bad thing. Or is it? I'm no exert on port timing so I have no idea. If I go with a replacement 2mm head gasket, timing stay intact. In both cases I'll have to measure the squish to really see where I am. Any pros or cons for either case? Opinions wanted. Thanks, Dave |
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| Author: | Jim [ Wed Aug 16, 2023 9:23 pm ] |
| Post subject: | Re: Piston height above deck |
I don't remember... have you owned/ridden a stock H2? I like to experience a stock configuration before I modify it so I have a baseline. It's easy to try thick base gaskets along with shortening the intake side piston skirts later if you decide to. |
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| Author: | Never2Old [ Thu Aug 17, 2023 7:02 pm ] |
| Post subject: | Re: Piston height above deck |
My H2 addiction began when I bought my brothers 72 in 75. I rode it for many years before selling it. I was a poor college student in need of cash, what a mistake. It was stock but it was a hand full, always a thrill to ride. If I start with a stock base gasket and use a 2mm head gasket the bike should be close to stock (other than the oversize piston.) Then if I want to I could experiment with a 2mm base gasket and stock head gasket to see how it affects timing/performance. That's one of the benefits of a 2 stroke, easy to rebuild the top end. But it's also more of an mystery, for me, when you start playing with port timing. Dave |
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| Author: | Jim [ Thu Aug 17, 2023 9:40 pm ] |
| Post subject: | Re: Piston height above deck |
The trouble with just raising the cylinder is that intake timing goes the wrong way. That's why I mentioned the cutting of the intake side piston skirt at least an equal amount. There's plenty of 2-stroke porting information on the web if you want it to be less mysterious. 
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| Author: | Never2Old [ Fri Sep 08, 2023 12:51 pm ] |
| Post subject: | Re: Piston height above deck |
Some progress, getting closer. Thanks to Lani at CopperGaskets.us I now have .080" head gaskets installed. He does a great job, nice looking parts, fast delivery. After putting it all back together I did a wet compression check and the readings were in the low 130s. I know this is a little low so I'm thinking of trying a new set of head gaskets for better compression. The next size down is .063" which isn't much of a difference, and then .050". If I go with .063" I run the risk of still having low compression, if I go to .050" I might overshoot or still be low. I measured the squish and got a reading of about .060". The heads look pretty stock so I doubt there was any machining done to them. Does anyone know what the stock dimension is for any H2? If I know what it's supposed to be I can easily calculate the best head gasket thickness to use. Getting closer but not there yet. Trying not to overthink. Thanks for the replies, Dave |
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| Author: | ALTERED IMAGE [ Sat Sep 09, 2023 12:59 am ] |
| Post subject: | Re: Piston height above deck |
You are overthinking this. |
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